was there something wong with the car to begin with to be pushing out so low BHP? You should have been at least at 480bhp pre-tuning.

I am confused.

 

That's HP to the rear wheels including drivetrain friction losses, etc, usually anywhere from 13-17% loss.

 

Great looking TT !!

 

Good explanation TT Surgeon. Now, excuse me as I engage in unnecessary and prolonged elaboration.

Let me start by saying that I DO NOT claim to be an expert on any of this. The following is just how I understand things from my limited experience. Those with more knowledge should feel free to correct me if I am wrong.

The way I understand it is that the hp numbers that are quoted by Porsche (and most other car makers) are bhp or "brake horespower" numbers. This hp number is measured with a water brake at the flywheel or crank of the engine. It is always a much higher number than the actual, real world hp you put down at the tires. A Dyno tests hp to the tires. There is about a 20% loss of power from the flywheel (bhp) to the tires in an all-wheel drive car like the 997TT (and a 10% loss on a rear or front wheel drive car). This loss starts at the under-drive pulley system that begins to transfer power from the flywheel to the axel. Each part that works in this chain moving power from the crank to the wheel is parasitic on power and bleeds the bhp number down. By the time the power generated at the crank reaches the tire, it has lost about 20% in an all wheel drive car. In the end, measuring hp to the tire - which will always be lower than measuring it at the crank - is more accurate and gives you a real-world idea of what the car is actually laying down on the road. Thus, the Dyno systems were created and the obsession began!

We ran the baseline test on an all-wheel Mustang Dyno and got 388hp to the tire. Add 20% (77.6 hp) to that and you get 465 bhp at the crank - right up there close to the 480 bhp Porcshe claims. After the modifications - and on the exact same Dyno - I did a non-sport mode pull showing 430hp at the tire. Add 20% (86hp) and you get 516 bhp. I have no problem rounding that number up to 520 bhp. . The car gets about 30 bhp more in sport mode due to a massive surge in torque. Do this same math with the torque numbers as well. This shows you overall hp gainsat the tires. But then you need to look closely at the Dyno chart that they give you showing the power through the entire RPM range. You may gain more or less at certain RPM points. For instance, on my Dyno chart it showed that we peaked with a 60hp gain over stock at the 3750 rpm range although the final hp numbers only showed a 42hp overall gain (see my chart posted below). This is where analyzing the smallest details gets a little crazy and OCD.

One of the things I learned through this process is that measuring your car's performance on a Dyno is a tricky and mysterious process. They don't always work properly and the test's accuracy has a lot to do with the skill of the technician running the test. He must be very familiar with running such tests and with the particular Dyno he is using. Each Dyno is a little different. There are often raging debates over whose Dyno is more accurate, whose reads low or high, the reliability of different Dyno brands (e.g., Mustang, Dynojet or Dyno Dynamics) etc. It can be very frustrating. Anyone and everyone can challenge a Dyno report and everyone has an opinion on it. It is just one of those imperfect measuring devices that has too many variables (like time of day, humidity, airflow, and more) to be completely accurate and reliable. But insofar as it gives you a ballpark idea of where you started pre-modification and where you ended up, it is useful. But always take Dyno numbers with a grain of salt.

Also, never lose sight of the fact that even a 10hp-20hp increase at the tire is a pretty substantial gain and is something you will definitely feel when driving. Around these parts people boast of 100hp gains or better all the time. That may lead you to believe that even a 50hp gain is meaningless. Not true. A 50hp gain added to the 997TT will transform the car. It is a very substantial gain and is in the range of realistic expectations for an exhaust and ecu upgrade. And don't forget, I read in Porsche Excellence magazine (the famous article about GMG's silver turbo) that the stock block on a 997TT can't be pushed much beyond 550 bhp without modifying the turbo system. Modifying or even replacing the stock VTG is where the real massive hp gains are found. But it is a very dramatic step that cannot be done alone. You will also need a new exhaust, intercoolers, etc. I know this statement is controversial so don't blame me - that is what the guys at GMG said in the article. But I am inclined to agree.

Personally, I would like to run one more Dyno with race gas in my car. I think it could hit up to 20hp more just with the higher octane fuel. That is what it feels like on the road anyway. Also, remember that horsepower isn't everything. The car already generates nearly 500hp to the crank. A new exhaust and ecu tune can also dramatically reduce turbo lag, give it a sweet exhaust note, increase top speed and just generally give you a stronger pull througout the entire powerband - all without generating a single additional horse. Also, dropping unsrpung weight can be as effective as adding power - and can be much cheaper. But it won't show up on the Dyno report.

I guess what my soapbox speech is all about is that you can really get hung up on testing the car on a Dyno or boasting about hp numbers. This can become obsessive to the point where you wake up one day and realize that you are not enjoying the car like you should because you are obsessed about not reaching your hp and tq goals!

My car is significantly faster now as opposed to pre-modification. I feel it each time I step on the gas. That is more important than a Dyno chart. And it really helps me relax.

Now, after all that, here is the non-sport mode Dyno report - let the debates begin!!!

For the uninitiated, the red lines are hp and the blue lines are tq. The dashed line is the baseline number and the solid line is post-mod. This was a non-sport mode pull with 91 octane pump gas. It was a hot and muggy afternoon.



As you can see, it was a pretty strong pull. I still think it can do better though - if it was done in the morning or if it was a cooler day or if the shop had a better ventiliation system or if I hadn't coughed during the test or if, if, if, if . . . . . ARRRGGGHHH!! The variables are endless . . . . Take my advice, don't engage in this madness. It will drive you mad.

For some damn reason the sport-mode sheet got corrupted when I transferred it to my thumb drive at the shop. I will request another e-copy and post it as soon as I get it.

All-Wheel Dynos are very hard to find these days. Even being in the LA Area I had to go nearly 50 miles to find one that was up and working.

 

So still shouldn't be under 400bhp

This is why I like engine dyno results!

 

+50bhp isn't what you feel in the seat of your pants, it's the jump in torque!

Mine went from stock 457 to 590 ft-lb torque (620 to 800Nm) with my Cargraphic powerkit (544bhp). That's in non-sport mode.

THEN you feel the difference!!

I have driven other tuned Turbos with around 550bhp and less torque than mine and they are nowhere near as fast.

 

Ah, and the debates begin . . .

This is exactly why the whole Dyno test thing is a tough area to get in to. Everyone has different results and expectations. As I said before, there are just too many variables.

I totally agree with your comment about torque being the key. It is what you really feel. We ran one Dyno pull that put the car at 500 tq to the wheel - or 600 tq to the crank in sport mode. I will post it when I get a copy.

Right now, I am very happy with how the car looks, drives and sounds. I don't need a Dyno to tell me that.

 

The entire package looks awesome and that exhaust pic is the best I have seen to date on a 997.

 

Wow. Thanks!

 

Looking good Mr.