My question is for which piston, RMW, Mahle, CP or Supertech, to use in a complete engine rebuild, I am the builder, all work except the bore and TRP2, will be done by myself, which means it will be done with **** precision. There will be a cylinder bore because my 150,000 mile engine bore is out-of-round by .0003 and conicity is .0005. My final decision is which piston to install. The original choices were Revolution Motor Works (RMW), Mahle, CP, OEM or Supertech. I have narrowed it down to RMW or Mahle. My research includes phone calls to Tony, at Mahle HQ tech, who, after an hour of discussion, insists I install a 9.3 cr instead of their 8.3 cr (OEM). The CP HQ tech support said install OEM and not their CP pistons. Supertech HQ tech said theirs were OEM knock offs at 88mm. The last conversation was with Jan at RMW. Jan generously spent 2 hours talking with me. He suggested that I install his 8:3 cr which he tested on the road/track and was designed for chamber swirl and ring position.
My old fart brain was on overload at the end of all of the information gathering.
My concerns are that the Mahle HQ tech 9.3 will leave me street gasoline pump challenged, therefore, I reject the 9.3 but still have the 8.3 in the running. The CP HQ tech is not self-serving but did not consider the extra boost I mentioned to him, so his 8.3 would be a good choice except for the extra clearances required. Jan at RMW is self-serving but has proven pistons and they are competitive at $600. I trust Jan at RMW the most. My impression is that he has lots of integrity and passion for the Mini. The problem is that I will have to wait for the RMW pistons.

Question to the forum is anyone using Jan’s RMW pistons with higher boost?

Has anyone tried both Mahle and RMW?

My application is 98% spirited street in Colorado’s Rocky Mountain twisties between 4000 and 7000 rpm for hours. Also 12,000 mile highway road trips at a little more than legal speeds. Also sleeper red light challenges. I want another 150,000 miles and 60 MPG :-).

I’m not lost because I don’t care where I am!

My engine rebuild is attached to a ’06 R52 w/factory JCW. Rebuild mods include, but are not limited to, TRP2, ACG, Schrick cam, ported SC with 16% pulley driven by a 2% AIG damper, gasket matched and polished intake and exhaust (aftermarket) headers. No CAT. Ceramic coated head, exhaust manifold, and piston tops. Dry film pistons, bearings, and supercharger rotors. Way’s ECU map. ARP bolts. Possible RMW oil baffle. I am the mentally challenged sadist who will do all of the manifold porting and polish and engine assembly. A machinist, who I can be sure of, will bore to piston size and tolerances. Thumper is building the TRP2 and ACG.

If it weren’t for tomorrow, nothing would get done.

Safe travels,
WTMF

 

I just got a set of CP's, (77.5mm's for my 212k motor) the price was decent (just over $600 w/ rings) & thats what they ran in thr original Mini drag car.

But, the Mahles are a good choice too, IMO, depends more on your future plans, basicly "boost" are you planning on sticking with the M45, or going to a different form of induction. If you're not planning an induction change, any will do & you can let price guide you more. Oh, who makes the RMW piston? I know it's a quality product, just don't know who actually mfg's them

But, no matter which you choose, YES, stick to stock compression & remove what has been shown to be many tuning nightmares.

I'm doing the CP's (8.3cr x 77.5mm) Crower rods (possibly Carrillo's depending on how sore my wallet is) the Mahle Bearings & ARP Rod & Head bolts + other specialty goodies because of the NOS & Probable Turbo conversion.

 

Not gonna happen on forged pistons. You'd be lucky to get 80k out of a set of forged pistons before a rebuild is needed. They just don't maintain compression after a bunch of miles. If you're looking for longevity then you really should be sticking with OEM. That's probably why CP suggested the OEM pistons.

EDIT: It also matters what alloy they're using in building the piston. Certain alloys have a higher rate of expansion so the tolerances have to be loose which means on cold start-up you get more piston slap which wears down on the rings.

 

Blwaway and V10Climber,
Thank you for your input and causing me to “worry” about this even more. :-)

Jan at RMW, when asked, says his pistons are made in the US but did not say what the material was.

