Brake conversion GT to ACR

[MoparJohn]

Question to the group.

I have been looking through the forums for several hours and have not found my answer yet.
I have a 2015 GT that I track heavily and I am working on acquiring ACR parts before they are all gone and next on my list is the ACR brake with iron rotors conversion. There are several threads that talk about it and how do it, but they all leave out some information on the rear brakes. How different is the ACR rear brake with iron rotors? I know I need new rear knuckles to mount the ACR rear caliper, but I am wondering what the piston size difference and rotor size difference is between the GT and ACR model. If I were to just upgrade the fronts to the ACR brakes how unstable would the car be?

[Lawineer]

I dont know the answer to your specific question, but you could always play around with pad compound and/or proportioning valves.

I'm not sure how it's adjusted now, but given that the front and rear are the same size calipers/pads, I assume there's something going on because my rears dont lock up way before my fronts.

[Hawk]

I’m really pleased with my TA brakes with Hawk racing pads. Lots of stopping power and they don’t get overheated for my track use. The only down side is lots of brake dust, I also went with braided front brake lines also helped. These guys are great with brake parts and pads
https://porterfield-brakes.com/
Viper George has the TA brakes and upgraded the them in this thread
https://driveviper.com/forums/thread...-Racing-Brakes

[Hawk]

Have you also upgraded the sway bars? It makes a difference on the track
ViperAlignment.jpg

[MoparJohn]

Have you also upgraded the sway bars? It makes a difference on the track
ViperAlignment.jpg

I have. Right now my car has TA aero and sway bars, ACR canards and rear diffuser all of it OEM. I have an OEM wing and splitter sitting in crates. Penske shocks, Arrow H&C kit all waiting to go on. Just deciding the brake part before I embark on this build.

[pokeyl]

OK, the big difference is the rear rotors are 4mm in-board, making you change the rear knuckles. I put the 390mm CCM on the front and stayed stock in the rear. So far no problems at low speed, hard braking, autocross. Hope to get to a track in the next 2 months. Or you can put a 4mm spacer behind the rotor and push the rear tires out 4mm.

[pony23]

I put the ACR brakes on my GTS. You don’t need to touch the rears unless you are going carbon. If you run the steel rotors you pretty much just need the rotors from Girodisc, 6 piston calipers, and a few more little parts. I did a write up with all of the part numbers needed to do it.
The rear knuckle on the ACR has a slightly larger diameter rotor so it’s not a wheel spacer needed, the rear caliper needs to move out and the mounting tabs on the knuckle are physically longer. You could have material welded on to the rear knuckle to move it out a small bit but it’s not worth the price or work if you are staying with the steel rotors.

https://driveviper.com/forums/thread...ht=steel+brake

[Lawineer]

I assume we also need a larger front wheel?

[Ritroman]

Racing Brake (RB) in California, does make a steel kit conversion for the Gen 5 to ACR brakes. They use their own two-part steel rotors. They claim to have solved the brake bias front to rear with the conversion using their own RB-manufactured rear calipers. I think they use 380 steel rotors up front and the rear rotors are 360. I am looking at using the ACR 6 piston calipers up front and leaving the rear caliper stock and going with larger steel rotors up front. Many Viper owners have used Girodisc rotors. Also, I am told the RB steel rotors are good and are sold as a kit, and will fit without issues.

Racing Brake also makes a Carbon brake setup that uses its own manufactured long carbon fiber rotors. The RB rotors are made in China and are much less expensive than Brembo rotors, but my research indicates the rotors are not suitable for the street because the RB carbon rotors have a rough surface and are noisy and eat up brake pads and transfer pad material to the rotors and look bad. I spoke with several users of RB carbon rotors and got this feedback. Users I spoke to complained about excessive noise from the RB carbon rotors. They also complained about the looks of the RB Carbon rotors once brake material transfers to the rotors. I was told by one race driver that the RB brakes do work well but are not preferred for street use because of noise. He races at Pikes peek.

