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canyncarvr

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I've read dozens of threads about timing, but have yet to sort mine out. Maybe just one more thread on the subject will get through to me.

I destroyed my last engine via detonation..and I never heard a thing. The current engine, I DO hear it once in awhile. The only way I've gotten completely rid of it: VP fuel, Trick fuel, or adding toluene to pump 92 octane fuel.

Engine specs that matter: 62cc heads (measured), 9.9 compression ratio (by the math of measured volumes, designed low to run on pump gas), HE3844 cam, A833, 4.56 gears, Holley 750 4-post idle set by vac and butt-in-seat gauge, mixture band on plugs is perfect..a bit rich, Performer RPM air-gap manifold, Mallory distributor with 20º in it..spring color I don't recall, but stiffer than it came with...all in @3000rpm, 11º vacuum can (adjusted from one limit to the other, will still ping). I hear it most often around carb secondary start (2nd pump clearance set to nil at rest).

I've been running 12º initial timing @1000rpm, total mech of 32º (like I said...dist has 20º in it). I asked the folks at Hughes Engines about it. They suggested that 12º was too much, that it would build heat in the engine that might help detonation happen. They also said the idle needed to come down. Set to 10º/30º and an idle of 800rpm: Still some rattle.

My question: Other small block folks here say 'more is better (if the engine likes it)' and talk of 15-18º initial, 36º total. There is NO way I can run that on pump gas. The engine runs better with a higher initial timing, but that would mean taking the distributor down to 15-17º or so.

I don't recall that low a mechanical advance ever being used. Does it sound reasonable?

Thanks!
 
Do you run vacuum advance? Also have you tried a little stiffer spring with the mechanical? In certain situations, running full, not ported vacuum advance with a higher initial works because as load increases, vacuum drops, retarding timing a little so no knock.
 
I've read dozens of threads about timing, but have yet to sort mine out. Maybe just one more thread on the subject will get through to me.

I destroyed my last engine via detonation..and I never heard a thing. The current engine, I DO hear it once in awhile. The only way I've gotten completely rid of it: VP fuel, Trick fuel, or adding toluene to pump 92 octane fuel.

Engine specs that matter: 62cc heads (measured), 9.9 compression ratio (by the math of measured volumes, designed low to run on pump gas), HE3844 cam, A833, 4.56 gears, Holley 750 4-post idle set by vac and butt-in-seat gauge, mixture band on plugs is perfect..a bit rich, Performer RPM air-gap manifold, Mallory distributor with 20º in it..spring color I don't recall, but stiffer than it came with...all in @3000rpm, 11º vacuum can (adjusted from one limit to the other, will still ping). I hear it most often around carb secondary start (2nd pump clearance set to nil at rest).

I run 20 initial with 14 mechanical, so yea they can run that low of mechanical.
Then about 16 more for the vacuum for a grand total of around 50 at light throttle cruise on 87 fuel.
5000 ft elevation here.
 
Vacuum: Yes. As noted, 11º in the can, attached to ported vacuum. I've been back and forth between ported, manifold and no vacuum at all to no effective resolution. I should look into a lower sprung canisters maybe. Vacuum at idle is close to squat and unstable...the 'dither' effect of that makes for a timing mess when using manifold vacuum. OR...go back to a no-can all-mech setup I used on my 292º purple shaft engine. I'm getting hung up on trying to make vacuum work in my current 'less' engine; that is maybe a mistake.

Re: 20º initial. What is your vacuum at idle..and what is your idle speed? 5000'el. makes for a huge adjustment factor for sure. I grew up at 4100', always enjoyed a trip to the valley where engines RAN!
 
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your wandering vacuum at idle may be due to the light springs in the mechanical advance.
I just recurved my dizzy to a slower advance curve that applies the last 5-6 degree over 3k slowly. After a short drive my car seems to like it. A longer test mey prove me wrong....?
 
your wandering vacuum at idle may be due to the light springs in the mechanical advance.
I just recurved my dizzy to a slower advance curve that applies the last 5-6 degree over 3k slowly. After a short drive my car seems to like it. A longer test mey prove me wrong....?

I wasn't clear. The 'dither' part is when I've used manifold vacuum. I edited the post to reflect that.

I have had idle settling (with an 'l'..NOT 'setting') problems in the past, but that was resolved with a drop to an 800rpm idle (Hughes' advice, I had been set to 1000) and, back-when a bit, stronger springs just as you said. Having any active advance, mechanical or vacuum, in play at idle speeds doesn't work.

I'd have to check my notes to be sure but mechanical doesn't start until around 1500rpm. Another tip from Hughes: Mechanical advance should start no less than 400rpm above idle. Sounds reasonable.

I don't pretend to be a tuner with mad 'skilz'. Not at all. I understand what I read or what I'm told but, when it comes to, 'This is the problem: Fix it!', I'll be doing a good bit of dithering myself.

Thanks for all the input!
 
Are those iron heads?
What elevation?
What cubic inches?
Is that Holley a Vacuum secondary?
A-body?

I have a 360 with the next smaller cam HE3037 and 10.9Scr measured. I also run the A833, but with 3.55s. She has over 100,000 miles on her and still going.
 
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Are those iron heads?
Yes. '69 'X' heads.

What elevation?
1400'

What cubic inches?
346CID (.040"-over 340)

Is that Holley a Vacuum secondary?
Holley makes a DP vacuum secondary? I've never gone looking for one, but didn't think such a carb existed. Anyway, no. My carb is mechanical.

Yes. '73 Duster.

I have a 360 with the next smaller cam HE3037 and 10.9Scr measured. I also run the A833, but with 3.55s. She has over 100,000 miles on her and still going.

