replicaracer43
Grumpy Old Man
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My 71 dart has a bone stock 5.2 magnum with a m1 dual plane and a sharply tuned thermoquad, 3:23 gears and a 904 and will get 20 on the highway steady driving.
Gas Mileage???
- Thread starter y2swinger69
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I have found the vacuum advanced hook up on my engine doesn't like much intal advance or total.
brasil
Well-Known Member
...same here VC doesn´t work ... not with 10 deg @ idle... not with 18 deg. @ idle
as soon as I use the VC the engine is pinging under LIGHT Trottle..
The AFR ist good...between 13.8 and 14.3 while crusing...
Perhaps one day I will build a new engine.... that works better
Greetings Juergen
as soon as I use the VC the engine is pinging under LIGHT Trottle..
The AFR ist good...between 13.8 and 14.3 while crusing...
Perhaps one day I will build a new engine.... that works better
Greetings Juergen
Are you driving it like a granny, or are you driving it like you should drive a mopar? (I love stoplights)
Juergen, disconnect the vacuum advance hose. It will allow more initial timing and only use the mechanical advance. This will limit total timing some but it will run strong.
BigBlockMopar
BigBlockMember
Vacuum advance is something that has to be tuned in as well.
VA is pretty much non-operational at mid/full throttle and comes in gradually again as engine-vacuum rises.
If the engine pings at light throttle, the VA should be limited a bit.
VA is pretty much non-operational at mid/full throttle and comes in gradually again as engine-vacuum rises.
If the engine pings at light throttle, the VA should be limited a bit.
10 mpg?! yikes. 
The 340 in my Duster is a '68 340, .060" over, 9.8:1 compression with 308 heads, 2.02/1.60 valves, 65 cc's chambers, stage II ported and flowing 264 cfm at .500", it has a Lunati 60404 Hydraulic cam, .513/.533", 276/284 advertised duration. I run it with an Edelbrock Air-Gap RPM intake, Holley Ultra 750 double pumper, headers, 2.5" dual exhaust. Timing is 20* initial, 34* all in mechanical, no vacuum advance. I have 3.55 gears, 26" tall tires and a 4 speed, and at cruise my AFR's are usually in the mid to upper 13's. Should be around 400 hp.
On the highway in with mixed driving I get about 13 mpg, I can do a little better with freeway only miles because it's easier to keep my foot out of it. And there should still be some room for improvement even with my set up because of my AFR's and timing, but I'm near the edge of detonation with the iron heads so I leave a little timing out and some extra fuel in. So, if I can get 13 like that with a 750 double pumper, you should absolutely be able to do better.
The 340 in my Duster is a '68 340, .060" over, 9.8:1 compression with 308 heads, 2.02/1.60 valves, 65 cc's chambers, stage II ported and flowing 264 cfm at .500", it has a Lunati 60404 Hydraulic cam, .513/.533", 276/284 advertised duration. I run it with an Edelbrock Air-Gap RPM intake, Holley Ultra 750 double pumper, headers, 2.5" dual exhaust. Timing is 20* initial, 34* all in mechanical, no vacuum advance. I have 3.55 gears, 26" tall tires and a 4 speed, and at cruise my AFR's are usually in the mid to upper 13's. Should be around 400 hp.
On the highway in with mixed driving I get about 13 mpg, I can do a little better with freeway only miles because it's easier to keep my foot out of it. And there should still be some room for improvement even with my set up because of my AFR's and timing, but I'm near the edge of detonation with the iron heads so I leave a little timing out and some extra fuel in. So, if I can get 13 like that with a 750 double pumper, you should absolutely be able to do better.
Not to highjack the thread, but I'm hoping this question will help the OP in regards to tuning.
Here are my specs as stated earlier.
My timing is set around 14 degrees adv. initial. And it seems to run the best.
I do have vacuum advance hooked up.
Low and Mid RPM response is phenomenal. I do have a audible ping at High RPM (around 4500+) even with 91 octane. I live at 4500 ft above sea level. I'm running a stock VA distributor. I'm thinking the total advance is within range. My fuel pump is a Carter performance one [120 gph, 6.9-8.1 psi]. So I know its not that.
So I'm thinking I should put the initial back down to 10 degrees. Any suggestions? Or should I invest in a performance distributor?
Here are my specs as stated earlier.
My timing is set around 14 degrees adv. initial. And it seems to run the best.
