bweSteve

Hey Tom,

first,.. yea I watched both the video's several times (friend owns the red 991GT3 in front of you),.. and don't care to see it again, so do not blame you for not talking about it anymore!
...... you & I have met when Mike was doing a PCA Tech Event session at your shop.

Re: Gas Cans (yea I've kept a couple in my garage too for display) : Re: Sunoco Race fuel. A buddy of mine sells race fuel (VP, Sunoco & Cam2)- local Sunoco & repair shop in Pasadena, and he is working on a discount program that I am hoping to setup for our local PCA Chesapeake Region members. If it is successful I'll let you know. Not sure if, after your cam swap, that you need to run it anymore,... but never know who might benefit.

I only use the expensive Sunoco Optima 95 unleaded (no ethenol) for winter storage since it has such a great/long shelf life. Then only use 93 pump gas during the driving months. Stock 7.2.

As many have said, great thread (been following along for years), and thank you for being such a phenom car-guy so willing to share.

=Steve
997.2 GT3 ABM

Tom@TPC Racing

Thanks, Steve! Even though I won't be "needing" 100 octane, I think I'll still treat my car to it because I love the smell and it makes more power!


Thanks again. I figure if I don't share I'll take it to the grave and that's no fun.

Tom@TPC Racing

Back to talking about fun stuff! We had snow today but we were able to sneak in a dyno session a few days earlier. A BIG THANK YOU to the head honcho of TPC Racing, Mike Levitas, for sparing his precious time to dyno tune my ECU for the new cams!

Here's how the engine sounds at idle-

How's does the engine run? Pretty damn good!!

Mike started the run with a custom tune file that he made for the most recent engine that he built using factory 4.0L pistons and crankshafts. Unlike the custom tune file that's he made for me last year this file had all the ignition timing and vario-cam timing that the factory compression ratio can benefit from. This dyno graph below show the best from last year (Run #24 in Blue) and current run (Run #13 in Red). The exhaust cams with the new tune shows a nice gain at the top end. Run #13 was made with 6-month old 100 octane that was in the gas tank since last August.


I then drained the gas tank and put in 93 octane pump gas from a nearby Exxon. Run #17(Red lines) is with 93 octane pump gas. Pump gas makes more torque in the mid-range than race gas because the lower octane burns slower thus the flame front contains more energy.


Mike said that the car was getting some tire spin on the dyno. He told to get some fresh rubber and dyno it again. Also, the runs were made in 4th gear to try to be consistent with the runs from before but he wasn't aware that I had the ring & pinion changed from 3.44:1 to 4:1. He said next time run it in 5th gear to be closer ratio to before and may even register higher power from loading of the taller gearing in 5th with the 4:1 ring & pinion.

There's more work to do but all in all, thanks to the exhaust cams, the tune is more proper, and the power is in 991.2 GT3 territory and I am happy as a clam.

flsupraguy

Nice. Thank for sharing. Curius why you chose the 4.1RP over the RS 3.89RP? Hows your RPMs in 6 going 70?

Tom@TPC Racing

Short answer:
I went with the GT3 Cup 4.0:1 R&P from PMNA simply because it was in stock, easier to acquire than the GT3 RS road car 3.89:1 R&P, and it'll work for my intended purpose.
My car is currently riding on a set of 5-year old all dried out factory size street transport tires. The Motec GPS showed 75mph @ ~3300rpm.

Longer answer:
The calculation that I have done indicated that for my application and usage the marginal difference isn't appreciable.
Going from the original 3.44:1 to 3.89:1 is a 13.08% final gearing reduction.
Going from the original 3.44:1 to 4.0:1 is a 16.28% final gearing reduction.
Difference in final gearing reduction between the two options is 3.2%.
Another way to depict the difference is to take 8000rpm multiply by 3.2% which comes to 256rpm.

The tire selection also comes into play. For example, the factory GT3 rear tire(305/30-19 size) is ~26.3" tall, the factory 997.2 RS rear tire(325/30-19 size) is ~26.7" tall, the difference of these two tire heights will account for ~1.52%, this makes up for half of the difference of the 3.2% shown above. I intend on running a taller rear tire than the factory GT3 size.

