Low compression pistons

[Judderi]

Just wondering why you need low compression pistons for a turbo or supercharger conversion. What are they? What makes them different? What is low compression? I dont know anything on this folks so start basic please, im just trying to learn.

[topher]

Basically to run forced induction properly you need to lower the compression in the chambers. You can do it several ways, cheapest being a thick copper head gasket, but in my opinion the best is with the low comp pistons. They will be shorter than standard thus creating less pressure at the top of the stroke to allow for the turbo/supercharged force of air that's going to get shoved into the system at 10-30 PSI.

Forced induction on naturally aspirated compression ratios = a big expensive bang

[Judderi]

so basicly the bar that holds the piston to the crank is shorter?

[topher]

You mean the con-rods ? Shorter con-rods is another way to lower the CR but I was referring to the pistons themselves. JE make custom pistons for most applications

[Judderi]

So you can get shorter con rods or shorter pistons to lower compression? What are the pro and cons? I guess shorter pistons would be lighter?

[topher]

That's about as far as my knowledge goes im sure someone else on here will know the benefits of one over the other... steve (mk1) should be along shortly

[Horney]

Depending on the car and application you often need the head modified as well. On mini's it is recommended to drop the CR and use sodium filled valves as they deal with heat increase much better when running high levels of boost. I have no idea if this sort of thing applies to VW engines though.

[AudiA8Quattro]

VW 16v gti engines already have sodium filled exhaust valves 

[Mr Blue]

VW 16v gti engines already have sodium filled exhaust valves 

you nerds 

 

[mk1]

Yes, thanks "6 , head will be OK for forced induction. Best way to lower the compression ratio is to use some custom pistons as topher said (some people will mod the pistons, but not recommended ). Mechanical modification is only part of the equation, what are you going to use for fuel and timing?.
Steve.