You can buy a addjustable vav control. If it pings turn it down some, if it is not pinging, I would run it as is. If your car starts hard, I would take a little intial timing out of it. You say your have 36 there,try 34 and see how it runs.

 

Guess would be that either mech or vac advance mechanism has a bit of flex, play or give. Remember at 3000 rpm, there is more force from the weights than at idle, so it will take up any give in the system. I think 19 initial is a lot, but mine runs ok at 16, although hot starting is not real enthusiastic.

 

Your 36 should be fine but that 19 from the can's too much.
Get an adjustable can or make a limiter to get down to 8-10 on the vac.

 

Thanks guys...I do have an adjustable can that I can put on so I think I will...I'm pulling enough vac ( 13") to have it all in at idle I think. I'm in the 18-20 range on initial...thats why I say 19 because I have a medium and light spring on the dist. so I have to idle it way down till it hardly runs to keep the mechanical out when setting up initial so when the timing lights on it, it kind of bounces between 18-20...

 

you might try the initial around 14-16 to help get the mech. advance out of the idle.
Stick 20 in the mech around 3000 and 8-10 in the can.

 

Initial sounds way too high, curve isn't enough, and, 19 for the vacuum advance is also too much. Let me guess, the vacuum advance is connected to ported vacuum on the carb, yes/no?

I wouldn't do it the way you outlined.

Regards,

Milton

 

FYI,If he's running any kind of non gm aftermarket cam (even very mild cam) the 18-19 deg base/initial timing he running is just right/exactly where his motor needs to be,not less base timing with an aftermarket non GM cam.

Most aftermarket mild to farily hot perf cams need a min of 16 deg base if not more like approx 18 deg bases timing. Real hot cams like even more base timing at approx 20-22 deg at times .

Also,with a perf cam 9 of 10 times they run better using full intake vacuum (notported vac) for better idle & increased idle vacuum esp for pwr brk's/better throttle responce & more power comming off idle/cooler running motor in traffic at idle/increased fuel mileage too with full intake vac vs ported .

Ported to vac adv with no vac at idle was something the car mfg's did back i 60's-80's to retard timing at idle which to increased ex temps/engine temps. They did that not to make the motor run better but to lower certain emmisisons and that's why they the main reason used ported vacuum,most times ported isnt the way to go with a street perf motor with perf cam.

Also,the suggestions made to lower limit the vac adv to approx 10 deg iare right on the money.

So the current 19 deg base timing he's at with 17 mech = 36 total which is fine,most sbc/bbc like approx 36-38 total with perf cams on street so your right in the ballpark.

You can make a little piece of metal to limit the vac adv arm travle to 10-12 deg and then you will be good to go. Crane used to mfg a special vac adv limiter plate for this very reason of limiting vac adv when trying to dial in ign curves running more base timing for perf cams.

Here's the pt# for the crane limiter plate i have used often to limit the vac adv. But that's if you can find one being NOS/new old stock in some local speed shop or online somewhere like ebay etc,i bet if you look hard enough on the intranet you will find one.

CRANE VAC ADV LIMITER PLATE PT # 99619-1

19 base + 17 mech adv = 36 total + 10-12 deg from vac adv when fully activated = 48 which is conservative for low load light thorttle cuise rpm will all timing in.

General rule of thumb is 50 to 52 deg with all timing in but your fine if you get anywhere close to 48-52 deg max with all timing in at low load /part throttle cruise with no detonation and proper octane fuel for setup being run.

But dont go over 52 with all timing in because you dont want to chance detonation ,but to be safe id run at least 93 oct fuelin your 396 with the above mentioned street perf ign timing curve to try to avoid detonation.

Those motors in stock from with short cam timing and 10,25.1 comp had tags in cars new stating must us minumum of 98 0ctane fuel so see my point?

Todays oxygenated/ethenoled/non leaded/low octane fuel is nothing like the fuel our older gen bbc's were designed to run on with short timing and above 10.0 comp that creates high cyl pressure. I remember back in those days that in the summer we had to run 100+ oct sunonco 260 to not detoante when motors were hot. Todays lower 93 oct ethenoled crap doenst cut it at times in our older motors not designed to run on it . Thats esp true in motors mostly in stock form with stock type heads/pistons/stock cams or even with a mild aftermarket cam that dont have a ton of duration to effectively lower cyl pressure a bit with over 10.0 comp to work better with todays crappy low octane non leaded ethenoled much different formula fuels.

Good luck.

Scott

 

Also you can buy the can with the vacuum you need built in, it will be cheaper too. I did this for my MSD HEI since the stock can had 20" vacuum.

http://www.hotrodders.com/forum/distributor-tuning-theory-part-1-a-59033.html, here's a good read on the part numbers and tuning.

 

Just an FYI that some of those vac adv cans esp for non hei dist that activate at lower idle vac and have less total adv that were used on older perf motors from gm that had decent cams with longer duration from factory that would be good to use here arent avail anymore .

Thats why i dont even rec them from this list anymore that i too have tucked away on file in my laptop because more times then not when i rec 1 or 2 vac adv cans fro this list people chime back to say where ever they go or who they call says that pt# isn't avail anymore.

