L39E

My polar silver '96 C4S has recently completed a 3.8 conversion. The engine was built by Gulf Performance with bore-in Mahle 3.8 RSR pistons and cylinders, Pauter rods, custom Elgin cams and some other trick extras. The car already has a very good suspension setup, with PSS10, RS tie rods/wheel carriers, front and rear RS adjustable swaybars, RS motor mounts, Elephant bushings, etc.

Sadly, the shop owner and mastermind of my build Vinnie Colosino passed away in the fall after a courageous battle with cancer. Vinnie was a great friend of mine and a huge asset to our community. His shop has been continuing business to honor his legacy, which is truly wonderful. However without Vinnie's great trove of knowledge, I am turning to the RL community for some help to get this project across the finish line. The engine is complete - I just need some advice on gearing, exhaust and ECU.

Gearing
While the car is currently in Florida, I will almost certainly ship it to Park City, Utah when the project is complete. Our home in Utah is at 7,000ft altitude and most of the driving I do is canyon carving at 5,000-9,000+ ft above sea level. As such, I want to regear the car to take advantage of the increased power band in the 3.8 motor - at altitude. One suggestion, which came by way of Gbox transmission in Colorado was to leave 1st, 2nd, and 6th alone and change 3rd, 4th and 5th to factory gears from a 997 (turbo?) GT3 RS with a 1.55:1 3rd, 1.38:1 4th and 1.1:1 5th. These are factory gears and they come with steel synchros. I have read many, many regear threads in this forum and one hesitation I have to the Gbox approach is the RPM drop from 1st to 2nd. If anyone has done a 3.8 conversion WITHOUT a re-gear, I would appreciate your feedback on the 1-2 drop with the beefier motor. I could go with a full set of gears with custom ratios as well. I do like the idea of the factory Porsche gears, and am wary of adding aftermarket gears, which would be more noisy. If anyone has suggestions for my situation (3.8, high altitude canyon carver, AWD) it would be very welcome.

Exhaust
I am also contemplating whether it would make sense to change the exhaust to let the motor breathe better given all the other improvements. Right now, the car has the stock motor sound airbox and a Fister III exhaust that I bought several years ago. I kept the stock mufflers, so I have those as well. For all with a 3.8, is there an exhaust system that would be more appropriate for the higher HP motor, without sounding completely ridiculous? I know exhaust sound is subjective. I do like the sound clips I have heard with the Fister II and Fabspeed Sport Cats. I also like my wide oval exhaust tips, and don't want to change them. Should I leave this alone with Fister III, perhaps add the sport cats or is there a better option?

ECU
As my car is an early '96, I have read that it is difficult/ to flash the ECU. This is somewhat confusing. I am not sure if I could/should send out my ECU to be reprogrammed, or if I should try to source a '97 ECU to use for this project. Is there any definitive answer as to what is possible with my '96 ECU? EDIT: I bought Kika’s ’97 ECU and will have it flashed, most likely by Steve W.

I appreciate any and all input from the experts. Here are a couple photos of the car for good measure. Thank you and stay safe everyone.

Kika

with a 96, You have 2 principle options with respect to the ECU.
1. daughter chip, soldered on to existing 96 ECU Motherboard. Not very popular as reports are that the solder connections are typically not very reliable.
2. Source a 97 ECU and have it flashed. I have an extra 97 ECU that I no longer need. i just reduced the price to $1875 shipped. ​​​​​

Fabspeed seems to offer another solution for 96's per their website, but details are not given, not sure if they truly have another method, or if it is similar to option 1 above.
You can also contact ECU Doctors, and see what they can do.
Sounds like a great project!

i have the Fabspeed sport cats, with Motor Sound mufflers, which is probably just a bit lower in volume from the Fister IIs, give or take. Personally, I love the note, it is not very loud, nor do I want it to be. The 200Cell cats definitely allow the engine to rev a bit easier, and spool up seems a little quicker. I got my Fabspeed cats in the group buy, way back when. since then, Soul has introduced their product, which also seems very nice, and might be another option for you.

I have no experience with re-gear, other than what I have read here. Have not heard anyone that has done it, regret it, other than the cost. Bill Verburg has many charts to help with gear selection.

L39E

Thanks for the feedback. I sent you a PM about the ECU.

Nurburger

I'd recommend calling an Indie Porsche performance shop located in a high altitude location with experience in tuning for those specific needs. Berg Performance in Denver has a great reputation.

M. Schneider

L39E -
The effect high altitude has on normally aspirated specific output is a bitch. .. An old rule of thumb is said to be; ... "negative -3% specific output for every 1,000ft above sea level."

Back in the day, 11/1997, taking delivery at a sea-level Florida dealership, the 1,000mi break-in period would take place in nearby Atlanta, Georgia.
A month later in 1997, the coupe made its way to Denver (elevation 5,280ft) it's home for the next 23 years. The 993 S coupes performance at Denver's high elevation is best characterized as "spirited." When driven to our Vail place, driveway elevation 8,291ft, the coupe was downright anemic. What-to-do? There's the HP/TQ output bump of the factory 3.8 kit that's Euro popular from production new. Either add the 3.8l kit or regear 93's MY98 gearbox via swapping for an earlier MY96 or older G50 with its noticeably shorter gear ratios.

