Quote:
Originally Posted by Henry Schmidt
10.5:1 is a ridiculous goal with a short stroke MFI street engine.
Any cam that would create enough mid-range performance would also generate way too much dynamic compression for any reasonable fuel situation.
With a short stroke engine, the piston dome would have to be pronounced, creating two distinct/separate flame fronts and detonation scenarios of infinite challenges.
Think seriously about 9.5:1, In these MFI engines, maximizing compression doesn't yield enough performance to justified the ignition struggles. Low compression and higher ignition will return the snap you get from higher compression numbers.
2.3 66/86 is what I think you're contemplating.
Mod S is one of my favorite cams but they are pretty much done at 6500 RPM.
I've built this engine engine a few times and it has a potential to return around 200 hp. Drop in a little more aggressive cam like a DC 80 [even 10:1] and thing come alive on top [7600rpm] but you lose a lot under 4500.
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Thanks Henry. Just to reiterate the comment above - is what you put still true with twin plug? Also, I'm happy to step up the overlap a bit and lose some compression low down because I'll be gaining a bit of low end power due to compression and cc. Also worth a mention, i'm in the UK and I think we have slightly better fuel than you guys. Our super unleaded is 97/98 RON and universally available.