NCLA951

Otto Mechanic

I did try reducing tire pressure in the rear 2psi to 32psi front, 30psi rear in an attempt to increase the rear contact patch. The road was dry today and I took it out again for a drive down Hwy 9 in CA from the Waterman Gap to the north into Boulder Creek to the south, then back again. I was lucky to have the road nearly to myself, with only a white WRX behind me but not close, just playing catchup mostly. The drive back was blocked by a lead car and I wasn't able to get much of a feel for the suspension.

The car did very well but it did feel a little loose in the rear at high speeds/rpm (torque) a couple of times. It didn't break loose on me at all. With the WRX behind, I was driving aggressively. To be perfectly honest, it felt a lot better and I had a great time with it.

I'll check the manufacture date on the tires and report back. I know they've been idle on the car for the three years I've owned it.

As far as suspension changes go, the answer is almost everything, but I also don't have any experience with the old setup since the clutch was pretty much gone when I bought the car and I didn't drive it. It has the new front and rear bars, new Koni sport struts and dampers, delrin bar bushings and poly bushings elsewhere. I've added a ZF LSD also, along with semi solid engine and transmission mounts (SuperMounts). I have a set of solid trailing arm bushings for the rear that weren't installed so I'm pretty sure those are factory original rubber (I'm sure they're rubber, not certain their factory original).

I've put both the front and rear struts/dampers in the middle of their range.

The car was just aligned by a shop I've used for decades in Campbell CA for my 928, but since the last time I was there the place has changed ownership. I wasn't too impressed with them the last trip in, they complained about the new Rennbay front ball joints and made a few uninformed comments on them. The front camber is set -1.5, all other settings are supposed to be factory spec but I have no way to verify that.

I'll check the tire dates as suggested and report back. Thanks for all the suggestions, lots of good ones here!

Regards,

Otto Mechanic

I don't. I had the alignment set to neutral factory specs, they did say they went with a mild -1.5 front camber. I can't be certain no mistakes were made though and after a couple of odd comments on the Rennbay ball joints in front my confidence dropped a little.

Otto Mechanic

Another possibility is I've developed bad habits on the accelerator. I tend to "stab" the pedal on exit, I suppose that comes from driving an automatic 928, which has very smooth acceleration no mater what gear you're in. I've broken the rear end loose with it before, but that was on a wet road. I usually work the tiptronic manually, but once I'm out of second all the shifting gets done by the transmission. Since there's a switch on the throttle that downshifts if possible when the pedal is on the floor, my usual habit is to hammer it down to the floor to force a downshift on exit.

It could be I'm just hitting the pedal too hard and need to work on smoothly applying it instead of flooring it coming out of the apex.

jderimig

How does it feel at turn-in? If its pushing a little at turn-in but you still have O/S at the apex with power then it sounds like it might be just bad tires (to me anyways). If its not pushing too bad at turn then I would try going the other way with tire pressure. Make the fronts softer to increase the slip angle up there. At least that's what I have been told.+

Edit: Apples-Oranges comparison but I am running 18mm rear bars with 23.5 front on my 84 stock springs and yellow Koni's with 215-60's and car is very fast through turns. But I don't have the power you do.....

Otto Mechanic

Otto Mechanic

It feels like it wants to turn in, as if it's amplifying a small motion of the wheel, almost like the wheel is turning in my hands on its own. "Slippery" might describe it. It doesn't happen just driving normally (i.e. within the yellow sign advisories on turns), only when I'm driving it aggressively.

Otto Mechanic

I suppose I should also mention I've de-powered the steering on the car. I did the full treatment on it, removing the internal piston in the rack and locking the hydraulic spools (the "T" bar). Steering is heavy when the car is sanding still and heavier than it used to be even rolling, but the feel is much better, I get every bump in the road.

Scott at Team Harco

Actually that is week number 3 of calendar year 2013. Age may be a factor. These are also street tires; and unless you plan to use them on the track, are not what you should be tuning to. Were it me, I would soften the rear bar and mess with tire pressures until you dial-out the oversteer. More air in the rear and/or less in front until you get it closer to where you want it.

Then when you get serious and get a good set of tires - you'll need to go through the whole process again, but at least you'll have some data to help, directionally.

Smooth application of throttle, brake and steering are all important. If you are stabbing the throttle, that's not so good.

Otto Mechanic

Thanks Scott. No, I didn't intend to run them on the track, they're just the tires that were on the car. I haven't started investigating a good track tire yet. I'm starting in beginner level HPDE next season and need to find the right tires. Honestly, before this conversation I hadn't appreciated the contribution the tires make and you've all convinced me I'll need to start there.

There's no doubt I'm stabbing the throttle, I'll also need to work on that. I think in the short term I'll also soften the rear bar.

I really appreciate the advice from you folks. This is my first intentional track build, up until now I've just been an avid recreational driver. The car is already teaching me, and that's really great. I came back home last night and told my wife I'd found a new love. Thankfully, she was happy about that

Scott at Team Harco

All serious (vehicle dynamic) tuning begins with the tires. That, and the nut behind the wheel...

Otto Mechanic

What sort of nut are you folks using?

thomasmryan

if your spring plate bushings are still original, you should really swap them out.

Scott at Team Harco

Instruction + training + practice + competition = experience.

Otto Mechanic

You're talking about the rear spring plates? I don't think I got into those. I have a set of solid Elephant rear spring plate bushings but they got missed during the re-build. I decided I'd leave them until I did a coil over rear kit installation, maybe next season.