vintage chromoly

iTrader: (3)

Hello all.
Question about vacuum advance I've been battling for a bit. Talked to several "experts" on this matter and, like most topics, getting conflicting thoughts.
I fully understand how and why this system works and why it's benedicial in a street driven car.
My question is this:
Under highway style cruise when the vacuum advance is fully deployed, if I were to suddenly go to WOT, will the vacuum canister release the advance quickly enough to not cause detonation. In other words, does the speed of the Pistons rise faster than the advance comes down?

I want to keep the vacuum advance for obvious reasons and my car is a relatively mild non track car.

446CI Chrysler RB
Solid flat tappet cam
10.5" of vacuum at idle, in gear
3.23 rear
2800 stahl
3700 pound car

Thanks

abones

Ported or manifold vacuum to the canister?

vintage chromoly

iTrader: (3)

Ported

That said, can you elaborate on both?

abones

In my opinion you will be fine. that is how I chose to run all my old school muscle car engines. Again that is just my opinion.

vintage chromoly

iTrader: (3)

It's not the vacuum signal to the canister that I'm concerned with, it's the speed of the reaction of the canister diaphragm. That's what pulls the advance out.

bck

I'd still think the canister and linkage would react quicker than the rest of engine for the same reasons. I did reconsider the whole argument for a different reason and delete my post while I thought about it. But you read it too quickly...

vintage chromoly

iTrader: (3)

My thoughts are that on a relatively light race car with a tall gear, the RPM's would increase much more rapidly than a relatively heavy street car with a lower stahl converter and a higher gear, where the diaphragm would have enough time to pull the added advance out.

abones

I think a lot depends on the type of springs that are on the mechanical advance, most cars of that era had heavy (strong) springs that would hold back the mechanical portion until engine RPMs came well up, with that said they used the ported vacuum to help bridge that gap! Now over the years many distributors have been resprung with custom curve lighter springs that guys thought would help racing from light to light. if you still have the original heavy spring in there and they have not been compromised by heat and time, you will be fine with the ported vacuum, if the springs have been replaced with the lighter aftermarket springs then there could be issues with too much advance. I have in the past ran a ported car on manifold to advance the idle timing to help prevent overheating at idle until air flow begins to pass over the radiator. Another thing to consider is the carb actuation, is it a vacuum sec or 1 to 1 mechanical

sutphen 30

this project is screaming for a daytona ignition box,,then its program it right,done.

abones

the engineers back then pretty much had the timing curves figured out for each engine they produced! they didn't want to be replacing pistons under warranty!