Gear Ratios For Reference:
997GT3 997.2RS '04 996Cup '06 997Cup '08 997Cup '10 997Cup
1st 3.82 3.82 3.15 3.17 3.17 3.17
2nd 2.26 2.26 2.00 2.13 2.132.13
3rd 1.64 1.64 1.56 1.72 1.72 1.72
4th 1.29 1.29 1.30 1.40 1.40 1.35
5th 1.06 1.06 1.09 1.15 1.13 1.12
6th 0.92 0.88 0.91 0.96 0.93 0.93

All the Cup cars listed above are factory equipped with 4.0:1 R&P and are factory configured to run 680mm-ish(26.8"-ish) tall rear tires. So my thinking is running the same 4.0:1 Cup car R&P and similar height rear tires, my car will do what I want it to do for non-competition track days since the street car ratios(except for 1st gear) is fairly comparable to Cup ratios. With the 4.0L engine I can short shift in some situations and really not worry about a few tenths of the second. I just want to blast by Miata's and Boxsters...sorry couldn't resist.

So...the sequence of events that led me to changing R&P was at first I wanted wider Hoosier front tires to improve braking, Hoosier sizes are somewhat limited, so in order to run the wider front tires that I wanted I had to go with taller rears tire to make the ABS happy. The wider front tires noticeably improved braking but the taller rear tires made the acceleration slower at certain sections on the track when an upshift occurred dropping the rev too much. The car wasn't slow in general but it was slower than before the tire size change when I got a taste of the hard acceleration! I even thought there was something wrong with the engine so I dyno'ed the engine mid last year and showed the same power as before the tire size change. Cams, R&P, and here we are.

flsupraguy

Wow! Thanks for all the detailed information Tom. Looks like I'll go with the 4:01 CUP RP

Tom@TPC Racing

To follow up to the above, here's the calculated mph on 680mm(26.77") rear tire @ 8200rpm:
997GT3w/3.44R&P. 997GT3 w/4.0R&P. 997.2RS w/3.89R&P. '04 996Cup. '06 997Cup. '08 997Cup. '10 997Cup.
1st 50.43,44.52.52.52.52.
2nd 8472.74.82.77.77.77.
3rd 116.100.102.105.95.95.95.
4th 147.127.130.126.117.117.121.
5th 179.154.158.150.142.144.146.
6th 206.177.191.179.170.176.176.
Note: Cup cars have 4.0R&P

I won't be using 1st gear on track. Looks like my 2nd gear is a little short, from 3rd gear on I think I can muddle through just fine. I used to crunch these types of numbers all the time from I was messing with front & rear sprockets on my motorbikes, which is A LOT easier to change than ring & opinion in a GT3 gearbox!

flsupraguy

Thanks for sharing

Tom@TPC Racing

One snow after another, ugh. Not much I can do to my car in the single-car garage at home beside this-

After the ring & pinion change the MoTeC dash gear indicator has been reading one gear off from actual. Here's the new calculation(Lower Right of image). Hope this will work. Won't be able to find out until the next snow and road salt treatment is gone.

Tom@TPC Racing

991 GT3 front uprights(aka wheel carriers). The physical dimensions are "close enough" to 997Cup for me to seriously consider. I can make them fit with slight modification of suspension links and brake caliper brackets, and swap the front shocks to 991GT3. The potential improvement is a change in roll center by the number which may or may not make the handling better in practical use. But forget that, I just want to do it because it'd cool as hell if I can pull it off!

The only uncertainly is wheel speed sensor signal to the ABS. 991 GT3 has different front wheel speed sensors and wheel bearing(the trigger magnets are inside the wheel bearing). This is where I need help. Does anyone know of a signal test that I can conduct to see if the signals match between a 997GT3 and a 991GT3.

