ZR1 Spec transmission in your ACR

[THEMASH]

After watching the record breaking "Ring" video, and reading that oval run in the magazine, i was thinking if swapping in a ZR1 spec trans in your Viper/ACR would be a mod worth while.... with all that downforce, it might be a good way to get it to pull in 5th gear (keeping stock hp)...

Ratios i found online:
ACR ZR1
First Gear Ratio 1) 2.66 2.29
Second Gear Ratio 1) 1.82 1.61
Third Gear Ratio 1) 1.30 1.21
Fourth Gear Rato 1) 1.00 1.00
Fifth Gear Ratio 1) 0.74 0.81
Sixth Gear Ratio 1) 0.50 0.67

So, do you guys think this mod would be worth while ? would it make a difference that was worth it ? any trans experts out there? maybe with a rear gear swap as well .. would like to see a before and after 0-100 and 1/4mile

So, who is going to try this mod first (Woodhouse, DC performance, you guys out there...) ?
thoughts , ideas ?
(Dodge, if your reading this, might be a nice upgrade for the 09/10 model )

 

[johnk]

I bet that they both are very close after factoring the rear gears and there would be no advantage. Viper runs a 3.07 stock, what's the ZR1 use?

 

[toomanymodz]

I think a rear gear swap would be better. And speaking of downforce, that brings a question. I believe the ACR rear wing has 7 adjustments. I wonder what setting they used at the ring. I saw a separate video where they tested the new ACR at the salt flats. Best MPH of 173 I think. Body treatments clearly rob top MPH in favour of cornering abilities.

 

[Grant]

Based on the numbers SRT gave us, the ACR should still pull in 5th gear under normal circumstances, just only to 177 or so It tops out before even reaching the torque peak. A 0.80 ratio 5th could, in theory, extend its top speed to 183 or so (meaning it would pull MUCH harder in 5th). A little more power should also help a lot, letting the car pull into the higher RPM ranges where it makes more power and torque.

The big problem is that the RPMs drop down to 4600 on a 4-5 shift with the stock ratios. So I've asked Mark J. if Woodhouse could swap a 0.80 ratio 5th in my car.

For he hell of it, I used CarTest 2000 to test the difference between the stock gears and a ZR-1 gearset with 3.42 and 3.90 rear ends. The results are attached in Excel format.

CarTest is far from perfect, but if you put good data in it (especially shift times when comparing gears) it seems to be pretty accurate (IMO, YMMV).

 

[THEMASH]

Thanks for the feedback guys ...
I read somewhere that the ACR had the rear wing set to position 3 (2 stock), and front splitter was stock (not raised 6mm as shown in the viper mag) .. but cant confirm...

Grant, nice table.. That is a major difference with the .80 5th gear upgrade, and seems to be the way togo.. how much would such a mod cost ?
can you please add the ACR with 3.33 rear gears only (stock trans) ... being the cheapest alternative ... would be nice to see how it stacks up to the other #s...
Thanks in advance

 

[Grant]

how much would such a mod cost ?

No clue. I'd imagine it'd mostly be labor? As I understand it, the TR6060 isn't a whole lot different from a T-56, which tons of shops know how to work on.

The CTS-V has a 0.80 5th, and the ZR-1 has a 0.81 5th. Both cars naturally use TR6060s, so the gears seem like they should be available. There would also be an option of putting shorter gears in the diff and sticking a usable 6th in it as well.

can you please add the ACR with 3.33 rear gears only (stock trans) ... being the cheapest alternative ... would be nice to see how it stacks up to the other #s...
Thanks in advance

Attached. I also added standing half and full mile tests.

Out of all of them I think I'd rather have the shorter 5th, myself. On a stock car the 3.33s might turn out better, but add some power and I'd bet you'd welcome the longer gearing and less frequent gear changes.

 

[Kai SRT10]

I have a shorter 5th and 6th gear in my car. Even with over 600 rwhp, it makes a huge difference pulling hard past 4th gear.

