OPINION ON DISTRIBUTOR

-
D

downsr

Well-Known Member
Joined
Dec 17, 2011
Messages
885
Reaction score
85
Location
waverly ohio
I HAVE A 8388 MSD THAT HAS VAC ADVANCE.THE VAC IS NON ADJUSTABLE.IT PUTS 20 DEGREES TIMING AT THE CRANK WHICH I FEEL IS TO MUCH. I DO NOT WANT TO WELD OR PUT A SCREW IN THE PLATE AFRAID IT MIGHT COME LOOSE AND PUT TO MUCH TIMING IN THE ENGINE.I WAS CONSIDERING GOING TO A PROTRONIX DIST WHICH YOU CAN GET AN ADJUSTABLE VAC ASSEMBLY.ANYONE RUNNING A PROTRONIX AND HOW DO THEY COMPARE TO A MSD
 
Im sure trailbeast will chime in on this. He's probably forgotten more about distrbutors then must of us know lol. May want to consider running one of his distributors.
Im not running vac advance so i have no idea

@TrailBeast
 
What is your initial and mechanical timing setting at? whats it do w/o the vac advance hooked up? I'd be exploring the lesser of evils vs exchanging a $400 distributor that i personally feel is alot better unit that a pertronix. How much vacuum are you running?
 
The total is 36.The vac on the msd puts additional 20 degrees.Which makes it 56 degrees at cruise.I do not want that much timing and msd dist the vac is not adjustable.And i do not want to lower the total timing.The vac on the engine is 15 idle when cruising at 2500 rpm it is 17".I want to use vac advance but not that much
 
Those MSD distributors have a bushing kit that limits the amount of advance.
 
The vacuum advance is a moot point as the only time it operates is at part throttle. It's job is to clean up unburned gasses at part throttle (which also increases mileage) and to offer a little part throttle acceleration. That's it.

It's not uncommon for total advance including the vacuum advance to be over 60*. Yours is fine.

You do not tune the distributor with the vacuum advance connected anyway. Get the engine the initial it wants, then limit the total mechanical to between 34-36 degrees. Then plug the vacuum advance in and forget it.
 
abodyjoe said:
That's for the mechanical advance though.

Or do they have something for the vac advance too?
Click to expand...
Some an the allen screw internal that can limit/adjust the vac advance. Apparently his doesn't, or he hasn't found it yet. I don't have that model here to pull one. They do come with a lock plate to remove the vac advance entirely however. I'd be happy with the mechanical #'s he has, and call it a day. w/o the advance. but thats just me. to each their own.
 
The initial and the mechanical which i have it set at totals 36 degrees and is where i would like to leave it.Now to get the total which is equal to the initial +mechanical +the vacuum advance if your a running a vacuum advance canister which in my case adds 20 degrees at the crank which is non adjustable.So my total is 56 degrees when it is all in at 2500.(20 + 16 + 20)= 56 degrees.I do not know if this would be to much timing(56) .So its limit the vac advance with a screw, plate or what ever or go to dist that has an adjustable vac.Or if 56 degrees is not to much leave it alone.I just read what rustyratrod wrote if 56 degrees is not to high i should be fine.Never could find any thing on this
 
Last edited:
If it's not pinging then leave it alone.

when you go full throttle the dist will go full mechanical advance because the vac drops out.

the vac advance is really only for part throttle like RRR explained.
 
explains it some.. i know yours isn't adjustable.

timing3.jpg

timing4.jpg
 
downsr said:
The initial and the mechanical which i have it set at totals 36 degrees and is where i would like to leave it.Now to get the total which is equal to the initial +mechanical +the vacuum advance if your a running a vacuum advance canister which in my case adds 20 degrees at the crank which is non adjustable.So my total is 56 degrees when it is all in at 2500.(20 + 16 + 20)= 56 degrees.I do not know if this would be to much timing(56) .So its limit the vac advance with a screw, plate or what ever or go to dist that has an adjustable vac.Or if 56 degrees is not to much leave it alone.I just read what rustyratrod wrote if 56 degrees is not to high i should be fine.Never could find any thing on this
Click to expand...

MSD:Tech - Set your Timing - Learn everything to know about ignition timing

excerpt: "Total timing is the term given to the highest amount of advance. This is when the initial timing is added to the mechanical timing. For instance, if an engine has 10° of initial combined with 21° of mechanical, the total timing is 31° BTDC. Note that Total timing never includes vacuum advance."

because of this:

abodyjoe said:
when you go full throttle the dist will go full mechanical advance because the vac drops out.
Click to expand...

...so unless you've done something to your distributor, MSD says the vacuum can adds only 10*...

All that being said, RRR and Joe already covered all the important parts for you.
 
