73-87 Chevy _ GMC Trucks > Performance

Two part question

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runnergeorge:
Greetings! I’m a relatively new DIYer on a 75 c10 Cheyenne with a 350. This is a two part question related to vacuum advance and warping, I will try to keep them separate as I don’t wish to cause any confusion.

Vacuum advance: I installed a brand new distributor and set the timing (with vac line removed and capped) to 8* BTDC and reconnected the vac line. I’ve always been told that the vac line goes to ported vacuum on the distributor and not manifold vacuum. However I just read on another thread that it should always be connected to manifold vacuum to avoid overheating probs and idling issues. Which is correct??

Warping: I recently had an issue where I had to remove and reinstall my aluminum intake manifold and I noticed that when I went to put it back on it rocked forward and back. I’ve heard of intake manifolds warping, however my actual question is if the heads are warped would that mean the block is warped as well? I don’t have a head gasket issue as of yet.

Thanks for the replies!

VileZambonie:
You can easily check for warpage using a precision straight edge and feeler gauge. Make sure nothing is under the mating surface, wires, gasket material, foreign object, etc. but yes they can be warped. Using the tightening and loosening sequence is the way to avoid warpage.

You will find increased performance with more advance and better throttle response with full vacuum. Using the factory method for setting timing is fine, but will not optimize performance. Back in the day, we used to pop the vacuum advance hose off and set the timing to factory specs, then go through the emissions test lane. Before leaving the parking lot, hood goes up, vacuum hose back on, distributor cranked and rubber laid.

dusterdude:
Ported vacuum and ive had aluminum intakes tweak a bit before and welcome

Sent from my LM-X420 using Tapatalk

TexasRed:
Ported vacuum was a crutch for emissions testing, hotter engine temps at idle to get the catalytic converter to be more efficient.

It only affects the idle, off idle manifold and ported are the same.

MOST engines prefer full manifold. Try both and see.

You may want to restrict the amount of degrees on the can (today's fuel isn't what it used to be). You may also want to speed up the mechanical advance (by a slightly weaker spring) and advance the initial to maybe 10 or 12* with the can disconnected.

runnergeorge:
Thanks for the replies everyone. I will try both vacuum ports and see which one I like better and probably stick with that, for now. For the warping; if the heads are warped then the only way to verify if the block is warped is to take the heads off and check the block. I am looking to install a Proflo4 system and I just want to prepare myself, and my wallet, in case the heads/block are warped.

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