I bought this dissy from summit, an hei type and they gave me a card that says
14 deg mech adv at 2200
10 deg vac adv at 11 inches
24 deg total at 2200
I thought hei's were supposed to have 20 degrees mechanical advance... and how is it getting 24 degrees total when the vacuum advance would show less than its max advance if you had your foot on the gas (less than 11 in vacuum)?

I thought you wanted like 22-26 degrees of total advance by 2000 or so even at WOT.

did I get gypped or is this advance normal for a small block.

I mean I dont want to time it at 18 degrees base to get a total 32 from the distributor at WOT....

 

BTT

 

Sounds familiar, I have the same question.

The tech article on this site says that all Hei's have a 20 degree max mechanical advance.

Hey BTW, don't worry, 24 degrees is a good thing not a bad thing. Set your base timing to 10 or 12 degrees and you are ready to go.

 

Too much stuff for me to read and comprehend...

But for total, add your base timing to the mechanical, for "all in at xxxx rpm's".

Remember when you put the hammer down, you've little or no vacuum...so vacuum advance is out of the equation...what you're left with is Initial/base timing+mechanical.

If it comes in too soo/late, adjust the weights/springs accordingly.

When cruising down the highway, you have (usually) high vacuum so you have vacuum advance+initial/base+mechanical.

 

Thats what I mean ...

this stupid distributor from summit says that it only has 14 degrees of mechanical advance at 2200 so with 12 degrees initial the Damn thing only gets 26 degrees total advance at WOT.

This sucks I feel ripped but I guess thats what you get for a cheap summit dissy.

 

Go to autozone, break out 5 bucks and get a Spectre advance kit. Put 1 light spring and 1 medium spring in it. This should give you what you want. BTW: do this after you install it cause you never know if that Summit Dist. will give you what you want until you try it.

Also I run at least 12 degrees of base timing in my cars ( I'm gonna up one to 16 and I already upped the other to 14, but my distributor gives me 20*, not 24*) and they run fine. 12 degrees will give you a total of 36 degrees which is probably best.

 

no no

maybe I dont understand what Im reading on this card but Im assuming it says 14 degrees of mechanical advance TOTAL... with whatever spring you want to put on it.

so at WOT it would give 14 degrees plus base which even at 12 would only be 26 degrees.

 

No, no, no, you aren't getting it. The reason that you get 14 degreea at 220 is because of the springs. If you put lighter springs in it, you will get more advance sooner, get it? You could get the full 24 degrees in by 3000 rpm so it's possible to get 18-20 I would think using the light springs.

 

how would weaker springs help if the advance weights wont go out any farther>????

Id just be getting 14* sooner but not more...

 

Are you trying to tell me that the weights don't move out any farther than 14*??? I'm pretty sure that you are wrong, you get 14* at 2200 but all the advance is typically in by 3000 or so at which time you should have a total of at least 20. The weights can move all the way to at least 20, trust me. Stock distributors don't move less than 20*, I doubt that summit machined the dist. so it would give you LESS timing when the advance is all in.

I thought you were saying earlier that the distributor was capable of 24* total mechanical advance PLUS base timning, that sounded good.

Maybe you should give the Sumiit tech dept. a call, if you won't take my word for it.

BTW: WOT has nothing to do with the mechanical timing, that's where the springs come in. If you want more advance earlier, you need to pull the stock springs.

 

The shape of the cam that the weights work against, and the shape of the part of the weights that runs against the cam, is what determines the total advance. The springs DO NOT limit the amount of advance, only the rate at which it comes in.

I'm at a loss to figure out why anyone would sell a distributor that only gives 10° of centrifugal advance. Somewhere around 24 - 28° would be more performance-oriented. 10° or so of static, centrifugal starting at 1000 or so reaching 26° at 2400 RPM, then 10° or so of vacuum advance on top of all that. You change the RPMs that the centrifugal part works at, by changing the springs.

WOT by itself does not affect the distributor, except for the vacuum advance. Centrifugal advance is entirely determined by the springs & weights.

 

yes we have all hit on the point I am making

I dont think the centrifugal advance on this dissy goes past 14*

or so the card says....

all the rest of what you are saying makes complete sense.

I dont understand it either -- I dont know why they would sell anything that would give less than 20* of advance (centrifugal) total??????

 

You got me....

I sure wouldn't buy it.

 

DOH!

just to be sure I will check it with a friend's advance timing light to see what it gets up to.

Is there any chance I can do some filing on the cams or weights or something to get more advance????

I am just taking a shot in the dark here as I have no Idea how to modify or tune HEI's I just dont want to go through the gauntlet of trying to return it now that its already installed.

 

It would be a good idea to test the distributor either on a distributor machine or in the car with a timing light
to see what the actual advance curve is like before getting all in a sweat. U"ll probabily find it has the typical 20/22 deg of mechanical advance @ high rpm. maybe not till 4000+ rpm.

