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Old 08-24-2008, 02:47 PM
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Vacuum advance help

This is my 1st post and I need some help! I have a 350 sbc with a 280H comp camshaft and was wondering if there is any advantage to not hooking it up, when going down the drag strip?

Thanks Caleb!

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Old 08-24-2008, 03:46 PM
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Quote:
Originally Posted by 75GMCman
This is my 1st post and I need some help! I have a 350 sbc with a 280H comp camshaft and was wondering if there is any advantage to not hooking it up, when going down the drag strip?

Thanks Caleb!
Vacuum advance is mostly for engines in a sustained cruise power range, such as seen on the street to and from the track. In a drag race vacuum advance isn't necessary.

Bogie
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Old 08-24-2008, 05:08 PM
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dist

In a drag race only application there is no need for one.

Keith
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Old 08-24-2008, 05:53 PM
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Quote:
Originally Posted by 75GMCman
This is my 1st post and I need some help! I have a 350 sbc with a 280H comp camshaft and was wondering if there is any advantage to not hooking it up, when going down the drag strip?

Thanks Caleb!

Generally speaking===
on a drag engine, a properly calibrated vacuum advance that is hooked to full manifold vacuum will make your drag engine idle better, smoother, with more vacuum, and less "loading up", and often makes the throttle "tip-in" crisper.

IMO any engine running without vacuum advance is not operating to its best.

There have been several threads about timing and vacuum advance in the past month. Search for them and read the links to information, including an article by Performance Distributors of Memphis.
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Old 08-24-2008, 09:42 PM
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If you drive your car on the street at all then you want to retain vacuum advance. There are no reason to disconect it.
If you want to get the best out of your motor with a 280H cam you need to modify the spark advance curve of your stock distributor. Including dialing in the vacuum advance amount and rate.
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Old 08-25-2008, 08:17 AM
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during a drag race manifold vacuum should be near 0 inhg, so the vacuum advance will have no effect.

However, the idle will be cleaner if you use the vacuum advance on the manifold at idle (if you use an adjustable vacuum advance and limit the travel to around 10 to 12 degrees). Could also help get you off the line just a little quicker when you first tip into the throttle. But after the throttle opens wide, the effect from the vacuum advance is gone.

For pure drag racing, I would just set the initial timing to 20 and total to 38.
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Old 08-25-2008, 06:49 PM
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Vacuum advance makes it run smoother & cooler in the pits and on the return road.
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