[bryanw1968]

Originally Posted by crazy longhorn

The old 60's stuff was hooked to manifold vacumn from the factory, whereas into the early 70s the trend was ported from the factory(emissions). Now you will get about a lot of different veiws on the proper way to set up the manifold vacumn, but as a rule a true performance eng should be hooked to manifold vacumn. Your run of the mill streeter (close to stock cam ect), may work out better in some apps on ported spark. Full manifold vacumn will smooth the idle, give better throttle response, & keep you engine running cooler(cyl head temps). My 383 (specs in the sig), likes a 34 degree total (all in @ 2800-3000) + 12 degrees extra in the vac can (hooked to manifold vacumn). The trouble with the HEI distribs, & too much advance, is that they need to be recurved to run properly in these old trucks. They were setup to run ported spark, & to run full manifold vac @ the can, you need an adjustable can , such as a Crane unit to cut the vac advance back from 20 or 22 degrees(that the can has) , to the more useable 10-12 that the hipo engins like. The only reason to disable the vac can on a street motor, is with a cam that is so "rowdy" that you dont pull enough vacumn to be able to use the can. you also dont need that vac can for racing, but you will like the mileage & throttle response that it gives on your streeter. Good luck tuning..... L

Interesting.....

If you had the VA hooked up to direct vacuum down here where it's hot most of the time wouldn't that make the motor drag when starting? Or would there not be enough vacuum present when starting to make a difference?