- Small update.
I have installed the rear springs, straight bolt on. No issues.
I purchased the 4.0 / gt2rs top hats to see what the difference is.

The white part below is the equivalent of the black oem gt3 unit, last picture in the post.
You can see side by side. The difference is the white one is completely flat and the black one has indent ridge.
Also the foam parts that go on the shaft of the shock. The gt2rs / 4.0 is much stiffer - could be age ?

Anyhow, the aluminum housing of the top hat is identical, even same part number.I set everything to equal height, going to wait a few days for springs to settle in adjust height and
go for a drive.

I asked mooty if he would volunteer to drive my car and do comparison to his 4.0. He agreed.
I asked what type/brand of tires he has - he has m cup2's. I went ahead and ordered some re-71 as they're also r comps and my buddy in the picture has some and he swears by them.

p.s.
oem spring rate weight is 2747 grams
gt2rs spring rate w/ helper spring is - 2450 grams

594 grams total of less weight or those who like imperial. 1.3lbs







unique part number to gt2rs/4.0


gt3.1 spring weight


side by side comparison.


assembled


gt2rs and 4.0 top mount that is unique


997.1 gt3 stock


helper spring weight


side by side comparison



gt2rs weight


other unique part to gt2rs and 4.0





left is gt2rs top hat vs. oem

 

Another small update :

I had 1 hour window yesterday to drive the car. Wow
The car is flat going side to side in lateral movement. The rear feels very predictable. If you push the X , it goes X weight transfer at the rear, if you push Y, you feel Y weight transfer in the back. Very confident inspiring. I set the rear bar to middle setting for giggles ( I have the 2rs/4.0 rear bar), with a slight touch on the throttle, before the apex, the car gets the tail out in slow turns and hairpins. Tons of fun. The rear feels very controllable, i don't have to move the steering wheel at all coming out of hairpins sideways.. If you apex properly and apply the throttle the car is surprisingly very neutral with a hint of oversteer.

This is all on crappy pirelli tires. The Re-71's i will mount this weekend and I will also check ride height that needs addressing a few mm's as it's off after springs settling in.

Any local people with stock .1 GT3 owners want to go for a drive and feel back to back the difference ?

 

nice! so that gives support for the mechanical bits being a key factor and it not only being some PASM trickery.

 

Very interesting project guys. Thanks for sharing!

Tom, if you don't mind I have a quick question about how spring rate values are determined for a car spring. As a general rule for compression springs (any spring really), even with evenly distributed coils, will be a little non-linear initially from free state. Which I'm sure is why those test #2 and test #3 techniques are used where you're measuring the rate of change in force over applicable initial and final force ranges.

Do suppliers ever just give you a force vs. displacement graph for the spring? Or do you just make your own by (for example) collecting force values at 1/2" increments? This seems like it would be a useful way to understand the force characteristics of a spring and determine how linear it is (or isn't), and calc the rate for working range for a given application.

Lastly, and forgive me if this was mentioned already, but that factory 997.1 spring looks like they designed it to have effectively an integrated helper spring. I would assume that those 'closer' coils are pretty much touching one another when the vehicle is static on the ground (like the (separate) helper spring on the 4.0 / GT2 setup).

 

I have refrain from posting on this thread as i do not want to cloud mooty's judgement when he drives the car. Awhile back Mooty and i planned a date for tomorrow - for now here she's - clean - ready to impress mooty tomorrow morning. After he drives -i'll post my personal take as by then i should have not clouded his judgement.

 

Hey Crazy! Good work and very well done research and testing both real world and in the shop. We haven't always agreed in this thread but I'm impressed by your deep dive diligence and the thoroughness of your research. Thanks for sharing. Best Josh

 

drove F1's car.
not sure what he did
it's WAY better than stock
he had GT2 rear bar, absolutely needed, the car doesnt' push like i remembered
corner transition is stable and flat.
minimal vertical motion
very predictable behavior.
i drove the whole route, which is VERY RARE. usually i get out of friends' car after a block (mostly b/c i am bored with their car)
the only other car that i borrowed and wont get out was CGT.

 

WOW!!! As Mooty knows I felt the same about my CGT. And Mooty has more seat time in these cars than anyone. So can we get a single list of all the secret sauce that went into this setup? Parts and part numbers? I think folks would be opening their checkbooks based on this review.

Mooty, How does it compare to your 4.0??

Best JBO

 

other than power, it's 9/10 close

 

Whoa! CrazyF1, I owe you an apology. Good work! And thanks to Tom as well. Awesome stuff. JBO

 

Would you do this suspension setup over Tractive DDA and DSC? Or have you not driven that full setup yet?

 

he had DSC on it.
for street i would do DSC and whatever he did.
for track ohlin TTX or MCS/JRZ motorsport stuff

 

thanks mooty for your time today !
Even though it was wet for a lot of the road we drove today i think it was great for feedback. A good setup shows well in the wet as tolerances have to be much tighter to have a good car balance. Keep in mind we were driving on R comps in that standing water and tree **** and the car dynamics took it so well ! Even thought the car has yet to get a corner balance and alignment from TCD after springs, it’s driving like butter for GT driving roads. Besides myself being a degenerate, for not checking my work and leaving a lose bolt on drop link making annoying noise (fixed when i got to my shop).

The car felt fantastic from the passenger side. Transition on back roads it handled them perfect, without upsetting the chassis. Specifically with the angulations of the road where road would go up then drop and you have a left hander with slight off camber or the switchbacks. Very nice and tight. Smooth transition. On your point, and you can really tell is the car is much more predictable. Best way to describe imagine when you hit a bump or surface imperfection, you have the shock spike, before the spike had a V shape peak, was very sharp however now the spike is round, U shape, absorbs better. Which in turn give the tire better contact patch and feel to the driver. Giving the tire more time on the road, allows for more grip .

I’m not sure if it’s more difficult to program and design a shock with a progressive spring vs. a linear spring. That said setup now feels like the shocks work less at peak level and the springs are assisting more. In return for working less at the peak levels of the shock, i think the shocks are working better in rebound/damping. Better grip, feel, confidence etc.


I think this is a great setup for backraods, where imo is where GT cars like the 3 are meant to live. For track, go with a full on track setup. For street, get in and drive, I’m very, very happy. Anyone in the SFBA who wants to go for a drive on a weekend, please feel free to ping me! If you have a .1 that’s stock and want to back to back driving, this would be great. I rather explain in person the sutle diffrences vs. typing out.

For the record this is the setup I have for the rear:
- 4.0/2rs oem top mounting hats
- 4.0/2rs oem rear springs
- swift helper springs ( didn’t think it was essential to go oem on helper springs)
- oem .2 rear sway bar and bushings (gt2,4.0,2rs)
- tarret : drop links , locking plates, toe arms, dog bones.
- 2pc rear rotors
- DSC module.

I mention the 2pc rear rotors as I felt a significant difference from PCCB, 2pc rear rotors and oem rears. The lighter the rotor, the LESS the suspension had to work and the SMOOTHER the car drove. I'll be switching back to PCCB sometime soon.

My only regret is not thinking of this mod sooner.

 

Very nice. Mooty said your car was really good.
Next time my antique is up north you'll have to drive it. I suspect you may find it a bit stiff for the street. Although your leaf covered wet roads scare the crap out of me on my bald NT01 :-)

 

i was on R compound? were you trying to kill me?