mikuni carb on 113

[dr dave]

mike: i have a 113 (screamin eagle 4.065 bore X 4 3/8 stroke) but have now replaced the cnc htcc ported heads and htcc pistons with stock 06 heads that have been professionally ported for performance and custom pistons to provide a 10.5-11.0:1 compression ratio to match the heads. currently have the head-quarters 575 cam for low and mid range rpm driving. the original 103 that was converted to the original htcc 113 motor had a 45 mikuni as part of the package (on a roadglide that is riden single only and for long cross country riding). the motor is much stronger than the htcc 113 motor with the only difference being the heads, pistons, and cam change from a s&s 625 cam. my question is for strong performance at 2000 to 4000 rpm, would a 48 mikuni or another carb be beneficial on this size motor now, or is the 45 going to be just as good at those rpms. currently have rb racing 2-1 exhaust.

[Mike]

The motor could certainly stand the 48 but for the 2-4k area it may not be any improvement vs the 45. We've seen this go both ways. If the heads, cams and motor size demand more air from idle on than the 45 can deliver, you'll see an increase in tq and hp across the board with the 48. However, smaller motors that may move a lot of air at high rpms but not so much down low will tend to loose tq below 4k with larger carbs, though making more hp up top (cannot maintian port velocity at lower rpms). If we were to look at what we would recommend before the build, it would be the 48, considering your heads and motor size.
Mike