With a distributor curve that looks like what?
 
Now we're talking!
Detonation is just too much heat in the chamber for the anti-knock limit of the fuel you are burning. And/or it can be preceded by pre-ignition, which is just something in the chamber starting the fire before the plug does. So when you eliminate the hot-spot or reduce the heat to below the knock threshold,voila no more detonation.
As to preignition; This can be caused by;hot plugs,hot exhaust valve, carbon, sharp edges in the chamber or on the piston, foreign combustibles in the chamber like oil, or winter gas.
And as to heat; This can be caused by; too much cylinder pressure, improper ignition timing, exhaust back-up/restricted exhaust, hot water temp, hot-spots in the heads, sucking hot underhood air.Electric fans not cycling on soon enough or not staying on long enough, or just not moving enough air.
So, I would start with measuring the cylinder pressure,lets see what pressure you are getting, then we can figure it out.
if it's under 150psi, that would be normal for your combo, and should be fairly easy to tune for pumpgas.
But if over 160, something is wrong and you are in trouble.
Then I would just cool thechitoutofit,until it she quits detonating, then reintroducing the heat little by little to get the power back.
And that starts with;
Colder plugs, a slower timing curve, perhaps slightly limited total timing,then clean out the chambers with a chemical treatment, and then attack the cooling system. And finally check the exhaust system.
I know you said you did the math and got 9.9 Static compression ratio. With that cam in at 106, the Ica comes to 69*. But with the Hughes people measuring their cams at .008tappet lift, the Ica is actually much later. So IMO,You should have no problem tuning this puppy at 9.9 calculated Scr.
You should be getting about 10/11" of manifold vacuum with a proper Transfer-slot sync,at 750/800rpm, with that cam properly installed and no vacuum leaks. With the transfer slot properly set, your timing might come in around 14 to 16 degrees. Forget about all other timings for now. Just work on the getting the transfer slot right and the idle to 750/800 FIRST, then get the vacuum stable and see if it comes in close to 10/11.
Make sure you got the right PCV and have it plumbed to the proper port, under the primaries. Disconnect the Vcan and plug the carb-port.Check all vacuum taps. If you have a vacuum booster, clamp off the line. Check the crankcase for vacuum, by flipping out the PCV and sealing the CC, then put a vacuum gauge on the dipstick tube. Check everywhere for a vacuum leak. You can't tune the carb if the engine is pulling in air somewhere, it's not supposed to.
You got electric fans on that sweetheart? if yes, then get rid of them. Put a direct-drive 6-blade hi-attack fan on her, and install a proven good hi-flo 180stat.
Now lets look at the D.
Your initial should come in around 14 to 16 with a manual trans, else the very low rpm will get jumpy. And it makes the very low rpm a lil lazier and the rpm easier to control. With 4.56 gears you won't notice a few horsepower down on account of just 14/16* idle timing. But you sure will notice the jumpiness at 20*.
And lets start the power timing off at 32 to 34 but make it come in later at say 3400.
These should get you out of detonation,and prevent pre-ignition.
Now the tuning begins.
First question; when do/did you hear the detonation? as in load and rpm.
 
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First, I am not lookin up specs for that cam when all you provided was a part number. Secondly, 9.9:1 is NOT pump gas friendly with iron heads, I don't care what some forum genius says. Unless you have a camshaft that does not allow complete cylinder filling because of a late intake valve event, you will have trouble on pump gas.

I would begin as AJ suggested and run a compression test. Post up your numbers. But remember, a compression test is not the end all be all, because as engine RPM increases, guess what? So does cylinder pressure. So by the starter, you may see 140-150, which is acceptable, but who knows where it is in the RPM curve of the engine? This is why fancy formulas and such are sometimes useless as tits on a boarhog.

Sometimes you simply have to get dirty and actually TUNE the thing. I suspect that's what you are going to have to do here. Let us know what those compression test numbers are and we can go from there.
 
First, I am not lookin up specs for that cam when all you provided was a part number.

Didn't intend to be cryptic. The Hughes Engines 3844:


INT .535" 237º@.050" .286"@.008" 108ºLSA 13.5ºBTC 43.5ºABC
EXH .540" 243º@.050" .290"@.008" 52.5ºBBC 10.5ºATC

Damper TDC verified during assembly. Cam installed within 1/2º of spec using rollmaster timing set.


Secondly, 9.9:1 is NOT pump gas friendly with iron heads, I don't care what some forum genius says. Unless you have a camshaft that does not allow complete cylinder filling because of a late intake valve event, you will have trouble on pump gas.

I would begin as AJ suggested and run a compression test. Post up your numbers. But remember, a compression test is not the end all be all, because as engine RPM increases, guess what? So does cylinder pressure. So by the starter, you may see 140-150, which is acceptable, but who knows where it is in the RPM curve of the engine? This is why fancy formulas and such are sometimes useless as tits on a boarhog.

Sometimes you simply have to get dirty and actually TUNE the thing. I suspect that's what you are going to have to do here. Let us know what those compression test numbers are and we can go from there.


I have no problem doing the work. I have the compression numbers noted somewhere. If I don't find them, I'll check 'em again. Hughes spec notes said 175psi is what the cam would work with best. I'm recall my #s not being close to that.
 
