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Bore taper with head in place.

Engine Building Fundamentals

Discussion and questions related to the course Engine Building Fundamentals


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Hi, I’ve just received an engine block, heads, pistons & rods, etc back from the machinest, I decided to bolt the head on and check P2W clearance from underneath as the engine was torque plate honed for oversized forged pistons, I’m getting 2-3thou taper between the bottom and the top on the thrust faces of the bore.

On average I have 3.5 thou ptw at the bottom and 6 thou at the top, CP specs recommend 4.2thou.

I just wanted to know if this to far out or if I’m just nit picking.

RB25 neo head on an RB30 bottom end. End goal is around 700hp to rear wheels and 7500-8000 rpm redline.

6 thou is pretty loose and is almost certainly going to result in an engine that's a little noisy when cold. It's not likely to be a major concern at operating temp but is excessive for the power aims you have. Likewise 0.0035" is a little tighter than I'd want to run. Have you raised this with the machinist?