Low compression Pistons

[Wafer_Thin_Ham]

I've heard of people on drag bikes fitting low compression pistons.

What's the score with this?

Usually more compression = more power(at the top end at least), so why would you want to lower the compression, esp. on a drag bike?

Unless it's got something to do with rideability?

Any drag racers or nerds spread any light on this one for me and anyone else that wondered.
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[cagiva gezzer]

So you can fit a high-boost turbo or supercharger.
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"because one stroke isnt enough and four strokes waste two"

[teampots]

or run a higher octane fuel ( a fair amount mind ) or to run nos
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[Wafer_Thin_Ham]

Yeah I though of this, but then surely if you ramped up the compression too, you'd be able to get even more power?

Or just kept stock compression and ran the turbo at less boost for better reliablity.
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[Blau Zedong]

If you ran a turbo coupled with the relativly high standard compression ratio of most 4T engines you'd blow the pistons to pieces. You generally lower the compression and fit more conservative cams, and let the forced induction do the work.
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[Wafer_Thin_Ham]

[Kickstart]

Hi

As above, fit them to run more boost, or if really desperate to use lower octane fuel (far lower than generally available).

You gain far more power from more boost than you loose from lowering the compression to avoiding the grenading the engine with the boost.

All the best

Keith
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[Pete.]

As above you lower the compression to reduce the dynamic compression-ratio on forced-induction engines. The higher the stock compression the less boost you can use before the need to lower it. As Kickstart rightly says, there's more gain from lowering compression and adding boost than from running less boost on stock compression but there's a small trade-off in terms of off-boost response.

You can run nitrous on stock- or highish-compression engines but you do have to retard the timing using more than low-power nitrous kits. This is because the burn speed of your intake charge is increased by using the nitrous, as the oxygen/nitrogen ratio is altered.
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132.9mph off and walked away. Gear is good, gear is good, gear is very very good