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We're getting ready for this season's events, and that includes swapping out our Tremec T56 6-speed for a beefier trans that we have had built. It is a Tremec TR 6060 with a Stage VI build done by RPM Transmissions.
The reason we went to the T56 trans to begin with is we were racing for three years with a 900 to 960 HP supercharged 6.54L 928 stroker motor and I got so I was hatching G28/13 5-speeds every three events. I broke 3rd gear the most often, the torque (654 ft lbs at the tire, 769 ft lbs at the motor) was simply tearing off the teeth off the gears. I'll include a pic of that below. Anyway, that's why we went to the T56. It did well for three years and never broke, but in the back of my mind, I knew I was exceeding its designed torque level by a goodly amount.
Late last summer, we found ourselves playing with camshaft grinds, lobe separation angles, and fueling on the race car again - and I'll be damned if we didn't find even more. Now we were measuring 1020 HP at the motor on the dyno before the clutch let go. Here is the thread about that: https://rennlist.com/forums/928-foru...t-of-fuel.html
We were just spinning the stuffing out of our SPEC Stage V clutch designed to hold 850 lb ft of torque. We aren't exactly sure where we are going to end up HP and Torque-wise because of this slippy clutch. But we could see what we had for HP and torque up to the point where it broke lose, and extrapolate from there. According to the math, if the clutch holds we should see 1200 HP.
The engineers at Tilton told me that if you are trying to hold 1200 HP, they like to build for 20% over. When I asked why, he explained that as the clutch gets hot, the springs soften a bit.... so they would make me a 1500 HP clutch to be sure to hold my 1200 HP when hot. Makes sense. The clutch is here and its awesome. I'll post a couple pics of it too.
Now I get to the transaxle... the next phone call was to RPM Transmissions, my go-to for this kind of thing. They had upgraded my differential and final drive last year to a 4.10 gear set that could hold whatever I sent its way, and it was fantastic. But now, At 1020 HP soon to be maybe 1200 HP, I asked Jeremy "how long will the T56 last?" I explained I was scheduled to go to Daytona in December with the car, and I did not want to tow it all the way down there just to snap another trans. "Will it hold up?" I asked. "No" he said. I said "what if I drive really nice, no hole-shots or anything, and accelerate smoothly?" "Nope" he said, "wont matter. When you get to about 200 MPH there will be so much load on that stock T56 of yours that it'll let go." Then he described the "ping" sound I would hear as the shafts failed, and then the silence as I would slowly roll to a stop. Argh. To hear him tell it was almost as bad as living that moment, but without the lengthy 1300 mile tow in each direction first.
So that's how I got here. The race car is in the shop, and I've pulled our T56 6-speed out to replace it with the custom TR6060. I say "custom" because RPM transmissions modifies the TR6060 so it can fit into Corvette C5's, and Porsche 928's This is it. Before I told any 928 customer that we could put a 6060 into their 928, I wanted to make sure that our 6-speed kit for the 928 actually fit this transaxle. It did, mounted right up no problems. They tell me this Stage VI TR6060 can hold 1500 HP too, and as I'm upgrading the clutch; and I already have a super-strong driveshaft and differential, we should be good. The axles are unknown but they are damn thick.
Enough talk. Here are some pics of the transmission swap.
The T56 on the bottom, and the custom TR 6060 on the top.
The T56 is a fantastic transmission and I don't want to disparage it at all. For your stock-to-600 HP 928, you couldn't do any better. The carbon-fiber synchros are a pure joy to shift, and the gear ratios are fantastic when coupled to the 928 motor.
BUT - for my purposes, at what is supposed to now be 1200 HP, it needed a little help. In these pictures I show the front or the transaxle and a few of the upgrades TREMEC built into the TR6060. They strengthened the casting, increased the input shaft size, and added a shaft-driven internal fluid pump to support a trans oil cooler.
A more complete listing of all the TR6060 upgrades is listed here: http://www.tremec.com/anexos/File/TREMEC_TR-6060.pdf
It's worth looking at. Note the massive webbing added to the case of the TR6060 on the right. The input shaft is larger and of a different alloy also. The T56 is on the left. Closeup of the shaft-driven internal pump on the TR6060.
Thanks guys. As this project moves along, I'll keep posting pics. I'm trying to make an event I'm registered for in April. Right now, the transaxle and TTube is ready to go up, but I'm going to replace the clutch with the Tilton triple-disc before I do.
DAYUM Carl, that is freaking awesome!! Not being familiar with all you did to put the 6 speed set-up in, what is the differential from? Is it a Porsche or GM component? Your car is already a beast, but wow, 1200hp is going to be insane! LOL. Good luck with everything.
The differential is a Getrag unit, very robust and OEM on Corvettes, Challengers, and many others. Getrag differentials have been in Corvettes that have raced three seasons of the SPEED World Challenge GT series - plus two seasons of Rolex GT including the Rolex 24 At Daytona.
That said, it needed to be beefed up for our application too. Did that a couple years ago with a complete performance rebuild and the installation of a 4.10 FDR gear set.
After reviewing what Centerforce and Clutch Masters said they could do for me, decided to go with a Tilton triple-disc clutch. They engineered this one to hold about 20% more than the expected output of the motor, or 1500 HP. I don't know what its going to be like to modulate on a race course, but I'll learn.
Mark Anderson sold me one of his old flywheels that he had a Tilton clutch on previously, and that really saved me some time. Thanks Mark! One of the more interesting discoveries was that the TOB-to-flywheel distance from the early bell housing to the late bell housing was so different. This required us to use a late-model bell to get enough room for the Tilton hydraulic TOB.
Note difference in height of the TOB mount. Early bell on left, late model bell on right. Spacers to level out the mounting flange. Mounting bracket in place. TOB in place Clutch in place Finished and in car. We have adjusted the TOB to Tilton spec, and the hydraulic lines now go up through the opening in the top of the bell for the release fork.
02-14-2019, 06:53 PM
T56 6-speed trans out, TR6060 in...
This is it. Before I told any 928 customer that we could put a 6060 into their 928, I wanted to make sure that our 6-speed kit for the 928 actually fit this transaxle. It did, mounted right up no problems. They tell me this Stage VI TR6060 can hold 1500 HP too, and as I'm upgrading the clutch; and I already have a super-strong driveshaft and differential, we should be good. The axles are unknown but they are damn thick. 
