Correct initial timing?

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You ever hear of these new things they got out now? Makes reading a lot easier. They are called paragraphs. Use them please?

AJ/FormS said:
Later timing also makes stick-cars with 3.55s, less jumpy, at or below idle speed.By lighting the fire a lil later the peak pressure in the chamber occurs a lil later with the piston already well on it's way down. This smoooothes the power delivery to the crank, and makes the engine a lil lazier to respond to throttle inputs.This makes it possible to run the engine down below idle speed with those hi-way gears, and allow you to perhaps parade the car with 3.55s instead of a much bigger gear. Comfortable walking speed is about 3.5 mph. Just try to drive your 3.55 stick down there. This is 410rpm; it ain't gonna happen.About the lowest my 360 230* cam engine will go before the vacuum is so low that the PV starts messing up, is 500rpm. With 3.55s and a 3.09 low, this is 3.66mph.
At 14* timing @500rpm,the car starts to buck like an old '80s Mustang. At 6* it still ain't smooth enough, so I took the CFII disc out and put in a nice Factory 340 disc.With the softer sprung hub,the reduced timing, and a big fat flywheel, things settled down enough to make it a doable thing, and I sold the 4.30s.
When my car was all shiny and new, parading was the thing to do. Not so much any more. Now I just do it cuz I can,lol. 3.66mph is still kindof a power-walk.
The power-timing window is very small. With iron heads it usually falls between 32 to 38 degrees. With top grade gas,and a well engineered chamber it may fall in a slightly tighter window of 34 to 36 degrees.
But the idle timing and rate of advance can be just about anything. With an automatic and a 2200 type stall, you can run a lot. But when it is just 1 degree too much, stuff makes noises and eventually breaks, so keep the engine quiet. Better it is to be even 5* retarded than to be 1* too advanced.
As to the vacuum advance, that baby is a gem.Yeah sure you can use it to good advantage in extracting every last bit of energy from a lean mixture and drive fuel economy to the max.
But there are other advantages. Remember that this device is almost in lock-step with manifold vacuum. And remember that leaner mixtures are possible when you start the fire early. Not only possible but the leaner mixtures demand the fire to be lit earlier.And the leaner mixtures are often where the torque is at,with these low throttle/high manifold vacuum settings. The lean mixture/early fire, seems to smooth the engine in low-speed, low-load applications such as cruising above about 1800 to around 3200. When I say cruising, I'm not meaning steady-state speed but rather just tooling around in traffic. This is where the engine could be wanting 40 to 50 or more degrees of advance, and there is just no way to get it without the Vcan. The engine will develop more footpounds with the extra timing, allowing you to reduce the throttle opening, and that means, you guessed it, less fuel being dumped into the intake.So here you have a double whammy; more torque on less fuel. What's not to like about that? And remember where a streeter spends the bulk of it's life; hyup, tooling around!
IMO, if you are not running a Vcan on your streeter with a typical street cam, you are either; unaware of the advantages,not talented enough to pull it off, or just don't care enough to pursue it...... I used to say; ignorant, stupid or just don't give a liquidfart. But that's just plain mean, and nobody like a meanie;and I prefer to be liked.
So now, you can no longer claim unawareness, and the talent you can learn.As to caring enough to pursue it, I guess we'll see.
BTW;
The window of operation of the Vcan is pretty narrow.I suggest you put a vacuum gauge on the spark-port and check it out while driving. You will see that from idle to well above,that port remains pretty silent. Then it begins to build vacuum and eventually catches up to manifold vacuum. Then it runs lock-step with manifold vacuum for a while, before starting to drop out. By the time the primaries are open enough to engage the secondaries, the spark-port vacuum should be dropping quite fast, perhaps already dropped right out. What I'm saying is that this spark port vacuum might only be working from about 20%primary throttle to a bit over 50/60% primary throttle, AND it may be highest over a very very narrow window of say 25/30% to 35/40% I'm being purposefully vague, cuz I've never actually measured the throttle opening. But since the spark-port is physically fixed in the throttle-bore, the amount of vacuum measured at the port is always related to where the throttle blade is in relation to it, can never exceed manifold vacuum,always reads highest when manifold vacuum is highest, runs lock-step for a bit and then joins the manifold vacuum in its declining stage, but dropping out faster.
So now, it's up to you to take advantage of this knowledge, and give the engine what it craves, when it is craving. If you start with too much idle timing you may limit the amount of Vcan timing possible. If you don't start with enough idle-timing, you may never reach the optimum timing. Therefore it follows that if you really want to find the optimum cruise timings, you need to start with an optimum idle-timing and rate of advance. To try and help you find that optimum idle-timing, you need to sync the transfer port. I believe this was already mentioned. You can check out the Holley website, or click on my signature down at the bottom of this post.
Do not be overcome if you see the cruise timing start to climb above 40 or even 50 degrees. And as you start leaning the cruise circuit out, you may revisit the vcan and find that it wants even more. Eventually you may find the total timing at a cruise speed of say 60 mph, wanting to be close to 60degrees. In all likely hood your dizzy won't go there. That doesn't mean the engine won't be happier with 60* But most will only go to 36 in the mechanical plus 24 max in the can for a total of 60*. But seldom does this happen simultaneously . More typical is 28* mechanical at 2800 rpm plus 24 in the can =52*; this being about 65 with 3.55s . But if you're running 3.91s and 65mph is 3200 rpm then it is possible that everything is all in and then that would total in the neighborhood of 60*. It's never enough until it is too much. Don't let it be too much, cuz stuff breaks.It's always better to be a little short on timing than a little too much!
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Yes i read it, some good info. However im not driving it in a parade. Idle is at 900 so it would be creaping faster then 3.5 mph.
So you set your initial first? Then whatever the vac advanced is at is what it is? Ive never even put a gauge on it to see if my cam is allowing the engine to produce enough vacuum. My 833 4th gear I believe is 1:1 and at 55 im doing 2k and at about 65 im doing 2500. Wouldnt that be too high of a rpm for vac advance to matter?
No matter what gear im cruising in I always keep it around 2k
 