Now we're talking!
Detonation is just too much heat in the chamber for the anti-knock limit of the fuel you are burning. And/or it can be preceded by pre-ignition, which is just something in the chamber starting the fire before the plug does. So when you eliminate the hot-spot or reduce the heat to below the knock threshold,voila no more detonation.
As to preignition; This can be caused by;hot plugs,hot exhaust valve, carbon, sharp edges in the chamber or on the piston, foreign combustibles in the chamber like oil, or winter gas.
And as to heat; This can be caused by; too much cylinder pressure, improper ignition timing, exhaust back-up/restricted exhaust, hot water temp, hot-spots in the heads, sucking hot underhood air.Electric fans not cycling on soon enough or not staying on long enough, or just not moving enough air.
Yes to all of that.

So, I would start with measuring the cylinder pressure,lets see what pressure you are getting, then we can figure it out.
if it's under 150psi, that would be normal for your combo, and should be fairly easy to tune for pumpgas.
But if over 160, something is wrong and you are in trouble.
I'll either find those numbers...or measure 'em again.

Then I would just cool thechitoutofit,until it she quits detonating, then reintroducing the heat little by little to get the power back.
And that starts with;
Colder plugs, a slower timing curve, perhaps slightly limited total timing,then clean out the chambers with a chemical treatment, and then attack the cooling system. And finally check the exhaust system.
I know you said you did the math and got 9.9 Static compression ratio. With that cam in at 106, the Ica comes to 69*. But with the Hughes people measuring their cams at .008tappet lift, the Ica is actually much later. So IMO,You should have no problem tuning this puppy at 9.9 calculated Scr.
You should be getting about 10/11" of manifold vacuum with a proper Transfer-slot sync,at 750/800rpm, with that cam properly installed and no vacuum leaks. With the transfer slot properly set, your timing might come in around 14 to 16 degrees. Forget about all other timings for now. Just work on the getting the transfer slot right and the idle to 750/800 FIRST, then get the vacuum stable and see if it comes in close to 10/11.
I'll check that. I know my idle vacuum is nowhere near 10/11", but I've never set an idle to 14-16º either.

Make sure you got the right PCV and have it plumbed to the proper port, under the primaries. Disconnect the Vcan and plug the carb-port.Check all vacuum taps. If you have a vacuum booster, clamp off the line. Check the crankcase for vacuum, by flipping out the PCV and sealing the CC, then put a vacuum gauge on the dipstick tube. Check everywhere for a vacuum leak. You can't tune the carb if the engine is pulling in air somewhere, it's not supposed to.
I don't follow that. With the PCV out, why would I see any measurable vacuum on the dipstick tube? There is no cylinder set-up that leaks nada. With no PCV, eight cylinders are going to put some pressure in the crankcase.

You got electric fans on that sweetheart? if yes, then get rid of them. Put a direct-drive 6-blade hi-attack fan on her, and install a proven good hi-flo 180stat.
I do have an electric fan, but it is in addition to a direct drive (no clutch) six-blade aluminum fan, a hi-flow t-stat (don't recall the particulars of that, but I remember having to do some looking to find one advertised to be exactly that). BTW... the fan edges are on the edge of the shroud where they should be. I use the electric fan if I run into a heating problem...slow moving on a hot day.

Now lets look at the D.
Your initial should come in around 14 to 16 with a manual trans, else the very low rpm will get jumpy. And it makes the very low rpm a lil lazier and the rpm easier to control. With 4.56 gears you won't notice a few horsepower down on account of just 14/16* idle timing. But you sure will notice the jumpiness at 20*.
And lets start the power timing off at 32 to 34 but make it come in later at say 3400.
The last notes I have say I used 2-pink. That doesn't sound right, 2-orange does. I know I wanted to get above a 1000rpm 'start' mark. The colors on the springs are less than obvious. I'll check that again, too.

0KKg9ct.jpg


These should get you out of detonation,and prevent pre-ignition.
Now the tuning begins.
First question; when do/did you hear the detonation? as in load and rpm.

Around 3000rpm (50mph) in 4th gear a quick throttle change (not a 'stab', but not a 'roll' either) to just before the secondaries open, I can hear it. That is the general area I've used to determine if it rattles or not because that is the most common place I've heard it before. If it's gone there, I won't hear it anywhere else. Being in 4th, that's the most load I can give it but with 4.56s things change pretty quick. All subjective of course, but that particular spot feels to be where the engine starts breathing the best...where combustion pressures (and load) are ramping up fast.
 
0kkg9ct-jpg.jpg


These curves are all to fast for what I am trying to do. even the Orange is in by 3000, and if it is limited to 24* then you can't run more than 10 initial for 24+10=34 total power timing. And 10 is gonna make it impossible to get the Transfer port synced.

Around 3000rpm (50mph) in 4th gear a quick throttle change (not a 'stab', but not a 'roll' either) to just before the secondaries open, I can hear it. That is the general area I've used to determine if it rattles or not because that is the most common place I've heard it before. If it's gone there, I won't hear it anywhere else. Being in 4th, that's the most load I can give it but with 4.56s things change pretty quick. All subjective of course, but that particular spot feels to be where the engine starts breathing the best...where combustion pressures (and load) are ramping up fast.
This statement tells me I am exactly on the right track,so you gotta slow the curve down and limit it down.Limit that D to 20degrees or less, and slow it down to all in by 3400.Then set the initial to 34 less whatever you managed to get in the D, and I'm targeting 14*.

I don't follow that. With the PCV out, why would I see any measurable vacuum on the dipstick tube? There is no cylinder set-up that leaks nada. With no PCV, eight cylinders are going to put some pressure in the crankcase.
Because you say your vacuum is so low, even with the initial timing cranked up, I'm trying to rule out an intake leak into the crankcase; that is what the test is for. Yes, there should be pressure in the CC with the PCV flipped out and engine sealed. Do not let it climb past 3 or 4 psi at most else it may blow a seal or gasket.

