Effect of Swapping 1.8 to 1.7 Roller Rockers?
12-13-2006, 07:21 PM
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Effect of Swapping 1.8 to 1.7 Roller Rockers? Is there a formula of the effect of down-sizing from 1.8 to 1.7 roller rockers? Like how much would duration and lift be reduced, ie. the valves wouldn't open as much or as long. Shouldn't this change move the torque curve down lower in the rpm range or do I just not understand the effect of taller rockers on an engine?
12-14-2006, 05:06 AM
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Somewhat depends on the rockers. I moved from Crane 1.8's to Crane 1.7's. Both come off the seat fast and at a higher ratio per the Crane design. I feel I lost about 6-7 hp with this move, but I am only guessing as I did it at the same time I put in my Dart heads so there was no measurement of the rocker only change. I did notice the cam sounded less "lopey" after I made this change. Valve timing won't change, only the duration at a specific lift point.
12-14-2006, 10:33 AM
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Yeah, in general instead of multiplying the actual lobe lift by 1.8 times (ex. .400 lobe lift x 1.8 ratio = .720 lift to the valve), you get a multiplication of 1.7 (ex. .400 lobe lift x 1.7 ratio = .680 lift to the valve). Duration should be similarly affected. Hope this helps.
