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Old 01-24-2008, 05:52 PM   #1 (permalink)
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SBC Rocker Arm Ratio

I was wondering what effects I might see if I change the intake valve ratio on a SBC. Here's my reasoniong: the stock rocker arm ratio is 1.5:1. If I change the intake rockers to 1.3:1 (using cam break-in rockers), then I will see less intake valve lift. Extraction (exhaust valve) will be unchanged. Since the intake valve is opening less, less fuel/air mixture can enter cylinder at any given rpm. The ECU will adjust mixture to stoich as long as I am running in closed-loop. In order for the engine to produce the same power, given the smaller valve opening, then I will need a larger throttle opening. This reduces pumping losses, slightly improving volumetric efficiency. This in turn might translate into slightly higher mpg. Peak hp of the engine would be reduced, of course, and that is the trade-off.

I welcome informed comments as to whether or not the above might be true.

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