987 Upgrades and Quaife Diff Feedback

[tcreswick]

Hi All,

I finally took the leap a few weeks ago and had some upgrades done to my 987.1 S.

It's a non-PASM car. I've gone with some lowering springs, shifted to 19-inch wheels and Pilot Sport 4S tyres. It's had a Quaife TBD differential installed, and a few other bits and pieces (exhaust, brake ducts, remap, full geo, fluids, brake lines etc).

For anyone debating the Quaife diff, all I can say is that I wish I'd done it a year ago. It's totally transformed the car; the handling is incredible and all the "twitchyness" of the back-end is gone. It's a total dream to drive, and along with the other upgrades it couldn't feel more different.

I had the car on track at Brands Hatch last week (https://youtu.be/36R3qS_iCiM) for a bit of a shakedown and without really pressing-on it was 3 seconds quicker per lap - the diff allows you to access the power more often and much earlier, but it just gives huge amounts of feel and confidence. The car skipping sideways at 80 mph through Paddock puts a grin on your face and isn't in any way the sphincter-tightening experience it used to be.

It's brought a whole new life to the car, and any thoughts I had of selling it are just totally gone. A spirited drive from London to Devon on the A30 last weekend in the pouring rain was one of the most enjoyable drives I've had in a long time; again the diff is just amazing in those conditions, although the PS4S tyres also have ungodly amounts of grip in the wet considering how fast they are on track.

Would be delighted to share more details if anyone is interested, but a massive +1 for the diff. When I was asking people about it I had quite a lot of feedback saying that you wouldn't really notice the difference. I think that's probably true in dry conditions on the road, but definitely not the case either on track or wet roads.

If I bought another 987 I don't think I'd drive it without making that change.

 

[Motorhead]

Interesting to read your comments Timothy.

I'm not sure whether or not the LSD was an option on the Gen1 Caymans but I specified it on my Gen2 CS. Although it was a standard fitment on the CR I've not come across many cars fitted with the option.

The Porsche LSD is of the disc-type and has fairly mild locking characteristics whereas I think that your Quaife diff is of the helical-type which uses gears and which probably has slightly different characteristics. I've no experience of an open-diff 987.2 but like you I'm sure that the LSD gives better traction in certain conditions, although with my standard geo set-up I can get a fair amount of understeer when pressing on in really tight corners (one downside of the LSD).

With the introduction of ever more sophisticated traction control/PSM systems I do sometimes wonder if locking diffs are really necessary, particularly for road driving. It must be tricky to match the charateristics of each to its counterpart and it's interesting to note that both Lotus and McLaren shun the use of LSDs. Neither manufacturer can be accused of producing poorly handling cars..!

From your description it sounds as though you've got a nicley focussed road and track machine. I note that you've lowered the car but are you still running with the standard dampers or have you gone for an upgrade?

Jeff

 

[tcreswick]

Yes, I've heard bad things about the CR diff, and the locking characteristics of those types of diff can mean that you're constantly fiddling with the setup.

The Quaife diff gives a feel almost like a go-kart; torque is delivered to the outside wheel, which gives a feel of really helping drive the car _around_ the corner. I found that getting on the power earlier really helped with the cornering, I think with a locking diff that would be quite different.

I hear what you're saying about PSM systems but I think the "fiddle-braking" type just doesn't quite respond fast enough, but also doesn't behave in a sufficiently predictable way. I had a couple of occasions where the car really snapped on me in the past. That's completely dialled out now. I was also struggling a bit with brake temperatures, and whilst I don't have any solid data on that, it can only have helped to not have the car applying the rear brakes all the time.

As for the Mclaren's open diff... it's a much more advanced braking system, and from an pure engineering standpoint it makes total sense. The practical reality is that my 10-year old Cayman is a much much simpler machine and the best way to improve this handling characteristic was with the TBD.

On your final point; I left the dampers alone. I considered doing an all-round coil-over upgrade but having already gone over budget on the upgrades I decided lowering springs were a good compromise. My main aim was to drop the car ~25mm - being a non-PASM car the ride height was a bit crazy and I think this contributed a lot to the body roll. It feels super-flat through the corners now. The springs were pretty cheap, so it won't really be much of a waste if I do a coil-over kit at a later date. Since I was going to 19-inch wheels I wanted to see what impact this had on the ride comfort before going to full coil-overs.

