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1.70 to 1.80 rockers

524 Views 15 Replies 5 Participants Last post by  BogiesAnnex1
I have a BBC with 1.70 rockers? Jesel Sportsman. How much reliability am I going to sacrifice going to 1.80 ratio. I am running a hyd roller with I/E 242/249 @ .635//647

The reason for change is I increased displacement from 496 to 557 and believe it needs more cam to compensate for the increase in displacement. Due to wet boat exhaust I can't really replace cam with more duration as it would likely increase overlap and engine screwing exhaust reversion, currently at only 13 deg.
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That doesn't really matter, just as long as the flow curve doesn't fall off badly and start backing up on flow above the peak flow lift point.
The bigger rocker ratio increases the entire area under the curve.

Johnsongrass1 indicated why in post #4
Weedy,
What lifters are you using??
in the original post there is no head specified. it matters.
a 550 inch motor probably needs heads that flow at least 400 to get close to optimum output. if the rockers are free then go ahead and trade them.
 
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