Porting and polish 850 head

[Guest]

Sorry I do not agree with the last answer.... for me, if intake ports are 34mm (not the valves diameter!), the carbs may end at 34mm, and also for the boots (even if you have to enlarge inside diameter of them). I agree with the fact that the speed has to increase all the way, but there are already one decrease of diameter inside the carb (to get fuel = venturi), the other important decrease of diameter is at the valve... the most important at the carbs / head interface is
- no "step" between diameters of elements
- no "increase of diameter"

You never ever want your carbs to be smaller than your intake port opening. Your carbs should be 1mm to 3 mm larger than the intake port for the best preformance. If your road racing then you would go to 1mm larger to help keep the air velocity up at the lower rpms and if your drag racing you want to be 3mm larger for wide open throttle. Now you can go the same size carbs as intake port size and I have seen some at the track run over 3mm larger on really high compression motors. The higher the larger the bore and compression the larger the carb can be and still maintain air velocity. If you use a carb that is smaller than your intake port you will lose air velocity every time.

[boris.h]

I agree with that
On my project (gs 550/650 head and jugs / pistons), all the ports will be machined. I want to use 600 gsxr full exhaust (33mm diameter), ported head to increase the compression ratio, 550 cams... I am not decided yet if I try to put BS34 carbs, or if I keep BS32 carbs... maybe do you have any advice here?