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Air movement in inlet manifold

General Engine Building Discussion

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Hi, I spent a few hours port matching an aftermarket plenum to my SR20VET inlet manifold runners. Is it worth continuing and removing the rough cast finish to the whole of the inlet runner (basically polishing) or am I looking for some turbulance in the air stream before the injectors?

A slightly rough surface on the port wall is actually desirable as it reduces the thickness of the boundary gas layer at the port wall and improves flow. That being said, you're not going to end up with a mirror finish using normal sanding rolls that are used for porting work and this will give sufficient roughness. It really comes down to whether or not the time taken is justified, or in other words, is the juice worth the squeeze? Only you can decide on that.