I am currently running a 1989 911 in the NASA GTS series. I still have some room left for improvement that will allow me to stay in my current class (GTS 3). Here are my choices; 1.) Improve exhaust system and increase horsepower by 14 (from 215 to 229 at rear wheels) 2.) Reduce weight by 151 pounds (might be difficult/expensive as car is already down to 2,319 pounds) 3.) Change from Hoosier R6s to a racing slick and add 64 pounds of ballast. This might be difficult as I am struggling to find slicks for my wheel size - front = 15x8, rear = 15x9. The car's power feels good but handling through the esses is only average (most likely due to rookie driver!). Would love to hear everyone's thoughts on the best way to improve the performance of my car.

 

I'd say that it depends on where you race. With long straights, you may want the HP increase, but otherwise my choice would be for the increased grip of the slicks. For handling & braking it would more than offset the weight disadvantage. They will be quite a bit pricier though. As far as the sizes, move to 16s or 17s.

 

Add HP in your case. I also race GTS3 and have around the hp that you could get up to with the mods. Even at that, I'm one of, if not the lowest whp car in GTS3. Although I feel I have an advantage over the other GTS3 cars in braking and turns, I am at a slight disadvantage on long straights or when working my way through traffic (mustangs mostly).

 

as a general rule, I think a lighter car is ALWAYS better.....going to slicks will improve your times even more...... but I don't know if the slicks are worth 64lbs?

Using your 2319lbs must be without driver...since that puts you in GTS4..not 3

http://www.nasagts.com/

assuming you are 2519 with driver....you could run real slicks AND 229hp to be right at 11.0 or right at the top of GTS3....thats what I would do!!

 

That's incorrect, if he runs "real slicks", which are non DOT-R, then the lower limit for GTS3 is 12.

 

If you run slicks I would be surprised if would not also have to change your suspension - spring rates and dampers. Hard to believe that a suspension optimized for R-compound would also be able to take proper advantage of the impact that slicks can have.

 

The weight of the car is 2,319 pounds. With driver and a gallon of fuel it is 2,516 pounds. You are correct - the limit with slicks = 12.0 and with DOT tires = 11.0. I would like to keep my wheel size at 15" as I already own two sets. Any other thoughts on the best way to improve performance for my car???

 

Here is my take.

more power + 17" wheels and fat tires. Remember in GTS wheels/tire are free

Running little 15's is limiting the grip. At 215 hp you don't have that much for GTS3. Weight reduction is great, but I won't get you much top end and unless it is easy it is probably not worth it.


If you add hp you may begin to be under tired. 15's are small and tire sizes are limited these days. Going with more tire and stiffer sidewall due to shorter aspect should help increase grip. The power will help too.


Now the other way to approach it is on track where are you slow? Are you getting pulled down the straights only to catch up in the twisties? If so go HP all the way. The reason is more grip (from slicks) won't help up much. It will just make your current problem worse. Less weight will help acceleration, but not top end speed much. It will help cornering speed, but agian if that is not the issue then it won't be that much of an impact. HP will help top end and acceleration.

On the other hand if you are keep up on straights, but are struggled in the turns then grip is good.


The last thing to consider is budget. A change to weight or hp alone can be "one time charges". This means you but parts X,Y,Z and run. However if you change tires it can be cheaper for the next weekend, but be more costly after a full season. This is something to consider as well.

 

If you are budget constrained attack the area in bold FIRST. You can do this by doing more driving, looking for advanced training, getting a data system to see what you are doing performance wise on track and/or ensuring the car as the optimal set-up.

 

Seeing as I don't believe there's as big of a difference between the Hoosier R100 slicks and the Hoosier R6's as most assume (and I'm the only person who has commented on these type threads who seems to have run them back-to-back on the same weekend), I would recommend either the power increase or the weight drop. I would not add weight just to go with slicks.

 

FWIW, here's an older post from the NASA forums out my experience with Hoosier R-comps and slicks:

 

Biggest change I made to my NASA GTS-3 car was adding widebody flares that allowed me to change wheel sizes from 8x9x16 to 9x11x18. Tires sizes changed from 225/265 to 245/285. On my home track I went from a 1:24.2 down to a 1:21.9 the very first time I drove the car with the new set-up. The other change made at the same time and contributing to the gain was going to a Tilton dual master set-up for the brakes.

 

how much do you want to spend? fiberglass widebody and wide 17" or 18" wheels would be a big performance gain...

 

Dont go slicks. I ran them on my GTS3 car for a while when I had a 3.2 that was not at class limit. Was great. Ran same lap times as the leaders, but could not convert it to a win. I was making up for straight line speed in the corners where it is much harder to pass, so I would get passed and have to follow the fellow through a few corners, maybe get back by and then get passed in the straight again. Very frustrating.

Also, slicks take a couple laps to heat up. Very bad in a race where everyone else is go from about a half a lap in.

Ed

 

For NASA as mentioned you need the power to run Thunder Group with the CMC cars. They will race and pass you down the straights then hold you up in the turns. I had a power issue last year and ran slicks to compensate one event. It helped, but still made it impossible to catch P1/P2 and I twice settled for 3rd on a tight track that could have advantages with grip. At a certain speed, hp will pull you down the straights better too.