AutoX, Sedan vs. Coupe
I would like to autoX my G35 6MT Sedan (assuming my wife will let me borrow HER car). I used to autoX my Neon ACR a few years back, but switched to kart racing, so I'm not an experienced autoX'er. I'm hoping for clarification from those of you that autoX either a coupe or sedan on a few points:
First, WHY??? is the sedan spec'd for DS while the coupe is in BS (SCCA national rulebook, also followed by my local region - San Francisco). To me this makes NO sense because:
1) The coupe weighs the same (actually slightly more) as the sedan.
2) They both have the same wheelbase, same (roughly) suspension geometries, same control arms and overall suspension type.
3) They have the same engine (more on this later), gearbox, gear ratios, LSD.
Ok, you coupe guys will now have to convince my WHY the coupe really is faster, and should be in BS (or the sedan not also in BS). Let's run down the list:
1) 280 vs. 260 HP - Ok, this APPEARS, based on other posts I've read to relate mainly to the differences in the exhaust from the CAT-back. It would be interesting to see a dyno torque curve comparison between a stock coupe and sedan. Based on the results from mods. (CAI, exhaust) posted here, I'm guessing that the sedan was intentionally designed to have a flatter, broader (i.e. more "driveable" as befitting a sedan) torque curve. Peak HP may also have been sacrificed to keep the exhaust a bit quieter. It seems irrelevant to STOCK class autoX anyway, since one item which IS allowed to be modified is the exhaust system from the cat back. The INTAKE cannot be modified (other than a drop-in filter replacement), under the stock class rules. The dyno numbers that members have reported with the Stillen sedan exhaust would seem to get it right up into the 280HP range, maybe even higher than an un-modified coupe.
2) Brembos - Yeah, these probably help on a race track (i.e. like the 350Z "track" configuration was designed for), but I question whether any advantage would be seen in the 1 warm-up, 1 hot-lap (maybe 100 seconds total) autoX format. Certainly Brembo brakes would help in a situation were heat build-up and fade were considerations. Again, that's not likely to be a problem in an autoX. In terms of brute stopping force, I think the standard binders are sufficiently capable - hey, it's the ABS algorithm that's doing all the hard work anyway.
3) Wheels - We're stuck here with the sedan since 18" wheels aren't a factory option. Still, any size tire or wheel WIDTH is allowed as a "stock" legal mod., as long as the diameter (and offset +/-.25) is unchanged. So, I can get 17x8" autoX only wheels, put some 245's
on, and I'm still stock legal. Yeah the coupe would be able to use a bit lower profile tires, but I doubt there'd be a noticeable time difference due to that alone.
4) Shocks/sway-bars - I'm not sure about this. Does the 6MT sedan (with sport susp.) use the same parts as the coupe? Anyway, the FRONT sway-bar is open for mods. in stock class, as are shocks.
As I see it, the ONE item that would be a HUGE benefit (and neither coupe nor 350Z have it) is a REAL LSD (i.e. not the viscous type). I read a post by someone who spent the $1k for a Kazz LSD (clutch-type) and claimed a 3 second improvement in autoX times. But
then that nice mod. would bump me out of stock class. BTW: The stock Torsen LSD that the IS300 has means it would probably kill a G35 or 330i on the track (need to go with an M3 to get LSD at all from BMW).
Finally (sorry for the length), could those of you who autoX the sedan give me some feedback as to what to do to prep. the car.
2004 G35 Sedan | Garnet Fire + Willow | 6MT | Wife's car - soon to "Stillenize"
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]). lead_foot put the Nismo LSD in his sedan, but took it out after one event because it was so awful on the road, so I wouldn't recommend that.
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