doba_s

After having lots of fun with my NOBULL GT3 car, I decided to go back to GT4 and give it another shot this season. I was lucky to get my GT4 from a Rennlister and it came with some mods like Finspeed wheels, toe links and GMG headers (which i am selling).

I didn't have much time to do any work on the car so I took it as is to Laguna Seca and was pretty happy with how it drove that day. I got into high 1:38s lap times fairly easy. This was a good baseline for me to see if I can improve my times when I get it dialed in. I had no plans driving it on the street so I decided to remove some weigh by removing some interior pieces (it's not gutted to bare bones and still has carpet, door panels and all that), passenger side seat, and switch Porsche Motorsport Lightweight battery. All in all I got a little bit over 100lbs form the car.

I left suspension (shocks and springs) stock and changed to Porsche Motorsport front LCA and Tie Rods. PM control arms helped to widen the track gain more camber while keeping front struts relatively horizontal. Lots of folks push them all in up on top to gain camber but I decided to take advantage of the longer PM arms. At the same time I added PM shock tower reinforcement plates just as a piece of mind to keep those towers from blowing up.

The rear suspension was left alone since it came with Tarett Toe Arms and the only thing I added is LCA monoball ends (from Tarett as well).

After an alignment and corner balancing I took it a few times to Thunderhill and Laguna and the car felt a lot better. Since I have never driven GT4 at Thill it took me a bit of time to get used to it and my times were not super quick and I was able to do 1:58s on 3m configuration over the top pretty consistently. Car had 0 understeer but a lot of oversteer and lack of rear grip. Laguna felt exactly the same (no understeer with lots of oversteer) and i was able to get my time down another .4sec compare to my last run.

Since I am not too big into Power mods I kept the engine as is all stock and didn't do anything besides getting a set of Dundon headers with catted pipes to run GT3 muffler. I had a spare GT3 muffler and really like how it sounds so it was a no brainer to this mod. It also turned out to be about 9lbs lighter than stock GT4 exhaust. At the same time the weather was pretty bad here in CA and it was a down time from tracking so I decided to get transmission re-geared.

After having a Cup car aero on my street GT3 I kinda felt that GT4 would benefit from a bigger wing to deal with oversteer. Luckily I was following @Verus-Eric posts and the development of the GT4 Aero parts and I decided to get in touch with them and acquired swan neck wing. Awesome quality parts and the fitment is spot on. Since the front splitter is not available yet I decided to use Verus dual element canards up front to help balancing rear wing. By no means the canards by itself are efficient enough to balance it out but they worked well on a high speed turns like T1 at Laguna to keep the front end planted. Also my AOA on the wing is very minor as i didn't want to go from oversteering car to understeering car.

Got lucky with weather and took my GT4 out to Thunderhill to see if these parts would make any difference. I am running the same Bridgestone RE71R tires (same kind not the same set to be clear) to have less variables and see which parts work and which don't.

I have to say that car felt pretty awesome and had some understeer. It would definitely need a front splitter piece to have a perfect balance and to run greater AOA but even without front splitter I got my times down to low 1:56s which I was able to replicated lap after lap session after session until it got pretty warm and understeer become pretty pronounced. I week later (yesterday) I took it to Laguna Seca and was able to shave even more time and got down to low 1:35s. Same thing consistently 1:35 lap after lap.

So far I am pretty happy with how GT4 comes along and it's definitely work in progress. For now my goal is to get my Laguna times to 1:33 on same street RE71R tires and match my Gt3 times. Just glancing over my data GT3 is significantly faster on straight aways by about 8-9mph. My theoretical time at Laguna is 1:34 which I think is possible in current configuration without any additional mods and 1:55 at Thunderhill.















Here is my Thunderhill run. I'll post Laguna video shortly


Thanks,
Aleks.

James88

Very nice driving, seems like you were consistently improving your your times each time with small increments.

Five12Free

Sub’d. Very cool and 1:35 at Latina Seca is moving.

IPSA

Do you have tune allowing you to pull to 8 k plus rpm?

JSA

I think you need more rear wing.

supercup

I see you noted you re-geared the car same time you did the exhaust. What did you go with for gears 2-6? What ratio's -

Did you feel that made as a significant a difference at the aero you added before?

How would you rate the mods for benefit of lap time? Aero or gearing more beneficial?

Thx for sharing what you are doing and progression

doba_s

Car is not tuned (at least not by me) so I can't say for certain if it does or doesn't . To my knowledge it doesn't and in real time i think i shift under 8k. Video may be showing it differently.

doba_s

I went with 3/4/5 gears from Guard. Gears definitely made car more alive. You surely going to shift a lot more but the car is in power band most of the time so it feels very responsive and not like a stock lazy dog. With that being said, it could have contributed to the oversteer in a sense that I would get on the throttle at the same time as before but RPMs would be hight which would output more torque when you on the throttle ... I might be wrong as I don't have a dyno graphs of my car to see the power/torque curves but this is kinda my theory and i'll run with it

The rear wing was added after the car was re-geared. So my runs were stock (or as purchased), re-geared, re-geared + wing. Wing adds downforce and minimal drag at least at the current AOA that I am running. My top speed pre and post wing at Laguna Seca are exactly the same!

paradocs98

Thanks for posting. Lots of info and data. A few questions/comments:

• I think the question from IPSA above regarding 8k+ rpm is based on the screenshot of your AIM Solo showing 8000+ rpm on laps 3 and 5. So I would guess either the Solo is not getting correct data from the CAN bus, or the Solo is accurate and your rev limiter has been disabled.
• It looks like you have AP J-hook rotors in the rear. What are the front rotors?
• Are the Finspeed wheels 19 inch? What size RE71Rs are you running?
• The Porsche Motorsport front shock tower reinforcement plates--are those actual PM parts, or are they the pieces from SP Motorsports?

Tunedm3

Are the GMG Headers you are selling catted? If so I am very interested.

doba_s

Ok that makes sense regarding RPM ... but again I am not sure if it's tuned or not. To my knowledge it's not.

I am running front prototype rotors that are similar in design to Type 5 but an improved version (they are not made by Brembo) and will bolt up to essex front hats.

Finspeed are 19: and I am running 265/285 sizes

Yes I am running actual PM parts not from SP.

doba_s

Yes they are catted. You can PM me. I have them in my storage.

jmartpr

You are missing the bolt that goes from the plate to the chassis....you need to get those in order to gain any benefit from the plates.

Tunedm3

Cant seem to send a pm. Please pm me or email tunedm3@aol.com

OldJedi

Doba, thanks for the great write up and information. I know you wrote that your GT3 was 8-9 mph faster down the straights and I’m sure that the 500HP is a contributing factor. But which car seems to be more sure footed and which one is more fun on track in your opinion?