Martin, at Supertech, and their website quotes: “Q: What is the difference between 4032 alloy and 2618 alloy? A: A) 4032 High Silicon (aprox. 11% of Silicon but enhanced with additional Copper, Nickel & Magnesium) Low expansion alloy. and B) 2618 Low Silicon High Expansion alloy. Because most use the 2618 they say it is better, but that is not always like that. In fact they are pretty similar and the difference is not that big. Q: What is the Expansion rate of 4032 alloy: A: 4032 expands 18% less than 2618.”

Supertech says they developed the piston for the Japanese market??? What is the application there, anyone, anyone?

Supertech pistons are made in Argentina. I have been to Argentina! It was during my 9 month, 50,000 miles, solo, motorcycle ride at age of 63 visiting every country in North, Central and South America (Prudhoe Bay to Ushuaia) and round trip to and from Colorado. I had to rebuild my KLR650 three times, on the dirt ground, with the tools I carried with me. Two pistons, one bore (Argentina machine shop), and one transmission bearing set, with parts from the US. I know that Argentina folks produce automotive parts but I do know to what standards. I will have to pause and take a deep breath before I put in my order!

Mahle, CP, and RMW, need .003 clearance. Supertech suggests .002 to .0024 clearance. OEM New is .001 clearance.

Mileage before another rebuild is my highest priority. I would like 150,000 miles or more.

I will continue to use the M45 but with an electric water pump. I have no plans for more running gear modifications after this rebuild.

I do not know what “remove what has been shown to be many tuning nightmares” means. Forums are full of nightmares, would someone help and tell me which of my planned modifications should not be done, based upon their own experience?

At first, I dismissed the Supertech piston because it only comes in 8.5 cr (vs 8.3) and 78mm. My re-thinking and reconsidering the Supertech is that the Mahle, CP and RMW’s sloppy Forged pistons will decrease engine longevity (thanks V10 for that insight).

The Supertech 8.5 is not that much greater than 8.3 cr, correct?

The Supertech 78mm adds displacement but may cause me to have to re-sleeve on next rebuild.

My boost isn’t that much over JCW.

The supertech price is $460 versus $1000 for oversize OEM (cost isn’t top priority, longevity is!).

I may have to carry some octane boost with me on my next road trip to Labrador, because they only have 87 octane at the pump. Maybe that is why my cam galled :-)? That was a 12,000 mile road trip not including the four ferry rides.

What is wrong with my aging thought processing? Anyone, anyone?

Back at you forum….Any thoughts?

Is there anyone who is using the Supertech piston and with what kind of modifications.

Will I need higher octane than 91 (highest in CO)?

Maybe a Japanese user of the Supertech piston would jump in.

I truly appreciate your insight.

Life’s a *****, then you die.
If it weren’t for tomorrow, nothing would get done!
Safe travels,
WTMF
My engine rebuild is attached to a ’06 R52 w/factory JCW. Rebuild mods include, but are not limited to, TRP2, ACG, Schrick cam, ported SC with 16% pulley driven by a 2% AIG damper, gasket matched and polished intake and exhaust (aftermarket) headers. No CAT. Ceramic coated head, exhaust manifold, and piston tops. Dry film pistons, bearings, and supercharger rotors. Way’s ECU map. ARP bolts. Possible RMW oil baffle. I am the mentally challenged sadist who will do all of the manifold porting and polish and engine assembly. A machinist, who I can be sure of, will bore to piston size and tolerances. Thumper is building the TRP2 and ACG.

 

This is your biggest issue. If you can't get past this then you don't even need to bother researching forged pistons because your decision has been made. OEM cast pistons for you. If you're worried about losing a piston again then you'll just have to detune your car. The 4032 alloy will be better for longevity but still not as good as cast. The biggest issues are cold startup where the piston can "slap" in the cylinder because it hasn't yet expanded. This wears down the rings and you have to pull the piston to re-ring.

Then again I'm not professional engine builder so I could be completely wrong

 

First, I'm super jealous of your trek!

My comment: many attempts at running higher compression pistons (don't ask about how high, I don't know exactly, but even 9.3) have been real PITA's to tune, some have been so difficult they've just given up & pulled them.

