SamboTT@ByDesign

One thing I will add guys, time, attacks, and road course sessions and racing are all very different. Or hill climbs for example. The power we produce especially out here in the states on these cars is straight line street stuff usually for fun and everyone has a good time with it. You accelerate for 10 or 15 seconds and then you slow down and do it again maybe. On a race track it’s completely different. Running that type of power level will limit everything and push your engine very hard lap after lap or even sometimes in a time attack. You can basically find the sweet spot of the car and set up mapping that will maximize efficiency for that period of time. Some guys are running their big power map on the track and you have issues for sure. It’s also not so safe because it’s just repeated hits of high torque and high temp. Just something to think about even if you call her down.

Randyc151

While I love this thread for getting the most from the TTS on track, I read a very good reminder today someplace: It's not the arrow, it's the Indian. (Apologies if that offends somebody!) I'm going to really look at coaching again this year. I subscribe to Ross Bently's "Speed Secrets" stuff, and read his SubStack, but I'm going to go back and look at his articles and courses again this Winter. His series on focus training and drills is really excellent!

TtimeS

Should have my 2017 991 turbo here next week. It’s steel brakes so want to run 19” wheels. I know early on Jean had a little issue with rear clearance and 19’s, has anyone else had that issue? I want to try running Apex 19x9.5/ 19x12 in 997 2rs sizes before paying double for forgeline or 8twelve. Planning on doing lca and coilvoers. Probably more misc suspension just have decided the specifics.

Jean

You will most likely get some inside wheel barrel grooving from the rear control arm, especially under heavy loading. I realized wheel brand and offset make some difference. I continued using them for 3-4 years.

TtimeS

that is kinda of my expectation, thanks Jean. Did solid mount in the rear make an difference?

TurboSlipNot

Curious to learn a bit more about the heat part (started a thread on it the other day). One of the first things i noticed about the built 4L in my car is its resistance to heat - thing seems to keep same coolant and oil temps despite fairly prolonged use at the middle to upper range. Though to your point, can't be lead-footed at that range as inducing that much boost for that long would make it impossible to enter the next turn safely.

Jean

Porsche have done the homework for us by building a turbocharged race car meant for endurance racing. The key to sustaining performance on a circuit is to keep temps in check. 1- correct turbocharger, 2- Optimized tune, 3- improved hardware.

A 700 fwhp tuned 991 turbo with modified compressor wheels will generally drop to ~550hp on lap 2/3.
A 700 fwhp Street GT2RS runs 700HP for 2/3 laps then drops by around 50-60hp
A 700 fwhp GT2RS Clubsport maintains close to 700HP lap-in/lap-out in 30 minute races.

The street and race versions GT2RS run the same larger VTG turbos, AFRs are kept between 12.5-14.5. Both run around 1.5/1.6 Bar of boost. You tune any of them to 1.8 bar and 800fwhp and you get one fast lap only.

The Clubsport upgraded the street GT2RS fin intercooler for a 20% larger one, and 2.7" thickness, they also slightly changed the positioning for better flow, and ease of access. Both run water air spray on their coolers.

Turbo sizing for circuit is complex, online models and most tuners base their decisions on theory and experience in dyno/straightline runs/high airfow. Once you analyze your actual engine data on track, you realize the 0.5 BSFC used as a guideline varies from 0.48-0.65 depending on boost levels, temps and RPMs, which suddenly makes your perfect turbo the wrong one, and you are running at 60% efficiency and seeing an IAT increase of 100F vs theory, which the cooling system struggles to dissipate.

Fastest 1 lap I have seen, is with max 23-25psi of boost, water spray on ICs and methanol, on lap 2 you drop by ~50-70hp, almost one second.

Sam has had the misfortune to go through several dozen of my logs over the years, long write- ups (much longer than this post ) and quite a bit of nagging, but we ended up with best performing track tunes that balance torque out of corners, performance and heat