J9BBY

I'm going to start rebuilding my spare engine and was wondering what the best pistons for the job are. My plan is to build a rock solid bottom end and then, when money permits, get head work done and suitable turbo attached.

My question is which pistons are best for the job?

Forged? If so, what makes do you recommend?

Standard Mahle? Can old pistons be reused, or is it best to use new? Can these be machined to lower the compression and for valve cut outs?

What compression ratio to use? This will depend on what the rest of the spec is i'm sure. But any views/opinions would be greatfully received. Worth lowering over standard comp ratio?


Again i am in debt to your knowledge. Thanks in advance




Pete.

bud-weis

standard mahle pistons are very good, and capable of over 500bhp....you can have them machined for valve cutouts and to lower CR however you like...

CR defo depends on spec.....if you went for a GT30 based turbo,7.2:1 is a good idea (so i'm told)

i wouldn't go lower than 7:1 personally on a road car though.!

J9BBY

Thanks Martin!

I didn't realise the standard pistons could take so much power This is the route i think i'll go then as not aiming for over 500bhp. Looks like i'll need to decide what turbo route etc to go for then before i get the pistons machined. So there is an optimum compression ratio for different turbos...... Would there be any benifits or otherwise to go for a comp ratio higher then 7.2:1 if say i went for a GT30?


The bores are in good condition and looks like i should get away with a hone. Would i be able to reuse the pistons or would it be recommended to replace these? I'm sure i read somewhere that they shrink due to the heat the engine produces



Thanks again!
Pete.

bud-weis

tbh you'd really be best going for a rebore and new pistons if your aiming for decent power (400+) you could always measure the piston to bore clearance.....and if it's good then re-use them.

as far as CR goes....i'm really not clued up enough myself to give advise on what's best. You could get in touch with a tuner and give them a rough power figure....say 450bhp, then they could spec the correct turbo,cams,CR etc...

also as regards to pistons shrinking, you may be getting confused with the expansion of forged pistons, these require larger piston to bore clearance because they expand once hot, the downside is they clatter a little from cold.

DAN P

iTrader: (1)

as above just done my rebuild using .5 4x4 mahle pistons