Gen IV ACR suspension on a Gen III

[Barrels]

I have an 03 with bolt-ons (480rwhp and 506rwtq). I am happy with the suspension, but the track use it sees and the 32k on the odometer makes me think an upgrade would help the car and keep me safer. I am considering a switch to a set of ACR takeoffs and want to know what to expect. I know it will help and the adjustability alone is a huge upgrade, but what specific advantages can I expect to feel on a road course? Will I be making a sacrifice in street drivability?

Everyone's educated opinion is appreciated, but I really hope to hear from those who have made the switch.

 

[steve911]

I am pretty close to what you are looking for. I have an '06 coupe that I added motons with ACR spec(rate) springs, comp coupe sway bars (OE style not the blade ones) and 1st gen comp coupe splitter and ACR rear wing. An aggressive street front end alignment is also a must. I also adjusted the ride height in between the smooth track and rough track specs in the ACR manual.

Other than the car riding a little harsher due the higher rate springs, the handling is fabulous. I put most of my miles on the street and even my wife has not complained about the ride. She has complained about my driving though, as I am able to take corners even faster than before and that scares the heck out of her at times.

Steve A.

 

[SoCal Rebell]

If I am not mistaking I believe the suspension geometry is completely different on the Gen IV from the Gen III.

 

[hou99gts]

IMO, the springs will be way too stiff unless you plan on adding the ACR aero bits, especially in the rear. You would probably want to consider a different spring rate otherwise. The ACR street ride is already stiff at full soft settings.

 

[AbsolutHank]

Don't do it!! It's gonna be way too stiff for anything unless tracking the car.

I bought a set of takeoffs for my stock 06 coupe, and it rode like pure hell...I'm pretty sure the bleeding has just stopped. I was also running 800 lb springs in the rear instead of the stock 1100 lbs. Also, do you have any idea how to set up suspensions? 3-way adjudgements are cool to have, but kind of overwhelming once on the car. I ran everything at full soft, which is what the ACR supplemental manual says to do on the street...still too stiff.

I recommend the KW Variant 2s for the street...Motons are the best but considerably more cash. I'll save you some more time...JonB has the best price - call him

 

[Barrels]

Thanks guys. I was considering the takeoffs because of the $2,500 price, but I can get V2's from Jon for $3,200. What would be the difference between V2's and V3's with the V2 springrates? It seems like I would get the same basic thing but with more adjustability.

 

[AbsolutHank]

That's the same reason I considered them too...

It was explained to me that the shock is valved differently as well in the ACR-spec'd KW3's....so for another $250, you could get much lower spring rates which are similiar to the KW2s, but then the shock isn't "matched" up the same as it should be. That's all the info I can provide...hopefully some other members can give you some more help!

 

[JonB]

V2s have just a bit stiffer spring rates than OE, but waaaay less pre-load.
G4 ACR Take-Offs moved to a G3, as noted by helpful folks above, are valved for and would require AERO downforce, and designed to ride on stiff ACR-like sidewalls, with light wheels. Otherwise you will 'skitter' on rough roads and be scary on washboardy roads.


Goldilocks version: V2 will be "Just Right" and can be 'set and forget' shocks on your G3. Whereas with 3-wasy, you might want a logbook and make changes as venues change.

NOTE: V2s CAN have stiffer spring options if you do add aero, or have aero at the start.

 

[Barrels]

So i'd be $2500 plus $250ish to get to have a V3 with the right springrate, but the shocks wouldn't work right with my car. It sounds like V2 is the way to go. That stinks because I was really looking forward to learning how to set up an adjustable suspension. Maybe when I buy a ACR in a few years...

I talked myself in to spending $2,500 but that extra $700 has pushed it out of my range. I will do it one day, just not today. You'll be my first call when I decide to do it Jon. Thanks for the help.

 

[Barrels]

And thanks to Hank too. A testimony from someone who had tried this out was exactly what I was looking for. I don't know if that is your real name but I named my 2-month old Hank. It's not his official name because the wife was not on board, but that's what I call him anyway.

 

[AbsolutHank]

And thanks to Hank too. A testimony from someone who had tried this out was exactly what I was looking for. I don't know if that is your real name but I named my 2-month old Hank. It's not his official name because the wife was not on board, but that's what I call him anyway.

No problem! I hate to see you not end up with anything, but I understand...they're almost an extra 30%!

And no, my name is actually Ryan...Hank is my old college nickname, and Absolut is my old college drink! I've been using the same screename for years, so I continue to use it

 

[Viper X]

Opinions will vary greatly on this, just like what's a loud exhaust and what's acceptable.

Here's my .02 cents after over 100,000 miles in 4 Vipers (about 30K on the track) with OE suspensions, Motons Club Sports, Moton Motorsports and OE ACR KW's.

The ACR OE KW shocks are adjustable over a very wide range. The other KW Variants, not so much.

