340 Static Compression Numbers and Test Procedure
Thanks so much for taking the time to explain this. I get most of this but have a few questions. Whats wrong with low RPM cylinder pressure? Is this why you think my engine’s cam is possibly advanced too much?
Low RPM, high load situations...like rolling down the road in high gear at say...45 MPH and you step on the throttle to accelerate up a hill or grade and you'll get a rattle. Most guys forget God made shifters on the 9th day. So they get into these high load situations and get the rattle.
It's really pretty hard to get detonation above peak torque, although you can do it.
So...I'm guess your cam is either too advanced, wrong for the combo or both. And you're tall gears make it all the worse. I'm not saying you need a big cam, I'm saying you need the RIGHT cam...two totally different things.
That's why a vacuum advance has issues. I'm not ruling out going to one on my car, but if you see how slow the mechanism responds, you'd see why it's hard to make it work when you are close to the edge. It just doesn't react fast enough to pull the timing out under load.
You've got several things working against you. The best plan is pull the valve covers and see where the cam is and start with that.
That's why gearing is such a big deal. Tall gears, tight converters, incorrect cam timing, timing curve out of whack, incorrect carb tuning all affect an engines ability to resist detonation. You can run much higher compression ratios if you plan for it. Also, coolant temp is a BIG deal in detonation resistance. I run my junk at 170 and I'd do it at 160 if it didn't make the heater almost useless. These are NOT modern cars with computers doing a rolling tune up. You'll be much more likely to run into rattle at 190 or 200 degrees than at 170. I did a ton of research before I picked my cooling system components. And it was worth the time. 100 degree days and I run at 170. I may hit 180 at a stop light. Maybe.
All things to consider.
