Vacuum Advance question?

[451Mopar]

How much is too much vacuum advance?

Problem: stock 1970 440-HP Engine running hot.

Found problem #1: Choke may have not been opening all the way - Problem Corrected.
Found problem #2: Over 60+ degrees total ignition advance when vacuum advance is connected.

The distribitor is the Accell Billitproof (I got it because it is adjustable.)
I reset the total mechanical advance to 34 degrees. This gives me 10 degrees initial advance at idle.
I inserted a hex wrench in the vacuum advance unit and turned the screw counter-clockwise about 6-turns to reduced the vacuum advance so I only get about 50-52 degrees advance (at 3,000+ RPM, no load.) This also delayed the advance starting point from about 5" of vacuum to about 7-8" of vacuum according to my mighty vac tester. The stock engine pulls an easy 15"+ of vacuum (no load.)

Does my new timming curve sound OK?
What is a normal total advance with vacuum advance anyhow?

[creative1]

sounds pretty damn good to me. thats what i am shooting for... 20-22* mechanical, 18-20* vacuum, and the balance in initial for a total of 50-52*.

[6 packin]

Way too much ADAVNCE for most any engine, even race egines only need 38-40 deg total. They could run more....but no gain in power..in 99% cases they loose power. Reset the intial to about 15 deg advance then set mechanical to 20. This is about 35 deg total all you will need. Forget the vacum advance, unless you want it. But still must need 14-16 intial and 34-38 deg total.....40 at the most. There could be your heating problem??? Also could be a lean condition too, check your plugs should be nice and tan.....not white!

[djswwg]

First of all, to determine if the vacuum advance is over advancing the timing to the point where it's causing the motor to overheat, simply pull the vacuum hose off and plug it. Now drive the car in the usual way. Still overheating? If so it's not the vac. advance causing the problem. Second, vac. advance only has one function, and that is to make the engine run as efficiently as possible at part throttle, (cruising) speed. It has NO effect at idle or wide open throttle, PERIOD. If it's still a problem, do this. Turn the adjustment all the way in, (clockwise). This makes sure that vac. advance will not happen till maximum of engine vacuum required hits it. (Read part throttle, cruising speeds). You can then make small adjustments, say 1/4 turn at a time, and road test after each till you get the best setting for your motor. here's another clue, when vac. advance is to much, it will make the engine surge or buck mildly, even though it may not make it ping. If it does this, push the throttle lightly and if the surge goes away, it's definitely over advanced. Hopr this helps......djs

[dkn1997]

if you are getting vac advance at idle, check which port it's hooked up to.

[451Mopar]

I's the stock Carter AVS, It only has one port for the vacuum advance (and a full vacuum for the choke pull-off.)

The engine seems to be running pretty good, but I'm going to pull a spark plug to see what it looks like.

I don't think this engine needs alot of initial advance as I think it has 10:1 compression and the stock cam. Do you think it would help it run cooler if I pulled the heads and install some composite head gaskets to drop the compression?

I think a good part of my overheating problem is airflow through the radiator. If I cruse at a steady speed the engine temps stay fairly stable (but still hot, maybe 220 degrees?)
Because the radiator is an aluminum crossflow, I currently don't have a fan shroud that fits. I'm going to make a shroud and see if it helps.

I just din't think a stock 440 should run so hot. It's easier to cool my 451 stroker engine than this engine?

[dartgt340]

i dont understand the extreme total timing concept. i run 36-38 total on everything in the driveway. i also believe in canning the vacuum advance altogether. the only thing vacuum advance is suppose to due is make the engine start easier with retarded timing. but if you are able to run that much timing i dont see it as a problem .i set all of my engines at 36-38 degrees at 3000 rpm or when full mechanical advance is reached.

[dartgt340]

as far as your cooling system,i have had more luck out of a 90 degree plastic fan than any stock or other aftermarket fan. a fan shroud is an absolute must also. good luck

[mtrv8n]

Get a 175 degree thermostat, and add some water wetter(or something similar) to your radiator.

Your timing of 34 degrees mechanical is in range, and should not cause problems. The vacuum advance will not cause overheating unless you've got more than 52 degrees there total.

I also have a flex fan, which moves huge amounts of air at idle, when you need it most, and flattens out at high rpm to save power.


dart GT - vacuum advance is useless to racers, but for the street it saves fuel and keeps the plugs clean. It's good if you need it, neither good nor bad if you don't. I can get almost 16MPG with my crate motor because of the vacuum advance. Of course, if I floor it, I can WATCH the gas guage drop...

[Luther]

451Mopar: Check out this link for tuning tips: http://www.sweptline.com/tech/engine2.html

Your initial + mechanical + vacuum advance sounds about right to me. I know some people will dissagree with me, but I would try to keep the vacuum advance if you run your car on the street and want half way sane gas mileage. If you only race your car, the vacuum advance is not needed and you can get rid of it.

Vacuum advance adds timing to the engine, but it is based on engine load. When the throttle is partially open (highway cruising), manifold vacuum is high and subsequently adds timing as vacuum advance. At wide open throttle, manifold vacuum is near zero and should not add any timing from the vacuum advance.

[jelsr]

As djswwg pointed out, the vac advance is an economy thing, not a performance thing. When you have the loud pedal to the metal you have virtually no vacuum to run the vacuum advance. If you are not running deep screws you can check it with the vehicle stationary. Run the engine at the approx cruise RPM with a vacuum guage hooked up. Crank the dist to advance untill the needle starts dipping occasionally then back untill the needle is steady. This is max! Limit your mech adv to 38 deg or less ( different engines like less than others) and adjust your vac adv to pick up the rest to the aforementioned max. Again, we're talking a streeter here, not a racer.

[451Mopar]

Thank's for the input. I know how the timming works, I need to verify that it is in the ball park for a stock 440?
My other engines are modified and like different timming curves, but this is the first stock 440 I have owned.

[renee]

My 2cents- a Carter AVS unlike a Holley Does use vacuum advance at idle (if initial timing is 0º without vacuum, it should be 6-10º with). Don't use more than 40º total advance! Use factory specs as a baseline! P.S. Turning clockwise on a vacuum unit will increase sensitivity, not decrease it!

[345Dart]

What % of antifreeze- water do you have? I changed to a 65/35 from 50/50 mix and it dropped 10-15* for me. It will also increase your boiling point. Use distilled water. M2CsW.
52-54* is max. total for 440s from the literature I have.
Happy cooling