I am thinking it's time for a new distributor, but wanted to double check my thinking. What I have is 292 Chevy (65) just got done putting on a Offy 4 bbl intake and Edelbrock 500 and loving that, I have gotten rid of my intake leaks and now trying to get things dialed in perfect. I read through Leo Santucci's book last night. Here are the numbers I have now. Vacuum at idle hooked to manifold 18 Vacuum at 3000 rpm 15 Base timing w/ no vacuum 11 deg. Base timing w/ vacuum 30 deg. So right here I am almost at peak timing for the motor with Leo saying 32-38 at 3000 rpm. 3000 rpm w/ vacuum 60 deg 3000 rpm w/ ported vacuum 50 deg. I am thinking the distributor may be worn, or vacuum canister. It's HEI and was on the truck when I got it so I have no idea what it was pulled from or how old it is. I have been eyeing a few on ebay, but may also play the ultra safe route and get a new one from the parts store. http://www.ebay.com/itm/290616883673?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649#ht_500wt_1054 http://www.ebay.com/itm/350518869050?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649#ht_6093wt_1270
What lead me to check all of this is the fact she idles great, slow acceleration no problems at all, ANY kind of quick acceleration (with a load) and it starts pinging bad. No other symptoms and will run good at speed. I do have a fuel pressure regulator and per Edelbrock set at 5.5, and new fuel filter with the carb replacement.
You are are missing the more important reading. Check the timing without the vacuum hooked up (and the port on the carb plugged). It should be around 32° all in by around 3000 rpm. If it is more than that, then you need to tweak the mechanical advance to limit it. As for the vacuum, 50+° is not uncommon, remember that as soon as you put your foot in it the vac will drop and the timing will back off. Also many aftermarket vac canisters are adjustable so you can back off the amount of vac as well.
Cool heading out the door to check that now. I was thinking about an adjustable vac canister. Found a good article on HEI tuning : http://www.73-87.com/7387garage/drivetrain/hei.htm I will also just reading the old thread about ported or manifold vac. with good info by themoose: http://www.jalopyjournal.com/forum/showthread.php?t=567069&highlight=timing+advance
Ok at 3000 rpm with vacuum unhooked from the distributor and capped I am sitting at 28 deg. So I can advance my mechanical more to get that dialed in closer to 30-38. Maybe continuing to bump it up will get ride of the pinging, but I thought the pinging was coming from too much advance?
I bumped the base mechanical time up to 18˚, now giving me total timing at 3000 rpm, 32˚. She's not all in until 4000 rpm. I'm thinking I'll be getting a weight kit with stiffer springs to get it all in at 3000.
Just went out for test drive, definitely heading in the right direction with the current settings. A normal driver would never hear it ping, getting into has it pinging over 2500.
Maybe I am misunderstanding what your saying. First softer springs will get it all in by 3000 if its all in by 4000 now, not heavier. Second you have to know how much mechanical advance is in the dist now... if its 22 total mechanical (example) then you set base at 10 degrees at idle and work with the springs and weights to get it all in (32) by 3000. Third yes many times we restrict the vacuum advance so there isnt too much. There is usually a slot the rod hits to limit the total movement of the vac advance. I have brazed or welded up the slot and ground it out untill I had what I wanted also many GM vac advances had the degrees of advance stamped on them so some digging in the yards or parts stores might help you find what your looking for.
yes, you would need lighter springs. If you can check your timing as it is all in, and then check the iniitial, you will know what you have in the dist. Toal minus initial equals mech advance in the dist. Here is a good read on types of vac cans http://www.corvette-restoration.com/resources/technical_papers/Vac_Adv_Spec.pdf
Went to tour the Blue Bell Creamery today so hopefully tomorrow I will have time to pull the cap and look at the numbers. I have note messed around with weights and springs before, reading up on it. I appreciate the help and tips.
The Jalopy Journal
