Throttle Body Size

[Alan_RHIT]

I know this has been tossed around alot. But I am running a CBR600 and was wondering what about the ideal throttle size has been. I tried to run a few calcs and got about 28. Is this too small?

Will it hold the peak rpm down vs a larger one?

[Alan_RHIT]

I know this has been tossed around alot. But I am running a CBR600 and was wondering what about the ideal throttle size has been. I tried to run a few calcs and got about 28. Is this too small?

Will it hold the peak rpm down vs a larger one?

[Gaanja]

Maybe. A lot depends on the geometry of the intake after the throttle body. We have been using 28mm for the last 2 years.

[wagemd]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Alan_RHIT:
I know this has been tossed around alot. But I am running a CBR600 and was wondering what about the ideal throttle size has been. I tried to run a few calcs and got about 28. Is this too small?

Will it hold the peak rpm down vs a larger one? </div></BLOCKQUOTE>

It wont affect your rpm range at all. What it does affect a lot is throttle response. I would suggest finding the throttle size that just leaves the restrictor as the limiting factor when wide open. Any bigger than that and you loose throttle response for no hp/torque gain, and any smaller, the throttle becomes the power limiting element.

It might also depend a little on what type of throttle you run, ie butterfly, single barrel, double barrel, plate, conical, etc.

[Alan_RHIT]

How do you determine the size that leaves the restrictor as the limiting factor?

[wagemd]

Well, its tricky. You can do a lot of work with CFD and modeling, but its hard to get an accurate result that way.

We ended up taking several diameters of throttles to the dyno and chose the smallest one that didn't hurt peak power or torque.

If you have access to a decent dyno, that is probably your best/easiest option.