I have no problem doing the work. I have the compression numbers noted somewhere. If I don't find them, I'll check 'em again. Hughes spec notes said 175psi is what the cam would work with best. I'm recall my #s not being close to that.
175psi would be right, but you can't run that with iron heads and pumpgas,on the street,even at 1400ft
I don't recall that low a mechanical advance ever being used. Does it sound reasonable?
Yes it does. You run whatever it takes to get your combo to live. I like 18/20 initial cuz it makes the engine real snappy down low. But in my combo that makes it impossible to sync the Tslot, so it runs lean down there unless I suffer a high idle. Then I can't drive real slow with 3.55s. Also. with 20 initial I can only run 12 to 14 more in the D, which is a royal PITA to achieve with an old Factory D. So I abandoned common consensus-thinking and just gave the engine what she wanted.
I have aluminum heads and run 185psi with the HE3037Al cam (230/237/110/@.050) on 87E10 At 10.9Scr Heavily loaded with 3.55s.But I have a dash-mounted,dial-back timing box with a range of +7/- 8degrees. By only running 14* initial,and dialing 8* out I can drive 4mph@550rpm with that combo.
With 4.56s you might be able to drive as slow as 4mph@600rpm, but there is no way yur gonna do that with 20* idle timing because she is gonna buck and jump and fart until you ride the clutch. Even at 14* she is not likely to idle down to 600 without drama. And so that is why I recommend 14* as a starting point. You are only gonna go thru that low-rpm/low-timing once every time you leave from a stop. The rest of the time you are gonna be above 2000rpm/13mph, maybe above 2500/16mph; so don't let a measly 14* scare you, cuz you make it up with rate. But first you have to limit the power-timing to what the engine can handle.And then you add Vcan later, as much as she'll take,to smooth her out. (I run 24*)

I do have an electric fan, but it is in addition to a direct drive (no clutch) six-blade aluminum fan, a hi-flow t-stat (don't recall the particulars of that, but I remember having to do some looking to find one advertised to be exactly that). BTW... the fan edges are on the edge of the shroud where they should be. I use the electric fan if I run into a heating problem...slow moving on a hot day.
In my experience the 6-blade flex-fan doesn't work in traffic. I threw mine into the rafters in ~2003 . I shift my combo at up to 7200, so I slowed my Hi-flow pump down some with pulley ratios, in a preventative measure to not throw a belt. With a stick car the rpm is always up anyway, not like an automatic at all. Well the flex-fan was hopelessly overwhelmed and the coolant temp kept rising in traffic. I finally caved in after two or three summers and tossed it.I mounted up a 7-blade and had instant relief, but the viscous coupling wasn't real happy, so I tossed it and bolted up a Ford pick-up truck thermostatic-clutch, and it was smooth sailing after 2004. ........... so I cranked up the minimum water temp to 205*F and cut a hole in my hood and routed fresh cold air down the 750DP, and she went 93 in the 1/8th.
I called it D-O-N-E.
 
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You asked so here's what I run
I have an ancient factory 318D . I limited the mechanical to 19/20*, and set the idle timing to 14*, for a total of 32/34 which is all the aluminum heads want. She's a streeter so I can't tell she's any slower at 32 than 36 so I just set it up the middle, and she makes plenty enough power to get into trouble with. So now because the 14* is in there to achieve the proper transfer slot exposure at 750rpm idle, I gotta run a two-stage rate-of-advance curve, So I reused the long-loop 318 spring which has about 4 degrees in it but won't be all in until 3400rpm. Then I dinked around with primary springs until I found one that barely keeps the idle timing at 14*@1000rpm and shes done by 2800.So
So now; my timing is 14* below 1000, then ramps up to 28* by 2800, then slows down to be all in of 34*@3400. So I mapped that out on a graph and went for a spin to see where I might find detonation, and finally found none. That is how I run 87E10 @185psi with aluminum heads. At 185psi the engine has gobs and gobs of torque at nearly any timing down there, so I quit looking for more.
After I got all that done, I started playing with Vcans, and found that my 230 cam/al heads liked lots and lots of cruise timing. I have an overdrive so she cruises at 65=2240rpm and the mechancal timing was like .78*/100rpm so 2240 was only about 24*. And you can imagine the crappy fuel mileage at that timing. So I went straight to the biggest in my collection which was 20*. So now I had 44 cruise timing. I went for a cruise. Every few miles I'd dial in some more timing with my box. Soon I was deep into the 50s and the running vacuum was still increasing at a steady-state mph. It plateaued at between 56 and 60*, so I decided 56* was good enough. So back at the shop, I modded that Vcan but could only get 24* out of her for a total cruise timing of 48*. Then I recentered my Dial-back to add the 8* difference.
So now when I hit the hiway, I just crank the Dial-back to where the Total all-source cruise-timing is 56* , and sit back and enjoy the ride. Sometimes on long drives, on what appears to be a level hiway, I still experiment a bit, but my vacuum gauge can't find much difference, and neither can the gas-pump.
If you recall, I just told you my all-in mechanical timing is 24* at 2240 rpm and 28* at 2800rpm. Most guys will tell you that is lazy timing. But the thing is my first gear TM (Torque Multiplication) is 3.55x3.09= 10.97 so this with the tons of torque that 185psi makes, is plenty enough torque to break the tires loose, and the then the engine spools right past the soft-timing zone. And any time I am in it, like in second or third gear, I don't care cuz I'm just tooling around. My opinion is you just can't run an automatic loose-convertor timing-curve, with a manual trans, and I don't even try anymore.
As to TM , in first gear you may be running 4.56x2.66=12.13, about 10.6% more than I am, so you should not have any problems with "lazy timing".
My second gear TM is 1.92x3.55=6.82, and my engine will break traction anywhere up to 50mph and more with 295/50-15s. Your second gear TM will be 4.56X1.92=8.76 which is 28.4% higher than mine. In fact your third gear TM is 6.38,nearly the same as my second gear! So I don't see lazy timing being a problem for you...... cuz it ain't a problem for me.
Bottom line then is; just limit the power-timing, and slow it down.
Then stabilize the cooling system temp to zero variance or as close to it as you can, and bring the heat up. You can't run razor's edge timing until the coolant temp is stable. If the electric fan is cycling, this is not stable. If the flex-fan cannot keep up, this is not stable. If the stat can't regulate to a single temp within a few degrees when the 7-blader cuts in, this is not stable. If the carb is sucking HOT!! underhood air that is constantly varying, this is not stable. So until you get the temp stabilized, play it safe with lazy timing and limit the power-timing to well below optimum.
 
