Engine Octane and many other questions

Currently I'm running
KZ750 Head+cams
700cc Wiseco kit (10.25:1)
VM24 carbs
4-1 Ex.
Pods

What octane should I be running?

What about my next setup
GPZ750 Head+cams
810cc Wiseco Kit on KZ750cc jugs (10.25:1)
Modern Keihen CV38mm carbs from bandit 1200 (if fit)
4-1 ex.
Pods

Any experience on this? I'm currently using 87 on my 700cc setup, however I'm not sure I know what knock feels like. Is it that stutter that occurs if the throttle is cracked open at low RPM? I've learned to change my driving style to avoid that mostly, it is tricky in Chicago traffic though. I kind of figured the problem was related to the VM series carb (no constant velocity action) but I might be misguided.

IN SUMMATION
-What octane should I run on the two setups?
-What is the source of the stutter that occurs if the throttle is cracked open at low RPM?
-What effect, if any, does CV carburetors have on the low-end crack the throttle stutter situation?
ALSO
-How does Wiseco keep compression constant when the stroke of my engine will remain the same but bore will increase signficantly (enough to go from 700-->810)?

Post edited by: newbikekiller, at: 2007/07/02 11:24

try some 89-91 in there to see if it helps.not sure about the 750 but on a 900/1000 with an 1100 head your 10.25:1 would become 8.25:1 ,forget those 38mm carbsB)

You can't really feel spark knock (ping), but when it's bad enough you can certainly hear it.
It sounds like a bunch of tiny elves inside your motor beating away with little hammers

Forget the 38mm carbs, I don't think there is enough meat in the ports to open them up that far, if you are going to run CV carbs, then I think BS34's would be your best bet.

Compression depends on piston dome height, and wrist pin location, in Wiseco's case I believe they vary the piston dome height to set the compression ratio.

Shave the head surface .020-.025" and use premium fuel if you are going to run the GPz750 head (search for GPz750 FAQ with Google).

I think the best description of the noise is like someone has dropped some marbles into the combustion chamber. You can certainly hear it on an air-cooled bike once you know the sound. It's usually worst at peak torque. Make sure your valve guide oil seals and rings are in good order, as oil lowers octane.

Do a compression check at open throttle. If you are under 150 then you can run 87.
Anything under 190psi cranking compression can be ran on pump fuel.

Post edited by: Snakebyte, at: 2007/07/16 12:10

Nice!
Thanks, The reason I was going to use the Keihen CV38mm's is because I have them laying around anyway.

These aren't a good match though huh? Will the performance be worse on the 38's than on 34-36? I want to keep CV's for the smoothness and considerable fuel savings.

I'm updating my designs to include shaving the head and degreeing the cams. See my new post for more new motor fun!

Post edited by: newbikekiller, at: 2007/07/03 14:05

Post edited by: newbikekiller, at: 2007/07/03 14:04