I do have vacuum advance hooked up.
Low and Mid RPM response is phenomenal. I do have a audible ping at High RPM (around 4500+) even with 91 octane. I live at 4500 ft above sea level. I'm running a stock VA distributor. I'm thinking the total advance is within range. My fuel pump is a Carter performance one [120 gph, 6.9-8.1 psi]. So I know its not that.
So I'm thinking I should put the initial back down to 10 degrees. Any suggestions? Or should I invest in a performance distributor?
rmchrgr
Skate And Destroy
Limit the mechanical advance. If you don't limit the mechanical, the vacuum advance can add too much timing, your total can end up being way too high.
Some V.A. canisters are adjustable though. If it is - stick a 3/32" Allen key in the hole and adjust it however needed to make the pinging stop. Clockwise is advance, CCW is retard, the Allen key will stop after a certain number of turns either way. Start at the lowest retard setting, drive it and see what happens. Work your way up until the pinging starts then back it off.
mguner
How many is too many?
What carburetor? Your metering rods or power valve may be too weak and pulling closed...
I tuned the carb with an AFR gauge. My jets and rods have already been set. The only thing I haven't looked at yet is the distributor. I'll do what rmchgr suggested its running so good other than the WOT ping I would hate to retard the timing less than what it is now.
MopaR&D
Nerd Member
+1 on limiting the mechanical advance, do you have a stock damper? You really need to know the timing at full mech. advance, either get some timing tape or make extra marks in your damper up to 60 degrees BTDC
jbc426
Well-Known Member
My daily driver '68 'vert with a 500hp Eddie headed 408" EFI'd Magnum pulls down 18mpg at 70mph with the top up. It does have a .67 overdrive and a lock-up converter spinning 275/60-15's though. 12 mpg around town if you go slow enough to pace regular traffic.
Jbc, what's your rear end gear ratio?
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Advance is the key. Actually,lighting the mixture off early enough is the key. With 3.23s and 26.5 tires, your cruise Rs at 65 might be around 2650. Iron open chamber heads like tons of advance at cruising speed.Ima guessing 40 degrees or more, perhaps as high as 48. And at cruising Rs she will be more than happy with 93. If it pings under tip-in, sacrifice a little centrifugal timing if you have too. I would delay the centrifugal to be all in around 3000 to 3400, then crank in a 22* Vcan as fast and hard as the engine will accept it. Lean her out as you go.Get yourself a dial-back,dash-mounted timing gizmo and start experimenting.That device will pay for itself real quick.
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mguner
How many is too many?
Do you have an accurate reading of operating temperature and or cylinder head temperature? What is the concentration of your coolant/antifreeze? Too much antifreeze reduces the efficiency of the cooling system. Anything to reduce cylinder temperature will also reduce the chance of detonation. Different thermostats that are rated at higher temperatures actually can improve heat transfer in the heads. Certain types of fans can actually get in the way of air at cruise speed and cause temperature spikes as well. If the tune is where you like it then perhaps you have been looking in the wrong place to solve the issue...... At least as far as not being able to run vacuum advance.
brasil
Well-Known Member
@ AJ/Form /S
I have 3.23 gears... 26.5 tires and Iron Heads ( x Heads ) and as soon as I hook up the VC ..the engine makes this strange sound at 50- 60 mph.. exact the range when I need the VC.... When I accelerate hard... there is no pingnig...
Greetings Juergen
I have 3.23 gears... 26.5 tires and Iron Heads ( x Heads ) and as soon as I hook up the VC ..the engine makes this strange sound at 50- 60 mph.. exact the range when I need the VC.... When I accelerate hard... there is no pingnig...
Greetings Juergen
mguner
How many is too many?
EGR solved some of these problems at the price of performance. They were intentionally running a lean mixture and just filling up space in the cylinder with a somewhat inert gas from the exhaust. The causes will be one or more of the following: high cylinder temp, lean mixture no mater what your wide band says, too much timing, poor fuel quality, too much compression for the cam profile, vacuum leak falls into the lean category and could also be expressed as to much bypass in the PCV valve.
The best thing about an EGR valve is that it closes at a lack of vacuum, AKA, wide open throttle. During normal operation, part throttle, the valve is open recycling exhaust gas from one exhaust port only. (Small block at least.)
Since at the cruise stage and modest acceleration, the performance factor is not missed.
Since at the cruise stage and modest acceleration, the performance factor is not missed.
mguner
How many is too many?
