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I thought I was done talking about pistons but here we go again- So this week I had an opportunity to check out the aftermarket Mahle Motorsports 102.7mm piston for another build that our shop is doing. Mahle is an OE piston supplier as well as aftermarket. The OE version has definitely proved its worth over the years as it was the factory choice for 997.2 GT3/RS/4.0 street cars, 997.2 Cup, and 991.1 Cup, but comparing side by side, well, the aftermarket Motorsports version certainly looks more impressive. Even though I am quite impressed and in fact have envy over the Mahle Motorsports pistons, I can't buy a third set of pistons! The lesson learned here is that I didn't think through all options and spent too much on unnecessary parts as a result of my own neuroticism and bad decisions. So at this point I can only admire. Here are the photos of the Mahle Motorsports pistons. Enjoy.
But first, let me brag a little about the scale platform that I made on Christmas day. Could've bought one but it was far more satisfying to BYO. And finished in time for dinner!
On to the pistons(Mahle Motorsports on the Left, Mahle OE on the Right.)
The dome on the Motorsports version is worth one full point of compression ratio.
Webbing on the under side. (Motorsports on the Left, OE on the Right.)
OE version weight in at 413.8 grams.
Motorsports version is 6.4 grams lighter despite of the dome and webbing. 6.4 grams is barely any weight but it was notable for the features.
For those who want Mahle Motorsports pistons for 3.8L and 4.0L builds...TPC Racing has them! Happy New Year!
__________________
PCA National Instructor
TPC Racing stats:
2023 Porsche Sprint Challenge 992 Cup Am Champion
2023 Porsche Sprint Challenge GT4 Pro-Am Team Champion
2022 Porsche Sprint Challenge 992 Cup & 991 Cup Champion
2020 IMSA GT3 Cup Challenge 2nd Championship
2018 IMSA GT3 Cup Challenge 2nd Championship
2016 IMSA GT3 Cup Challenge Champion
2013 IMSA GT3 Cup Challenge Champion
2006 Rolex-24 @ Daytona GT Champion
2004 Grand-Am SGS Class Champion
Well, I have been going back and forth between using the factory RS 4.0 Pankl Titanium rods versus aftermarket steel rods for my build. The Ti rods oblivious are lighter weight, at an average of 405g per rod. Steel rods weight ~550g per rod. The heavier aftermarket steel rods will make the engine rev a littler bit slower(combining the weight difference of six rods equals to adding 2 pounds back on to the LWFW). Despite the added weight to the rotating assembly(which might not be a noticeable "real world" difference), steel rods are more robust for an extra peace of mind for the long-term, very long-term. Also aftermarket rods offer overkill rod bolt options(such as ARP 2000 or ARP 625+) and custom rods can be specified for the rod bearing of choice(a popular choice is factory RSR rod bearings). Speaking of bearings, that was one thing that led to the indecision as the factory RS 4.0 Ti rods have the bearing tang grooves for upper and lower machined in an "inline" manner, as oppose to the more common split-groove machining(see image below). I emailed Pankl about the different styles of groove machining, an engineer responded back and wrote that there is no difference to the rod strength, the one continuous groove is for manufacturing convenience(less machining operation per unit), the bearings are locked in to position by proper tightening of the rod bolts. The continuous groove however does require a different upper and lower bearing shells(see image below). Ordering the upper bearing shell was easy, they are readily available. BUT, the lowers...let's just say I had to jump through hoop to get from Germany. So I got extras just in case. During those weeks there were moments of doubts and thus how the indecision manifested. I want to point out that TPC Racing has built 4.0 NA engines for street and race cars using both factory Ti and aftermarket steel rods and have not experienced a broken rod. The doubts and indecision is me being neurotic. I need to overcome my neuroticism and decide on the rods by next week.
Factory 4.0 Ti rod on my Christmas day DIY platform.
The "inline" groove shown on the rod's big end.
Big end weight.
Close-up and comparison of the bearing tang grooves(split on top, inline on bottom). The split groove is considered the norm in Porsche world, it uses the same part number bearing shell for upper and lower.
Factory 4.0 upper and lower bearing shells for inline groove.
Tang position is "mirror image" to fit inline groove.
