4 replies to this topic

[mini_cooper_s]

Hi!

Ive been running my turbo engine for 10 years (allthough only about 10000miles) when my diff gave up in the middle of Lithuania after IMM 2015.
Since I needed to sort the diff I decided to rebulid the engine. When removing the piston I found cracks in the ring land on 2 of the pistons!!
Pistons looks mint except for the cracks....

The pistons are +40 Mini Spares Mega machined to 11,3cc.
CR 8.5 and max 13psi pressure. No detonation/knock

Seems like Im not the only one with ring land problems on Mega pistons... so, looking for something better to replace them with.

+40 12cc pistons would be ideal and would keep my CR, but I cant find any.

Omega cast pistons seems popular and available in +40 10cc.
This would give me a CR of 8.8
Would it be safe to run 15psi on 8.8 in CR?
If so, how high would be safe with 8.8?
(Im using std Metro turbo Dizzy)


Both MED and Avonbar sell +40 10cc Omega cast pistons, MED@ £330 and Avonbar @ £270, large price difference!!
Are these the same pistons, or am I missing something?
http://www.med-engin...ast-pistons-040
http://www.avonbar-r...0-10cc-Dish-set


Have a nice day!
/Jonas

 

 

[Steve220]

Hi Jonas
Firstly, what condition are your bores in? Cracks can lead to minor expansion in old critical areas of the piston and cause wear. Are the bores perfectly round?

Cast pistons would be fine. There's a bit of metal to remove more if you want a lower compression ratio, however 8.8 will be fine. A lot to of modern turbo cars including Evo's 4-9 run a similar ratio.

[mini_cooper_s]

The bores are fine, the crosshatch honing marks are still visible over the entire piston stroke area.

 

I dont want to machine the pistons this time, my option is to take some more of the combustion chambers (now 24cc).

 

MED call them "die cast", Avonbar call them "cast", but they are still the same?

[Spider]

Turbo Phil would be the guy to talk to, however, if it were m and after looking over your specs and taking in to account different fuels you may come across in your travels, I'd be inclined to suggest Forged Pistons, something like Ross.

[Turbo Phil]

For that kind of boost/spec the cast Omegas will be more than adequate. Can you not take a touch out of the chambers to drop the compression ?

Phil.