Doing a parts search on PET this is what I know so far-
991 Carrera/981 Cayman use the same wheel bearing as 997GT3.
991 Carrera/981 Cayman use the 991GT3 sensor.
This means the 991GT3 sensor itself is compatible with 997GT3 /991 Carrera /981 Cayman wheel bearing trigger.
But 991GT3 has different wheel bearing so there might be different number of magnets which will change the # of triggers per revolution.
991GT3 wheel bearing happens to cross reference part number to '11-17 Cayenne wheel bearing so a Cayenne should have the same number of trigger per revolution.

Any intel would be appreciated!

rbahr

Hey Tom,

Tom@TPC Racing

Thank you very much for the info, Ray! Sorry I have too occupied to do any testing.

Tom@TPC Racing

I have decided on staying with using front uprights from the 996/997 car generation because I don't have the time to sort out any potential 991 wheel speed sensor/ABS issues with such a conversion. As far as 996/997 front upright go here are my options-
1) 997.1 GT3 with PCCB/RS - available new
2) 997.2 GT3/RS- unavailable new, with no estimated available date
3) 997Cup - temporarily unavailable

So should I go with option #1, #1, or #1....its one of those situation.

For you entertainment I have a few different 996/997 front uprights laid out for a photo shoot. May be you guys will find it interesting to see the differences and similarities.
Upper row from left: 997 C4/Turbo/Turbo S , 996 GT3/Cup , 997 Cup '07-'13 , 997.1 GT3 w/ PCCB/RS
Lower row from left: 996 RSR/997 Cup Grand Am spec , 996 Cup World Challenge spec



Same lay out at a different angle.



Here's the differences of the steering rod-to-axle height between the GT versions. This height affects steering during suspension travel(aka bump steer).



Here's the difference of the LCA ball joint-to-axle height. This height affects vehicle roll center.



Here's my new front uprights. They are 997.1 GT3 with PCCB/RS version. Hope to find time to install them next week.



Got these sweet brackets from Stoptech to transfer my Stoptech Trophy brakes. They beautifully machined and fit perfectly. Love true bolt-on with no machining on my end!

powdrhound

Tom,
I am running the 997.1GT3 PCCB 380mm front uprights in concert with rear 996GT3RS uprights. These were the homologation parts for the RSR and were used on the 996GT3RS street car except that car used the 350 front brake bolt spacing on the front upright. Both of these front and rear uprights use the 997Cup Motorsport (6 bolt bearing retainer) wheel carrier castings but have the pick up points machined for ride heights that are appropriate for street cars. BTW, as you know, the OEM 997GT3 rear wheel carrier is a street specific part that uses an inferior 4 bolt wheel bearing retainer as opposed the the much beefier 6 bolt retainer the Motorsport carriers get.

The ABS pick up sensors are the same as all 997Cup, 996.2 and 997.1GT3s so it's plug and play and allows you to bolt on the 7RS 380/350 brakes. I am using 997RSR LCAs on all 4 corners along with 997RSR thrust arms, 997RSR upper rear control arms, and 997Cup front and rear tie rods/toe arms. You can fine tune roll centers with all these components through the use of various length RSR LCA trunnion pins and shims on the tie rods/toe arms. It all OEM stuff so you are not dealing with any aftermarket crap. This is what I would use if I were you. Below is a link that shows the rear 6GT3RS Motorsport wheel carriers in detail. Note that to use these you must use a 997Cup style pin mount rear shock as opposed to the 997GT3 street pitch fork mount shock. Good luck..

https://rennlist.com/forums/996-gt2-...omparison.html

Tom@TPC Racing

Thank you for the info! I am going to use 997.1 GT3 PCCB front uprights. Currently I have 997.2 RS 4.0/GT2RS street car rear uprights. The front and rear subframes are stock(I might replace the rear subframes with Cup version in the future to set the lateral arms more parallel). My target ride height is 108/135mm on 25.8/26.7" tall tires. This combo should work pretty darn good for a streetable track car.

I do have to respectfully voice my opinion that not all non-OEM parts are crap. I have non-OEM parts on my car that's been holding up well for 3+ years, as do many of my track day, time trial and club racing customers. But I am also aware that I don't have the level of build, hp/torque that you have on your car. So all variables come into play for parts selection. I am sorry to hear that you had bad experiences with aftermarket parts.

Thanks again.
Tom