Posted by chriscase on Sunday, January 02, 2005 at 2:25PM :
In Reply to: Re: Title should be "How and why to re-curve a distributor& posted by MoparNorm on Sunday, January 02, 2005 at 12:54PM :
So you've made cam changes, carb changes, exhaust changes, compression changes, air filter changes, rolling resistance changes,load changes, gearing changes...and not changed total advance? If total (inital,centrifigal,and vaccuum added up) is not critical, then why worry about initial only?
Initial advance shows 2 things- starting position, and a reference as to where the full curve goes. All those items I mentioned in the previous paragraph will change engine loads and neccessitate a recurve to gain maximum benefit of those improvements. Yes Norm, changing the initial timing is beneficial, but still running the factory advance curve is only doing half the job.
Re: Vaccuum advance- it only works at partial throttle. It usually has a ported source that doesn't allow vaccuum to the diaphram until throttle is opened, and since vaccuum drops at full throttle vac advance then decreases. So adjusting the diaphram won't effect full load performance. Optimum vaccuum advance will increase gas mileage though: since centrifigal is limited by harmful full throttle pinging, but you can run additional advance at partial throttle. You can notice this on some cars that ping when you peg the gas but the pinging stops as the vaccuum bleeds off of the diaphram.
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