Big Engine/Small Engine Question

[bugguy1967]

Just curious; I have a suspicion that larger engines (all things being equal as possible, e.g. same piston size, same engine temps) are more resistant to detonation than smaller engines. It's is a fact that larger, more powerful engines require a smaller percentage of their power to move a given vehicle. So could that translate to a larger engine can get away with more?

So for example: a 1915 and 2332 that both make peak HP at 6,000 RPM and peak torque at 4,500. The 1915 makes 130 HP and the 2332 makes 170 HP.

Can the 2332 get away with a higher DCR because it will be less stressed under load?

[Dan Ruddock]

Lot of it depends on how the car is being driven. Lots of full throttle and the smaller pistons resist detonation better. In lots of small throttle it's a toss-up.

My 83mm piston 2016 Miata has 13.0 CR and the chevy LT1 with 103mm pistons has 11.5 CR.

Dan

[FreeBug]

From what I understand, detonation is more likely in a larger bore; small bore means charge gets burned in less time.

So your example, where both have same bore, is not interesting as an illustration.

Also, seeing as both engines make peak hp/torque at the same rpms, they must be running the same cam, and have the same DCR to C/R ratio?

So, if they both make the same BMEP, there's no difference in knock limit...except if there are differences in temps, turbulence, etc, but there isn't, because "all things equal"...not sure your HP numbers correspond to that or not.

[mark tucker]

it realy depends on the entire engine package. all things being equal...there the same motor...so...neither is bigger. a small motor can detonate all to hell and a large one may not. and visa versa depending on the build. wide deck/little quench can be prone to detonation.tight deck with lotsa quench can tolerate more cr. before detonation. I dont do the dcr thing. IMHO unless you have a cc requirement....build big with tight deck.

[modok]

I KIND OF... see what you mean, far as a general trend, the smaller CC builds tend to be over-geared and under cammed and the exhaust system isn't tuned right.....but that's not how it should be.

Should be able to have even higher CR on the smaller ones, slightly.

[bugguy1967]

Oh, wow! The answers are the opposite of what I expected! I was going to use an example with a smaller bore, but 94 strokers are so common. Thanks for the replies.