mechanical advance or vacuum advance?

[myhemiram03]

I'm building a motor for a blunderbust car (a chevy 350). I've rebuilt street motors before, but never one for a division car just for the track. All the machine work was done by shops i'm just assembling the motor and installing. I just dont know what distributor to run, a mechanical advance or vacuum advance. I would greatly appreciate any advice as to what other people in the division run on their chevys. any and ALL advice is greatly appreciated!!!!!!!!!!:confused:

[art11758]

The rules state "stock". Which means it should have both. I have been told in the past they were required to be functional. I'm not sure what the current status quo is.

[myhemiram03]

I currently have a rebuilt stock HEI with vac advance, I was just wondering if anyone is using early stock type mechanical advance units? From what I have read, unless you change the weights and springs the timing gets too far advanced at high rpm's.:help::confused:

[voodoocadoo]

I have a brand new vacume advance HEI distribtor if ya need one

Russ

[VNYLGRFX]

From What I recall you have to have both, I think you
can remember ART we were ther many times I would state
You need both......The vacuum part needs to be there weather it works or not....

:cool:

[Coyote Racing]

I think dales correct, the vacuum advance doesent need to be hooked up but it does need to be there.

[myhemiram03]

;):help:If that is the case, then can you use a lockout plate for the advance or change weights but still retain the advance can on the distributor? When I ran the car last year, I had detonation issues.

[art11758]

Nope no lockout plates. As Dale, Doug, and I mentioned everything in the distributor has to be there and functioning. Not for nothing and not getting too technical, you can buy a fresh HEI from Summit for $89.95. Not the way I would go, but it solves a myraid of issues.
What I would suggest is take your distributor to the local guy with a distributor machine. Have him spin it up and tell you where the advance comes in and how much. Explain in great detail what it is that you are doing and what your limitations are.(4000# plus car and crappy cam rule, blah,blah blah....) Have him dig thru the "reject box" for weights and springs he took off of other distributors and get you "in the ballpark".
There are other solutions, however they stretch the spirit of the rules a bit more than you should. Not to say of course that everybody else isn't doing that and more. Let the venom flow....

[myhemiram03]

Thank you so much to everyone who gave me advice on my distributor dilema, Special thanks to art for the repeated attempts to help. I am looking for a place to take my distributor to have the curve checked. Thanks again!!!!:cheers::D

[nascar071]

if your looking for the cheapest and easiest way to do this, just leave the vacuum advance on the dist. just dont hook up any vacuum to it. run the motor up to 4500-5000 rpm and set the timing ,to whatever your max advance would be)( 32-36degrees) by then the advance weights will be at full advance , thats the way i've been doing it for years, stock gm distributor, no trick parts. If your what to change the module i do beleive an after market one is legal. PS you can buy a stock replacement from S-k speed or i think Oval speed has them also . price range anywhere from $100-$200 Ron

[nascar071]

the stock dist. is good to 7000 rpm's so why mess with a good thing

[art11758]

Oh I agree Ron. Trouble starts when you have an HEI with no history and unknown curve. Every GM application had its own curve and advance and if you are trying to use one out of a dually pick up with a 350 in a 305 (like I did once)((don't ask......)) things get wierd. Like all well intentioned mistakes I have made along the way, there was a lesson there.

[myhemiram03]

I ran the advane with vac on it during the first practice sessions last year, then disconected it during the first heat races, but didn't know not to time it off idle!!!! So who knows what my timing was at 5000 !!!! I guess lessons learned can ba lessons tought!!!! Thanks guys, looking forward to seeing you at the track!!!!:cheers:

[Dennisc]

scott if you find anybody to look at your distributor let me know cause I was having all sorts of problems with mine. I've been looking myself and I cant find no one.

[myhemiram03]

I have gotten a ton of help since a started this thread. As far as a local place to do distributors, I havent found one closer than jersey. The unit I have I bought from summit last year. (the same one that art mentioned earlier) I got an upgraded module too. By the time you send yours away it probably cheaper to buy the summit unit. Rich mentioned he has a rebuilt unit if your interested. As far as the timing, Ron told me just disconnect the advance vacuum hose and set the timing at race speed (4500-5000) and said this has worked for him for years!! :cheers:

[nascar071]

(" Dont ") hook the hose back up, otherwise your timing will be to far advanced and you'll burn a piston or worse!!!

[myhemiram03]

I thought I said Not to connect the hose, sorry!!!! As far as the burned piston thing, I already learned that expensive lesson last year!!!!! I should have asked this question then!!!:-B

[vsmidge68]

Are You Kidding Me? Setting the timing on a motor fully advanced is not brain surgery! Setting the weights, springs, and the curve in the distributor can be done by a good Old School mechanic. Setting it at fully advanced @ high rpms is not rocket science. All you need is a good timing light. Feel free to pm me if you need help....there are a few tricks.....

[art11758]

Something occurred to me. Which balancer / pointer setup are you using?? For a SBC there are three different ones, depending on date of manufacture.
If you are unsure, bring the piston up on #1, mark the balancer by the "0" on the pointer plate, and spin/bar it over til the piston comes up again, mark it and go in the center between the marks. According to Jeff Smith at Car Craft Magazine, that is the true mark you should work from.
Oh, and sorry if I sent you on a chase for a distributor machine equipped shop. I do 'em at home now and haven't paid to have one done in probably 25 years. Back then, every speed shop had a machine. It was a simple deal and like everything else, it isn't like it used to be.

[myhemiram03]

what month car craft are you lookin at? I have every issue since 1989!!! I'll look for it on their site!:)
I always find some info in those mags.

[art11758]

July 2007 page 71

The reason I mentioned it is cus I have a SBC with either a turned balancer or some other ill and I have yet to time it by the marks. Even with a dial back light and a good tach, I can get it in time, just never to the marks. I have been waiting to freshen it (again) and was going to try that exact method to see if I could figure out what was up.

Another really old resource is the July 1996 Popular Hot Rodding. On page 26, there is an article on which wieghts and springs produce which advance and when, as well as the pitfalls of using an "early" HEI.