www.zxrworld.co.uk

Hi guys,
I am soon to build a racing buggy in the 450cc class. Most chaps use YZ450 or KTM 450cc singles. I am thinking outside the square and have bought a crashed ZXR400 H to use the motor. Not having owned a ZXR400 before, I will be relying on your experiences here but I am forseeing the need for a stronger midrange.
What engine mods would you recommend??

A ZXR750

In the 450cc class...

You can install 440ccm pistons, adjust the timing (earlier inlet open, retarded exhaust close), get some longer bellmouthes for the carbs and a bigger (ram) airbox. This will give you some more power at lower rpm.
All in all the zxr engine isn't designed for midrange power and you will achieve better results if you go for top end...

Thanks Dominik,
Has anyone tried changing the cam timing? What was your experience??

I haven't changed the timing in my bike yet as I don't have adjustable cams (only sp models have those) and changing it by a whole tooth won't work for me.
I know that some have changed the inlet cam timing by one tooth and they achieved more midrange power so you might find something about it here.