As it happens, the ride is really really nice even on b roads, so I think coil-overs are in this car's future.

Before that I think brake upgrades are the main item to deal with - with this setup I can get far too much heat into the front end in about 10 minutes on track. The brakes are heat-soaking into the wheels which is causing tyre temps to go off. Larger diameter, floating rotors ought to deal with that and allow me to run longer stints on track. At the moment (and in the video above), I'm being really conservative with the braking in order to enjoy more time on track - after all, it's not a race...

 

[crafty72]

Thanks for posting this Timothy. I've been thinking about a LSD for my Gen 2 S for a little while. I've recently added Ohlins Road and Track suspension and I am very impressed with it so far, I did a track day at Snetterton and for the most part traction was great but ideally I'd love to be able to switch PSM off completely and added with a LSD I think it would finish it off nicely. Without being rude could you give me some idea of fitted cost for the LSD ?

Brakes were an issue for my car also, so far I have the GT3 master cylinder fitted for better pedal feel, braided lines, Endless fluid, and GT3 front ducts, I modified a set of 997 Turbo rear brake ducts but so far I don't think they are really in the airflow enough to do much cooling so I will try modding these further. I ran EBC yellowstuff pads but these were useless and crumbled fairly quickly so its will be Pagid PS29's for me next time. I am also looking at Girodiscs but they are quite expensive...

Car looks great too btw.

 

[tcreswick]

Yeah this is a TBD not an LSD which personally I prefer.

I always run with the PSM turned off on track, even on wet days. The feel is much more progressive that way. With these upgrades the car moves around underneath you a lot on the edge of grip, but the balance is phenomenal and it feels totally controllable. The easiest way I can describe it is that it's like driving a video game - the car gets a bit sideways and it's really straightforward to collect it up and carry on, and there's just no drama about it.

I've considered the GT3 master cylinder upgrade but honestly I'm quite happy with the feel of the brakes - as someone else recently pointed out, the very progressive brake pedal feel makes the heel and toe a lot easier. It's running racing brake fluid and the GT3 ducts on the front. A relatively small increase in rotor diameter is of course a huge increase in braking surface and also in the ability of the brakes to dissipate heat. Floating disks would help prevent the heat soak into the hubs and wheels.

I think therefore the obvious upgrade is just bigger (floating) rotors for the purposes of thermodynamics rather than anything else.

 

[ralphmusic]

You might want to consider grooved discs to avoid the cracking that emanates from the drilled holes. Girodisc seem to have a Marmite reputation with some having good experiences and others bad. The key point about brake upgrades is to have calipers with a choice of disc size and pattern upgrades.

 

[tcreswick]

Thanks Ralph.

I haven't started my research on the available options for brake upgrades yet... it's constrained by the wallet rather than the imagination at the moment

I'll bear your suggestion in mind though.

 

[MrDemon]

After a lot of looking this is the best set up for brakes on the 987 imo

its a 355mm set up with AP Racing CP9661 Radi-CAL six piston calipers, it's the tool for the job.

works with the normal MC and oem rear brakes also.

DO it once , do it right ;-)

 

[ralphmusic]

Are the ones above actually available in the UK? I've tried a number of companies and AP Racing for 991 front versions of the J pattern without success.

 

[MrDemon]

It's a USA kit custom design by the company for the 987, it's the cream of 987 brakes imo.

 

[Contraband]

With doing so many changes to the car at the same time, is it not difficult to determine if the increased amount of feel is just coming from the new tyres?

 

[tcreswick]

It's definitely not just from the tyres. It's a total change in the way the car feels at the edge of grip, and of course you no longer have the problem with the inside wheel spinning.

On a wet road it means you can launch the car as aggressively as the open-diff'd car in the dry. On track it means that you're able to get on the power seconds earlier when coming out of a corner. The back end of the car just feels completely different, totally predictable and a complete hoot to drive.