 

the more rumpy your cam the more initial you will need to keep throttle response decent.

you probably want the standard 35-36* total advance, and the sooner it comes in the better (for rumpety engines). vacuum advance @ 11" of mercury? wow, thats like borderline part throttle. maybe thats why the centrifugal is so little... because at part throttle with a mild cam you will still be pulling 11"~ of vacuum... that means if your total WAS 36 WITHOUT vacuum advance, you would have over 46* of timing! thats bad for taking off from stop lights... esPECIALLY with crap octane. I wonder what summit was thinking?

I bet if you call you can get different weights or bushing to change the AMOUNT of centrifugal advance, as well as springs to make it come in sooner... AND hopefully somthing to make the vacuum advance come in LATER (like @ 15" - 10* of timing is normal for MSD)

The MSD's all come with both bushing and springs...

 

I have different springs but I havent looked at total advance with an advance timing light yet.

I will call summit.....

 

ok so I called tech and turns out these things are made by accel an all the accel ones are only 14 degrees of mech advance also.

or so the guy said.

he recomended I modify the weights (file/sand for more advance movement)

or do something inside the vacuum canister with an allen screw to adjust the baseplate or something????

I tried to sound like I knew about distributors but I dont

the only thing I was sure of and he knew it was that I wanted 32 degrees of total advance at WOT at the springs max stretch.

so I will first look at the total advance with a light when i go home this weekend but in the meantime please tell me if you thing this guy was full of it or if any of his suggested fixes make sense

incidentally he said I could send it back no problem too so I may just get on with more --

FRICKIN advance!!!!!

 

Maybe looking at Accel's web site, or an e-mail to their tech support dept. might be in order.

http://www.mrgasket.com/accelmain.html

 

I think what you purchased was a stock replacement HEI for the '75-'81's..??? If so, could be due to the "smog years"..limiting HP potential via timing at WOT, yet still giving up to 48*'s at cruise rpm for mpg's.

I flipped through a JEG's catalog last night and noticed the "performance" GM HEI's mentioned something like "performance weights and springs". Interestingly these "performance" HEI's did not mention they were 50-state legal, as the stock replacement ones are.

 

You should send it back.

You could drill out the grooves in the arms to elongate them, or IIRC, you can buy new ones. If you choose to drill them out, then it's better to go a little big because it's easier to add bushings to bring it back than it is to keep taking them off to make them a little longer.

The vacuum @ 11"/Hg is the most the vacuum advance will climb. Even if you have 14"/Hg at idle, it won't advance anymore than 10*. What the guy on the phone was talking about isn't doable UNLESS it's an adjustable vacuum advance. If it is, it'll have a allen screw inside the vacuum port to turn.

If you CAN adjust the vacuum advance, and do, it still won't change the total advance at WOT. So you're still left with elongating the slots, or buying new ones.

As I said, you should exchange it. I wouldn't spend $XXX for a new dissy, just to have to modify it. If you wanted to modify one, then you would have gotten one at the scrap yard, right?

 

The distributor in this post is now around 6 years old. I am sick and tired of it...

Reccommend me a good new one, HEI coil in cap, adjustable vac advance with 20* mechanical advance. Actually - I can supply the vac advance canister as that works pretty well.

Thanks for all the help,
James.

 

Did you ever verify the advance?

Most specs are stated in terms of distributor advance, not crank advance. Therefore, 14 degrees mechanical becomes 28 crank, which when added to 12 degrees initial equals 36 degrees (typical total for SBC's). However, 2200 RPMs would also become 4400 engine RPMs.

If you have other issues with this distributor that justifies replacing it, does the replacement have to be coil-in-cap? Are you using an ignition box? The MSD 8362 is their large cap HEI that should fit the bill. 8360 is the small cap/separate coil ready-to-run (more bux).

 

Oh yes, Many Many times. I ended up getting about 4 sets of weights and springs for the thing. Thought it was the advance limit slots at first, but then modified the crank arms on the weights to be shorter for more leverage on the center crank. That did get me more advance but unpredictably so. Now the advance curve has a hitch at 2500 rpm or so where the advance stops breifly before going up again to the max. I guess I should just get another set of weights and do a really thorough job of grinding them. It does seem however that no matter whose weights I buy - they all end up with about 11 degrees of crank advance total in this particular dissy.

Eventually this motor will go TPI with an EST controlled small cap dissy. I guess I am just venting and looking for suggestions for quality replacements.

 

Check this out! I found the new instruction sheet on summit and it actually says that the total mechanical advance is 11 Degrees at 1500 RPM!

http://static.summitracing.com/globa...i%206-2-08.pdf

This is the dissy I have.