isv

stout

RS 3.8 is great. RS 4.0 is, to me, noticeably better.

All GT3s on the way up to these cars were very sensitive on alignment. You could feel it when a 996 GT3 was off, and pretty easily. Both the RS 3.8 and RS 4.0 I gathered impressions from were set up correctly by a tech who knew what he was doing. The changes to the 4.0 may seem (and be) small, but suspension is an area where small tweaks can make a real difference and one not always measurable.

Of course, YMMV, but I stand behind my words: The RS 4.0's chassis was something very special, a sort of 987 Boxster Spyder of GT3s. The suggestion that the RS 3.8 was rubbish, however, is laughable.

Point about how few 4.0s are driven stings me every time I think about it—but doesn't reduce or remove the car's handling brilliance.

Good point about helper springs. Add those to the drop links, PASM control box, and maybe the dampers (though I am not sure?). I remember Alex at Sharkwerks looked into installing the 4.0 items in an older GT3 (maybe even a .1) and the parts were available. May be worth reaching out. Suspect any savvy parts tech can discover the "secret" sauce via the part numbers...

F1CrazyDriver

^
I already ordered parts from gt2rs/4.0 Main springs are at TPC Racing. Tom is doing a spring rate test to find out the rate.
I never said it 3.8 RS is rubbish - some members here came to that conclusion themselves after i said the 4.0.:

" drives leaps better then .1,RS and .2,RS and .2 GT2
Looking at the picture above i'm assuming the GT2RS drives equally as great. When i say drives, I'm referring to Damping: Bump /rebound/spring rate combo. " (sensitive bunch, shaking my head)

I'll be installing the rear suspension of gt2rs/4.0 next Saturday on my lift i'm excited.

Mr. Adair

Between Alex and Tom this seems to be something right up their alley. I'm interested in how this project turns out. Unless the suspension architecture is different from the 3.8 this should be doable. If the chassis and attachment points are the same then it should be able to be duplicated right? What I can't wait to hear is that once everything is matched up and the setup is exactly the same as a 4.0 someone will say it still doesn't drive like a 4.0 because it's missing the secret sauce

F1CrazyDriver

Tom is helping me on this project. Alex is to late to the party. Yes i'm surprised no one else has tried this. I'm surprised i have not tried this 6 years back !

Anyhow everyone per PET

Below are the other items that separates the others 2/3s vs. 2rs/4.

- wheel carrier
- track rod
- rear control arm (wish bone)
- cross member (gt2 rs only)

+

Then the 4.0 and 2rs :Hence i wanted to see the rear springs guys - thanks to jcastle again i can conclude same rear setup.Highlighted is difference between 2rs and 4.0. Shock and springs, only.

Mr. Adair

This is good work. Nothing different in the front at all? Strut? Curious to know the spring rates difference and if there is anything different about the strut?

F1CrazyDriver

Right now my focus is on the rear of the car. I will migrate to the front at a later time and analyze. Tom @TPC has the gt2rs springs - hoping to find out the spring rate any minute now. I asked him to share with the community.

Tom@TPC Racing

The GT2RS springs and spring rate results belong to F1CrazyDriver. He gave me permission to share the info.

The Spring
997GT2RS rear, part # 997.333.531.81
Free length: 202mm , Upper ID: 86.5mm , Lower ID: 61mm.
Notes: with the exception of the tail end coils which are flattened to mate to the OEM platforms, the four main coils are evenly spaced, so I consider this to be a linear-rate springs. Which is inline with the OEM's decision to use in conjunction with helper spring since this isn't a progressive-rate spring. The "25/10" marking on the spring I believe has nothing to do with the spring rate nor height, my guess is it means that it was manufactured in the 25th week of year 2010.








The Spring Rate Test
I did three different spring rate tests using a prototype billet aluminum top plate as the upper compression platform. This was necessary since the top ID isn't a standardized diameter.


Let it be know that the height of the lower compression platform on the spring tester is a height of 30mm from the base. During the tests we will be subtracting this height of 30mm in order to know the actual compressed height of the spring.