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As noted originally, the distributor has 20º in it now. No argument about a too-fast curve, but it is set to 20º. I'll check that curve again, too. I questioned the tach I used at the time, will use another.

I'm running a 17" Flex-a-lite aluminum with a 2" deep blade. An 18" would fit better. They do make a 7-blade that is 2-1/2" deep. It is stainless though, NOT aluminum...it's going to be heavy.

My fan has no t-stat. I manually switch it...don't use it often enough to worry about it.

I have a backwards mounted 5" Mopar Bracket style scoop on the car with a hole in the hood even. The pressure well at the cowl puts air INTO the engine up to around 100mph.

Having referred to syncing the transfer port, I assume you are of the ported vacuum group and not the manifold vacuum group? For the former, by 'sync' you are referring to the amount of slot exposed, correct? I would appreciate some expansion on where you want that to be.

View attachment 1715250479
....and I'm targeting 14*.

You are NOT of the belief that 12º+ will build heat that leads to detonation? At some point 'more' initial advance is going to heat the engine. OR, you are saying you want 14º and if that builds heat...just get rid of it!

Thanks for your help.
 
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Comments inside the quote
As noted originally, the distributor has 20º in it now. No argument about a too-fast curve, but it is set to 20º. I'll check that curve again, too. I questioned the tach I used at the time, will use another.
The idle timing will come out in the wash, while setting the Transfer-slot exposure. Make the slot slightly taller than wide to start.Figure out how to get there once the carb is bolted back on. What I do is this; after the exposure is set, I back off the curb idle screw until it just lifts off the adjusting block, counting the turns as I go. Then I screw it back in the same number of turns. And write it down. Then I reset all the mixture screws to the factory settings. On old Holleys this is 1/2 turn from lightly seated. IDK about 4-corner Idle. Also on old Holleys, I close the secondaries up tight but not sticking.Do whatever your carb instructions say, But I have tuned a few Mopar 292/108 cam equipped SBMs, without any secondary cracking.
This is your starting point. Make sure you can get back to it any time you want without taking the carb off again, that gets old in a hurry. Make sure the float level is to the factory spec and remains stable at all times, ESPECIALLY at idle!
Make sure the engine temp remains stable. You can't mess with the carb if the engine temp is going up and down, you will tear your hair out looking for the tune.
Ok now, this is your stating point. You may have to adjust the exposure slightly more or slightly less.. later, to fine-tune the transition from idle to just off-idle, to make it smooth and hesitation-free. But just leave it alone now for a bit. Now pull in a little timing and fire it up. Warm it up to normal operating temp, which should be 180 or so, measured with an IR gun right under the Thermostat. Ok now rev it up to 3500rpm and reset the timing to 32/34, with the Vcan not working.Lockit down, and let the idle return to whatever, and recheck the idle timing. Which should be what? 32/34 less 20 in the D =12 to 14 so that should be close enough for now.
Now what's your idle speed? You are targeting 750/800, 850 tops.
If you are not in the ballpark, DO NOT adjust with the primary curb-idle screw! Cuz that will mess up your Transfer port exposure! Don't do that!.
Ok wait, if you only need like 50 rpm, you can crank the screw up to 1/2 turn either way. If that gets you 750 or 800, super. If not we gotta try something else.
Now , up to this point, I have assumed you don't have ANY vacuum leaks, that your PCV is newish, correct for the application, and properly plumbed, and that the crankcase is properly ventilated. The PCV is your main idle-air bypass. Engines with big cams..... like yours, like lotsa idle air. Since you can't mess with the curb-idle screw without upsetting the Transfer-slot exposure, you only have three places to supply the engine the air she wants , namely; the PCV circuit, secondary cracking, and thru the throttle blades.

>>Ok now here's something you probably know. At idle, the engine is getting it's idle fuel from two sources. The transfer slot is supplying the bulk of it, and the mixture screws are the trimmers. You have 4 trimmers.
If you find that they all have to be set to the very rich side...... then the engine is not getting enough fuel from the transfers, or it's getting too much air from somewhere else. If you dump in more transfer fuel then the idle-speed will just go up. If it goes past the target , you will have to hunt for the unauthorized air.
If you find that the trimmers have to be leaned out, then the transfers are too rich.
SO

