A SHORT rod and tight quench will do more for detionation than a long rod. It is due to the dwell time at TDC. Mine is 13.3-1 static compression and will be running on 92 octane.

 

This is interesting. . . I made my own spreadsheet some time back to plot piston motion (though I made mine to compare to valve events). I re-ran Reher-Morrison's numbers and got the following for a 3.75" stroke comparing a 5.7" versus 6":

Difference at 10 ATDC: 0.0005"
Difference at 20 ATDC: 0.0018"
Difference at 30 ATDC: 0.0039"

Once interesting point of note is piston velocity versus intake valve lift. I would think (neglecting momentum and resonance) that you would want max valve lift (supply) to occur at the same time as max piston velocity (demand). With the 5.7" rod, max piston velocity occurs at 74 deg ATDC. With the 6" rod, max piston velocity occurs at 75 ATDC and the speed is lower. So, with an intake C/L of 102, the 6" rod better matches piston speed to valve lift (though by only 1 deg) and the peak air demand is less.

 

Gearheads while some are inovators LARGELY are stuck on old antequated beliefs like needing octane to make power or that AFRs are decent heads . Use a head with a good chamber, VERY important for high compression detonation resistance. Chamber design and better understanding of quench are big reasons why modern engines get away with the compression they do.

 

Do a test to see what the 1* difference gives ya. Bet it won't be much.

 

Perhaps I wasn't explicit enough, but my point was that longer is better, but the difference between 5.7 and 6.0 is tiny.

A 15" rod makes peak piston speed at 84 degress ATDC. 10 degees might be a sizeable difference! An infinitely long rod will produce peak piston speed at 90 deg.

Come to think of it, street bikes run very high rod/stroke ratio's and ICL's of 100 - 104 deg. The R6, due to a rod/stroke ratio of 2.25, reaches max piston speed at 79 ATDC. So, the offset of max lift and piston speed is only 23 deg. A typical 350 Chevy has an offset of 34 deg. Perhaps this is part of the reason street bikes have reached 200 hp/liter. Imagine a 1140 hp, smooth idleing, pump gas 350.

Mike

 

I agree that the AFR chambers could be better. But they have enough other redeeming qualities to more-than make up for it. I've seen some real dyno duds that used Vortec or Fast-burn heads. What's the point of making max power at 26 deg ignition timing, when max power is way low?

Mike

 

Imagine having to rev it 12-14k!

 

Yeah it is torque that feels good in a car. A bike is so light they can go fast strictly on HP, and a lot of them are scary fast these days. Think the average crotch rocket would require a rollbar if it were a car going as fast and seen a good number go below 10.0. I prefer to go fast with a couple ton of mostly steel around me, I can honestly say that too since I drive a Caprice not an f-body, it is over 2 ton and the chassis dates back to the 70s so there is lots of steel.

 

Out of pure curiosity, I normalized the torque and hp curve of a ZX-10R (my bike) to 5.7 liters for comparison. What I got was this (all in rear-wheel numbers): 296 ft-lb at 3500 rpm, gradually rising to a torque peak of 456 ft-lb at 9750 rpm. Hp peak of 923 rwhp at 11750 rpm. For the detail sticklers, I DO realize it can't simply be scaled up...