WillyDaP

I plan to run Time Trials with NASA ( have run TT or W2W with them for 10 years ) but I need the obligatory Dynamometer run on a Dynajet to determine my Classification. I think I can plop down into TT 3, either with 200 TWR tires or hopefully with Hoosiers, if the max HP or average HP comes in around the 330 rwhp range? With a stated 384 flywheel HP I am figuring there will be a 15-20% parasitic loss, but friends are telling me that is not what many Porsche owners see , since they believe Porsche undervalues their horsepower ratings. I figure with the weight of the car, fuel, and my fat little butt , I will come in around 3501 as my mandatory minimum weight. So, if anyone has done a stock Dyno pull with a GTS 4.0, how about posting your numbers ( or PM me if you want to keep it secret ) so I can get little idea of which way I may need to go? I realize my GTS 4.0 is not even here, but I am a planning fool, and I like to have things ready as soon as I can , since we get a bit less track time here in the Midwest than our friends in Sunny a) California or b) Florida or c) other States with only one or two Seasons.

Thanks for any help or comments.

AC53

Yes, Porsche typically understates their horsepower and acceleration figures. Part of that is to ensure that the production variations don't bring a customer's vehicle below the official figures.
Due to production variations, tolerance ranges, etc., no two GTS 4.0's are likely to produce exactly the same figures, but they will be within a reasonable range. The biggest variations you are likely to see are in Dyno readings which are often not well calibrated.
An old trick for fudging dyno figures was to run hot air into the intake of a heat-soaked (not overheated) engine. I don't know if that actually works or not. FWIW, the GTS 4.0 engine is rated at 394, not 384.

momo360

Google answered this question in 2 seconds. But here's someone who got 365whp stock Back from the dyno with numbers for my 718 BGTS 4.0 with headers | Porsche 718 Forum

Like stated above ^ Porsche underrates these cars. IIRC the peak power at dyno for GTS 4.0 and GT4 are more or less the same

spdracerut

Drivetrain losses should be relatively low with the transmission basically bolted straight to the engine. No long driveshaft/bearings/drag in front engine/rear drive layout.

WillyDaP

Appreciate the correction as I am aware of the correct HP, but this old man was typing too fast or my bifocals were fogged over, ha. Thanks for the notes and interesting about heating the intake , but NASA is pretty stringent in how you need to get your Dyno numbers and many of the places who do the testing are Approved Tech Centers by the organization so I was just hoping to find a few folks here who had actual numbers on a stock motor. There can always be some variations with Dyno tests , but I figured if a few folks offered there numbers it would give me a better guesstimate if I would be able to stay in TT3 with the car or if I may need to view TT2. I am guessing that I can probably run TT3 with a solid 200 TWR tire ( like Bridgerock RE71 RS ) but I am hoping to stay with some A7s. Good call on the fact that driveline loss is likely to be less with a mid engine layout -- logical thought I had not considered.

turbo8765

As required by EU law (yes law), Porsche do not “under rate” hp figures.

People who don’t understand dyno’s often state they do, but they do not. They are compliant with EU law and would not expose themselves to unnecessary liability.

WillyDaP

Well, EU law and US law are essentially quite similar , but the 394 HP is flywheel HP, and for NASA and most other track organizations they look for rear wheel HP, hence the number is lower. Just hoping for a few folks who may have done a stock test, but if not I guess there is no hurry, since I don't have my car yet, ha!

BlueBarchetta

Couple things… don’t forget that peak HP is only important as the starting point for your HP average calculations. Remember to get the 50 rpm printouts. Since you are NA, and rev above 7k, you will get additional data points to average out. Also, remember you can add ballast, unless you want to keep the car stock.

Lastly, an A7 is gong to be a much higher modifier over an R7, and likely not worth it, unless you have power:weight in excess.

WillyDaP

Thanks Blue Barchetta , your ideas are mine exactly and I have been doing the ridiculous Porsche Power Postulating since my Cayman is not here yet and since I traded in my Mach 1 early I am missing the Time Trial Season. I know you are probably correct on the A7s, but since I may autocross ( with SCCA ) the car occasionally , it is part of the hypothesis. When push comes to shove I probably will just run Goodyear F1 Supercar 3Rs since I can get a killer price on them through USAA. Eventually someone may drop a Dyno Sheet they have done for NASA and I can get a slightly harder bit of data , but I have a feeling you are spot on. Not too anxious to add weight, but interesting idea as it seems adding a bit in the frunk might even help with the Cayman push? Have some old Viper buddies in Canton and great place for a track rat to live with easy drives to Pittrace and Mid Ohio!

BlueBarchetta

Hope you get your car soon, my BGTS has reached the port, so hopefully I’ll get it before winter, lol

NASA keeps a national database with the car classification forms in it. It’s probably somewhat searchable. Look in TT and ST, you might find someone running a 4.0 with the dyno sheets already there. However, you will not necessarily know if they have a tune modifying the stock output.

Also, don’t forget, the NASA tire modifier will be based on the widest tire on the car, using the approved templates. To help the “push”, give you rotation options, and more fitment options, eventually you might want an 18 or 19 in squared wheel track setup. Seems like many use Apex wheels for that. The square setup should also help autocross. It’s all a slippery slope, lol.

Mid O, is our “home” track, and is technically excellent. Unfortunately, it’s in great need of maintenance. Both the track and facilities. The owners of Pitt Race (coincidentally they are viper racers), have done an amazing job with the track and the facilities. If you haven’t been there, I’d highly encourage it.

WillyDaP

Great idea to check out the National Database, but not sure what you are discussing about the tire modifier since in TT3 it is N/A unless there is something new this year I missed. Same with A7 , since I was running them in the past and they are okay ( went to R7 though for more wear ) since they are DOT. I have know the Stouts for over 20 as we first met when all of had just starting racing Vipers. Good folks and interesting about Mid O as I has heard things were not up to snuff anymore and that is tough to hear. Will see what I can find out and thanks for such a brilliant thought;