If the idle-speed is too fast, that would be highly unusual, and points to a vacuum leak, so go hunt for it.
If your idle speed is too slow;
This is the usual problem; then she wants more idle-timing or more idle-air. If you are at 12* idle timing, go ahead and put 2 more in, but resist the urge to crank any more in, cuz that will just make her jumpy in gear, at very low throttle settings. And if you crank more idle-timing in you will have to take an equal amount out of the D. So if you reset the idle timing to 14, remember you now have 14+20=34 power-timing.
So what happened? Did the idle-speed come up into the target zone? If yes, then fiddle with the mixture screws now to get best quality idle. and then we can move on.
But if no, the idle speed is still less than 750, @14* idle-timing.
Then crack the secondaries until you get 750. Now back to twiddling the trimmers, for best idle quality. If the trimmers want to be lean then close the transfers a half turn. If the target idle speed falls below 750 than increase the secondary opening back to 750. Then twiddle the trimmers some more. Sooner or later the back trimmers and the front trimmers are gonna get crossed up. If that happens, close the secondaries a half a turn, and open the primaries the same 1/2 turn. Return all the trimmers to stock and start over, realizing that you can no longer add air at the secondaries. Just aim for the best you can.
In really stubborn cases I just drill tiny holes in the primary throttle valves to get the idle speed I want. Or rather the engine is wanting.
Ok now lets see what happens at throttle tip-in. First, you might have to reset your accelerator pump linkage. So check that out. And check that the engine is up to temp. Then, just open the primaries very slowly a tiny amount. 1000 rpm is lots. Then back to idle. Try it several times. If no hesitation, you are good to go. I think you will be fine.
No we can mess with the D


I'm running a 17" Flex-a-lite aluminum with a 2" deep blade. An 18" would fit better. They do make a 7-blade that is 2-1/2" deep. It is stainless though, NOT aluminum...it's going to be heavy. I am no fan of flexblade fans. And you already know why. Because you already have a backup electric that you have to manually cycle, to push the air thru the rad when the flex fails to keep up.You can't tune the engine with the water temp going up and down. I would get rid of it all and go with what I know works.
My fan has no t-stat. I manually switch it...don't use it often enough to worry about it.

I have a backwards mounted 5" Mopar Bracket style scoop on the car with a hole in the hood even. The pressure well at the cowl puts air INTO the engine up to around 100mph.
Hmmmmmmm,
are you saying that the air under the hood is being forced down and out of the engine bay by this high pressure air? At what speed does this phenomenon begin? Does it interfere with the air pressure differential across the rad which is the only way that the rad can get rid of the heat? Does it interfere with the carb calibration? or is the carb sealed to the pressure box? Have you actually measured the pressure in there?

Having referred to syncing the transfer port, I assume you are of the ported vacuum group and not the manifold vacuum group? Absolutely, I am all for hooking the Vcan to the sparkport,with a manual trans car. Here's why. The spark port is usually deactivated at about 1500rpm. That means between idle speed and 1500 rpm your engine is seeing very limited advance and it is stable advance,not jumping around with Vcan fluctation. So you can drive down there without the car doing the donkey-kick routine. In your combo, 1500 rpm is about 10 mph in first gear.You need the car to be acting grown-up below 10 miles an hour with a manual trans, cuz you will be spending a lotta time down there. Automatic guys get away with it cuz they don't have a clutch, slamming that bucking-horse routine into the chassis, back into your big right foot, and straight back into the carb. But,why does that happen? Well for starters when you punch 20 or 30 degrees into the idle timing, your throttle opening gets really really small. And your low-rpm torque gets really really big cuz you are re-timing your peak cylinder pressure to occur sooner after TDC,so the cylinder pressure in there is about as high as it can be at idle.
So your throttle sorta turns into an on/off switch. When your foot inadvertently moves the throttle even just a tiny amount, the engine jumps into action. That don't work with a manual trans and 4.56s, because even small amounts of torque spikes get amplified by the gears. Say just 3 ftlbs; that would translate to 3x2.66x4.56=36 ftlbs slamming the rear springs and into the chassis. 36 ftlbs is, for a teener, to die-for.
You are of course welcome to try it. I have 185 cranking psi cylinder pressure. At your possible 150 psi, you might not have as huge pressure spikes. But I sure wouldn't try it during this tuning stage. In fact the Vcan should still be disconnected as per stated, a long time ago,lol.

