Recently been blessed with a cracked valve, 156,xxx miles. I was able to get my hands on another engine, but deciding to rebuild with forged parts.

Looking at the different pistons available, I have decided to go with Wiseco pistons, feel free to suggest others. I wanted to know if anyone knew what the compression ratio is, I've looked a bit but was seeing both 10.5:1 and 9.5:1

For connecting rods, I think I am going with sneedforspeed, or supertech rods, would like some advice on this.

Thanks for the help

 

R56 base is 11.0:1 CR
R56 MCS is 10.5:1 CR
R56 JCW is 10.0:1 CR
With 156K miles I suggest oversize pistons (77.5mm vs 77.0mm). If not building for big power, I suggest staying with OEM CR.

When mixing piston and rod manufacturers, be wary of piston / rod interference. Search for previous builds using the combination you want, and ensure they had no problems. My build used CP / Carrillo, a pair that used to be one company so I had lotsa confidence the combo would be OK.

 

Following up on OBW's response:
The choices also depend on your goals: Stock performance, more performance - low end or high end, more boost etc ...
The Carrillo's were the gold standard for rods and pistons a while back, during my Miata days - but as OBW states - there have been a few company changes since then. The Wiseco has/had been known for having a good top piston geometry to prevent detonation ( not sure if this is true for Mini applications - just in general. I used them when doing obscene boosts in a turbo application on my old Miatas ). Again - old data ..

If you are going with the Wiseco for a street application, I would try to make the 10.5 work with a thicker head gasket ( even thicker yet - if you do a head shave and clean up ). I have heard guys have gone up to 10.3:1 CR on the JWC N14 - but with good tuning. The plus is better low end especially if they can advance timing. You might want to talk to one of the good tuners on here who have built engines more than once - because I am not talking from experience, just over view of what I have read about minis and experience on other cars.

If you are going for a track car and higher boost ( top end ) - then the 9.5 CR might be ideal

If you are staying at stock performance ( no increase in boost ) - these pistons and rods should be bullet proof at the stock CR.

BTW - I believe the Wiseco pistons match with the K1 rods, CP Carrillo with CP rods etc ... I agree on matching with the same company or known combinations that work. IIRC, the K1's are one of the lightest rods - so could add a little there.

I think your choices might be determined by how fast you want the pistons and rods and who has them in stock

 

@oldbrokenwind The machine I am building was one I picked up with ~55K miles on it, but had piston issues which resulted in scoring of the cylinder wall. Machine shop said I have two options, sleeve the wall or bore .25mm (also haven't seen many .25mm options)
@gauss66 The idea I had in mind was to rebuild to reenforce the bottom end since everything is out, to prevent any issues down the line. I wouldn't mind adding more speed in the future which is kind of why I decided to do forged things, but for now it would be stock speed with stock CR. I believe you are right to say that my decision would be based on availability, didn't realize some of these parts take months to arrive.

With that said I thank you both for shedding light on the matter, besides CP/Carrillo are there any other piston/rod combos either one of you have seen before/heard of?

 

I have seen an engine rebuild with Mahle pistons ( attached ). I have been told good squish area and bigger valve relief ( just repeating what I was told ) - but have no knowledge of the application. Seems to be some threads on here with questions on pistons and rods, albeit several years old.

One thing I have heard is there is a potential low oil pressure problem on these engines ( we have an idiot light sensor ). I have seen discussions of over filling the oil, tuning to a higher idle rpm and perhaps shimming the spring. Not sure if there is a high pressure pump available or not. If you are doing a rebuild - I would see if that can be addressed too.