Before we get to testing, here is the free length reference which the tape ruler shows 232mm, and we are subtracting 30mm of that for the height of lower compression platform. The actual spring height is 203mm with 2 in-lb of preload.



Test #1: Using the standard method of compressing the spring 1.0 inch(25.4mm) from its free length. With the compressed height of the spring is 174mm(204mm minus 30mm for the lower platform) the spring rate is 624 in-lb.


Test #2: The spring was compressed until the display shows 100 in-lbs and then from this height, the spring is further compressed 1 inch(25.4mm). As per the display shown 732 in-lb minus 100 in-lbs equals 632 in-lbs as the spring rate in this test.



Test #3, part 1: I compressed the spring 15mm to simulate static load, at 15mm of compression the spring rate is 298 in-lb.


Test #3, part 2: From this height, I then further compressed the spring by 1 inch(25.4mm) and came to 952 in-lb. Taking the 952 in-lb minus the 298 in-lb(from Test #3, part 1) of the simulated static load the spring rate measures 657 in-lbs.

The average of the three tests is 637.6 in-lb (114 kg/mm).

Protocav

huh...I thought that was the same spring rate from the 997.2 non RS as well. Perhaps the rates are all very similar and the damping or controller are the magic, as was noted before.

F1CrazyDriver

Thank you Tom for reporting your findings.

Is it safe to conclude that the springs on the rest of GT models (excluding 4.0) are not linear but rather progressive ?
They all seem to have ~115 kg /mm but it's HOW they get to 115 kg/mm that makes the difference ?

Mr. Stout, you're the clever one - would appreciate your opinion !

Tom@TPC Racing

You're welcome.


Yes, the 4.0 and GT2RS rear springs look to be the most linear-rate of the bunch, thus the most race car-like of the bunch.


Correct. Even having different numbers of coils that produce the same rate can have different characteristic.
More info on this link- https://www.hypercoils.com/tech-tips...nsion-springs/


Between the different 997-series GTx generations they all have different design rear springs. Very different actually. The 4.0 and GT2RS look to be the most linear-rate of the bunch.
Here's an image of the different rear springs for visual comparison.
Left: 997.1 GT3/RS, Middle 997.2 GT3/RS 3.8, Right: GT2RS

gt2-josh

I also want to thank Tom. This is awesome detective work. The data is invaluable. Greatly appreciated.

Crazy F1, can you please leave stout out of this thread. I think we have a sufficient answer to the original question. Why don't you check out what Chris Harris said when he drove it if you want another opinion?

We've got enough data to chew on for awhile.

Sorry brother....

PS stout is no mere mortal. He is the fastest driver on the back roads I've ever encountered.

stout

A second on the thanks to Tom. Real data, collected intelligently, is always great to get.

If there's one thing I've learned after studying Porsche for 20+ years, it's never safe to conclude anything!

I don't know about that! When it comes to parts and development, there's only one good source: The source. I do know of a guy I can try to track down next time I'm over. It ain't gonna happen over the phone, and the last time I saw him, I was sitting at a junction in the countryside near the Ring in an R, and he flew up in a 991.2 RS proto and flipped a fast U-turn. A nod with a thin smile, and then he was gone...dispensing at least five gears in rapid succession. Or I'll bug a friend in Flacht—but it might take a while to get a proper answer. I am curious too, now...

Thanks, JBO, but FIFY. I enjoy using a sports car as intended, but I'm no wild man on the street and don't appreciate those who are. BUT, these are road cars, so how they go down a road and what feelings they elicit while doing so means a lot to me.

jcastle

Also per jcastle's picture the helper spring is fully compressed so isn't actually doing anything and that I assume is already with the car jacked up??[/QUOTE]

helper spring is compressed because the car was on the ground. snapped photo thru the wheel.

F1CrazyDriver

I got the main springs, helper springs. thank you Tom for the fine packaging. Really appreciate it.
I'll document the retrofit this weekend. Any request in particular from the rennlist community ?
I'll weight the spring individually, in grams and post.

Random thought. Does the DSC have anyway i can log data driving same roads w/ oem springs and with these springs and share with the community ?
Just to see logs of the behavior of the shocks rebound/compression if any effects ?