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Author Topic:   To use Vacuum Advance or Not to ues it?
posted April 27, 2004 11:18 AM
I have heard of people who do not use the vacuum advance for there circle track racing. I have always just plugged it in. What is the difference in using it or not using it? How would you time the motor W/O it. I run my current timing @ 28 degreese @ 2500 RPM with the Advance plugged in.

posted April 27, 2004 12:00 PM
I wouldnt run vacuum and I wouldnt mechanical either. I would prefer to run the advance all locked up so that there were fewer things to cause problems. Then you set your timing at your final number and thats it no matter what rpm your at your timing is set to your best number.

On the track I doubt you ever drop below 3000 even 3500. If all your mech advance is in by that point then there is no need to even have it. The advance wont affect anything above that speed. I know guys will say it makes it hard to start but htere are ways around it.

[This message has been edited by dirtbuster (edited April 27, 2004).]

posted April 27, 2004 02:50 PM
Couldnt you just hook up the vacuum advance and then set your total timing at 3500 rpm? Or will the timing keep advancing as the rpms increase? For some reason I always thought that the vacuum advance would retard the timing so it would make it easier to start. I tell you what, understanding how vacuum advance actually works is probably one of the hardest concepts to understand for me when it comes to an engine.

I always just leave mine plugged and set total timing at 36 degrees. I do have a mini starter but with the cam I use it is difficult to start at times. Was actually thinking about hooking up the vacuum advance.

So if I do this, you say to set total timing at the highest rpm's I'll be seeing?

posted April 27, 2004 03:19 PM
small rock,
As for starting I assum you have a switch and a push button. Wire it so that you can turn the engine over with the button with the switch off. When you start it get it spinning over with the button the hit the fire switch. Thats how the big boys do it and it does make a difference. It may take a little practice to get the timing right but its worth it.

As for vacuum if you source your vacuum from the intake or below the throttle plates in the carb then vacuum is highest with the throttle closed and decreases as the throttle is opened.
If you source it above the throttle plate in the carb vacuum will be lowest at idle and increse as rpms and airflow through the carb increase, increasing timing. If you dont have a stop on your vacuum can then timing will continue to increase as vacuum increases at higher rpms.

In my opinion vacuum advacne has no use or place on a race or high performance engine. If you want to run mechanical advacne i would make wure you keep an eye on it to make sure it doesnt cause problems but i would ditch the vacuum advance.

If you run mechanical advance rev the engine until it no longer advances. This is the point you have full mechanical advance and is usually around 3000 rpm with high performance advance curves. Set your total timing at or above that rpm. Then dont worry about what it is at idle just let it fall back where it does.

[This message has been edited by dirtbuster (edited April 27, 2004).]

posted April 27, 2004 04:45 PM
i'm with dirt buster no vac or mech advance get a plate for the vac and weld the rest i've been a victum or those ****py bushings letting go while leading never again

posted April 27, 2004 05:31 PM
I have been running the vacuum advance for 4 years now, I never get more than 5000 RPM. I have never had a problem either. But my question is, will I get any better performance by unhooking it. If I do unhook it do I need new springs and weights or do I just unplug it?

posted April 28, 2004 01:31 AM
I put in a curve kit[about $8.00]and set timing at 36/2500 rpm. this helps the car start easyer. If you let off in the corner then stand on it you lose your vac and your timing drops evan though you may still be at 3000/4000 rpms.I just plug vac and make sure it can not move around inside dist. Put a vac gauge on car and hit the gas and watch the gauge.

posted April 30, 2004 08:12 AM
Unhook the vacuum and lock the mechanical down. That's how most every race engine is set up. This way, there's less moving parts in the distributor and you alwys know what the advance is set at. You can spend the rest of your life chasing power with springs and weights.

One thing that might help you squeeze a little more performance out of that motor is to add some gear. 5000 rpm at the end of the straight is pretty low. What rpm are you coming off the corner at? Its amazing how the correct gear can wake an engine up.

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