turbo build spec
Turbo Mini Forums

Hi, new member, first post. My objectve is to build a good 'compromise' engine, fast road and occasional track day use but still drivable and well mannered on the road while being reliable, no temp issues or lumpy tickover etc etc.

I've built engines before (just not mini turbo) previously I've aimed for low CR's around 8.5:1 and this has worked well but I'm struggling to find pisons with a large enough dish vol unless I go super expensive forged (Avonbar 18cc) As I'm thinking only around 10 to 12psi boost I'm guessing cast pistons can handle this?

Another issue I'm struggling with is deck height. I cannot find any figures for this. The more the better for low CR but how much can you expect?

Any good advice would be helpful

Welcome to TM

You can drop the CR to 8.5:1 by having the chambers in the head enlarged. This should open up the range of pistons you can use. Cast Omegas have earnt a good name for themselves, even on high boost applications.

Most turbo'd As' are well mannered as you won't need a lairy cam to achieve your desired power output.

I personally went for close to zero deck. I'll let someone more knowledgeable explain why.

Don't forget about the transmission if you are after reliability.

Edited by theoneeyedlizard on 28th Jul, 2010.

In the 13's at last!.. Just

you could also use 21253 pistons and have the dish opened up. Nick does this in his clubby and has had good results

EDIT: Fat fingers

Edited by apbellamy on 28th Jul, 2010.

If it was me my pennies would be going on 10cc cast Omega's and a few CC's in the cylinder head.

Says he who has 18cc Accralites :$

If something is worth doing, it's worth doing half of.

I'm not real comfortable machining the meat out of piston crowns, I always think it must be there for a reason. I've just come across Iasa forged pistons from Minispeed. In a +20 15cc dish for £400 inc rings pin and vat, seems a good deal to me. Never heard of them though, anyone got any info?

you can get 14cc acrolites for about that money - fit and forget

Thanks for the info, I checked it out and they're actually cheaper! £375 inc. 14 and 18cc

Seems like the Accrolites are the best choice which raises another question, 14cc or 18cc?
Assuming 0.030 thou in the gasket and 0.010 thou in the deck I can acheive around 8.5:1 CR which is ideal using the 18cc pistons and leave the head volume standard (21.4cc)
Or use 14cc pistons and take a few cc's out of the head. Obviously the 18cc route is easier and cheaper but which would work the best?

Still need info on how much deck height I can expect to find and also are head gaskets available in different thicknesses. Thanks

I'll throw these in for good measure
http://www.med-engineering.co.uk/product_d...25&vlang_id=169

If your only aiming at 12psi i would use cast pistons.

On the other hand, fit 18cc dish forged jobbies, leave head standard and run lowish boost. When you want more power just have the head sorted.

Edited by sturgeo on 28th Jul, 2010.