I've recived my advance kit in the mail today which I got from Ebay and my distributor that I rebuilt with the correct number for my '72 Skylark 350-4 is ready to go so I plan to power time in the next couple of weeks. My question is in the kit, besides the springs, it came with an adjustable vacuum advance and a cam. Do I need these or can I just use the springs? I don't plan on racing the car and for the most part the engine is stock with the a/c removed and most smog stuff except for the pcv valve and fuel vapor canister that hooks into the air cleaner snorkel. Thanks for any advice... Brad
Brad, My advice is to have Ken from Everyday Performance rebuild and recurve your distributer. Best performance upgrade I have done since my stock rebuild.
Thanks guys, I've been to Everyday Performance web site and can tell they know what they're doing. I didn't want to spend the extra money but sometimes that's the best way. Thanks for the link Bill, I've read that post and forgot all about the section that shows what to do with the kit I have! Think I'll mess around with what I have and if I don't like how it works out I'll send the distributor in to Everyday Performance for a rebuild. Thanks, Brad
Unless you plan to modify the amount of mechanical advance in the distributor you are using, you can just use the springs. The springs will change the RPM where all the mechanical advance is in. If you bring it in much earlier than stock, you will need to modify the vacuum advance as well. Why? The stock distributors typically delayed full mechanical advance until as late as 4600 RPM. That means at your typical cruise RPM, only PART of the mechanical advance was in. The vacuum advance canister supplied 14-18* of advance in addition to whatever partial mechanical advance was in. Now look at what happens when you use lighter springs to get the mechanical advance in earlier. Now, at your typical cruise RPM, ALL of your mechanical advance is in. Add the 14-18* of vacuum advance, and your cruise timing can go above 50*. That's too much. The engine may surge at light load cruise. It therefore becomes necessary to restrict the amount of vacuum advance in the canister from 14-18* to 8-10* maximum. That lets you get the mechanical advance in early to boost low end performance, yet keep the cruise timing in check. Most engines will tolerate cruise timing in the low 40's. That being said, you need to experiment with your engine and see what works best. Experiences will vary. All of this is in the 1st post of the Power Timing thread.
Thanks Larry for the clarification! I work tomorrow and there's a muscle car show at the LA convention center this Sunday which I plan to go to so next weekend will be the time I plan the change out the distributor. I'll post how it goes. Thanks, Brad
I had a Pertonix unit for 20 years worked great. Replaced for cosmetic reasons and it lasted 2 weeks. Go back to the points for now. Replace to pertonic when running. You need another distributer with points to swap in for diagnostics. My Pertonix was the same exact unit as you have. Remember, the rotor goes around twice per stroke and only fires on one of them.
The crank shaft turns twice (720*) for every one turn of the camshaft. It takes 2 crank revolutions to fire and exhaust all 8 cylinders. The cam turns once, it turns at 1/2 crank speed. 1* of distributor rotation = 2* at the crank.