And yes, I had the chance to go to 78mm too but figured the 77.5 would give me at least 1 more rebuild shot, as long as I can avoid a major catastrophy....:fingerscrossed: :timberknocked:

 

V10 and BA, Thanks again, the impending brain overload is somewhat abated by eliminating the 2618 forged pistons. At this point, until someone else chimes in and muddles the waters, the choice is narrowed down to OEM cast or Supertech 4032. I may sacrifice a few miles with the Supertech, but I may die first, so what the heck.
Update...I just phoned my parts supplier and the OEM pistons at a cost of $1050 are only in Germany which is a two weeks delay. Therefore, unless someone jumps in with "avoid Supertech" within the next day, my decision is made and mine will be the trial test engine. Stay tuned.

 

I wouldn't go with supertech. Supertech is a honda focused company at the moment. I would go with a company that focuses on multiple cars in the industry at the moment. I had CP 9:1 pistons in a a bored out dohc 1.6 that never gave me any problems. I had 22 pounds of boost from a garret turbo making 420. The downfall of the engine was the ferrea valves which ironically enough were installed by one of the part owners of ferrea valves.

The rings seated nicely on the slicone CP pistons and I never got any blowby. That's big to me. I don't care how fast a car is having blowby on a turbo car makes the car look cheap imo and I never got any after break in.

 

Quick question for those who know. Cast vs. forged, with all else being equal, why would forged reduce the longevity of the engine?

 

Forged pistons have better longevity than cast under high power applications, but
due to the increased clearances needed (they expand with temperature more than
cast), there is increased cylinder wear with forged pistons, especially in high power
applications, hence overall lower engine longevity.

 

Spiderknight, My research, but not first hand knowledge, confirms Cristo. Also, the "slap" or looseness of the piston causes the rings to have to be further away from the bottom of their groove in order to maintain contact with the cylinder wall. Reportedly, that issue translates into more lateral flex against the ring land. All looseness translates to rings may wear out faster. The conclusion is that a rebuild of at least new piston rings may come sooner. Technicians logically conclude that the cylinder wall may wear faster or at least may feel the effect of the looser piston "slap". Race engine builders fit their pistons looser than normal expecting to have to rebuild sooner. They pay to play! The forged piston is stronger and will withstand the effects of detonation better than cast. Reportedly ring land failure is common in cast pistons under high boost and high rpm.
My final choice of piston was supertech, made from 4032 alloy with higher silicon content than other forged pistons. They report less expansion than others. I will bore to the lower limit of factory spec of .002. I will keep my engine as cool as possible with other add ons including an additional intercooler cooler (I have not figured that part out yet), ceramic coating on piston top and ceramic coat the entire head and exhaust header. Then I will cross my fingers and pray for a long engine life. Stay tuned, it may take a few years before I know, or a few days.
Anyone willing to offer real experience, please jump in.

 

Working on a rebuild. Which piston did you end up choosing?

 

I looked at the Mahle sport catalog. It appears that their piston specifications are completely wrong in the catalog. Mahle is the OEM manufacturer for Gen 1 MCS pistons and they are forged. I doubt very much that they are 9.3:1 compression ratio due to the error in the catalog (the listed compression height looks wrong). Due to the grafal coating, piston clearances are extremely tight (actually 5 micron nominal interference fit between the grafal and bore wall in production engines). The piston skirt has almost nothing to do with bore wear. Bore wear is associated with the rings. Personally, I'd go with Mahle, but clarification with them on the specs. listed before committing (I'd have them measure a piston for compression height).

If they really do have 9.3:1 pistons, that is going to be a huge problem for knocking unless you want to spend the rest of your life running turbo blue gasoline! If you try to calibrate for 95 or 98 Ron (91 & 94 pump), you'll run into the rich misfire limit (you'll need to run so rich that you'll start misfiring) and your fuel consumption will be horrible. You might get away with 9.3:1 if you run a huge cam with a very late intake valve closing. Stock cam no way.

 

Brining this up again.

Hope some of you can chime in with some good intel.