Good stuff. That 40 intake makes a real difference at top end. Shop did a simple 4l build and dyno with factory 38 then put 40 and the difference up top was not insignificant. Let’s the engines breathe.
A 4l is showing restraint. Lol The costs from 3.6 to 3.8 to 4.0 to 4.2 are large.
But damn these things in 4l or 4.2 spec are fun.
On the .2 variocam... when in track use power bands, will you even notice it?
With 44k miles on mine I’ll be doing this at some point.
Hmm, those Motorsport pistons sure looks tempting for the .1 RS. But aren't there a difference in wrist pin diameter between .1 and .2 cars? No valve clearance or knocking issues due to the different dome shape and higher comp ratio? Do you know the weight of the OE 3.6 piston?
That 40 intake makes a real difference at top end. Shop did a simple 4l build and dyno with factory 38 then put 40 and the difference up top was not insignificant. Let’s the engines breathe.
A 4l is showing restraint. Lol The costs from 3.6 to 3.8 to 4.0 to 4.2 are large.
But damn these things in 4l or 4.2 spec are fun.
You're spot on. The 4.0 intake makes a pronounced difference.
Originally Posted by Spyerx
On the .2 variocam... when in track use power bands, will you even notice it?
Yes, .2 have variocam on the exhaust camshafts as well on the intake(.1 has variocam on intake only). Having adjustable exhaust cam timing and of course the slightly better cam lobe profiles to begin with, the .2 conversion pulls harder above 7700rpm.
Here's sample dyno below for .1 and .2, both are 4.0 conversion using factory 80.4mm stroke crankshaft, factory 102.7mm pistons, 4.0 intake, but both kept their original camshafts. Red is .2.
What's neat about these builds is that there's a number of different ways to configure the build between pistons, custom crankshafts, camshafts, head and valve work. To me, the configuring process is part of the rush, much like the rush(and sometimes stress) when shopping for that special car! On a .1 conversion one could change to more aggressive lobe camshafts to match or exceed the top end power of the .2 but I am not going to do that because I will be satisfied with the results with my original cams shifting gears at 8K rpm. I've always tried to shift at 8K or slightly under, since I'm not doing wheel to wheel competition with my street car. And then there's the cost of camshafts $$$$ Having the camshaft regrind is another option but I can't afford the downtime. Anyway, cams are off the table for me. Once all the parts are situated I plan on doing the build over course of 2 weeks(evenings and weekends).
Hmm, those Motorsport pistons sure looks tempting for the .1 RS. But aren't there a difference in wrist pin diameter between .1 and .2 cars?
Yes, they do look good! And Yes, .1 and .2 do have different wrist pin size, so different rods are required from .1 3.6L to 3.8L using Mahle factory or Motorsport pistons.
Originally Posted by 964RS_NGT
No valve clearance or knocking issues due to the different dome shape and higher comp ratio?
No, not when using factory cams.
Originally Posted by 964RS_NGT
Do you know the weight of the OE 3.6 piston?
Don't know, I'll weight one when I get to that point in my build.
Thanks Spyerx!
What's neat about these builds is that there's a number of different ways to configure the build between pistons, custom crankshafts, camshafts, head and valve work. To me, the configuring process is part of the rush, much like the rush(and sometimes stress) when shopping for that special car! On a .1 conversion one could change to more aggressive lobe camshafts to match or exceed the top end power of the .2 but I am not going to do that because I will be satisfied with the results with my original cams shifting gears at 8K rpm. I've always tried to shift at 8K or slightly under, since I'm not doing wheel to wheel competition with my street car. And then there's the cost of camshafts $$$$ Having the camshaft regrind is another option but I can't afford the downtime. Anyway, cams are off the table for me. Once all the parts are situated I plan on doing the build over course of 2 weeks(evenings and weekends).
Thanks for the dyno plots. Ok, my question / statement was really assuming you were changing CAM. So yes, totally get like for like no cam change the .2 is better. The builds I've seen are changing out cams/regrind for a more aggressive profile to match the rest of the changes. Its only $ right????
Thanks for the dyno plots. Ok, my question / statement was really assuming you were changing CAM. So yes, totally get like for like no cam change the .2 is better. The builds I've seen are changing out cams/regrind for a more aggressive profile to match the rest of the changes. Its only $ right????
