I think that 3/4 race is an antiquated term, dating back to the flat motors.
Duration as you quote it is primarily a sales device. Of more importance is
duration at .050, which is where you would check it. There are many aspects of
cam design that effect how your engine responds. Most cams of substantial
duration need increased compression to function as intended. Lope at idle is
effected by lobe center. The same duration and lift may be cut with different
lobe centers. On my TR8, a lobe center of 110 degrees will probably idle fairly
smoothly, whereas the same cam cut with a lobe center of 106 will be quite rough
at idle. John
Thames800@aol.com wrote:
> What is considered 1/4 race? I have a 280 degree duration cam with about
> .410 lift. When I bought it I had my choice of cams.. 270, 280, 290 degree
> duration with various lifts. I'v heard the term 1/4, 1/2, 3/4 and full race
> cams but the grinders don't advertise there cams that way. I'v always
> wondered what thoes designations ment. As far as Idle... I cant seem to get
> mine under 1000 either.. It has a real heavy lope much under that. I'v been
> playing with the carbs, put in #6 needles. That seem to help a little. I
> also have a Maniflow header and exhaust with K&N filters.
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