okay so im having trouble getting rid of spark knock. its a 350 crate motor, 9.8:1 comp ratio. the problem occurs when i hook up my vacuum advance from the distributor. ive turned the little adjustment on the nipple so there is as little advance as possible as well as as much as possible from it and still i get it. so far ive set the timing to 5, 8, and 10 and all 3 give me knock with the advance. the only way ive been able to get rid of the knock is to unhook the vaccum advance.

I did manage to get rid of the knock with 5 timing and 3 turns on the advance but power wasnt what i wanted it to be and ive read that i needed to be btwn 8 and 14 so ive gone to 8 and its what im currently running with the advance with zero turns. oh and the knock occurs when i throttle up to about 2000 rpms while driving go past or below and it goes away.

Also im using r45ts ac delco spark plugs, these are the spark plugs that came with my crate engine should i use a colder range spark plug? i have not verified mechanical advance curve. im using a streetfire hei distributor, springs are not broken inside. hydraulic lifters are noisy as well especially at startup. cam specs are: 275I/277E .462I/.482E
verified 20 inches of hg at idle so im assuming there are no vaccum leaks.

and ideas or suggestion would be appreciated.
thanks in advance guys

 

leave it unhooked. i have an s10 with a 350 510-533 cam holley street dominator intake 750 holley.i dont run it with vac adv. hooked up. been that way for years ,no probs.later jimmy

 

You need the vacuum advance. Without it, you lose SEVERAL miles per gallon at cruising, as well as throttle response and overall driveability.

Get the Crane vacuum can. It's the best, if you have any other, it's no wonder you're having trouble. Buy the whole dist curve kit that comes with the can.

Yes you probably want colder plugs than 45; especially if they're not fouling now. Step down to a 43 heat range.

I don't recognize the cam specs. What cam is it, exactly? What pistons, heads, and head gaskets is it made out of? This "9.8:1" type business is notoriously inaccurate.

 

My first suggestion is to DITCH whatever information you have read that insist on 36* BTDC total advance all in by 2,800 rpm being the end-all for ALL small block chevy combinations, it is FAR from in MANY cases.

There are MANY different factors that lead to the knock sensitivity of ANY engine.

Dynamic Compression ratio, engine temperature, fuel octane, density altitude, engine load, transmission type, vehicle weight, overall gearing, the list goes on.

What I typically end up finding is that my engine will not reliably restart without a gear reduction starter on a HOT day in the Texas 105* heat, with any more than 8-10* initial advance. Most of the small block combos I have built seem to run best around 28-32* total advance. I have found the overall curve seems to make more of a difference than having the extra degrees. That means, make the curve suitable for the engine, and you have it made. Most centfrifical advance mechanism's have 22-24* advance built into them, but it comes in WAY too late. Stock vacuum advance comes in rapidly with way too much total. You need to back off on the total to stop the detonation.

 

comp cam 275deh. pistons are hypereutectic, heads are stock ported and polished. intake valve: 2.020 in
exhaust valve: 1.600 in
81.4 cc combustion chamber

http://www.street-fire.com/distributor.html
how do i limit my total advance with this dist. ?
obviously heavier springs will make it advance slower.

 

bump

 

Never heard of such? where did you get this # from?

What heads are these?

What pistons are in it?

What is the deck clearance?

When EXACTLY does it ping? High RPM, low RPM; WOT, light tip-in while cruising, going up a hill, a rattle when it shifts, etc.?

Without this sort of info, all anybody can do is just GUESS.

 

the numbers came from a spec. booklet that the company sent to me with the motor.

ill have to get back to you on heads, pistons, and deck since im in class right now and cant tell u right off hand. here's a link to the company's page www.prestigehighperformanceengines.com 350/331 hp package

it pings at light tip-in while cruising
also ive had an occasional problem with it wanting to run a little longer when i cut it off, my buddy calls it dieseling.