For the former, by 'sync' you are referring to the amount of slot exposed, correct? That's correct.
I would appreciate some expansion on where you want that to be. See above; a little taller than wide, to start with.
You are NOT of the belief that 12º+ will build heat that leads to detonation? 12* at idle has nothing to do with detonation. Even if it did build heat, a proper-working cooling system would get rid of it long before the engine gets to third gear at 3000rpm.
At some point 'more' initial advance is going to heat the engine. OR, you are saying you want 14º and if that builds heat...just get rid of it! Lemmee go find the context... Can't find it,
but idle timing has nothing to do with detonation. Well ok it could if you had a graintruck. Cuz those operators might floor it at idle, and the loaded truck on soft field-earth barely moves.
But if you floor it at idle with 4.56s, the engine should jump to redline in microseconds,lol. And your engine will not again see idle timing until you stop the car or de-clutch. I think this is a non-issue..
Except that I see you are setting power timing by adding the 20 in the D to the idle timing. That is backwards thinking. You must think power-timing first, and fixing the D to get whatever idle-timing the engine is telling you it wants, including getting rid of the low-rpm jumpyness.
And if you have to slow the rate-of-advance to be all-in after 3600 then that is what you do to eliminate detonation.
Elimination of detonation is job #2 right after getting the darn thing to idle.
You can set the idle-timing anywhere you want, until the transfer slot is thoroughly messed up, and it won't even take throttle opening. Try it if you like. I bet it will idle with 36* idle timing, now slow it down to 800 with the curb idle screw. I bet you can't do it. The transfer will be too short and the engine will stall. Even if you max out all the trimmers and somehow get it to idle at 800.... I bet it will stall the instant you open the throttles...... cuz now the transfers have dried up. and they can't get going fast enough to prevent fuel-starvation and probably a stall, a huge hesitation or a backfire thru the carb to set your face on fire.Don't have your face there when you try it,lol
I gave the target of 12 to 14 to help you get started with a minimum of experimentation. You are free to run more, up to 20* even, but if she gets jumpy at 10 mph down to 6, you are gonna get to hating that.
Do not try to run less than 12*, and here's why. Your engine wants the idle pressure spike to occur at about 15* to 20* ATDC. This gives the best transfer of energy to the crank ; all the fuel in the chamber will get burned up as the piston works it's way to the bottom. Your exhaust valve is gonna open at about 79* ATDC, so you only have 101 degrees to get it all burned up. Whatever is not yet burned will continue burning in the headers heating THEM up, and creating a pressure in there. Now, you have 290* to get rid of that exhaust pressure. If you don't two things are gonna happen; 1) the pressure is gonna back up into the intake during the generous 68* overlap cycle, messing up your idle-vacuum, and 2) the pressure inhibits scavenging during the overlap cycle; and maybe the header sucks a slug of fresh charge right across the top of the piston dwelling there, and into the header..... which is still 400 or so degrees, certainly high enough to ignite that little slug, which then burns right in the header before moving on down the pipe. Some of it may still be there the next time the exhaust valve opens.
So how do you prevent this negative work from being done? You gotta get the pressure to peak where it's supposed to. And that starts with setting the idle timing to some number, to allow the fire to get going and the pressure to peak in the zone.
You can tell where that zone is for your combo, just by watching the tach as you pull timing into it. When the rpm peaks, you are there. Well not exactly,cuz the manifold vacuum is also carrying the zone with it. The peak is gonna be up past 20/25 degrees. And unfortunately,your carb won't work properly with that much idle timing. You can also see it as the header temps drop, maybe a 100*
So, again, I offered 12 to 14 as a starter for your combo, to expedite the search. She might like 16, it depends on your cylinder pressure. But not less than 12* because it's hard on the headers, and with a marginal cooling system I suppose the heat may get up into it, thru the exhaust port. If you have TTIs they're tough, I haven't killed mine in over 125,000 miles.Hyup 3 zeros. Because I have the dial-back timing-box, I can run whatever idle-timing I want,+7/-8 degrees. And I do.Even down to 5 or 6 when the situation calls for it. Can't do that with the Vcan plumbed to manifold vacuum..............

Thanks for your help.I really hope it does help,lol.

done I think
 
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I have a backwards mounted 5" Mopar Bracket style scoop on the car with a hole in the hood even. The pressure well at the cowl puts air INTO the engine up to around 100mph.
Hmmmmmmm,
are you saying that the air under the hood is being forced down and out of the engine bay by this high pressure air?
No. A pressure well is a low(er) pressure, the reason cowl induction works. The low pressure in the cowl area develops due to the windshield.

At what speed does this phenomenon begin?
Phenomenon? I hear the scoff and see the sidewise glance from here...... ;)

I am saying that, if it's misting or raining, I can see drops from the top of the scoop opening get sucked into the engine compartment. Also, I have taped ribbon to the top of the scoop opening and have seen IT fluttering into the engine compartment.

Does it interfere with the air pressure differential across the rad which is the only way that the rad can get rid of the heat? Does it interfere with the carb calibration? or is the carb sealed to the pressure box? Have you actually measured the pressure in there?
I have no answers to the first two questions. What the scoop does to the pressure differential across the radiator, what it does or does not to the carb calibration I can't say. The folks that made the scoop (Harwood as I recall) said mounting it backwards was preferred, up to a bit over 100mph; backwards keeping detritus out of the engine compartment. It was their recommendation that convinced me to put it on backwards. They supposedly did the airflow testing to know what worked with their product. It is not a shaker situation...the carb is not sealed to the hood opening. I have not measured pressures.
 
Ok I'm thinking............... I've never had any experience with a thing like that.
But I have this thought; Air flows from a high-pressure area to a low-pressure area. That means speed is creating a high pressure area at the mouth of the scoop. Since you have proved that air is actually rushing into the scoop, it has to be going out somewhere.
You said you hear detonation at 3000rpm in 4th gear, as you load her up. The math points to 53mph with 27" tires.
At this time,(3000rpm/53 mph), about the most air your 345 can draw at WOT is mathematically 300cfm at 100%VE. So lets say 180/200 as you roll into it, and 250 as the secondaries open. My thought is that most of the in-rushing air is going around the carb. I gotta wonder if air is still able to enter the engine compartment thru the rad.
What if the air pressure under the hood was greater than the pressure in front of the rad? That's a scary thought. You might have to install a chin spoiler....... to help Ram-air slam thru the rad, cuz at 3000rpm that flex-fan is probably doing squat. Rev it up sometime and see. I hate those things.

What is the engine temp gauge saying at this time?
 
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As far as all the pressure issues, I am aware such matters DO matter. Admittedly, I am relying on the scoop manufacturer to not have been lying to me about it.

An aside: I do know the pressure differential changes at higher speeds. I know that from a few years of taking the car to the local strip. It took me awhile to figure out why I had fuel dumping out of the bowl vents onto the windshield.

They told me the scoop stopped working backwards at a certain speed. They were jolly-well right-o about that part!

I don't have temperature control problems without severe environmental input. If it's over 100º outside, I don't want to be in stop and go traffic....not that there is a lot of that around here. The engine keeps 180º most of the time. It might nudge 200º from time to time, but it's not a performance limiting problem. My headers are coated, thermal on the inside, powder on the outside. Headers, being a common culprit of too much heat in an engine compartment are not a problem in this car.

