An O.E style dist's has way too much mech advance,isn't geared towards performance that much.installing a stop just outside the weights to stop them from slinging out isn't the hardest thing to do.
distributor advance
- Thread starter jcelk
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taking the vac advance out for simplicity here-you want limit the amount to about 10 degrees or so of mechanical advance in the distributor & roughly 24 - 26 degrees of initial timing on the crank to make your total timing somewhere close to 34-36 degrees.
You do know that too much initial timing will cause hard starting issues when the engine is hot.
A slightly warmed over stock engine(mild) doesnt require that much initial advance, 24-26 is more resirved for radical camshaft engines that produce very low vacuum at idle, i would suggest for 14-16 max would be more ideal, thats what i run with my ZZ4 crate engine, and its considered a mild engine for what it is.
it's always worked for me,but like most thing's in life-everyone's mileage may vary.this's why i said"about 10 degrees" and " roughly 24-26 degrees of initial"...
It seems like everyone is in agreement total mechanical should be about mid 30's. Only a dyno or trap speed will dial it in further than that. Combustion chamber design pretty much dictates total.
As for initial. More the better. Listen, watch a vacuum gauge or notice throttle response. 30 is better than 20 is better than 10 and zero is soggy as mud but the starter is the limiting factor for initial. Manifold vacuum advance is the only method for having both. So at light throttle cruise and idle you can have 30, 40 or 50 but around 10 to start up.
This is also another way to keep the throttle blades almost closed but still have a decent idle speed. A lean idle mixture needs to be lit early.
As for initial. More the better. Listen, watch a vacuum gauge or notice throttle response. 30 is better than 20 is better than 10 and zero is soggy as mud but the starter is the limiting factor for initial. Manifold vacuum advance is the only method for having both. So at light throttle cruise and idle you can have 30, 40 or 50 but around 10 to start up.
This is also another way to keep the throttle blades almost closed but still have a decent idle speed. A lean idle mixture needs to be lit early.
yep,you want to be all in with the advance in at "about" 2400.3,000 is too high, 2,000 “might be” a bit on the low side but every engine combination's different..so somewhere in there is where you want to be.You need advance at lower rpm's to make that engine pull hard. It'll have better throttle response, a better idle vacuum and it'll run cooler.definitely want it all in before the converter sees all the stall.
Quivelling over straws here imho. melloelky described needed timing advance number and rpm best - every engine is different.
If your all in timing is 30-33 degrees by 3000 then you’ll be more than safe on any SBC that isn’t running Vortec heads. After that the ignition timing needs to be tuned to get the last bit of HP out of it.
I’ll throw out there that for a street driver, the term ‘safe’ should rule the day because of the changing conditions the car will see when daily driving. This does not apply for a race car in consistent conditions.
If your all in timing is 30-33 degrees by 3000 then you’ll be more than safe on any SBC that isn’t running Vortec heads. After that the ignition timing needs to be tuned to get the last bit of HP out of it.
I’ll throw out there that for a street driver, the term ‘safe’ should rule the day because of the changing conditions the car will see when daily driving. This does not apply for a race car in consistent conditions.
As for the vacuum can, you can do yourself wonders by limiting the amount of total advance that bugger gives you. You can probably buy a new can that limits it further than 20 degrees, maybe a 14 or 16 if you can find one. Still, 20 seems like an awful lot. Got to recall, HEI distributors were made for emissions vehicles. NOT performance applications necessarily. Although with a few tweaks...
JMO, but you probably would want to run about 12-14 initial, and I think you mentioned 25 mechanical? Could be wrong there, but if so, that should net you 37-39 as initial + mech advance. So roughly 45-50 on the street total advance (and this can vary with engine mods, compression, etc.) would put the math about 6-13 degree vac advance, roughly speaking. If you ran the full 20, you'd be closer to 60 and that's just a tad too much for nearly any engine. The only way you're going to do it consistently is put a limiter on your canister. Don't bother with those "adjustable" deals as it just limits the initial movement vacuum signal to overcome the adjustable spring pressure. It's a PITA to even get those repeatable anyway, at least in my experience. And it will still give full vacuum advance on decels. I'd go with a physical stop.
I'm just benching it here. There's many more real-world conditions to deal with, but the consensus for most engines is 34-36 all in (without vac advance) at whatever RPM you decide you want it all in at, whether 2500 or 3000, etc. If you got it at 34-36 where you want it, now you're talking limiting to 14-16 degree on the vacuum can. You'll never know until you do it, then test it. Your car will let you know what it likes.
You can always make a stop yourself, but Crane had a small, toothed rotating cam plate that had notches in it to limit the full travel point, but required drilling the vacuum can to install it. Regardless, it's been out of production for quite a while now and you'd be lucky to find one.
You could try the MSD 84281 vacuum advance limiter. It's nearly infinitely adjustable for tuning the amount of vacuum advance. Too much V.A. will give you lotsa pinging and issues you just don't need.
Instructions about how it works and how to set it is here:
Here's what it looks like installed. You can get them for around $20-ish bucks. They were designed for MSD distributors, but they are known to fit GM HEIs as well.
Or make your own.
JMO, but you probably would want to run about 12-14 initial, and I think you mentioned 25 mechanical? Could be wrong there, but if so, that should net you 37-39 as initial + mech advance. So roughly 45-50 on the street total advance (and this can vary with engine mods, compression, etc.) would put the math about 6-13 degree vac advance, roughly speaking. If you ran the full 20, you'd be closer to 60 and that's just a tad too much for nearly any engine. The only way you're going to do it consistently is put a limiter on your canister. Don't bother with those "adjustable" deals as it just limits the initial movement vacuum signal to overcome the adjustable spring pressure. It's a PITA to even get those repeatable anyway, at least in my experience. And it will still give full vacuum advance on decels. I'd go with a physical stop.
I'm just benching it here. There's many more real-world conditions to deal with, but the consensus for most engines is 34-36 all in (without vac advance) at whatever RPM you decide you want it all in at, whether 2500 or 3000, etc. If you got it at 34-36 where you want it, now you're talking limiting to 14-16 degree on the vacuum can. You'll never know until you do it, then test it. Your car will let you know what it likes.
You can always make a stop yourself, but Crane had a small, toothed rotating cam plate that had notches in it to limit the full travel point, but required drilling the vacuum can to install it. Regardless, it's been out of production for quite a while now and you'd be lucky to find one.
You could try the MSD 84281 vacuum advance limiter. It's nearly infinitely adjustable for tuning the amount of vacuum advance. Too much V.A. will give you lotsa pinging and issues you just don't need.
Instructions about how it works and how to set it is here:
Here's what it looks like installed. You can get them for around $20-ish bucks. They were designed for MSD distributors, but they are known to fit GM HEIs as well.
Or make your own.
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