You can easily change the spring rates on the ACR OE shocks, like Motons. Other "set and forget" type shocks are OK for the street but are really too soft and can be dangerous on a race track. Several of our local club members have tried them and upgraded for track use.

"but what specific advantages can I expect to feel on a road course?"

You will be able to control your car much better and can adjust for different tracks or even different track conditions at the same track. With a good alignment and set up, body "roll" will be much less and more controlled. Hard braking will be much more predictable and controlled. You will be much more comfortable in high speed turns and will run faster lap times, safer. Tire wear will also be improved. You can adjust for "understeer" and run larger tires up front if you'd like, etc.

You can also add "aero" later if you decide you want to improve you track experience.


Will I be making a sacrifice in street drivability?

Yes. It's a trade off. However, if you are mechanical, you can easily change back to "street" springs and "street" shock settings.

Once you get accustomed to better shocks and spring rates, you will have trouble going back to the "over sprung" and "under dampened" OE set up on the Gen III cars.

And, the Gen III and Gen IV shocks ARE interchangeable. Geometry is the same.

Good luck,

Dan

 

[Barrels]

Opinions will vary greatly on this, just like what's a loud exhaust and what's acceptable.

Here's my .02 cents after over 100,000 miles in 4 Vipers (about 30K on the track) with OE suspensions, Motons Club Sports, Moton Motorsports and OE ACR KW's.

The ACR OE KW shocks are adjustable over a very wide range. The other KW Variants, not so much.

You can easily change the spring rates on the ACR OE shocks, like Motons. Other "set and forget" type shocks are OK for the street but are really too soft and can be dangerous on a race track. Several of our local club members have tried them and upgraded for track use.

"but what specific advantages can I expect to feel on a road course?"

You will be able to control your car much better and can adjust for different tracks or even different track conditions at the same track. With a good alignment and set up, body "roll" will be much less and more controlled. Hard braking will be much more predictable and controlled. You will be much more comfortable in high speed turns and will run faster lap times, safer. Tire wear will also be improved. You can adjust for "understeer" and run larger tires up front if you'd like, etc.

You can also add "aero" later if you decide you want to improve you track experience.


Will I be making a sacrifice in street drivability?

Yes. It's a trade off. However, if you are mechanical, you can easily change back to "street" springs and "street" shock settings.

Once you get accustomed to better shocks and spring rates, you will have trouble going back to the "over sprung" and "under dampened" OE set up on the Gen III cars.

And, the Gen III and Gen IV shocks ARE interchangeable. Geometry is the same.

Good luck,

Dan

See...this is what I was thinking all along. I doubt I would switch back and forth between springs, so I would pick a stiff but streetable springrate and adjust the shocks for the track. However, since I am not going to add aero and the shocks are set up for it, I would think that I would only be able to use the softest 1/2 of the adjustability. This makes me think i could end up sharing Hank's unhappy experience.

I guess I'm still on the fence. Where could I find different springs if I do choose the ACR setup? And what springrates would be a good balance?

 

[AbsolutHank]

Hyperco or Eibach have springs for coilovers...I'm assuming you are getting the take-offs from DC Performance? Speak to Dan...I'm sure he has an account with one or the other, and could get your hooked up.

 

[Viper X]

A friend and now our local club president bought a set of 800 lb rear springs from me for his 09 ACR just prior to VOI 11 in SLC.

I don't sell springs but just happened to have a set that I bought and never used.

He drove the car to SLC from LA and according to him, the ride was very similar to a stock car.

Good luck,

Dan

PS Springs are 60 mm ID

 

[Nine Ball]

I just received one of those $2500 sets of ACR KW's from DC. He said it should still ride better than my current Eibach springs, which are kinda horrible. He recommended giving the setup a try first, then if I want to later I can always get softer springs. Any improvement over my Eibachs would be welcome here. Once I get them installed (likely this weekend) I'll do a nice write-up on comparing them to the Eibach springs.

Tony

 

[Nine Ball]

Oh yeah, what are the spring rates for the OEM ACR? What rates are recommended for street ride quality?

 

[Viper X]

OE springs are metric, 90 N/mm front, 190 N/mm rear.

OE ACR spring rates are about 514 front, 1085 rear in inch / pounds.

As above, 800 lb rears ride pretty well with the 514 lb fronts.

Nice thing with these is that you can adjust springs rates to you liking by swapping them out to lighter or heavier rates.

 

[Nine Ball]

Found a spring rate conversion calculator. http://www.hraefn.net/projects/spring_rates.php

OEM ACR
Front 90 N/mm = 514 lb-f/in
Rear 190 N/mm = 1085 lb-f/in

800 lb-f/in = 140 N/mm (this is recommended for rears, street duty)

Good info. I'm surprised the front doesn't require a change too?

Anyone know the non-ACR Gen 3/4 spring rates?