This is reference to the R53 supercharged engines.
To be clear... I'm not interested in pistons for high-boost or 'racing/track' applications.
This will be a simple 'spirited' street driven engine, running on 10%-eth 91 R+M/2 octane, using the factory R53 intercooler... with mild upgrades.... 16% SC pulley, 380cc injectors, Shark injector tuning, factory header, a take off stock head that was removed in 2005 from a zero-mile mini for the JCW upgrade at dealer. (shelf stock that I'll be putting new valve stem seals on)

A few questions for those that may know.

Has anyone confirmed the availability and specs on the Mahle pistons?

Mahle:
What is the part number for the Mahle piston?
Forged, but what alloy and/or silicon content? (AL142-alloy ???)
Compression ratio... is it the same as stock/lower/higher?
Other details (Quench, dish etc)??

Stock Replacement OE pistons:
What are the different OE BMW/Mini R53 overbore sizes available and what are the corresponding part numbers for these?
Did the final evolution of the W11 in the 2008 MCS-Cabrio run a different OEM piston than, say, 2005/06 R53-MCS?

I'm really not looking for a 2618 "Forged Racing Piston" ... just not running where I would need to sacrifice that much long-term durability and do not need the benefits that a 2618 piston is designed to provide.
I would much prefer a piston with a fair amount of silicon, 4032 or similar for better results in real-world, daily, driving.
I have read a lot of conflicting info on the factory Pistons for the Supercharged Gen-1's... some say they are cast/hypereutectic pistons while others insist that these factory slugs are similar to 4032, and are in fact in made by Mahle-OE.
I have yet to see any factual evidence or proof of either side of the coin about the super expensive factory pistons.
Hmm.



.

 

RMW offers both a custom Mahle piston, and Supertech pistons in their online catalog. Here is the description on the 8.5:1 Mahle:
https://store-revolutionmini-com.3dc...-Gen_p_90.html
I have RMW's Mahle stroker version of these Mahle pistons in my daily driver (a 1.8L, 286HP street car, with a big fat torque curve). There is virtually no piston-slap when cold on mine (and I've built "smallblock" powered cars with forged pistons that did have piston-slap at startup, for perspective).

As others have said, you don't want to increase static compression ratio, especially if you are running a smaller supercharger pulley. If you do, without getting exotic (like injecting methanol, or running on it) detonation/ping will cause the ECU to retard ignition timing, and you will lose any potential horsepower gains and maybe do damage to the engine if it continues. Sustained detonation is a quick way to break pistons on a boosted engine.

 

What's going on? So I also purchased the Mahle power pack forged pistons for my R53 in 77.5mm and my machine shop has a concern about the tight piston to cylinder wall clearance of .0015 per manufacturer. I couldn't remember what Jan mentioned to me but wanted to know if you kept your install that tight or if you cleared your walls to .002 or above and if you had any issues or noticed anything. Engine is in the shop right now so the bug is getting to me. Peace!

 

The RMW Mahle pistons claim:
"These pistons have the tightest bore clearance on the market and will be quieter than all of our competitors pistons. Mahle's Grafal coating on the side skirts (to reduce scuffing) just like the factory pistons."

So, unless Jan says something different, I would go with the Mahle's recommendation for clearance.
The machine shop is probably using a generic guideline for clearance, based on bore diameter. Better to follow the recommendations for your specific pistons. . . And if either (Jan or Mahle) provide surface finish recommendations for honing, confirm that the machine shop will follow those also.

 

The machine shop is probably concerned with that thight of a clearance on a "Forged Piston" in general.. and many machine shops are not familiar with typical clearances of specialized, high silicon content, forged piston alloys like 4130...

This is where it would be great to have Jan chime in here about the questions posed above (quoted below) ... this will give us more 'Ammo" to make good, informed, decisions in our overhauls and will give people a better end result IMO..

 

so for sure. Got a chance to speak with Jan on the topic and the pistons were designed to run that tight with the coating and perfect for daily driving. Confirmed with mahle on the specs and min.0008 to max.0016 giving a quiet startup with no rattles like other pistons designed for .004 and above clearances. I was hesitant at first but can’t go wrong with a known engine builder and manufacturer specs. Just need to ensure my oil system is up to snuff with new gears and really like the quality of the pistons. I can’t speak to longevity but 80K like previously mentioned earlier is good enough for me to go to 1.8 on next rebuild.

 

Jan,

Hoping you can take a few moments to chime in here and answer some of the questions above on your products.

