EVOlutionary

iTrader: (38)

Hi All,

Please vote in the Poll if you have experience racing BOTH an EVO with the VCU center diff, and the ACD unit. Please give feedback on both, specifially which you feel is better and for what reasons. Here is why I am asking for your input.

I am building a P.A.M - Project AutoCross Monster. I currently have an '04 USDM EVO with the Viscous Coupling Unit (VCU) center differential. I am trying to decide if I should switch over to a newer EVO with the Active Center Differential. I will admit that I have never driven an ACD car, but I still feel that sticking with the VCU is the best course of action. Can you help me change my mind . . . or reinforce my thougths that the VCU is best??

My reasoning that the VCU is best (for me) is thus:

• completely mechanical - it is in simplest terms a diff with the two sides connected with Silly Putty. It should react the same every time and be very linear with changing grip situations, smoothly transferring power from front to rear.
• light weight. At least lighter than the ACD and it's pump and everything else.
• I can keep my IC sprayer, which running 400hp on a stock IC I may need!
• cost - for me to buy an '05, swap all my parts, then sell my '04, I would be facing at least $5000 expenditure just to gain an ACD.

Benefits of an ACD -

• possible reprogramming of unit - if anyone figures out how to make it better
• ALUMINUM ROOF - will cost $$$$ to swap an aluminum roof onto a VCU equipped car

So can anyone tell me from an engineering standpoint if/why the ACD would yield faster lap times, specifically in autocross situations, or even in general?? It must, otherwise for world spec EVO's Mitsu would not have abandoned the VCU and switched to the ACD, right??

Currently my car is set up to power oversteer in sweepers under accelleration, and everything seems to work well. I have trouble sometimes with spinning the inside front tire (even with a Quaife front LSD). Don't know if any of that matters, but I thought I would throw it out there just in case.

Thanks for any input you can give!!

EVOlutionary

Jeff_Jeske

iTrader: (66)

I have an 03 with FLSD. The ralliart unit made a HUGE difference but it still doesn't handle as nice as the ACD cars I have driven. I was under the impression that ACD really didn't do much but after driving one it definately controls the delivery of power to the wheels better than straight LSD front and rear. Also, go test drive a stock 9 once. Hands down its the best spooling and handling evo of the bunch. I had the pleasure of driving one and a medium speed track with tons of tight corners......after driving the stock 9 (less alignment and race pads) I didn't even want to get back into my highly modded EVO.

I'm not sure if all of that can be attributed to ACD or if other improvements such as suspension and weight reduction do more than we suspect but the 9 is a much better car than my 2003 on a low to medium speed course.

kekek

iTrader: (22)

Honestly....I don't think it's worth it. Your suspension setup and frt and rr diffs is going to dictate the balance of your car more than the ACD, IMO. A few weeks ago we had the chance to drive 3 different evos back to back, here is a quick results summary.

BSP 2003 Evo 8 w/RS frt diff and Tein RA's = very balanced and handles very well
SM 2005 Evo8 w/revalved JIC's = handles like crap and won't turn irregardless of ACD or not
SM 2006 Evo9 w/Vishnu Ohlins = handled quite well despite extremely poor alignment, did not feel as balanced as the 03

Time results, 05 was slowest, 03 was 2nd by about 1/2 sec and 06 was quickest all of the cars are pretty well prepped and were contenders at the Pro and Devens tour. I personally would have know the cars actually had ACD if nobody told me, it was simply transparent in my eyes. The Sti however has an almost intrusive system with the DCCD.

money pit

iTrader: (4)

well i know where you can find a really nice 05 RS, right here in michigan. that is, should you plan to go that route.

me, haha.

Jeff_Jeske

iTrader: (66)

I would hope the same thing. It should be noted that my 03 has a moon roof and stock suspension. I'm sure the new 9s Al roof and lower stiffer suspension helps more than the ACD.

dohcvtec

iTrader: (5)

Not all 9's have the aluminum roof, just the RS and MR.

SRT-TO-EVO

iTrader: (12)

And SE's.

SRT-TO-EVO

iTrader: (12)

Read this thread, this should answer what you want to know about the ACD, and why it's better.

https://www.evolutionm.net/forums/sh...ht=acd+answers

EVOlutionary

iTrader: (38)

I read it and added to it. Thanks.

Anyone else car to chime in with racing experience on both units? Thanks guys for all the info so far!!

EVOlutionary