Cam upgrade'n.....
^^^ exactly, on stock heads, yes more exhaust duration is helpful but with GOOD ported heads you could loose scavenging affect, it is better to close up the split or even go straight up on the duration. Had a car with excellent porting done, changed out the cam and the only difference was the duration, the first one had 10* overlap, the second was straight up, better drive ability, better gas mileage and made more power..
^^^ exactly, on stock heads, yes more exhaust duration is helpful but with GOOD ported heads you could loose scavenging affect, it is better to close up the split or even go straight up on the duration. Had a car with excellent porting done, changed out the cam and the only difference was the duration, the first one had 10* overlap, the second was straight up, better drive ability, better gas mileage and made more power..
also, please pardon my anality here as I clarify for anybody reading closely
Both "straight ups" above should be "single pattern". Straight up refers to cam installation, eg. a 112 LSA cam installed at a 112 ICL instead of the typical 4 or 5 degrees of advance.
For "overlap", I think you meant split.
For the cam in my motor below, 228/234/108 on a 103 ICL, I picked up 1/4 mile performance by stepping back to 1.5 rockers on the exhaust. Don't know about peak power effect, but it certainly enhanced the powerband below 7100 rpm where I could use it.
[QUOTE=bowtienut;19108345]Picking up the gas mileage with the shorter exhaust duration is the telltale sign that you were OVER-scavenging with the previous cam.
also, please pardon my anality here as I clarify for anybody reading closely
Both "straight ups" above should be "single pattern". Straight up refers to cam installation, eg. a 112 LSA cam installed at a 112 ICL instead of the typical 4 or 5 degrees of advance.
For "overlap", I think you meant split.
Yup, meant single pattern, too early, too much coffee, coffee, coffee...
also, please pardon my anality here as I clarify for anybody reading closely
Both "straight ups" above should be "single pattern". Straight up refers to cam installation, eg. a 112 LSA cam installed at a 112 ICL instead of the typical 4 or 5 degrees of advance.
For "overlap", I think you meant split.
Yup, meant single pattern, too early, too much coffee, coffee, coffee...
