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Thank you for sharing, it was a nice read. Happy to see that Mr. Huxham choose the 997.1 version to fill his GT3 void and customized it to his liking. At work I drive 991's frequently(before and after alignment/setup and for diagnosis...), they are VERY fast indeed! But I like my little 997 more because it has more character, in my opinion, and its modded exactly I way I want it(for now). But of course if I had the means I'd own one of each generation.
Hello all, it has been a few months since I've done anything to my beloved GT3. During the last few month I've just been completely consumed with work creating new products, track work, and shop routine. TPC Racing will be releasing a Summer catalog that features our new products, which we are very excited about! Anyway, back to the GT3... I signed up for a 3-day event at Watkins Glen starting this Friday. No better time to do stuff than 2am on Monday! LOL
I wasn't completely satisfy with the installing of the aftermarket decklid from earlier this year so let's do some cutting and modding.
If you recall from a previous post, I had a stack of washers on the latch and was going to delete the latch for Cup car hood pins. It turns out to install hood pins on a 997 same as a Cup car I needed to weld nut inserts on the body. I'm not doing that so I machined an aluminum spacer to replace unsightly washers. (FYI, installing Cup hood pins on a 996 is A LOT easier, No welding requires on 996).
The rubber ducts don't contact the air box inlet to seal the inlet from hot engine compartment air so install 10mm thick rubber gourmets to raise the air box to form a good seal.
And I feel the air tunnels need to be separated better engine air so time to cut a 3-month old decklid.
I estimate an increase of air flow to the engine compartment by 25% with the center opening enlarged.
Made separation walls from T6061 aluminum. With these walls separating the air box tunnels from engine compartment heat, it is now a proper ram air set up. Later on when I have more time I want to make them from a sheet of carbon fiber but the aluminum will have to do for now.
Here you can see the walls through the scoopes.
Before & after surgery. I also want to use heat reflective tape on the air tunnels in the near future.
With the MoTeC dash, this is now a routine. I can get used to this.
When people ask me at the shop what hot tire pressure to run on Hoosier R7 on a 997 Carrera, GT2, GT2 or Turbo my default answer is always follow the tire manufacturer's recommendation which in this case is 38-40psi for rear-engine cars that weight >3000 lbs. My boss, Mike Levitas, who's the owner of TPC Racing and a champion pro driver with vast experience on these tires also recommend upper-30's. Against the recommendation of Hoosier, Mike L, and what I tell people, I drop my hot pressure to 34-36psi because it feels better to me at the "front end" or initial of steering input. Last year I had no problem. This year when I added the .1 Cup replica rear wing running same tire pressure with only two 20-minute sessions this happens-
The lines are not from rubbing. I think last year I was right on the boarder line of hot pressure relative to load(vehicle weight + downforce). The wing puts it way over the line. The good news is I know the wing works well, bad new is having to buy new rear tires one day before going to Watkins Glen. Lesson learned on listening to people who know more than me.
***As a public service announcement, keep in consideration that bigger rear wing adds stability and grip but can consequentially increases enough load to the tires to potentially cause a failure. And upping tire pressure can increase margin of safety to the increased load. ***
Looking forward to your feedback on the Motec system once you got it de-bugged.
With support from Joe Hullet of Digital Competition(aka JoTec) we now have steering angle and brake pressure in the data. The GPS lap timer is working great. Have yet to get the opportunity to sort out the predictive timer. I am pretty sure its something in the config on my end. The dash display and shift light works flawlessly. The display have everything that I need to see including gear indicator, which I am training my eyes from occasionally taking a glace at the shifter lever.
Getting there from Maryland takes 5.5 hours. After the first two hours the beautiful scenic takes over. Turn the phone off, put on favorite tunes and enjoy the drive.
The town of Watkins Glen is historic and beautiful and lots of wineries nearby. Only wished I had more time outside of the track to see more of the local sights.
I was fortunate to secure a garage spot.
...which was nice to shelter from the infamous mid-afternoon storms that quickly roll through.
As for the car, it performed totally awesome. Only wished the driver was on the same level of awesome'ness as the car. From my worst lap to best lap was a 17 second improvement. Next year if I can get into the :09's I'll be grinning for a week. Regardless of the times, it was simply an amazing track to experience with the feeling of "holding my own" flatout full throttle up the esses between the walls, nailing the reference points through the bus stop and into the laces and through the boot!
The hot pressures I ran on the R7's were 36-38psi front, 40-41psi rear. The wear was good at these pressures on this track.
