So, i have driven around with my timing set as follows:

30 initial
36 total timing
vacuum adv. disconnected.

drives okay, but pings at full throttle in mid range rpm.
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locked out timing at 36 timing.

pings at mid rpm range (duh)


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What i want to do now:

initial timing at 20
total timing at 36 (or 38)

vacuum advance an extra 10 degrees

i want the 30 at idle.

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But here is my question:

I do have a cranecams adjustable vacuum can,

if i turn the adjustment screw in the vacuum can, does it change the amount of total timing or does it change the amount of vacuum (Hg) needs to advance timing?

I.O.W: turning the screw clockwise makes it more sensitive to vacuum?

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i ask this because at 20 initial timing and in Gear the motor has a pretty low vacuum

like 5 or 6 Hg.

So i need the vacuum can to activate an extra 10 degrees at 5/6 Hg vacuum.



I hope imade myself clear about what i need/want.


thank you and drive safe

It changes the vacuum timing added to your total.

I'm not sure how you get 30* initial. Your initial should be around 12* with about 24* mechanical advance = 36* total. (no vacuum advance). Either set your initial with car at idle OR hold at about 3000 RPM and set your total at 36*. Then hook up your vacuum advance and see how it runs.

Vacuum advance controls the rate and amount of mechanical advance in your distributor. Most people don't use an adjustable one. (I don't)

Adjusting the vaccuum canister changes the amount of vaccuum advance generally from 1-10 degrees. It doesn't have anything to do with changing the amount of vaccuum needed to get that timing. Having 30 degrees at idle will only worsen the problem. I would back your initial timing 5 to 10 degrees and the problem should clear up. Make sure you are running the vaccuum advance off of ported vaccuum not full.

And this is how I would do it:
First we need to know what engine you're running. Longer stroke and combustion chamber and head material all come into play.
Let's pretend you have a BBC.
Start at abut 16 to 18° initial.
Limit total advance to about 38 to 42° at 2600 to 3000 rpm.
Then plug vacuum advance into FULL TIME VACUUM.
How's it running?:D

with onl 5-6 hg of vacuum you wont be able to run manifold vacuum, it will cause a erratic idle , I to have a simular situation. I recently puchased a crane adjustable can. It takes about 9 hg of vacuum to pull the advance all the way in if it is adjusted all the way clockwise. so I was going to try to pull the can in with my mighty vac to 5 or 6 hg then make some kind of limiter at this point. then I will reinstall and pull in the vacuum advance with my mighty vac to see how much timing it gives me , and set the initial from there. I to only have 5-6 hg of vacuum at idle. I may try to do this later today if I get time , If I do I will let you know how it works.

Robert - there is a plate that lets you adjust how much vacuum is pulled in and the alan wrench adjusts how much vacuum it takes to operate the vacuum advance.

http://cranecams.com/?show=browseParts&lvl=3&prt=30&showAll=yes

http://cranecams.com/index.php?show=browseParts&lvl=3&prt=29

ported vs. full manifold vacuum:

http://www.camaros.net/forums/showthread.php?t=122103&highlight=full+manifold+vacuum+absolutely

first of, my engine is in my sig!

second, i get 2 different answers about what the adjustment does.

but ill assume DJD got it right.

But i must say that im seriously considering a different camshaft, i hate this ISky!

with onl 5-6 hg of vacuum you wont be able to run manifold vacuum, it will cause a erratic idle , I to have a simular situation. I recently puchased a crane adjustable can. It takes about 9 hg of vacuum to pull the advance all the way in if it is adjusted all the way clockwise. so I was going to try to pull the can in with my mighty vac to 5 or 6 hg then make some kind of limiter at this point. then I will reinstall and pull in the vacuum advance with my mighty vac to see how much timing it gives me , and set the initial from there. I to only have 5-6 hg of vacuum at idle. I may try to do this later today if I get time , If I do I will let you know how it works.


that's a nice idea, i will look nto taht myself also.

You can't really say what your Vacuum is, until you have your timing set, at least in the ball park. I have read your combo, and that Isky cam should work good. If you can't get decent Vacuum, I think you have a serious Vacuum leak !

Is that cam a special grind ? I can't seem to find it on Isky's site. Is this a hydraulic or solid cam ? That also seems like a lot of Duration, without much lift. Is 234° @.050 or at seat ? This may be a good candidate for 1.6 rockers. (this is not going to solve your problem now though).

i must say that it was running pretty decent at 30 initial and 36 total.

the only problem is that it pings a bit at full throttle in the midrange rpm.


234 is at @0.50

http://store.summitracing.com/partdetail.asp?part=ISK%2D201278&autoview=sku

the motor loves to idle at 30 initial, im fine with that, but i want it to fall back to 20 when i step on the gas in midrange rpm.

Something is wrong... It should run just fine at about 12. Are you checking your timing with a timing tape on the balancer or with a dial back timing light ? Is the distributor in properly, with #1 firing with timing mark at 0 ? Are you using the N0. 1 cylinder plug wire as your timing lead ? Did you install your timing chain with both dots on the gears at 12 o'clock ?

This is Isky's Cam list:

http://i263.photobucket.com/albums/ii152/tjs69_photos/cams/isky270megacam.jpg

Yours must have been a custom grind, that Summit sold to you. Your cam falls in this neighborhood. With 1.6 rockers you would get .480 lift.

its the 278mega/

234 duration in combination with 106lsa IS bit much ofcourse.

timing and balancer and all that is accurate

http://iskycams.com/timingchart.php?product_number=201278

the 270/280mega is at 112lsa, not comparible with 106lsa

The 280 mega is on 106 lsa... It looks very similar to your 278 mega. I would contact Isky and ask them, how much vacuum, that you should have, and what they might think is wrong. Maybe you should try using a vacuum tank ? I'm just afraid with that low of vacuum you may have brake problems etc.

i do have brake problems since this cam