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turbo conversion update - pistons and cr

hi all.

been looking at pistons for the turbo unit.

the standard turbo pistons are 9.5:1 compression ratio

it would appear that the standard head volume and piston bowl area at 9.5:1 = about

53.71 cc

on a 172 at 11:1 it is about


so, apx 9 cc is in the piston bowl.

it would appear the standard turbo pistons can be used to obtain about 9:1 by removing 4 cc from the piston bowl (lathe n polish).. or by increasing the head volume by 4ccs - might be difficult......

to get 8.75:1 would need another 5.5 ccs removing from somewhere..

I might decide to chop a turbo piston in half to examin the thickness of the areas that I intend to remove metal from.

hopefully a picture later of half a piston

so, bottom line, might be able to get away with standard renault parts.

will probably go this way for the first engine and only consider forged pistons after I see the results.

from an engine remanufacturer, these pistons will probably be very inexpensive.


Other breaking news

the inlet and exhault valves on the turbo head are exactly the same as a 172 !.. the porting on the 172 is marginal and in the are of the intake port (head inlet) only.

an interesting theoreticall hybrind would use the 172 inlet cam with vvt and the turbo exhaust cam with its greater duration.



yeah, when we took the head off my 172 we found that the basic design can be largely improved on. but we dont have the facilities in HK.

Oh, that RR is sitting in our basement if you want it?

top job on the turbo so far!

Cheers Ben m8 !

I have doubts about improving the 172 head too much.

its all a compromise on the 16v units between drivability at low rpm and top end grunt.

the cams are dual profile too.

I am in the process of measuring lift and duration on the 172 cams and also the turbo cams.

the vvt is still bothering me though.. it really does seem to make sod all difference.

Joe (Sawing a piston in half at the mo to measure thickness of metal in the important places)

correction to 1st post.. I meant use the 172 inlet cam with the turbo exhaust cam with its shorter duration.. not longer

this should help reduce spool up time without affecting the power. due to forced induction.


compramise yes, but not to me....being used to racing 2 strokes....bottom end grunt aint too much of a prob....and it wont get so bad that itll the 125 did!!!