I am particularly proud of the last deck lid mods. After each half hour session I can put my hand on the airbox and the aluminum intake manifold to feel that they are barely above ambient temp! Through the weekend with ambient temp in the mid-80's the engine coolant temp never exceeded 200F and oil temp ever exceeded 230F, according to Motec data.
...which by the way I still have to convert the data from Celsius to Fahrenheit.
This past Saturday I did a repair/upgrade that I had been deferring for a while - LSD (Limited-Slip Differential) rebuild. When I first got this car the OEM diff preload was around 10 lbs by my estimation by hand feel, which is typical for OEM spec. As expected, the preload had degraded down to zero pretty quickly and had been at zero for a while now. I deferred the diff rebuild on my personal car because as a "suspension guy" my preference is to focus on the suspension first. With a well-setup suspension on a modestly-powered car the zero preload diff is a lot less noticeable than say on a high-powered car with stock suspension. Not to say that a well-sorted suspension is a substitute for a proper LSD at all, but it did mask not having one for me to some degree and for some time. Over the past couple years both my car and my driving skill became more developed and now I am seeking even better corner exit performance from the car.
Ultimately every great track car should have both a well-sorted suspension and an LSD that is setup to work together as a system. Some prefer to do the suspension first(such as myself), while others start with the diff, and some do all at the same time. It is of my opinion that when building a car up in stages it doesn't matter which component to start with as long the finished product performs brilliantly as a system. Working with a shop that has experience in systematic build is ideal.
With that said, here is LSD rebuild/upgrade journal using "GT" Guard Transmission billet ramps and 10-plate clutch kit(5-plate per side including belleville spring).
Getting started here. I clean the bottom of my car frequent.
Just enjoying the view of the RMS that I replaced in 2015 is staying dry.
Let's crack open that drain plug. Actually I always remove the fill plug first.
The gear oil is pretty clean after 8 track days which to me meant the diff clutch plates are a gonner.
Minimal to almost none metallic particles- good for the gears, not so good for clutch plates...
Off came the axle bolts.
Off came the stub flange bolt.
Off came the stub flange.
Diff cover.
One blow from the handle...
...and off came the cover.
Just so happened that the diff is still hot to the touch after the car has been parked for two hours. Good thing I used to work at a restaurant and can handle hot plates.
I have not delivered a baby before but I imagine carefully handling precious goods might be similar.
Wiping it clean before the disassembly.
Just showing off the beautiful Guard Transmission parts next to the OEM diff unit.
Yada Yada...
The OEM belleville spring(top of image) versus the Guard belleville spring. The OEM is not only thinner, the tension is significantly less just from a glance. The static preload is a function of the amount of tension stacked with the total thickness of all the other plates within the space inside the housing. Presuming the ramps have same height as OEM of course.
The OEM clutch plates(friction plates) are not worn. My inclination is insufficient tension from OEM belleville springs causing the open-diff type of performance.
A closer look at the beautiful parts from Guard Transmission(right of image) versus OEM(left).
The OEM 28/40 ramp(right) is cast metal. The Guard Transmission ramp(left) is billet metal with two available settings: 40/60 and 50/80.
Into the belly of the beast...
I didn't bother to measure the height of the OEM plates, ramps, OEM housing nor any of the new Guard Transmissions parts because I trust in Guard that their kit is full sorted. The preload is definitely strong! As you can see I had to strong hand the screwdriver to close the lid. An initial preload of 60-80 lbs before wearing-in is plenty good for me doing HPDE's...coming from zero preload. For advanced LSD tuners like my boss Mike Levitas he measures and tunes LSD relentlessly.
Ready to go back in.
5 more minutes to road test!
Shameless plug of the day- TPC Racing is a dealer of Guard Transmission products. Feel free to contact us for LSD and gearbox services.
Last edited by Tom@TPC Racing; 08-01-2017 at 01:11 AM.
Reason: inserted better photos
WELL!?!? How does it drive? I still remember the day I put in my GT pro diff... it was night and day in 2 particular corners of my favorite track, and I had to relearn how to drive a few others as the car wanted to push more due to the grip, so a couple other minor tweaks, but the traction on exit and the lack of sketchiness under heavy braking were very welcome. Still performing well after many, many track days.
04-14-2017, 01:44 PM
At work I drive 991's frequently(before and after alignment/setup and for diagnosis...), they are VERY fast indeed! But I like my little 997 more because it has more character, in my opinion, and its modded exactly I way I want it(for now). But of course if I had the means I'd own one of each generation. 
Awesome! Thanks for sharing.
