Stopping the knock: Lower compression and ported heads...

Frankenduster said

Now I realize that all of the advice given here is done free of charge, but I have asked the ABOVE question before and RRR has not responded. I have reread the threads I started and it was mentioned several times that I needed a slower and later advance curve. RRR was one of the members that suggested it. I have asked before how a "full advance delay to 3000 rpms would help".
I will write it again in as plain English as I know.
If I floored the car from idle, the car knocked. When i floored it from 2000 rpms it knocked. When I tried running the car at any road speed in either 1st or 2nd gear, rpms of 3000, 3500, 4000 rpms, at light throttle, THEN tried to floor it, the car would detonate.
I interpret this to mean that whether the spark timing was all in by 2200 rpms or 4000, the engine knocked. Delaying the point at which it was all in made no difference. If my thinking is wrong, I surely would welcome a clear explanation.

Click to expand...

you have a thick skull, delay and limit are to different things. you delay (retard) or advance the curve to come in faster or slower. Limiting timing is adjusting slots or keys so the total mechanical timing is more or less.

Real world example.

Stock slants are usually timed 0-5* depending on the year at idle, but run much better with 10-16* initial timing. by increasing the idle timing you have also increased your total because mechanical and vacuum adv ADD to initial. So when I curve my dizzy's I set them for 14* initial, remove the heavy spring for a light one for about 2300 all in curve. Now being I play with mine the stamped number isn't correct but I see how much advance the slots allow, usually 10* to much. so after welding the slots I LIMIT my total timing to 30*. Now with the can (currently a VC-208) I get another 22* for 52* of advance when the vacuum can is in full force.

Understand?

Rice Nuker said

Franken, you may benifit from a timing curve coensiding w manifold vacuum advance. If you run high initial to get it snappy off idle, limit your total mechanical to +10 then the vac adv at part throttle will improve torque at part throttle and remove its advance under hard throttle. Don at fbo is a big proponent of this method from what i understand.

Click to expand...

that's how the chevy guys do it. By doing that you are effectively loosing your vacuum advance benefit. By using ported vacuum your dizzy curve controls everything all the time. Your initial timing is always where you want it, and your total timing is tailored to your spec. Now by using ported the vacuum can can add MORE timing at cruise conditions, where it couldn't before because it was already maxed out because you don't want to pull the dizzy apart. Its a lazy way to do it...