Dave Lapham:
One thing you might consider doing is modifying the SUs. According to Dave
Visard's book, it possible to increase the airflow of a SU with a few
modifications, such as: ram pipes, chamfering the piston (leading edge about
30 deg, trailing edge 15 deg), cut off protruding screws on the throttle
shaft, reduce the diameter of the throttle shaft, knife edge butterfly, etc.
These modifications done to an H4 SU will raise the air flow from 130 to 176
CFM. I don't know what this would translate to in terms of horsepower but it
would certainly help and looks to be fairly inexpensive. Vizard also states
that an HIF6 could be updated from 240cfm to over 300 cfm with these
modifications.
Glenn
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