My 1399cc dilema....
Turbo Mini Forums

Hi All,

Its taking me ages to sort out my turbo project. Work commitments, uni etc etc etc

I orginally thought that the motor that I had bought was a 1380cc, never had any real plans of FI'ing it. When I stripped it, top of the pistons read +020, to which I though, I'd been had. So being a 1293cc I thought that the block would be a suitable candidate for my first turbo project.

I've bought a fair amount of stuff for the build, just popped out to the garage to have a look at the block before finialsing the spec. Discovered I had made a retarded mistake, the pistons are actually AE 20659 +020. Which I have now found out that they are 73.50mm pistons, +020 to make them up to 74mm and 1399cc capacity!!! DOH!

Seing as the block is now at its max bore, and I still want to pursue the FI route, could I safely boost it?

I have a morspeed stage 4 turbo head with 30cc combustion chambers. I was planning on running around 9.0-1 compression ratio, no more than 10 psi boost, with a decent intercooler. I have a T3 that needs work, but was thinking more of a GT1752.

I would have thought that spec would make a nice driveable motor, what are your thoughts?

Could anyone seen any possible problems with such large bores? Like gasket problems? Or would running 10psi max be safe?

dont rely on whats stamped on the piston, measure the bore,

however if your only going to run 10 psi I'd be confident that it will be ok at 74mm you might find you have to run the copper gasket rather then the bk 450 though (holes are bigger in the copper one)

incedently I ran those pistons at 73.5mm in mine and they were fine, and I'd dished them out to 17.4cc too, but I did have oil jets.

Just measured the bore, came out at 74mm.

I think the dish on them as standard is 10cc, would have to measure. I was planning the CR around a dish of 6cc, so if they do work out at 10 I can bring the compression down a little to be on the safe side!

I think it might be worth me running the undercrown cooling, just to be on the safer side of things!

Are the copper gaskets as good as the bk450s'?

dunno if the gaskets are as good, but somtimes you find the BK450's can overhan the bore on large over bores.

if the pistons are not for forced induction ..... (ie) the ring lands are narrow between them the slightest touch of detonation will quickley kill them.

sorry to be a little negative but i have seen it so many times with the AEs.

use a DK450 head gasket, dont overshaddow the bores so much.

if its a transverse engine ....going in a mini, trust me undercrown cooling jets are not needed................. undercrown cooling jets will not compansate if you get detonation and those weak AEs lands break

Edited by BENROSS on 19th Oct, 2011.

Not negative at all benross, very helpful. I will just have to make sure everything is spot on so detonation never happens!

If I do happen to find some extra pennies, I will invest in a decent set of pistons. :)

EDIT: Maybe 9.0-1 is a bit optimistic, will have to work it out properly...

Edited by TrialsLife on 19th Oct, 2011.

Measure the chambers in the head and confirm they are infact 30cc.

Many people have bought heads and found there not what they are stamped.

Cheers, that's the plan. I bought the head secondhand, and I know people who have had bad experience with Morspeed. Everything is going to be measured, can't afford to risk anything.

EDIT: Also planning on running MegaJolt

Edited by TrialsLife on 19th Oct, 2011.

The Powermax 74mm pistons are +.020" pistons and marked as such. The 73.5mm powermax pistons are marked up as STD.

Powermax pistons have not been available in 74mm for a very long time.