Anyone know what the max PSI is for the stock turbo before it loses efficiency? I ask because come winter I am pulling the motor on my MINI to replace the rings (I have oil consumption issues). I don't want to go back to stock rings so I will be buying CP-Carrillo forged pistons, they offer a stock 10.5:1 CR and a lower 9.5:1 CR. I want the 9.5's because they are cheaper and because I can run more boost on a bigger turbo in the future. However I'll need to add boost to make up for the lower compression with the stock turbo...

 

One more option to consider is the Mahle Motorsport pistons. 10.2:1 compression ratio and they're a different alloy than the CP with a lower coefficient of expansion. Since they expand less your bore tolerances are a lot tighter. The CP's need larger tolerances and you will hear piston slap when the engine is cold. Also when cold you'll have more blow by and oil consumption. In addition the Mahle pistons can be used with Carillo rods. Both are straight cut instead of taper cut like the factory piston/rod combo. Only problem is they are more expensive than CP pistons but many consider them worth it. One final thought, if you reinstall the head with the thicker JCW head gasket the CR drops down to 10:1.

 

Great input, thanks! Do both the CP's and Mahle's require new rods, or can I use my stock rods? Or is there an option to use better rings with stock pistons? I have been researching like hell and not finding much...

 

use eagle rods if they make any for the mini

they are cheap but proven

 

I think you can order the Mahle Motorsport pistons with the taper cut but its not recommended. The factory rods are fairly strong. I've read of an R56 making 373 ft lbs. of torque on a stock bottom end but it didn't do it for long due to bolt stretch on the connecting rods. ARP doesn't make rod bolts for the R56 and the factory bolts are weak. The Carillo rods bolts are rates to 285k psi tensile strength so no worries there and the H beam rods are strong as hell.

 

I found ARP's for the rods, they are currently on my buy list for this rebuild:

http://www.outmotoring.com/arp-mini-rod-bolt-set.html

I was also planning on ARP headstuds and studs for the main bearings.

The only issue I have so far is I am using my buddies machine shop for this, and he doesn't have a bore small enough for the mini. That's why I was trying to use the 77mm CP's. Now I come to find out that I may have to bore for the CP's anyway due to cylinder taper. So I guess I should just buy the Mahle's and bore .5mm over. I'm also trying to save money as well which is why I am doing it myself. Do you think stock rods with ARP bolts will hold? Or should I just spend more and get rods too?

 

What exactly are you trying to accomplish here? If you're just doing a rebuild then why all the aftermarket piston talk? If you're trying to make more power then you would want to stick with closer to stock compression ratios if you're not going to be swapping to a larger turbo. Also, if you're looking to make more power why are you sticking with stock rods. Do you know that your rings are the issue or are you just assuming?

 

I am 90% the issue is the rings, however I am going to be doing a leak down test to verify. I am using oil at a rate of 1 quart every 1k miles. Intake is free of oil so I don't think it's the turbo seals. I have seen more than a few threads on ring issues, and none on valve guides/seals so I believe it's the rings.

The reason I am looking at aftermarket pistons is that I can't find any better rings for a stock piston, and with it using oil at 52K I'm not going back to stock rings. I found the CP's in a stock bore for $900, however stock bore 9.5CR is $775, quite a difference. So I was trying to find out if 9.5CR on a stock turbo is even possible. I wanted to use the 77mm CP's because I can hone the cylinders, but not bore them. I could go back to stock pistons but I just wanted a stronger one for the future. I was asking about the stock rods because if they are strong enough and the bolts are the only issue then why bother swapping them? Now if they are a liability then they will go...

This thread turned into a deeper discussion which I was going to ask about later, but I'm thankful it switched to the internals because I am getting good information. I should have just asked about the pistons off the start.

With me buying my first house this month I am trying to save money on the build. So that's why I am trying to see what I can get away with...

 

Well the life of the rods will depend on how much power you're intending to make. If you're building the motor with the goal of a turbo swap and more power down the road the rods aren't a bad idea. If you're just going to do a "refresh" and keep running the power levels you're currently at then I wouldn't worry about the rods.

If you have a solid tuner then you can run the 9.5 compression pistons but you're just going to be down on power compared to the 10.5. I'm not smart enough to know how much. The lower compression won't make boost as quickly either. I'd spend the extra and get the stock compression pistons.

 

Have to agree there. 9.5 CR only makes sense if your building a race engine running very high boost. If your going to be going into the short block at 52K miles you might as well get the 77.5mm oversized pistons, replace the rods and get new rod and main journal bearings, oil pump and timing chain.

Unfortunately ARP makes these for the R53 only.

 

run a compression test before the leak down, both a dry test and a wet test, if compression numbers are lower dry than wet your rings are bad

 

Thanks, I'll stay away from the 9.5 pistons then. I fear I just can't afford to replace the rods too. $1500+ for rods, $900+ for the Mahle pistons, then more for gaskets, bearings, pump, timing chain. I also wanted to do the clutch while the trans is out, but I just can't afford all that. I will preform a compression and leak down test before I move ahead, need to make sure 100% it's the rings, I'm getting a little ahead of myslef If it is the rings guess I'll just replace with stock and do the clutch. Thanks for all the help everyone.


Guess Out Motoring needs to fix their site, the rod bolts come up under R56 when I search:

 

Another consideration --- Mini breaks in a new engine using synthetic oil --- a significant cause for oil consumption. This is probably one reason why Mini says 1 qt per 1K miles is typical. If your only concern is oil, I suggest only do a ring job (if tests show bad rings) and break it in with non-synthetic oil.

As for rods, an on-line friend thought the OEM rods looked strong enough, so he didn't replace them when he changed pistons --- to match his hybrid turbo. He blew a rod during break-in!

If you want more power, find a tuner first, and work with him. I'm currently breaking in a set of CP Carrillo 77.0 and 10.5:1 pistons and rods. My cylinders mic'd pretty good, so no machining was req'd. Pistons / rods were changed to ensure reliability at 25+PSI from my Garrett. Been running that boost for over a year now, but only randomly. For track use and a lot more time under high boost, I want the reliability. Check out my build journal --- https://www.northamericanmotoring.co...a-stuff-2.html Lower compression ratio, 10.0:1, is recommended when raising boost --- I chose to ignore that recommendation --- my risk!

 

Yea I guess I will just be replacing the rings with stock. I wanted to do forged lower compression pistons while I was in there just for future mods. However I just can't afford rods at this time. If the rings are bad I'll pull it and do a clutch while it's out. Dang it why did I have to be an adult and buy my first house