J-Rho's '67 Camaro Z28 STX build Jason Rhoades builds a 1967 Camaro Z28 clone for SCCA STX autocross

17Feb/150

370z first runs in STR

Ran a local practice on the west lot of San Diego's main autocross venue, Qualcomm stadium. First the video:

Overall it was a good day. As a driver there was a tremendous amount of rust to shake off, plus the challenge of basically a brand new car with a whole new setup, and not having driven on this (deteriorated asphalt) surface hardly at all in years. Dropped a second from run 1 -> 2, then stayed pretty flat time-wise for the next 6 or so runs, but finally broke through on the last couple with another 1.5 seconds. There weren't any other top prep cars in the group to compare to, but had there been, suspect I'd have been about 1 second off the pace. The video is of my last run, which still had lots of big misses, but starts to show what the car can do.

How did the mods work?
Oil Cooler: Indicated temps were in the mid 90's throughout the session (yay San Diego "winters"!) but the oil temp stayed in check. I took 9 runs all about 10 minutes apart. Leaving with temp around 180, would come back in with it around 220, but it'd be back to 180-ish by the time the next run started. Kept the car idling with hood open and fans on between runs. By the end of the session it was only dropping to 190-ish before the next run, but still not really going over 220.

Wheels/tires: No rubbing, and grip was acceptable. Overall I was running too high of pressures for the surface, and kept having to lower and lower. Think I ended up at 36F, 32R, and still wasn't getting the tire to roll all the way over. Some of that is the low grip asphalt, may need to go with higher pressures on grippier surfaces.

Suspension/handing: Surprisingly the initial handling balance was quite good. I didn't adjust shocks or bars or anything all day, to give myself a chance to learn the car's behavior, and find base tire pressures. What I found in the later runs where time was dropping, was that I had to be making inputs very early - early braking, early turn-in, early turn-out. Despite the much more racy spring rates and dampers, the soft-sidewall'd tires underneath it all still don't provide the response of a good DOT R-tire. These tires require a much more gentle ramp-up to their limits to keep from shooting over. The mid-corner balance seems good, and exit is good, but there's a little push on entry, and I'm not thrilled with the way the car feels in transitions - but haven't put my finger on root cause yet. Might try softening front bump damping a little.

For the Z crowd, this is my initial setup:
FRONT
1100lb. springs
Custom Koni 30 series at 8/13 clicks of bump (13 = full stiff) and 1.5/2.5 turns of rebound (2.5 = full stiff)
Hotchkis non-adjustable front swaybar
Approx -4 degrees camber, zero toe
36 psi on 255/35-18 Hankook RS3v2 on 18x9 wheel

REAR
650lb. springs (stock location, not coilover)
Custom Koni 30 series at 3/13 clicks of bump (13 = full stiff) and 3/9 "sweeps" of rebound (9 = full stiff)
Hotchkis adjustable rear swaybar on full soft
Approx -2 degrees camber, zero toe
32 psi on 255/35-18 Hankook RS3v2 on 18x9 wheel

Shock damping curves were provided in an earlier post.

Engine/Power Car ran strong. Still haven't had it dyno tuned yet, based on others' experiences there's a lot on the table in a tune. Gearing is a lot shorter, acceleration is lively enough to be entertaining. Exhaust gets pretty loud at high RPM and throttle openings, car blew 92.0db on the best run past the meter. If it's cold/foggy out for other SD events, may have a problem with sound. Should be fine elsewhere though.

One place where the tune interacts with the handling is in the realm of lift-throttle behavior. Whether it's for emissions or a byproduct of Nissan's VVEL (throttle butterflies are almost always wide open) - or both - the car hesitates to cut power when you lift the throttle suddenly. It's maybe only a half second or so, but the delay is there, and at the pace things happen in an autocross run, it could be contributing to some of what I'm not liking about how the car enters transitions. For a left-foot-braker it may not be as noticeable, but for right-foot-only me, there may be room to increase handling consistency by having engine braking more closely follow pedal position.

Quaife diff - no problems with inside wheelspin here. Based on the handling and power-on/off characteristics of the car, I'm happy with the choice. Haven't really done much in the way of diff mods before, and it was interesting to feel how it changed the behavior of the car - on course and on the street.

Seat/Interior The seat held me in great, and the position is nice and low which I like. There is one problem however - it's hard to see out! Between the wide base of the driver's side A-pillar, and the big side view mirror tucked right next to it, it is very difficult to see cones approaching from the left where the radius dictates a speed of 30-40mph. Above that speed you can see them coming through the windshield, and below you can see them out the side. In the video you'll see me lean forward and move around trying to find the cones in a couple left-handers. I also tend to miss those left-hand apexes the most. Had this problem with the stock seat too so I don't think it's a height thing, so much as where I sit fore/aft. I tend to sit further back than most people my height, may have to try sitting a bunch closer... or just get used to it.

Next event will probably be the SD Tour in about a month...should have it tuned and aligned by then, but it was "close enough" probably won't change much beyond maybe that slight shock tweak.

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