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Tom, I just went through the full 80 pages!
Thank you so so much for the whole writeup so far! Please never ever stop it!
I've done more or less the same to an e92 M3 (just look on youtube or instagram for lukecustoms) which started life as an avarge joe streetcar and has been converted to more or less a better M3 GT4.
Unfortunately the hole 100page build and story is in the German M-Forum so probably won't understand any words.
I won't do the same to my 997.2 GT3 RS which I just bought last year - that's gonna stay my enjoy sundays and mountain roads car.
But this thread here is more or less the 997 bible - don't know if you know it already?!
Wish you all the best wishes from Germany and whenever you will make it to the Nuerburgring Nordschleife - send me a message.
(search on youtube for "RootsRacing VLN" - that's what we do here 9x a year)
Cheers, Luke
Hello Luke, Thank You very much for reading this thread and for your very kind words. I will be sure to check out your E92 M3 stories and use Google translater!
__________________
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
Before we get on to it I have two decisions to make on the clutch/flywheel. The clutch pressure plate is a no-brainer, the 4.0RS version featuring the locking nuts(instead of rivets) is the way to go on a 8K+rpm larger displacement engine. The decision are 1) go with 3.6RS or 4.0RS flywheel? 2) which clutch disk?
For reference, this is the original dual-mass flywheel.
Here's the 3.6RS. Been using one of these old and faithful with zero issue. It is an all time great flywheel. Notice the contact surface width of 40mm.
Here's the 4.0RS. Notice the contact surface width of 32mm.
With the 4.0RS flywheel there's a little bit of compromise on the contact width in order to lose that 2.6 lbs compare to the 3.6RS version. Also the back side of the 4.0RS flywheel has material machined off between the bolt holes. So there's considerable amount of machining involved to shed that 2.6 lbs. Let me say that the reduced contact surface is not a concern unless the engine is turbo making 700+hp.
Both the 4.0RS and 3.6RS disk has a contact width of near 40mm, so that means there's an overhang of ~8mm when using the 4.0RS flywheel. I don't foresee the overhang to be an issue, since its a factory approved design and lot of GT3 owners have this setup over the years. It is just an interesting observation, that's all. I do wonder though, with enough usage/wear if the overhang will cause a little bit of dragging on the release if the contact surface is worn down enough creating a step...only time will tell.
Another observation, when I unboxed the 4.0RS sprung hub disk, it felt noticeably heavier than the 3.6RS sprung hub disk that I had. This is due to the extra thick spline hub and likely heavier spring designed to handle higher engine torque. At 5.15 lbs, the weight reduction of the 4.0RS flywheel is negated by the heavier-duty disk. So, I am going to try something unconventional to the general public and pair the 4.0RS flywheel with a rigid hub GT3/GT2 disk. Even though the rigid hub is not as thick, its factory designed to handle the torque of a GT2 so it should be plenty good for me.
To add to the clutch section Tom, last year we switched from the 4.0RS sprung disc to a 4 puck 996Cup disc. The 996Cup disc pucks are 32mm wide which perfectly matches the 4.0RS single mass flywheel friction surface width without any overhang that you reference in your post. I guess this makes sense as the 4.0RS flywheel is the same flywheel that was used in the 996Cup so it's a matched set with the Cup 4 puck disc. The Cup disc at 1lb 15oz is almost 1/3rd of the weight of the 4.0RS sprung disc and by design has a significantly lower MOI, by my calculation about 80% less as a majority of the weight is removed from the perimeter. This reduction of MOI makes a huge difference is how much faster I can shift the gearbox now and it's easier on the synchros to boot. It's night and day compared to the 4.0 disc, really effortless. The other advantage of the Cup disc is that is that the pucks are slightly thinner which results in the clutch engaging higher up closer to the top of the pedal stroke. This further reduces the time to shift as you don't have to depress the clutch as far and works really well with a clutch stop which limits the pedal stroke. I consider this one fo the best track clutch mods I have done. Cheers....
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Last edited by powdrhound; 05-21-2020 at 01:58 AM.
To add to the clutch section Tom, last year we switched from the 4.0RS sprung disc to a 4 puck 996Cup disc. The 996Cup disc pucks are 32mm wide which perfectly matches the 4.0RS single mass flywheel friction surface width without any overhang that you reference in your post. I guess this makes sense as the 4.0RS flywheel is the same flywheel that was used in the 996Cup so it's a matched set with the Cup 4 puck disc. The Cup disc at 1lb 15oz is almost 1/3rd of the weight of the 4.0RS sprung disc and by design has a significantly lower MOI, by my calculation about 80% less as a majority of the weight is removed from the perimeter. This reduction of MOI makes a huge difference is how much faster I can shift the gearbox now and it's easier on the synchros to boot. It's night and day compared to the 4.0 disc, really effortless. The other advantage of the Cup disc is that is that the pucks are slightly thinner which results in the clutch engaging higher up closer to the top of the pedal stroke. This further reduces the time to shift as you don't have to depress the clutch as far and works really well with a clutch stop which limits the pedal stroke. I consider this one fo the best track clutch mods I have done. Cheers....