Long story short a new MY96 G50-21 LSD was fitted. The shorter gearing from the earlier years 993 production did the trick. In this 8,291ft elevation circumstance, "gearing" had a leg up on 200cc (3.8l) displacement increase. However, with your `96 3.8l C4S G50 gearbox, you might take a wait-and-see approach driving the Utah canyons for a bit first.

The bloody high altitude of 6,000' to 10,000' - there's no air. Thus, making meine Frau's MY96 Audi UrS6 wagon w/RS2 enhancements the preferred dare I say Uber Ski Wagon.

Meenrod

1. I have a 96 and had the ECU re-flashed by Todd at Protomotive. The (early adopter) reports of solder failure are just that, and when done by a reputable shop that knows what it is doing is a much more cost effective way to flash a 96 ECU - AND allows you to keep your original unit. I would recommend Todd and Protomotive in a heartbeat. He is very helpful just to chat things through.
2. I have the Fabspeed x-pipe and sports cats with the Fabspeed Supercup muffler system which is in effect open mufflers with only the cats muffling the system. It is very loud. Pops and bangs and burbles are epic. I did notice a significant performance boost when switching out from my motorsound mufflers and stock cats.
3. No direct experience on re-gearing although I am considering for the future.
4. In terms of bang for buck, I recently installed a supercharger and intercooler and the results have been astonishing. The car has close to factory Turbo power, for way less money than a re-gear and was optimized by Todd at Protomotive with a custom tune. On a 3.8 engine a supercharger would be a significant incremental addition!

I love threads like these.

cgfen

Hi.
Sounds like a great project.
Have fun.
I can't speak to your questions, but i can point out a recent post by Matt Monson of GT Gears (guard LSDs) in a current 996 GT3 thread.

"I didn't read the whole thread, but wanted to add a couple of comments. Sounds like the previous builder may have been Gbox. I know he closed his shop location a year or two back, but heard he was doing boxes out of his home garage still. If he's really gone this time, that's great news for the community as he was the Motormeister of gearboxes. He was a notorious parts trader, putting used parts in and billing for new, or as seen in this box brass synchros when steel are called for, etc.".
you may want to disregard any info from Gbox.

Cheers

Craig

L39E

@cgfen - thanks for the input on Gbox. I didn’t see that thread, but after a google search I did see some similar issues reported with them from years ago. Fortunately, I will say that I spoke to Stan at Gbox and he only gave me recommendations and didn’t try to sell me anything. In fact, he suggested that I purchase the 997 GT3 RS gears directly from Porsche. He also suggested I look into upgrading my stock LSD to a Wavetrac torque biasing LSD.

L39E

@Meenrod thanks for the feedback. I decided to buy the ECU @Kika had for sale as I like to keep all my stock parts when I make any changes. I saw some YouTube videos with the Supercup exhaust. Does your Supercup system have the turned down exhaust tips or were you able to keep your stock tips?

L39E

@M. Schneider the first time I drove my C4S up to Mirror Lake in Utah (over 10,000ft elevation) I was pulling back onto the road and thought I had plenty of time to accelerate ahead of a pickup coming from way down the road. I couldn’t believe how anemic it was, and I was pretty embarrassed as he almost caught up to me while I accelerated under full throttle.

L39E

@Nurburger thank you I will give them a call tomorrow.

Meenrod

Very good. I have the turned down tips, or track fangs as they call them, but I don't use them. They look a little silly to me. I prefer the Supercups as they come- it's one piece so no tips are needed. See below on my car. Note, since that photo was taken I adjusted the angle of the pipe so it exits the bumper horizontally now.

samurai_k

Another option is leave your car with Chris Cervelli /Cervelli Technical Services in Golden CO. He used to race 993s back in the day and does race car prep now. His ppi was exactly what I confirmed later as I started to repair my highly modified WB car... BTW, Matt at Guards transmission let me know Chris works on his cars.

Churchill

I built an RS gearbox on the cheap by leaving 1, 2, and 6 alone and replacing 3, 4, and 5 with RS ratios. I love it. The gears you use most on the street (2 through 5) are an RS stack. Who cares about the short first, you only use it to pull away from a stop. And the stock tall 6th is great for highway driving. It's 90% of an RS box at 1/10th the cost. I had the stock LSD rebuilt with Guard plates. Best money I've spent on the car. The alternatives get very expensive very quickly, and you don't actually want steel syncros on street car.

As for the motor (I also have a 3.8 with some custom parts), I would have 100-cell cats installed in your stock cat housing and call it a day. There's really no other power to be gained in the exhaust unless you want to run straight pipes, and those are awful on a street car. Save your money and ears. This is what I did and it sounds just right. A little livelier than stock, but not punishing.

I would also have the car live remapped on a dyno. Not sure how the altitude factors into this, but it's much better than ballparking it with a chip.

L39E

@Churchill thank you very much, this is really fantastic input. As for the exhaust, I assume you are recommending I go back to the stock mufflers with the 100 cell cats? The Fister III is pretty aggressive, and it seems to be a little much for most that have the 200 cell Fabspeed cats. It seems Fister II with their sport cats is the sweet spot for most. I like the Fister III with stock cats, but I think with this motor and 100 cell cats it would be too much?