I appreciate your sentiment good Sir. I had my mind set from the beginning on no cam change and also no ECU tune. My goal is a 8K rpm motor(will be running taller rear tires to get the mph) with good mid-range. For pulling over 8K revs then 991 Cup or 997 Cup S exhaust cams would be the choice.
I would like to point out that the 4.0 street car and 4.0 GT America race car parts catalog calls for different chain tensioner blades(the white color shorter ones) whereas the 4.0 R/RSR race car calls for the standard blades.
More decisions to make. I think either blade will work fine for me.
Sorry for the lack of updates on my 4.0 build, well, actually there hasn't been any updates because January was extreme busy at TPC Racing. We prepared 9 cars to run a series of track days at Sebring International Raceway. Opening the week with David Murry Track Days and closing PCA 48 Hours at Sebring. Here are some of the cars we prepped.
On top of prepping those beautiful cars, I had a customer who needed an engine rebuild desperately and quickly so I "channeled" some of my 4.0 internal parts to his build to get him on the way. Here are some pics of my parts in his engine. He wanted the Pauter X-beam chromoly connecting rods so that leaves me with the OEM Pankl Ti rods.
After a few weeks of working around the clock on customers cars I finally had some free evenings to start my own build. This is disassembling phase, there's not way around the dirty and messy nature of it. I'll let the photos speak the words. Hope you guys enjoy POV photos of the Mezger GT3 engine anatomy.
With the original 3.6 case halves separated, I measured the distance of the critical low clearance areas(crankshaft counter weight to oil pump) using reference points of the case.
Took this photo just before disconnecting the battery to take the engine out a week ago. The engine had just under 60K miles on it prior to this build. Most of the miles are street, I did 44 track days(equated to roughly 80 hours of track time). The engine was running perfectly prior to the build, I am doing this only because I WANT TO, not I need to. In fact, my last track day was my best.
Here's the bank 1 case half "as is" after being lifted off the stand. The main bearings look good and can definitely go more street/track miles.
Here's the original 3.6 rods and pistons.
These factory Pankl Titanium rods sure are a beauty. Too bad we can't appreciate their beauty when they're installed. We can only appreciate the fact that these are exactly the same rods in factory race cars that endured 24-hour(and beyond) as in our GT3 street cars!
The rod bearings aren't perfect but I didn't expected them to be. Being that the rod bearings are subjected to reciprocating force(back and forth, push and pull motion) they do take more beating than the main bearings(which support the crankshaft spinning one direction). Like I said, engine ran perfectly and held good oil pressure, even with imperfections on the rod bearings.
Scrapping off retaining gasket and sealant material. Takes hours of not so glorious work. Even putting the parts in a hot tank doesn't guarantee all the stuff comes off.
Test fitted the 4.0 oil pump(the 4.0 pump is at the bottom of the image with blue numbers) on to the block. The 4.0 pump has more clearance for the increased stroke 4.0 crankshaft.
I didn't want to grind any metal off the new pistons and the new rods for balancing, so I did my best to group the pistons, pins, rods to achieve the least weight differential for opposing cylinders. After an hour of weighting each item time after time to verify the weight consistency, I brain whacked for another hours for all possible combinations and using the formula on the paper below to achieve the weight grouping(with the heaviest items on the middle of the engine- cylinder #2 and #5) with the highest differential of 2.9 grams nearest the flywheel(cylinder #3 and #6). Its not a perfect zero balance but its as good as factory assembled engine tolerance. 2.9 grams is equal to 0.0064 pound, or 0.1023 ounce. For perspective, using US coins, a nickel coin weights 5.0 grams, a dime coin weights 2.27 grams, a penny can be 2.5 grams or 3.11 grams(apparently there are two versions of the US penny).
Last edited by Tom@TPC Racing; 02-10-2018 at 11:41 PM.
12-29-2017, 06:06 PM
Piston Envy
So at this point I can only admire. Here are the photos of the Mahle Motorsports pistons. Enjoy.
Happy New Year!
Having the camshaft regrind is another option but I can't afford the downtime. Anyway, cams are off the table for me. Once all the parts are situated I plan on doing the build over course of 2 weeks(evenings and weekends).