Thank you for sharing the measurement and your experience on using the 996 Cup disk. I too have been enjoying the shifts of the lighter weight non-sprung hub disk for the past 2 year. Although I am using a street car disk that weights in right in the middle between sprung hub and Cup puck. Waiting for the friction material to wear down ~0.5mm for faster shift As a side note, I seriously think I put more wear on the clutch by feathering it backing up my steep hill driveway into my garage then actually driving on track with a NA engine with only ~300 ft-lbs torque.
Waiting for the friction material to wear down ~0.5mm for faster shift As a side note, I seriously think I put more wear on the clutch by feathering it backing up my steep hill driveway into my garage then actually driving on track with a NA engine with only ~300 ft-lbs torque.
I ran the 4.0RS disc for several hard track years and when I removed it I measured the thickness compared to new. Believe it or not, there was ZERO measurable difference from used to new and this was on an engine with 700 ft.lbs of torque. In other words, I would not count on the lining to wear down anytime soon. If you are not excessively slipping the clutch, the disc lining will last forever. One difference that I notice is that the sintered metal clutch disc pucks really "lock/engage" a lot harder (faster) during shifts than the organic lining of the street disc which has a lot more slip to it (for obvious reason) before engaging. This results in power getting to the wheels faster during shifts. I will have to look at my Motec data for the precise difference but in my estimation I am shifting about 30-50% faster with the Cup disc. I'm betting this translates to saving 0.7-1.2 sec per 2 minute lap. I'll post up the actual number when I examine the Motec data regarding this.
I ran the 4.0RS disc for several hard track years and when I removed it I measured the thickness compared to new. Believe it or not, there was ZERO measurable difference from used to new and this was on an engine with 700 ft.lbs of torque. In other words, I would not count on the lining to wear down anytime soon. If you are not excessively slipping the clutch, the disc lining will last forever. One difference that I notice is that the sintered metal clutch disc pucks really "lock/engage" a lot harder (faster) during shifts than the organic lining of the street disc which has a lot more slip to it (for obvious reason) before engaging. This results in power getting to the wheels faster during shifts. I will have to look at my Motec data for the precise difference but in my estimation I am shifting about 30-50% faster with the Cup disc. I'm betting this translates to saving 0.7-1.2 sec per 2 minute lap. I'll post up the actual number when I examine the Motec data regarding this.
Is the 996 Cup 4-puck friction disc like a light switch compared to the 4.0 street disc? Would it be tough for street use from stoplight to stoplight?
Is the 996 Cup 4-puck friction disc like a light switch compared to the 4.0 street disc? Would it be tough for street use from stoplight to stoplight?
The engagement window is smaller and the engagement point “sharper” and near the top of the pedal. Honestly I expected it to be a nightmare based on what you read about but most of that is from guys without first hand experience. I was pleasantly surprised actually that is not that bad. The clutch does chatter a bit on engagement when you get the car moving in 1st but after that it’s a no brainer. What made the clutch substantially easier to use is a clutch stop which takes away the bottom of the pedal travel and takes the guesswork out of where the clutch will engage. I have never stalled the car with this set up.
With that said, I would not recommend it for a street driven car but if the car is 80-100% track it’s fantastic. Honestly, one of the best performance mods I‘ve done.
I spent last night prepping and painting the cage footings.
Turned out decent for a spray can.
Took this opportunity to give the inside a coat of shine and let it paint dry overnight.
Putting it in. This back half cage being one-piece is a lot more difficult to maneuver in the car than the multi-piece bolt-in roll bars. Oh, and there's no way this goes in with the full interior intact.
Because I grinded out the holes to clear the nuts I replaced the nuts with ones that have larger flange to cover the openings.
The larger flange nuts are from 987 Cayman rear subframe. I like the silver color of the nuts, its very OEM looking.
Looks how I envisioned. The add-on rear shock tower brace bar has just enough room underneath should I wanted to put the carpet piece on to protect the ECU from external elements.
For the main hoop bolts, I went to get lengths to find M10x1.5x20 bolts that are the same OEM silver colors and have built-in flange. After hours of research online I found engine mount bolts from a BMW to be suitable. I am very superficial on the nut & bolt color...its a sickness.
The BMW silver flange bolts look very good, BUT, The flange OD of 20mm barely grips on because the bolt holes are pretty big. I much as I love this look I am going to find bolts with 25mm flange. That's another task for another day.
Now I need to drive my car home to free up space at the shop. That's it for now. Happy Memorial Day!
05-11-2020, 01:27 PM
As a side note, I seriously think I put more wear on the clutch by feathering it backing up my steep hill driveway into my garage then actually driving on track with a NA engine with only ~300 ft-lbs torque.