Another aside, but it's a relatively new (same age as this engine..2000 or so) 3-row brass radiator in the car; scale-free.

If this engine has more than 2000 miles on it, I'd be surprised. It has sat. A lot. It's only recently I figured I might as well drive it as try to 'save' it. I'll die before it does, most likely.

I have a velocity stack on the car. That puts carb breathing easily into where I 'see' air going through the scoop hole.

pXpw8IU.jpg
 
I have never run 200 with iron heads, high compression, and a big cam. With fresh ambient air going down the carb, you should be OK.
I am very keen to change your mechanical timing to 18 in the D, and to delay your all-in timing to nearer 32*@3600rpm. That would be 63mph. If that cures your detonation, I would sneak up on the timing,by first moving the rpm down 200rpm, to 3400, and retest. Then 34*@3400. But if still detonation-free there, I think I would stop the hunt. With 4.56s, IMO, there's no point on the street to strive for the limit. Anytime you nail it, she will spool up quick, and you won't miss a few horsepower; let it go. Top of second gear will get you 60mph in 6 seconds or less, so relatively speaking, loosing 5 or even 10 horsepower is as small deal. Whereas to gamble your engine for 2*or 200rpm, and loosing it, is a really BIG deal. Sometimes less is more.
Don't get hung up on the shape of the timing curve. Just get it slowed down for now. Put the stiffest shortest springs in there you got and buzz it up till it stops advancing. Then crank it back to 32*.If it comes all-in before 3600 you will need stiffer springs or lighter weights. Do what you gotta do to delay the all-in to at least 3400; at least!
If factory springs fit in your Distributor, I very highly recommend a two-stage curve. This requires one spring to have a long loop in it and to be very stiff.This guy will slow the second part of the curve right down, and since it does nothing in the first part, the curve down there will be very fast, so put the shortest stiffest spring you got on the other posts. So now your job is to set the changeover part of the curve as low as you can without getting detonation. Then the second part will/should keep it out of detonation.
But if factory springs do NOT fit in your D, then just slow it down as best as you can and delay the all-in as earlier described.
__________________________
My kink/bend ended up at 2800; and the second and total part is all-in at 3400. I have 20* in the D, and run 14 initial, for a total of 34* possible. The curve starts advancing at about 900 rpm .This keeps my aluminum headed-combo out of detonation and I can run 87E10 full-time, with 185psi cranking cylinder pressure.
I could and have, run a faster first part, but I didn't feel any gains on the street in my combo, so I took the safer route, with the idea that I might work on the curve at a later date. I never did bother ....... cuz I never needed more power,lol.
My cooling system runs at 205*F full-time, within a few degrees.
I run the next size smaller Hughes cam;
HE3037AL; 276/286/110/61overlap and 230/237@.050 compared to yours at
HE3844AL: 286/290/108/72overlap and 238/243@.050
With yours in at 106 and mine in at 108 almost all the difference is in the overlap
 
I have never run 200 with iron heads, high compression, and a big cam. With fresh ambient air going down the carb, you should be OK.
I am very keen to change your mechanical timing to 18 in the D, and to delay your all-in timing to nearer 32*@3600rpm. That would be 63mph. If that cures your detonation, I would sneak up on the timing,by first moving the rpm down 200rpm, to 3400, and retest. Then 34*@3400. But if still detonation-free there, I think I would stop the hunt. With 4.56s, IMO, there's no point on the street to strive for the limit. Anytime you nail it, she will spool up quick, and you won't miss a few horsepower; let it go. Top of second gear will get you 60mph in 6 seconds or less, so relatively speaking, loosing 5 or even 10 horsepower is as small deal. Whereas to gamble your engine for 2*or 200rpm, and loosing it, is a really BIG deal. Sometimes less is more.
Don't get hung up on the shape of the timing curve. Just get it slowed down for now. Put the stiffest shortest springs in there you got and buzz it up till it stops advancing. Then crank it back to 32*.If it comes all-in before 3600 you will need stiffer springs or lighter weights. Do what you gotta do to delay the all-in to at least 3400; at least!
If factory springs fit in your Distributor, I very highly recommend a two-stage curve. This requires one spring to have a long loop in it and to be very stiff.This guy will slow the second part of the curve right down, and since it does nothing in the first part, the curve down there will be very fast, so put the shortest stiffest spring you got on the other posts. So now your job is to set the changeover part of the curve as low as you can without getting detonation. Then the second part will/should keep it out of detonation.
But if factory springs do NOT fit in your D, then just slow it down as best as you can and delay the all-in as earlier described.
__________________________
My kink/bend ended up at 2800; and the second and total part is all-in at 3400. I have 20* in the D, and run 14 initial, for a total of 34* possible. The curve starts advancing at about 900 rpm .This keeps my aluminum headed-combo out of detonation and I can run 87E10 full-time, with 185psi cranking cylinder pressure.
I could and have, run a faster first part, but I didn't feel any gains on the street in my combo, so I took the safer route, with the idea that I might work on the curve at a later date. I never did bother ....... cuz I never needed more power,lol.
My cooling system runs at 205*F full-time, within a few degrees.
I run the next size smaller Hughes cam;
HE3037AL; 276/286/110/61overlap and 230/237@.050 compared to yours at
HE3844AL: 286/290/108/72overlap and 238/243@.050
With yours in at 106 and mine in at 108 almost all the difference is in the overlap
I didn`t read all the b.s. in these posts, long story short w/o eoins of red tape, why don't u seal the scoop/ ur pressurizig the engine compartment which IS working against the radiator. I learned this on my own caqrs, and a 505' chevy pick up a friend had.
 
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