I don't think so at all. Having driven both on track many, many times, I prefer the VCD on small courses with lots of transitions (e.g. autocross). I find it distracting to have the electronics locking and unlocking the diff during such busy driving. It feels much more natural on a road course where the elements unfold slower.


Handling is the name of the game for autocross -- and to that end weight. I'd be curious to see the weight difference between the ACD and VCD units. My understanding is that the ACD weighs quite a lot more. Most people don't realize that 04->05 the RS gained an aluminum roof, but got significantly heavier with ACD and extra side impact reinforcement.

d

 

When thinking about what coilovers to run what you want to look for is a set where the rebound and/or compression dampning adjustments work well. That is, the adjustments actually work, are evenly spaced, and move you in the correct direction! If you haven't read it yet, go read Dennis Grant's thoughts on shocks.
http://farnorthracing.com/autocross_secrets.html
Pick one from his list of favorites (Ohlins or Penske or Koni I believe) or give JRZ a call. AMS has switched to JRZ from Ohlins on thier TA car and has been really impressed. Unless you plan on doing all the work (testing and R+D) yourself you want a company who you can tell exactly what you want and they will get the valving pretty close. Tein I'm sure doesn't have a clue what makes a good autocross suspension.

I am running Ohlins double adjustable piggy back rezzie shocks with custom valving and spring rates. The rates are pretty high, but not the highest I've ever seen. That's about all I can say on that topic.

As for diffs, the VCU is absolutely smoother. Problem is it can not transfer as much torque as the ACD. If you have a high amount of traction difference front to rear and enough power to spin the tires, you will get more wheelspin with the VCU (generally). Theoretically you could set the ACD to be fully engaged all the time so that the front and rear are locked (like with a spool). Then you would have zero wheelspin unless you had enough torque to spin all 4 tires, or to overpower the gripping ability of the ADC clutch pack (whichever comes first).

In my opinion, the HOT setup for next year (don't think anyone has it this year) will be the GSC 40:60 center diff along with either the VCU or ACD. The VCU route will be alot less expensive, as I think with the ACD you will need to get the Motec MDC ACD controller to optimize it's performance with the 40:60 center diff.

I don't know anyone with a Cusco front diff, but I suspect it would work better than a Quaife IF you have trouble with inside tires getting light and spinning.

For the rear either a Cusco or KAAZ or TRE rear diff should be an improvement. The rebuilt stock rear that Jon at TRE does is great and very reasonable. Improves lock up on acceleration by around 30-40%.

EVOlutionary

 

Are you saying that the doors from an '03 or '04 are lighter than the doors from an '06??? If so, I know my next mod! Anyone want "safer" doors??

EVOlutionary

 

There is an entire hydraulic assembly sitting about the same distance forward as the oil cooler, which is the inner workings of the ACD. I haven't weighed it, but it doesn't look very light.

-Jon

 

The 40:60 should come alive on a BSP Evo9 or any SM car. With lower power levels it's torque split isn't readily apparent (like in an '03 BSP car). The rear diff will make a more pronounced difference on throttle than the center.

I would fully agree that a Cusco front/GSC Center would kick ***. I couldn't afford both so only tested out the GSC center. Once I started really pushing the car on high grip surfaces and the low stroke (droop) travel of the Tein Super Racing I got lots of inside wheelspin (even in slaloms!), so the Cusco front should help, it's just damn $$$$$$.

Edit: Forgot to mention my diff setup is OEM frt Helical LSD/GSC 40:60 center/OEM rear

 

I've been very pleased w/ the RS LSD in my '03--big difference & much better IMO, especially coming out of tighter manuevers...

BTW, I've exceeded the goal in dropping weight. We did the final corner-weight & the car weighed 2989 empty with 3/8 tank and sunroof intact--I was looking for 3k# even--yessssss

 

First off I was unaware you could change the center diff in the SP classes. Shows how much I've studied those rules!

If you are getting that much inside front wheelspin with the 40:60 center diff sending the majority of the torque to the rear tires, something doesn't sound right. Are you running a soft rear sway bar?? Softer rear springs? Maybe TOO stiff in the front transferring too much weight off the inside front??

One other thing to think about -- maybe your VCU is shot?? On a stock center diff that would cause alot of front spin, but since you have the GSC I don't think that would be the case. Just trying to brainstorm ideas for you . . .

Interested in selling or trading the GSC?

EVOlutionary

 

Any diff is fair game in an SP car.

I don't have any of those setup issues. I am quite sure it has alot to do with lack of droop travel in the front struts. Mark and I had "similar" setups in the beginning of the year and he never had any problems with inside wheelspin to my knowledge. He also does not think it is a "big" problem, but when you're driving the car anything that delays forward momentum on corner exit feels like it's taking light years.

The VCU is fine. All 4 wheels spin on launch so I know it isn't having trouble there.

The GSC won't be coming out of the car as it's waaayyyy toooo much work. I never said it doesn't help either . There are situations on the throttle, particularly in transitions, where the rear moves around more and allows you to stay in the throttle and just turn the wheel.

Good Luck with Mark at Nationals, he's been tough to catch lately.

John

 

You may want to talk with Jon at TRE about getting the rear diff reworked. It's only about $400. I know changing the rear to fix a front wheel spin problem sounds backwards, but that is exactly what I found with my car. Even on pump gas at ~320whp and 290tq we were having a little bit of front wheel spin earlier this year. Now with ALOT more torque and the new rear diff it seems to actually be better.

You're going to Topeka too, right? Good luck with Aaron Miller and Tom Berry. They're fast!

 

i wouldnt have tien do the valving, there is a guy that builds race evo's locally who is entering evo's in speed world touring and world challenge and he knows his stuff. he runs in grand-am, daytona, currently running srt-4's in the speed series and has been building race cars for quite a while. he suggested that I go with tiens as thats what he does on all of his race cars w/ suspension under the $6k mark.

the diff thing is interesting i might have to look into one.

car weighed 3070 last time it was on the scale, since then i have cleaned up a lot of stuff in the engine bay, removed some brackets, took out the radiator fan, replaced illegal metal undertray w/ plastic, taken off the wing and am about to put on the AMS diff braces. that should get me down toward the 3000 mark, i want it to be under 3000 by nationals

anyone know is there noise restrictions at nationals??

can anyone help me tidy up a low altitude race gas map? coming from 7000 feet makes a difference

 

I don't think so. If there are, it's nothing you'd have to worry about.

 

sweet thanks, i usually run a turn down right after the downpipe, that is cool under sm rules right??

btw evolutionary, thanks for the amazing article i spent an hour last night reading up on that stuff and there is some great info

 

Exhaust has to exit behind the driver or to the side of the vehicle. I don't think a turndown after the downpipe would be legal unless you are sitting in the engine bay.

 

Wow! Has this issue gotten any better... or are you simply driving around it?

 

It's not a huge issue, but does come out every now and then. Typically it results from crappy driving on high grip asphalt. Changing the way I enter the slalom usually helps (Thanks Tony Crea!).