Hank Cohn

It was a perfect day at Road Atlanta today with clear skies and low to mid 70s temperature. Adjustable shocks are a good thing when they are close to right and a curse when they are not. My car has triple adjustable JRZs and as I have changed so much about the suspension I set them at back to the factory defaults. The first session out I found myself driving the rear end. The front turned in great but the rear wanted to keep coming around (a lot of oversteer). I started by softening the rear sway bar (to full soft) which helped a lot and decreased my lap times by a second, however, that caused the car to take an initial set at the rear followed by a second set mid corner (not fun in T12 at Road Atlanta). Increasing the bump setting at the rear all but eliminated that problem for a gain of another 7/10ths of a second. My car has stock engine mounts could this be part of the problem? Next the problem moved to the front of the car causing the front tires to skip wide (understeer) at turn in. Softening the bump setting up front cured most of that characteristic making the car more comfortable to drive.

My basis for comparison is the stock 997 GT3. Compared to that car the 996 GT3 is much dartier and requires significantly more smoothness and heightened driver commitment. This in itself is not a bad thing and there is a lot of adjustability left in the suspension. My car’s front ride height is probably to blame for this. It is set at 102mm and as a result, bump steer is very apparent. Under heavy braking it's quite a handful. I will change this before the next track day. The rear end of the 7GT3 is much more stable and therefore makes the newer car significantly easier to drive. My lap times are 1.5 seconds slower in the 6GT3. My best time today was a 1:37.0 with several other 1:37.xxs. Mid to high 1:35s is what the 7GT3 would trun consistently. On the plus side, the 6GT3 feels much lighter and more nimble. Driving out of turns, the 7GT3 accelerates at a faster rate; however, speed at the end of the back straight is comparable and perhaps higher – I will confirm this with data tomorrow.

Overall the 6GT3 is a very competent car. Higher rate springs, correcting the front ride height or installing the parts necessary to fix the bump steer problem and careful tuning should yield a more stable platform and faster lap times.

More tomorrow…

Hank

Chris L.

I feel like I have been sitting here at the computer awaiting this post. Not surprising at all. In fact. . . it sounds like almost exactly what we talked about.
I would think you are 100% on about the ride height. Even with those spring rates you are probably close to 5mm too low and maybe even more.

Can you use low speed compression to help with the second set in the long sweeping corners? Sorry. . . looks like you said you used that to correct the issue. I can't wait to hear more from tomorrow.

By the way, that's you in the passenger seat of my car at RA from back in June in my avatar.

wbrownie

Thanks for the post Hank. Although my 6GT3 is stock, I had similar thoughts comparing the two cars on track. 6GT3 definitely feels lighter and seems to have the potential to be faster and possibly more fun to drive. Just need to make it more comfortable to drive fast. Sounds like you're well on your way to getting there.

Have fun!!!

mooty

more fun for sure, you can move the rear around a lot more.
lighter... haha, when i drove my RS off the lot, i felt it was at least 250 lbs heavier and it was!

hank, glad you are loving it.
did your car have shortened gears? that will make you love it more as it squirts out slow tight turns.

Jager

Hank, its great to have you making this comparison. I want to see if you can groove the 6gt3 to lap times below your best in the 7gt3. That would be really cool.

Hank Cohn

Follow-up:

Today was another perfect day at Road Atlanta. In the morning I added one more click of bump to the rear shocks to try to get rid of a little more of the unwanted secondary suspension movement. As there was no discernable change I decided to just drive the car, take notes and focus on getting everything out of the car that I could in hopes of coming back to the next event with a plan. I was driving on Michelin Pilot Sport Cups in 235 and 295 stock sizes on CCW C14 9” and 11” wheels.

My impressions of the car are much the same as the first day. The car is fast and very involving to drive. Compared to the 7GT3, it is very twitchy. The front turns in faster and in a more precise manner, however, inputs must be extremely carefully metered. Either the steering ratio is significantly faster than the 7GT3 or my bump steer issue is exacerbating the car’s turn-in behavior. The rear is where the issue lies. It is very controllable with throttle; however, it is much less ‘planted’ than that of the 7GT3. I had to wait to add power, if you’re familiar with Road Atlanta, at the top of the esses and in turn 12. There are a few tenths to be gained there. I still believe this can be overcome with proper suspension tuning.

I use the Traqmate data acquisition system and putting up a virtual race between the two cars is very interesting. The difference is that the 7GT3 accelerates slightly faster. The 6GT3 seems to brake more efficiently. Terminal velocity at the end of the long back straight at Road Atlanta shows that the 6GT3 is actually 1 mph faster than the 7GT3! The most interesting fact to me is that the 7GT3 was bone stock and the 6GT3 has over $8K of suspension. I've posted the laps from both cars on the Traqmate site should you want to look at them.