So incase you find a good match on the vac adv list and its not avail anymore you still may be able to find an NOS cran vac adv limiter plate. Thats easier to isntall then a new vac adv and te crane limiter plate only takes approx 10 mins to install.

But then you need to tweak it to dial in the vac adv max deg timing it gives with limiter plate.

Scott

 

That's a good point Scott, thanks for the heads up, in my case I was able to buy my HEI can to match my needs

 

Thanks guys for all the great info and advice...particularly SWHEATON...I have based most my settings off your recommendations...:thumbsup: I did put in the adjustable vac can that came with my HEI upgrade kit and my numbers are now more in line...18 initial, 18 mech, and 14 vac adv for a total of 50...I do have a performance cam, not totally sure of the specs...I think 218-228 @ 0.050 / 500/500?...and I do use 93 octane by the way. This site is great and I really appreciate all the people out there willing to help...:beers:
____________________

Dave V.
70 SS clone
396

 

Sounds like the Performer/Summit clone cam. Good all around street cam in a 454.

 

Hi Dave,how's it running with the 18 initial, 18 mech, and 14 vac adv for a total of 50 like you said it currently at vs before getting the ign timing curve setup like it is now?

But where you timing is a now looks good & should run fine there and at most would only need a slight tweak in either direction timing wise if at all for optimal perf.

Gald all of us in team chevelle were able to help get your squared away.

Scott

 

Maybe a full mechanical distributor with NO vacuum advance might like 19 degrees initial with a hot cam, but, what he has, IF he is running full manifold vacuum, is just plain too much for that engine. Add the 19 initial, with the 19 vacuum degrees, and he'd have 38 idle degrees, way, way too many, and even if the vacuum advance were restricted down to 10, that would give him 29 idle degrees, still way, way too much.

Running the vacuum advance on ported vacuum is never an option for me, I just don't do it.

I suspect the vacuum advance is NOT on full manifold vacuum, and that is the reason the initial has to be so much.

I have a couple of old Corvettes in my collection, both use non-vacuum advance distributors and fairly healthy solid lifter cams, they use 18 degree initial timing, but, if there was a vacuum advance on the engine, the initial would sure need to be set lower, and the vacuum advance set to give an overall idle timing of 20 to 22 degrees, no more. And, IF the intake cloding degrees of the cam are radical enough, then, using a vacuum advance would become a moot point, there wouldn't be enough vacuum to operate a vacuum advance, and a mechanical advance only distributor, set to 18 and upwards initial/idle degrees would be the way to go.

As I said, I wouldn't have done it the way it is. But, my experience comes from learning from a person that actually knows how to do correct timing and distributor setup for engines.

Regards,

Milton

 

Milton,no disrespect intended but your " way off base on this one " for all the reasons already stated above by me & other people too.

The 18 base & 18 mech adv for 36 total + 14 deg vac adv for 50 deg @ cruise he is currently running is right on the money for a street perf ign timing curve when running an aftermarket non gm mild perf cam like his motor has in it.

Yes he could run less base timing and and less timing from vac adv and it will still run but would feel soggy loosing considerable perf in all rpms below where total timing is fully in .

Then if he were to run less base timing like you suggest and more mech adv to get the perfered 36-38 deg total timing where most sbc/bbc street motors with perf cam's end up timing wise along with adjusting in less deg timing from vac adv or vac adv hooked on ported vacuum for no vac adv at idle at all in his case would be NG ,perioe,wpuld run lke a slug intll you got it would upand all total mech adv in. With his mild perf cam'd motor the retarding the base timing and limited or no timing from vac adv at idle hooked to ported will also signifcantly degrade perf loosing power in rpms below where total is fully in making the motor feel very soggy/make it run hotter in traffic/reduce fuel mileage/loose power/poor idle/reduce idle vacuum thats already lower due to more duartion with aftermarket perf cam that may affect pwr brakes/etc.

Again,ported vacuum was mainly a bandaid 30-40yrs ago to retard timing at idle by 20+ deg which is alot to significantly increase exhaust /engine temps which in turn redeuced emissions which was the auto mfg's goal with ported vacuum at idle ,not to make the motors run better,the motors didnt like at all.

Once in a while a setup may prefer ported vacuum but after dialing in litterally 100's of street perf motor setups with aftermarket perf cams for over 38yrs + i have the 1st hand experience to confidently say when running aftermarket perf cams in street most motors like approx 16-18 deg base timing (real hot cams 20+ base timnig)/36-38 deg total/and approx 10-14 deg max from vac adv to full intake vacuum for very roughly 50 deg + - deg with all timing in at low load part throttle cruise.

And moderate to farily hot perf cams on street benefit a lot from from the additonal 10-14 deg the vac adv gives when on full int vacuum for better idle/little more idle vacuum esp for power brakes/cooler running motor in traffic/better fuel economy.

Scott

 

"Way off". I don't think so. I run a 355, 10.50:1, 310/318 overall duration cam, and 14 initial, 34 total, 8 vacuum on full manifold vacuum, for 22 initial, and the thing rips. Sounds like the engine in question is fairly mild, and needs the crutch of far too much timing to work.

To each his own, it ain't my engine.

Regards,

Milton