intake and exhaust diameter

[fourstroke]

Hi
My latest engine has a 32mm x 40mm bore and stroke, The intake and exhaust passages are 5/32" id, can anyone tell me if this size is too small or adequate
Its a twin 180 deg crank
Thanks
Dougie

 

[kuhncw]

Dougie, as a point of reference, I know of a 4 cylinder that has a 1.00 inch bore and 1.2 inch stroke. It has 0.206 (#5 drill) exhaust passages and 0.189 (#12 drill) intake passages. This is a low speed engine and runs very well.

Chuck

 

[fourstroke]

Thanks Chuck
I have already gone ahead and increased the size of the passages to 1/4", leaving an internal diameter of 7/32"
My thinking was if I need to adjust the size of the passages I can decrease it by sliding a smaller diameter brass tube inside, but when its all soldered together I have no way of increasing the passage
Fingers crossed

Thanks

Dougie