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Discussion Starter · #1 ·
Due to a major F$$k up by the machine shop that cleaned my intake manifold with bead shot and didn't wash it all out. (They actually only cleaned the as far into the runners as you can put a finger and left the rest of the manifold full of carbon, junk and hmmmmm... steel beads!)

So the cylinders are being overbored, new pistons and rings, new gaskets. All paid for by them of course.

This is a stock l28 and n42 head with stock cam and stock dished pistons. Can I put flattop pistons to increase compression and get a performance boost without doing any other major mods?

Steve Graber
 

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Discussion Starter · #2 ·
Sorry: N47 head n/c

> Due to a major F$$k up by the machine shop
> that cleaned my intake manifold with bead
> shot and didn't wash it all out. (They
> actually only cleaned the as far into the
> runners as you can put a finger and left the
> rest of the manifold full of carbon, junk
> and hmmmmm... steel beads!)

> So the cylinders are being overbored, new
> pistons and rings, new gaskets. All paid for
> by them of course.

> This is a stock l28 and n42 head with stock
> cam and stock dished pistons. Can I put
> flattop pistons to increase compression and
> get a performance boost without doing any
> other major mods?

> Steve Graber
 

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107,597 Posts
Discussion Starter · #4 ·
> As far as compression ratio goes, you would
> get a nice increase to about 10.0:1 using a
> stock 1.25mm head gasket. Using the 1mm HKS
> metal gasket would give you @ 10.2:1. With
> the increase in compression, and the
> overbore, you should notice a nice increase
> in power. This would be the limit for the
> compression on a street engine. Any further
> and you might need some better ignition,
> polishing, etc.... The compression also
> gives the exhaust a little more powerful
> bark also. You'll probably be sounding alot
> more like a Ferrari with the high
> compression, rather than a American V8.

Yeah, at least I do have something positive to get out of this. Like more horsepower. But not really the way I expected it to go what with scored cyl walls and shot pistons. Luckily the bottom end is still solid.

What sort of horsepower increase can I expect out of the increase in compression and bore? 5 - 10 horsepower? I already have a header and 2.25 exhaust as well as a K&N ram air.
 
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