In theory as long as you keep it clean yes. They are still a problem on many new models, especially diesels.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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55 is about 2200/2300, so if you free rev it to that rpm and read the advance with the Vcan hooked up, you can read what the engine is seeing. Then you can decide what needs to be done. Obviously the engine is complaining. So if the rotor is not crossfiring,(due to a phasing error) then it must be too much advance. But you don't know how much. So the easiest thing to do is back up the initial about 4 degrees and road test.Back up in 4 degree increments until the engine is happy. Then read the damper again at 2200. That is your cruise timing target. Now go make it happen. Either limit the Vcan, or back off the centrifugal. You can do the same thing at 2400 or 2000 or 1800. From the data you can build a cruise curve to hit as many bases as possible. Concentrate on the important ones,cuz you won't hit them all. You might hit one or two or at most three if you are good, or patient, or lucky.
Sometimes you have to reduce the engine running temp. And sometimes if the engine is sucking hot underhood air there is almost no cure
I run 205 at the top of the stat-house, but have fresh cold air, and aluminum heads. The temp is rock solid.I run .8 degree per 100 rpm centrifugal timing, below 2800. So at 2200 I would be running 2200 less 1000(where the curve starts) x .8 =9.6 over the base 14. So that adds up to 14 + 9.6 =23.6 @ 2200. To this while cruising,my Vcan adds up to 22* , so that totals 45.6 degrees at 64mph. To this I can add/subtract up to 7.5 more with the dash-mounted, dial-back, timing-gizmo. So 53 is possible.
For inquiring minds, after 2800 the timing changes to about .6*/100 rpm, so somewhere around 3400 it totals around 34*. This is what it takes to keep a near11/1 aluminum headed engine out of detonation on 87E10. Most days I have more power than I know what to do with. If I need to blast of in a hurry, I just rev it to over 3400 where I have full timing,slip the clutch out,and hang the heck on.Otherwise, at lower rpms I am almost exclusively at part throttle, so those extra 22* from the can are contributing to the manufacturing of torque and saving me mountains of cash, at the pump.
For instance;
at 1200 rpm, the centrifugal timing is (2 x.8 )+ 14= 15.6 plus up to 22V = 37.6
At 1600 it is (6 x .8) + 14 = 18.8 plus up to 22 =40.8
At 2000 it is (10 x .8) +14 = 22, plus up to 22 =44
And so on to 2800, when the curve changes.
Those 22 degrees are adjustable from the driver's seat via the gas pedal; how great is that?! When you get it right, you won't even know it is happening.
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brasil
Well-Known Member
got you !
I think now I know where my problem is... first I have too much timing @ idle..( 16 deg ) and the curve is to fast... all in 35 deg @ 3000 prm
So I will keep your advise... go "down to 12-14 deg @ idle...with 20-22 deg advance all in around 3500 rpm....
I have a Vacuum caister from CRANE so I think this canister can be limited ( in case )
Thank you
Juergen
I think now I know where my problem is... first I have too much timing @ idle..( 16 deg ) and the curve is to fast... all in 35 deg @ 3000 prm
So I will keep your advise... go "down to 12-14 deg @ idle...with 20-22 deg advance all in around 3500 rpm....
I have a Vacuum caister from CRANE so I think this canister can be limited ( in case )
Thank you
Juergen
67Dart273
Well-Known Member
Pisses me off the multi quote doesn't work
67Dart273
Well-Known Member
Pisses me off the multi quote won't work
You've left a lot on the table. Has your mechanical been re-curved, that is, shortened? You cannot just crank up the idle / initial timing
There's a lot of nonsense with vacuum advance. You/ we are dealing here what amounts to re-engineering the engine package. "Back in the day," my 340 saw over the years.....a Thermoquad, an adapted square bore Holley, a COUPLE of the then new Holley spread bores, and a GM Quadrajet, then an AFB!!!
NOT ONE of those carbs had the same characteristics at the vacuum port!!!!
The LAST thing is......are you guys running "ported" vacuum, or intake vacuum? FBO claims you MUST run intake vacuum, but that is NOT the way the factory did it, and also not what I've ever done. Running intake vacuum requires an entirely different mechanical advance to get it to work
67Dart273
Well-Known Member
The old article posted here by AbodyJoe is a huge help
new distributor vacuum advance causing hesitation
new distributor vacuum advance causing hesitation
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