Decompression Plate
Turbo Mini Forums

I've been thinking of uprooting my 649 cam and going turbo on my 1275 but the other limiting factor is the powermax KA2079r flat top pistons.. They are squeeze cast & hold up well to abuse.

If i use a decom plate, i think i should get my compression down from 11:1 to a decent 8:1 which can handle a bit of boost.
Is there a commercially available plate for this purpose?

i 'm weighing the optipons of having one custom fabricated as opposed to buying it new if available..

These are very bad ways of lowering the compression.

Aside from obvious extra head gasket failure risks....

It will effect the valvetrain geometry, as ideally you will no need equally longer pushrods.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

You can get plates from vmaxcart if you must

Metro turbo weekend driver,Mini turbo in the making again!

you should be able to get a fair bit machined out of the head, probably enogh to get the compression down enuogh.

this is a far better way of achiving what you want.

arrggh!! i didnt think it was that bad..
Okay.. what are the safe / sensible ways of lowering compression?
opening up the combustion chambers?
could these be enlarged suficiently to drop the compression for boost?

the very last resort would be changing out the pistons

Try to find as much CC in the head chamber as possible and/or fit dished pistons.

The same as on any engine.

A CR of 8.5 is a great start, nice off boost and room for winding it up a bit.

JF.

Hi,
It depends on how much boost you want to put in. On 9.4:1 you can stick 10 psi via an intercooler in there.
If you looking to put more boost in your goning to need to lower it more.
I say this as you may be able to get it to around 9ish by opening out the head, which would save you piston work / replacement.
Cheers,
Gavin :)

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yep unlessthe heads been skimmed loads tou should be able to find enough in the chambers,

best bet is to get some perspex, a small syringe and a set of verniers and get measuring!

Get a new set of pistons and hone the bores. You need to take the engine out and gearbox off to change the camshaft anyway. Do it properly. This will not be much more expensive than to have a silly decompression plate made either.

My last N/A engine had 11cc in the pistons and 15cc in the head.
So if you have flat top you would req 26cc in the head for n/a

So don't see how you would get it low enough as max head size is around 33cc

Metro turbo weekend driver,Mini turbo in the making again!

thanks for the advice gents..

i guess leaving this engine NA is the best bet
I have a spare 998 rebuilt with new pistons & decent headwork so i guess my next project will be bolting the turbo to this.