Pinging

[nthang]

I was telling the tech guy at GBE the specs on my new motor so that we could select the proper diameter exhaust system. The motor is about to be fired up, run, and shipped from the builder (thebugpatch.com) to me for my 74 thing. The tech guy said that its set up at too high a cr (8:1) for the 93 octane that I will run it on. He said it will ping and the fuel will pre-ignite causing power loss, and other bad stuff. Two things: Is this ALWAYS correct? (you would think that my engine builder would understand this and avoid it). Secondly, can the cr be stepped down to the recommended cr (GBE said 7:1 is optimum for my specs), even at this late date in the process.....its complete and ready to produce 140 bhp. Thanks.

[mschilling]

Don't worry about it. The pinging will depend on your motor combo, and how much advanced the timing can be set before pinging occurs. You simply adjust the timing accordingly. More timing advance = more power, but more likely to ping.

[jasonb]

The combo is the thing. I am running 8.2:1 on 87 octaine with no pinging.
Now if, for example, I were using...semi-hemi heads on my engine at this CR I would be in severe danger of pre-detonation. The flame front has to travel further in the hemispherical combustion chamber making the design more prone to detonation. To counteract this tendency I would have to crank the CR waaaay down.
So, if I did a minimal amount of testing on CR and I only used semi-hemi heads I might conclude that anything but ultra low compression would cause pinging.

Don't lower the compression on your engine. I'm sure that the people building your engine know exactly what they are doing.

[nthang]

Yeah, 22 years in the business working on air-cooled engines would tend to clue you in on Type 1's. The Bug Patch seems to have a significant following, especially on thier cnc head work.....c r work. Duhhhh. I'm an idiot, again. Thanks