Oversize pistons for 1.7 boxer - Alfa Romeo Forum
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Oversize pistons for 1.7 boxer


i'm thinking to increase my 1.7 16V boxer engine capacity. understand that i can either use either 88mm or 89mm pistons to do it. but i would like to know, Are a standard piston used from another car, and if so which car?? other than replacing the piston and bore the engine block, do i need to change anything else? i also do heard before saying there is a 1830c.c piston taht can be
fit in.

your kind assist, very much appriciated. thank you
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I think Autodelta sell a 1900cc conversion.

I don't know what pistons might otherwise fit but generally if you over-bore a cylinder beyond a certain amount, the limiting factor becomes the cylinder head. If you bore the cylinder out too much ("too much" depends on the cylinder head shape) you get a step at the edge of where the cylinder head meets the bore.

This "step" can interfere with the combustion process or it can even hit the piston.

You can get round this problem by machining the cylinder head step out but apart from making sure you keep the shape of the combustion chamber consistent, machining it increases the volume of the combustion chamber, which reduces your compression ratio (less power).

So, you then have to restore the compression ratio by reducing the height of the cylinder slightly. Generally this is done by removing the head gasket (and lapping it to the cylinder) or by using higher-crown pistons.

Either of these reduces the distance between piston, valves and head, so you can see that depending on the engine, you can only go up in bore-size so far before the whole thing becomes an engine re-work.

Going to 18-1900 cc's should be okay as the combustion chamber is usually big enough to fit on the new bore without having to be reprofiled.

Have you considered a new chip? You just take the old one out and put a new one in, and you get the same power as a mild overbore for a whole lot less hassle.

Ralf S.

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whoa... I'll have to print that one out and read it over the weekend...!
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I think what Ralf is basically saying is, get a scrap engine and practice on that one first!
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boxer , oversize , pistons

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