I looked into buying Brembo carbon rotors for the ACR. The first problem is that the rotors were not available anywhere. Talking to Brembo directly did not help. Bremb will not sell stock ACR CCB rotors to the public directly. Brembo does not support the stock CCB rotors. They sell only to Dodge and Dodge has them on backorder forever. I was told by a Brembo sales rep that the Corvette C7 CCB rotors are the same rotor but with a Viper 6 stud hat. Corvette rotors are available but you would have to make your own center hat but no dimensional specs are available from Brembo. Steel rotors are really the only practical option for those who want bigger brakes on their Viper.

[steve911]

There is always the SRT version of the Stoptech 355mm 6 piston ft brakes along with the 4 piston (larger dia) rear caliper and the 2 pc rotors that came with the kit.

I have 2 of the kits on my cars and they work great! I happen to use Hawk pads as the Stoptech ones that came with the kit didn't work so well in my opinion.

[white out]

It is not cheap, but Brembo GT-S front BBK and rear GT rotors would be a good option.

[Lawineer]

I assume we also need a larger front wheel?

anyone know what the min wheel size is?

[pokeyl]

A few forged 18" wheels fit, very tight! Go 19 inch to be safe.

[MoparJohn]

A few forged 18" wheels fit, very tight! Go 19 inch to be safe.

I wish I could, but there are too few options for racing slicks at 19". The only option you get is the Hoosier R7 or A7

[pokeyl]

Forgeline has 18" that fit.

[Pappy]

Forgeline has 18" that fit.

So does Finspeed. That is what I run. 12X18 and 13X18
Here you go - try these.

Yokahama Slicks.png

[ViperPete]

I wish I could, but there are too few options for racing slicks at 19". The only option you get is the Hoosier R7 or A7

I love my Hoosier A7's on my stock 18/19 wheels

[Lawineer]

OEM wont fit, I assume?

[No hemi]

OEM wont fit, I assume?

Nope , they wont.( reason why I haven't done it to mine yet.)

[MoparJohn]

Nope , they wont.( reason why I haven't done it to mine yet.)

All the parts are now on order including new rear knuckles that are back in stock so if anyone is thinking about this change they should do it now before the knuckles are discontinued like every other viper part

[Lawineer]

Ugh, I want the big brakes but I don't feel like getting all new wheels and tires
Well, I guess I could get new wheels and keep OEM tires and forgeline 18s, but it's probably cheaper to get signature wheels in a bigger diameter and new tires

[No hemi]

Ugh, I want the big brakes but I don't feel like getting all new wheels and tires
Well, I guess I could get new wheels and keep OEM tires and forgeline 18s, but it's probably cheaper to get signature wheels in a bigger diameter and new tires

I want to do It and i,ve been thinking of getting a set of 19/19, and a pair of 18's w beadlocks matching the fronts for the drag days, and the big brakes for the road course and " just looking cool" days , but it gets expensive quick and my oem wheels have brand new michelins .

[Arizona Vipers]

A few forged 18" wheels fit, very tight! Go 19 inch to be safe.

They "fit", but you will get massive scoring on the fronts from rocks until the caliper shaves itself down.

[Arizona Vipers]

Question to the group.

I have been looking through the forums for several hours and have not found my answer yet.
I have a 2015 GT that I track heavily and I am working on acquiring ACR parts before they are all gone and next on my list is the ACR brake with iron rotors conversion. There are several threads that talk about it and how do it, but they all leave out some information on the rear brakes. How different is the ACR rear brake with iron rotors? I know I need new rear knuckles to mount the ACR rear caliper, but I am wondering what the piston size difference and rotor size difference is between the GT and ACR model. If I were to just upgrade the fronts to the ACR brakes how unstable would the car be?

Why would you do this conversion and not do the CCB rotors? They save nearly over 70 lbs. That's unsprung, reciprocating mass. Huge performance gains everywhere, braking, accelerating, cornering.

[Lawineer]

Why would you do this conversion and not do the CCB rotors? They save nearly over 70 lbs. That's unsprung, reciprocating mass. Huge performance gains everywhere, braking, accelerating, cornering.

Fun token consumption.