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"

 

Coupe has wider wheels (8" vs. 7") and you can't change the wheel width in stock class. I think the coupe is also a bit lower and has slightly stiffer suspension.

 

Here's the specs I've been able to find as well as my opinion on the advertised power ratings.

G35 Sedan
Engine VQ35DE - 260HP / 260 ft/lbs torque *
Curb weight 3336lbs - 3398lbs.
Drag Coefficient - 0.027 Cd / 0.26 Cd
Wheelbase - 112.2 in.
Turning diameter - 36 feet
Ground clearance - 5.51 inches
Spring rates, Sport Suspension - 357 / 407
Sway bars - Same as 350Z

G35 Coupe
Engine VQ35DE - 280HP / 270 ft/lbs torque *
Curb weight 34316lbs - 3435lbs.
Drag Coefficient - 0.029 Cd / 0.28Cd
Wheelbase - 112.2 in.
Turning diameter - 37.4 feet
Ground clearance - 6.3 inches
Spring rates - 347 / 419
Sway bars - Same as 350Z

The 350Z, G35 Coupe and G35 Sedan Engines are identical, as are the transmissions by type and gearing.

* The advertised G35 horsepower and torque differences may be more for marketing than anything else. Especially the 6-speed cars.


DaveO

2003 G35 AT Sedan / DP / Willow / Premium / Sport
350Z Air Duct, Engine Cvr & T-Stat / Stillen CAI / Crawford Plenum
GG 10-Wire Kit / TS ECM / E-Fans
Street Edge TC / B&M Cooler / Stillen Exhaust

 

The Coupe has greater ground clearance than the sedan? whoa!

---------------------------------
http://www.anythingbox.net

 

I noticed that too. Where do they measure ground clearance? I'd like to measure my sedan with the Z suspension.

 

The coupe does handle a little better than the sedan in the twisties in stock form, and autox is more about handling than about power.

I don't even know if the sedan is competitive in DS yet.. we've got national caliber drivers in our region running in Sentra SpecV's and Integra TypeR's, and I've only been doing this for a year. I'm slowly edging closer to them though.. about three seconds back instead of my usual 5-6 seconds back last Sunday. On a side note, the IS300 last weekend didn't beat me.. but like I say, no way to tell if it was the car or the driver at this point. One of our forum members, 6speedG35sedan, runs his car (I'll let you guess which model) here in ESP. He has some intake and suspension mods and the Kaaz LSD (which I think he likes, judging by last weekend). Sometimes we get a 330i running here. None of the usual troop of WRX's ran in DS last weekend.

Considering the Coupe competes with the 350Z in BS, it's probably at a slight disadvantage there. The S2000 seems to be a great BS car, though we had an RX-8 win BS last weekend here, a 350Z 0.007 seconds behind an S2000, and a BMW M Roadster behind that -- all 4 within an 0.4 second spread. However, the thing about autocross, is that you can't make enough classes for every car to be competitive. You either run the car you have and have fun, or you buy a car based on what class you want to run in.

I'm actually thinking about buying an early '90's Miata at some point in the future instead of doing any mods to my Sedan.

 

Thanks for the response ryoken. Yeah, after autox'ing a Neon, I know all about handling vs. (no) power. That's why I'm looking forward to trying the G35 (finally some power oversteer)! I guess my conclusion is that the coupe really shouldn't be in BS, given the competition. Have you done anything (legal, of course) to your sedan? It appears from DaveO's post that the sedan (sport) has the same suspension as the coupe. In BS, competing with the S2000 or 350Z, the coupe would get killed just due to its 15" longer wheelbase! Sounds like the sedan is appropriately classed in DS, but the coupe is getting a raw deal from SCCA!!! If the coupe does handle better "in the twisties", what is the reason for that? Is it only due to suspension differences (maybe the shock valving is different)? Is there a center of gravity difference (coupe may have more clearance, but the roof line is lower)? Is there something (simple) that can be done to the sedan to make it handle like the coupe? My limited autox experience has taught me what matters (in order) are: #1-#3 - Tires, tires, and tires. #4 - driver ability, experience, #5 tie between handling and HP. Good luck ryoken! I'm sure everyone is rooting for you to thrash a BMW or two. Beating an IS300 is quite an acomplishment!

 

Gokart,

I run with Ryoken here in the local San Diego region. Right now I'm running in ESP because I have the Kuhmo Victoracers. I have also done a few mods that have been very helpful. Kaaz LSD, Stillen CAI, Eibach sways Eibach Prokit springs. I also have a Stillen exhaust tip which does nothing. I ran about 2 seconds quicker (58 sec) than the DS G35 of Ryoken in ESP class. I then went out on the X runs and ran 57!. I was still about 5 seconds behind the ESP class winner a Z28 which is totally race preped. Their raw times in class would have put then 2nd and 3rd in PAX. Not to bad.

I think I'm going to run with the Falken Azenis tires to get back into STX. I like the cars that run there better. Plus hopefully I can still run times like the 57. If so I would be in pretty good shape time wise. I think the best time in DS was like 58 so I'm close to that with the mods I have. Now all I have to do is get better at driving. I would have to say that my favorite two mods that I have done are the Kaaz LSD and the Eibach springs. The sedan stock sport suspension has a bit of body roll.

Good Luck.

Base 6MT Silver sedan
Stillen Exhaust
Stillen CAI
Eibach Pro Kit
Eibach Sway Bars
Kaaz LSD


265890-g35 #3B 2-14-04.jpg

 

Considering your #1-#3 there, I should mention that I've worn out the Turanza's that came on the car and replaced them with 225/55R17 Goodyear Eagle F1 GS-D3's. It's helped just a little bit. [img]/w3timages/icons/wink.gif[/img] Eventually I hope to scrape up some spare change for a second set of rims and some Kumho race rubber.

A lot of cars get a raw deal.. you can't place every car in a class where it'll be competitive, it's just not possible. There's a proposal in the works to move all AWD cars in STS to STX, which would place quite a few cars that are no longer competitive in STS in an even tougher class. If you want to win at autox, the G35 coupe is probably not the best car for the job.

I'm not sure what would put the coupe on a higher plane than the sedan. I thought it had a slightly tighter suspension, but I guess not. However, 225 front / 245 rear Pilot Sports probably do a lot better than 215 all-around Eagle GS-D's (not F1's).