Chris – Thanks for all the input. I’d like to compare setup notes. I know our cars are very different with regards to springs and I may just stat all over with your same spring rates. It would be a fun thing to think about during the off season.

wbrownie – I feel like it could be faster than the 7GT3 as long as the 7GT3 doesn’t have similar mods. The 6GT3 requires more skill and the car feels ready to bite you if you make a mistake though it is very catchable. I messed around a few laps and had a good time hanging the rear out – silly but fun!

mooty – I don’t have shortened gears. It sounds like I have something new to learn about. Please teach me! Second gear is perfect for Road Atlanta There are two important turns (7 and 10a) that are second gear turns and you run out of gear just after you get the car straightened out. If it were shorter, you would be a busy boy!

Jager – I got close to the same lap time. Best to best the 6GT3 was 4 tenths slower. If there were more contiguous clean laps I’m sure I could have bested my time in the 7GT3.

Hank

mooty

i am not familiar with road atlanta, but most CA tracks, i find 6gt3's gearing too tall and 4th gear is all i ever get to. brian copan (porsche gear box guru) should have gearing chart for tracks in your area and he can help you figure out what you need.

NJ-GT

What kind of spring rates are you running now?

You can re-gear the car for about $3,500. Get a shorter 3rd, 4th and 5th, and install the stock 5th into 6th. Brian Copans is a excellent resource to do this work. There is too much gap between the 2nd and 3rd gear with the stock transmission. You could also upgrade to the GT3 Cup LSD.

While the transmission is being re-geared, you could install a lightweight flywheel as well.

If you switch to the rear calipers from the PCCB car (350mm), you can get better brake balance compared to stock with iron brakes. This change is also possible re-using the stock rear calipers with a 10mm spacer between the upright and the rear brake caliper, and the two upright caliper bolts used at the front axle.

Jager

Hank, some of your comments about the 6gt3 are bang on how I see mine. Very interesting about terminal speeds between the two. Other guys seem to feel the 6gt3 can outpull the 7gt3 on long straights. I also think that with time to get acquainted, you in the 6gt3 might better the lap times of you in the 7gt3. It's just my bias, but I find that once you learn you can trust the 6gt3, it really starts to get grooved and you can really feel the car. Anyway, great posts, thanks.

DanH

Are your sway bar settings not a bit soft? Most setups I've seen seem to be at 1 off full hard.

boqueron

NJ-GT

I am curious on which results ( lap time ) should one expect from the re-gear alone ? (I have the LWFW which has not produced much difference on the track lap time.. . ) Perhaps one/tenth of a second....

PS.- Trying to stablilsh my upgrading priorities AFTER the new suspension..

Chris L.

Trust me. . . there are smarter people out there from which to take notes for a possible start over! Heck - most think it ridiculous that I run the springs I do in the combination I do as you well know. I am as always wiling to help in any way I can.

1. I'm not surprised with the evolution. I mentioned how the 997s felt the exact way you describe the 7GT3 compared to the 6GT3. I have driven my friend's 7GT3 though not on the track. I can tell how much more lively mine is. There were many suspension geometry issues that Porsche corrected, with much more expense than the 8k you have invested, on the new platform!!!

2. I am sure with some time in the car things will fall into place. Adjusting the ride height and tweaking the shock/spring package will as you have mentioned take time and notes. Heck, that is the fun part.

It has been about a 6 month road with Nic and Kinetic helping me get started on the car and having David Murry tweak both the car and me to get to where I feel comfortable in the car completely. That is where I am with the car now. It feels GREAT! It is still "lively" but not in a bad way any longer. It is predictable and I feel that I have got the shock/spring combo working.

I have no doubt that soon you will enjoy this one much more for all the reasons you mentioned (more involving, requires more "skilll", etc.). Those are things you both possess and look for in a car.

Hank Cohn

mooty – Thanks for the tip on the gears. I am familiar with Brian Copan and his work.

Rad – The springs are very conservative at 600 lb fronts and 800 lb rear. Thanks for the braking information. I haven’t had a chance to look closely at the data, but it looks like the 6 brakes faster than the 7 (deceleration over distance).

Jager – I think you’re right regarding seat time. There were very few clean laps. A private test day would be great. I hope to get in on one of those in the near future.

DanH – I started the weekend with the both the front and rear bars set at one off of full hard as per the Kussmaul settings. I ended up the fronts unchanged and the rear at full soft.

Chris – Thanks for the input and you’re right. This is the fun part of the ownership experience. When it gets to where it’s perfect for me, it will be time for a new car.

Hank

DanH

Hank I realise, was just wondering if you were compensating for soft ARB with stiff dampers and ending up going up the wrong path? Its not just kussmaul that uses those ARB settings - Manthey do too.

largeandturbocharged

Hank,

I think the best way to cure all your handling issues and probably also save a great deal of $$ is to just sell that P-Car and get yourself into one of those Mitsubitchy thingys.

L&T