Thanks !
MH

 

Mountain Horse, I believe the RMW pistons are part of Mahle's PowerPak line. Most of these will be either 4032 aluminum alloy to allow for tighter cylinder to wall clearances and improved temperature stability, or 2618 alloy to allow for increased detonation resistance. Features are described here: http://www.us.mahle.com/en/motorspor...erpak-pistons/

If you want a set for the R53, talk to Jan. There is no Mahle part number for these because they are a custom design made by Mahle to Jan's chamber design specs for the R53. He has them made for different strokes (like my 1.8L) and different static compression ratios depending on application. What that means is that Mahle will have an internal designation that represents RMW/design, but because it's a custom application they have to be ordered through RMW (just like some high-security key & lock combos that are unique to an individual customer, and key blanks are not available on the open market).

BMW Mini pistons are available in standard bore, and 0.25mm oversize. I suspect those are available through RMW also, but expect them to cost more than the RMW Mahle pistons, which don't have BMW's added markup.

Mahle does make a standard set of pistons for the R56 Prince engine, #930067351, in a special M142P alloy, but that doesn't answer your questions for the R53.

 

Thank you for your thoughtful replies.

I have immense respect for Jan and RMW... and also for his need to make a profit from his IP and design work.... proprietary designs allow him to stay competitive.

My question is mostly related to silicon content of the pistons... which is a big deal when making decisions. Not what I would consider a 'trade secret' as choosing available alloys is not something that MAHLE allows even high volume shops to custom formulate unless you are Ferrari ...or making 10's of thousands of pistons.

Head/skirt/pin etc certainly are able to be specified in smaller batches... but the alloy choices are rather set to a few available in the semi custom series for perf suppliers like RMW from Mahle.

Would love to get this info on the actual metallurgy of the pistons.



.

 

4032 is a great material. The perception in the industry is that it is not as strong as 2618. The truth is that in equal conditions the 4032 is not as forgiving as 2618 due to its higher silicon content. 2618 can take more abuse from detonation, pre-ignition, etc. This is the difference between the two. The downfall to 2618 is that you must run larger piston to cylinder clearance due to its higher expansion rate, and this causes engine noise on cold start.

RMW Mahle custom pistons are actually an M142 material. It is considered to be the best of both worlds (4032 and 2618). With this proprietary Mahle material, we are able to run the tight piston to wall clearance, but still maintain some of the forgiving characteristics of the 2618 alloy. This means it is "quiet but deadly" In short, it's simply the best piston out there for the Mini Cooper........period


The Chrysler engineer who posted above also had a hand in the development of this piston which is in his own personal Mini. The dish is also designed by him, it's what he wanted to originally do on the S but the factory was cheap and just wanted it to pass emissions. As far as the rings, they are by far and away better than the others. All the other piston packages we looked at used cheap $45 rings and too large of PTW clearances. These pistons are designed to run at 50psi and 9000 rpm all day long.

 

I'm still a bit of a noob to the Mini, but are these RMW pistons a good choice for a daily driver build? I don't plan to run tons of boost, shooting for a 220-240 power level, keeping it as stock as possible, my main goal is to have the engine live in a daily/weekend track day car. Working on an 03 R53.
Thanks

 

I am running the RMW Mahle pistons on my healthy street car, and there are no disadvantages, in fact there is a pleasant improvement in one area.

Generically, depending on the pistons, the usual concerns when running stronger forged race pistons on the street centers around noise (piston slap) with some forged pistons (particularly when cold), or a too-high compression ratio for street gas. Some "race" pistons also have shorter skirts, which can lead to more "rocking" in the bore and noise. On my car, there has been no increase in piston noise with the RMW pistons, and the compression ratio is similar to stock. Piston-to-bore clearance is spec'd fairly tight for these pistons, and that seems to eliminate both noise and oil consumption concerns.

The RMW pistons are designed to provide better flame travel which should reduce detonation, and the Mahle alloy chosen is stronger than stock pistons at elevated temps.

The unexpected benefit for me is reduced oil consumption. My car consumed oil since new, and the dealer claimed anything less than one quart every 500 miles was not a concern. My oil consumption is now next to nothing, and that's a new experience.