Advance on a Prestolite dual point

[Richard Cranium]

The mechanical advance on my hemi car pulls 15 degrees & with vacuum advance, it pulls a total of 45 degrees, which I know is too much. Is there a way to limit the amount of vacuum advance that the diaphram will pull?

 

[dieseldazzle]

Put an limiter on the arm or put an adj vac adv canister on it. Or maybe it is adjustable did you try to put an allen wrench in the end of the canister?

 

[rscurtis]

I checked my Hemi supplement, and didn't find specs. for a total advance. Keep in mind that when you are at full mechanical advance, the vacuum advance is really out of the picture as the throttle plates should be significantly open, reducing manifold vacuum. The vacuum advance is for improved light-load fuel economy, if you can use that term when referring to a Hemi.

 

[dieseldazzle]

vacuum advance does nothing at WOT unless maybe your carb is way too small and you are pulling engine vacuum at WOT which Ive never actually seen in person but it could happen I suppose.

 

[Pops1967GTX]

The mechanical advance on my hemi car pulls 15 degrees & with vacuum advance, it pulls a total of 45 degrees, which I know is too much. Is there a way to limit the amount of vacuum advance that the diaphram will pull?

if I remember changing the tension of the spring for the weights can change advance...

 

[Richard Cranium]

Thanks for the input guys. So, it sounds like I should be more concerned with getting full mechanical advance & just plug up the vacuum advance. If that's the case, at what RPM should it be at full mechanical?

 

[Hemi Rebel]

Total advance on a hemi is 53degrees

 

[Richard Cranium]

Total advance on a hemi is 53degrees

Why does that sound like too much?

 

[Hemi Rebel]

Why does that sound like too much?

Thats vacuum advance included. You should only see that number on a hard decel.
Mechanical advance tuned for max performance should be 35 degrees all in by 2000 rpm

 

[lewtot184]

45 degrees with the vacuum advance fully open is not too much, should be more.

 

[dieseldazzle]

You can adjust it but on decel and cruising throttle, just like todays computer and efi cars, it is not uncommon to see up to 58 degrees of timing with vacuum advance hooked up.

 

[440+6]

On my six bbl I have 38 mechanical an 55 total with vacuum, when there is no load on the engine at cruise it needs more timing that vacuum provides, it will run cooler and you'll gain 20 to 25 % better gas mileage.
Hemi's use a little less timing, I believe the above numbers are correct.
I'm from the school that unless it's a dedicated race car you should always use vacuum advance.

 

[Richard Cranium]

It really sounds like i need to get the distributor sert up. Fortunately, there is a shop close by with a distributor machine & I'll have to stop in tomorrow and talk to him.

 

[snakeoil24]

Cranium go max 32 degrees on Mechanical.

 

[miller]

It really sounds like i need to get the distributor sert up. Fortunately, there is a shop close by with a distributor machine & I'll have to stop in tomorrow and talk to him.

Never had the pleasure of fooling with a Hemi, so don't know the timing advance numbers.
But, on a distributor machine, you find what you really have. There should be a mechanical stop adjust, to set the full advance, either screws, or bending tabs. Can't remember on Prestolites, since I usually go Mallory, but along the same lines. At Prestolite's website, several docs on 'em.
Advance springs only set the advance 'rate', or how quickly the advance comes in.
Vacuum canister could also have a stop adjustment built into it.