At light load is when you need the vac advance, since lean mixtures burn slower... such as a steady cruise. 2500 rpm is not too high - the vacuum depends on how much throttle opening it takes to maintain speed.
The cans with the hexagonal end are adjustable via 3/32" Allen wrench through the hose nipple. Too much advance may cause a light load bucking or surge, so just turn the wrench until it goes away.
 
Why in the world are you idling a 68 340 with an assumed to be stock cam, at 900rpm?
I'll tell you why, cuz the T-port sync is out to lunch, and this how you got it to smooth out. Am I close?
Even my 292/508/108 cam did not need 900 rpm.
Slam the secondary butterflies up tight but not sticking. Then, turn the idle down to 700/750. Reset the mixture screws as may be required. Stop the engine, pop the carb off, flip it over reset the curb-idle screw to expose the transfer ports to be square to slightly taller than wide.Make sure the fast idle cam does not interfere,if you have one. Now put it all back together. After this do not touch the curb-idle speed screw. Start her up.Reset the mixture screws as may be required.Now if the idle speed is too slow, crank in some timing, to a maximum of 20*. If the idle speed is too fast, crank out some timing, down to a minimum of 10*. If the rpm still is not acceptable, you will have to add or subtract air. Adding air usually increases the rpm, and is done by cracking the secondary butterfly,NOT the curb idle screw. Subtracting air is more difficult, and is only very seldomly required. The idle speed with a stock 340 cam stick- car can be as low as 600/650rpm. An automatic needs to compensate for the TC. Depending what TC is back there you may have to add 100 to 150 rpm, to get that 600/650 in gear.
If you can't make this happen, then,either; the engine is tired, or broken, the TC is too tight, the parts are out of spec, or the cam is not stock .
What did I miss?
Oh yeah; the fuel is crap or the fuel level is wrong.
You might be thinking, "can he really tell all that from a 900rpm idle? " No, I guessed at everything. Now prove me wrong, pop the carb off!
 
Everything is new. Idle was tuned by the engine builder after car was done. Isnt the idle spec at 900 rpm? It runs and drives great. seems fine to me. Idle is between 850 and 900. Why would you want the idle so low in a stick car? Its not the factory cam. It has a lunati voodoo cam and Its a fully built high performance engine
 
Spec/schmec.
That spec was for to pass emission tests.
And stick cars got a throttle kicker to close the throttle at key-off so the darn things would actually shut off.

Forget specs, give the engine what she wants.
 
Im just askin. What is the benefit to have it idle at 600 vs 850 or 900? Im sure it will idle down that low but seems perfect where its at. I thought manuals always idle higher than autos. Carb has not been touched since it was on the dyno.
 
Idle with that Lunati Voodoo may just be smoother at 900... depending on alternator it may keep things charging at idle too.

My Mini-Express (slightly reground) is 312 advertised, [email protected], and likes 1100-1200. Also I have found that it idles best with over 30 advance, but I currently have 24 initial so I can start it hot, and a relatively decent 7" vacuum at 1200.
 
No benefit, just when the T-port gets lost driveability suffers.
900 in neutral bangs pretty good into gear. If you are putting it into Drive, this shock gets absorbed by the rear over-running clutch. This part is the first part to go into the tranny so when it gives up, you are looking at a complete teardown. The U-joints take a beating too, as does the differential.
Occasionally the sudden loss of air speed through the venturies also causes idle issues and stalling.
The higher rpm causes the engine to pull harder at a stoplight, and so you have to press harder on the pedal, and stay alert.
And
you can't hear the cam :(
 
280/240? Guess who's not paying attention;me.
Now the T-port sync just became priority one!
I happened to see that the timing spec on a 68 340 is at tdc and 69-72 is 5 degrees btdc. Im running 15 degrees of initial timing and car runs fine. Is there a reason why the factory timing is so low?
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Ok I guess there's no saving my dignity

Your engine is not stock, so why are you curious about stock specs?
 
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But it doesn't bang into gear with a 4 speed. I give it some rpm as i let out of the clutch maybe around 1200 ish.

I assume the engine builder set it up correctly before thry dynoed it. I didnt install the carb and havent touched it in 4 years and seems the same as it's always has been
 
AJ/FormS said:
280/240? Guess who's not paying attention;me.
Now the T-port sync just became priority one!

Ok I guess there's no saving my dignity

Your engine is not stock, so why are you curious about stock specs?
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You have plenty of dignity aj. I was just curious why the timing specs were so weird. Ive never heard of setting timing at 0* tdc lol
 
You can tell that just by hearing it? The engine builder tweaked the carb after it was installed in the car. He went to the back of the car about three times and listened then he would go up and tweak the carb
 
Stable idle at 1200 rpm, 27 degrees timing, 8" vacuum. :) It would like even more, but that'd be too much for street driving.

Here's a quick idle & rev. I need to take the wideband sensor out and give it a good cleaning... it quit reading again after a shutdown! The displayed swing from 8 to 10 and back indicates warmup mode for the Autometer gauge. The heater may have failed. Anyway it's normally about 12.5:1.

 
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