Where Angels Fear to Tread

[hombre]

I run my fuel cut at 7000 RPM, which means my R3 still makes power to 7250. This means a missed shift will show 7400-7500 RPM before the fuel cut actually kills the revs. I'm not proud of missed shifts, but they do happen. However, the point here is that my engine has seen 7500 RPM occasionally with no ill effects. No bent valves, kissed pistons, rod stretch, or spun bearings... with a 14,000+ mile engine.

I don't recommend the 7000 RPM fuel cut to those with stock cams, as a stock cammed R3 can't breathe over 6800 anyway... no power up there for you. Remember, longer duration cams move the torque curve higher, giving you more power at higher RPMs (they let the engine flow better at high RPMs) and also take stress off the crankshaft in moving the power band higher. A supercharged R3 with long duration cams makes great power to 7250 RPM... possibly beyond.

 

[wilbur-t]

I would think that the R3 engine should be fine up to at least 8k. Over head cams with no rocker arms flapping around. Hell, some of those jap bikes turn 14k with the same valve train, although much smaller pistons.

There are only 2 ways to make [Naturally aspirated.] horsepower, cubic inches, or RPMs. Heck, I used to turn the 289 in my old drag mustang 8k. Ran mid 11's in the 1/4 mile. Ran the quickest that I ever ran it shifting at 6500.

 

[hombre]

Wilbur, the problem with 8000 RPMs in the R3 isn't piston size, it's rod length (piston speed). If we de-stroked, we could do it... but it's an expensive experiment.

 

[wilbur-t]

Yeah, I wasn't thinking of the stroke you have to have to get 2300 ccs out of 3 pistons. Those long rods give a lot of leverage against the crank, good for low end torque, not so much for high revving.