You are misunderstanding total advance. Total advance is initial plus mechanical. PERIOD. The amount of vacuum advance IS NOT INCLUDED in figuring total advance for an engine. See my last post. I gave clear, concise, and correct instruction. The vacuum advance "is what it is" when the can is non adjustable.

downsr said:
The initial and the mechanical which i have it set at totals 36 degrees and is where i would like to leave it.Now to get the total which is equal to the initial +mechanical +the vacuum advance if your a running a vacuum advance canister which in my case adds 20 degrees at the crank which is non adjustable.So my total is 56 degrees when it is all in at 2500.(20 + 16 + 20)= 56 degrees.I do not know if this would be to much timing(56) .So its limit the vac advance with a screw, plate or what ever or go to dist that has an adjustable vac.Or if 56 degrees is not to much leave it alone.I just read what rustyratrod wrote if 56 degrees is not to high i should be fine.Never could find any thing on this
Click to expand...
 
downsr said:
The initial and the mechanical which i have it set at totals 36 degrees and is where i would like to leave it.Now to get the total which is equal to the initial +mechanical +the vacuum advance if your a running a vacuum advance canister which in my case adds 20 degrees at the crank which is non adjustable.So my total is 56 degrees when it is all in at 2500.(20 + 16 + 20)= 56 degrees.I do not know if this would be to much timing(56) .So its limit the vac advance with a screw, plate or what ever or go to dist that has an adjustable vac.Or if 56 degrees is not to much leave it alone.I just read what rustyratrod wrote if 56 degrees is not to high i should be fine.Never could find any thing on this
Click to expand...


One more time. The vacuum can ONLY works at part throttle. Very rarely will you see 56* of advance, but if it ever does, it is perfectly normal. There are cars running around that have over 60* advance, including the vacuum can. IT IS NORMAL. Read the last paragraph of post #10. That is as simple an explanation as you will ever find.
 
Rusty you do not have to talk down to me.At least that is what it sounds like to me.I appreciate your help.The msd advertises that it only puts 10 degrees timing in is not correct i know it puts in 20 because i put a timing light on it.I also drove and wrote down the vacuum readings at different rpms.Also put timing light on it and wrote down the timing at different rpms.I just did not know if 56 at cruise was to much when i plug in the vac advance.I did not tune the dist using the vac.I put in the springs to bring it all in at 2500 with 20 initial and 16 mechanical.I fully understand the meaning of the initial and the mechanical part and how they work.I know you lose vacuum when you are at full throttle . I was worried about at CRUISE if 56 was to much.You said earlier that it was okay and i agreed
 
Last edited:
That is so odd that the MSD instructions lay out advance numbers in crank degrees for everything except the vacuum advance. DOH!

There is probably a way to limit the vacuum advance via a hillbilly engineering method. It won't, or shouldn't activate in any condition except constant throttle position cruising. I think it said 15 pounds of vacuum, should be 15 inches, to activate the vacuum can. Since you are barely over the threshold, it shouldn't be much of an issue. Any roll into the throttle should dump vacuum below 15" in most cases.
 
That's right they tell you the canister only puts in 10 but it actually puts in 20 degrees at the crank.
mderoy340 directed me to a web site on a hot rod forum that shows a pic of someone that fabricated a small plate to limit it which i probably will make.It just sucks you pay four hundred dollars for a distributor with vac advance and you can not adjust it for what you want. Pertronix has a vac that is adjustable and so does mallory.
 
Last edited:
I was not talking down to you. I was stressing words so that you would understand.

IF I had talked down to you I would have started out something like "LOOK, STUPID............"

I did NOT do that, because I was trying to help you and I wanted you to take what I was saying seriously.

Trust me. If I ever decide to talk down to you, you WILL know it, but I had no reason to. You've not been ugly to me, so why would I be ugly to you?

Don't read something into it that's not there and don't be so sensitive. I was trying to help you.

downsr said:
Rusty you do not have to talk down to me.At least that is what it sounds like to me.I appreciate your help.The msd advertises that it only puts 10 degrees timing in is not correct i know it puts in 20 because i put a timing light on it.I also drove and wrote down the vacuum readings at different rpms.Also put timing light on it and wrote down the timing at different rpms.I just did not know if 56 at cruise was to much when i plug in the vac advance.I did not tune the dist using the vac.I put in the springs to bring it all in at 2500 with 20 initial and 16 mechanical.I fully understand the meaning of the initial and the mechanical part and how they work.I know you lose vacuum when you are at full throttle . I was worried about at CRUISE if 56 was to much.You said earlier that it was okay and i agreed
Click to expand...
 
You must log in or register to reply here.
-

Back
Top