Open road racing, where I was constantly shifting between 4th and 5th gear convinced me to make the switch. The gap between 4th and 5th is just too large with the stock gearing.

 

[PhoenixGTS]

I have a shorter 5th and 6th gear in my car. Even with over 600 rwhp, it makes a huge difference pulling hard past 4th gear.

Even with 200 hp less in my Gen II my .80 5th and .64 6th ratios are the slickest mod on my car.

Check this out: assuming aero limits 08 ACR to top spead of 190, and that the rear tires on the ACR are 27.2" tall, if you plug 4.10 rear end gears along with a .80 5th and .64 6th into a gearing calculator you get the following speeds @ 6,200 rpm redline:

1st: 46
2nd: 68.7
3rd: 94.1
4th: 122.3
5th: 152.9
6th: 191.2

Perfect given the aero drag of the ACR, and WOW if you could hook up think of the 0-60 time!

But for a regular GenIII.5 3.73 rear gears gets you this perfect combination:

1st: 50.6
2nd: 75.6
3rd: 103.4
4th: 134.5
5th: 168.1
6th: 210.1

The 3.73s would put you just under 5,000 rpm as you hit 6th and made a run for your terminal velocity.

 

[Grant]

1st: 50.6
2nd: 75.6
3rd: 103.4 [4276]
4th: 134.5 [4464]
5th: 168.1 [5000]
6th: 210.1 [5000]

I dunno, I'm not liking this combination too much. 1st and 2nd, especially with more-than-stock power, are probably going to be more useful when they're taller. The rest of the gears aren't any more closely spaced than stock (5->6 drops back to 5,000 just like 4->5).

The 0.80 5th is as follows:
Gear: MPH (RPM started at)
1st: 62
2nd: 90 (4276)
3rd: 126 (4464)
4th: 164 (4808)
5th: 205 (5000)
6th: 329 (3906)

I think this more or less achieves the same results while keeping the "cruise" gear, unless you need to go faster than 205 MPH? I suppose it all depends on what ratios are available. 0.81/0.67 might work out better.

 

[Lee00blacksilverGTS]

Pretty sure the wing was not adjusted for the Ring run as in the interview they ran with the driver at VOI he said all they did was tweak the adjustable suspension for that track.
As far as the 5th gear deal that was all about a major headwind the car was running into, they tried shifting to sixth and it was slower that way.

 

[Grant]

Pretty sure the wing was not adjusted for the Ring run as in the interview they ran with the driver at VOI he said all they did was tweak the adjustable suspension for that track.

Some sources seem to indicate that the wing comes in position 3, others say position 2. MT said the 'ring lap was done with it in position 3.

As far as the 5th gear deal that was all about a major headwind the car was running into, they tried shifting to sixth and it was slower that way.

At 164 mph, an '08 car should be at the top of 4th. After the shift, it should be at 4625 RPM. At the ACR's quoted top speed of 177, It'd be at only 4980 RPM. This is before the torque peak, and far below the power peak! Even without a headwind, a gear change in 5th should make a huge difference in acceleration above 165 mph.

The normal coupes have so much less drag that they can pull into the high RPM range, where their quoted top speed of 202 puts the car at 5680 RPM (which is at least close to the power peak).

 

[Kai SRT10]

Pretty sure the wing was not adjusted for the Ring run as in the interview they ran with the driver at VOI he said all they did was tweak the adjustable suspension for that track.
As far as the 5th gear deal that was all about a major headwind the car was running into, they tried shifting to sixth and it was slower that way.

I can't imagine that they ever tried shifting into 6th.

A lower 5th gear would have allowed them to run the straight in 5th gear rather than bumping along in 4th.

 

[Paul Hawker]

Just remember that a 3:73 gear is gonna be spinning like crazy on open road races. I used a 3:54 for running the 155mph class at Silver State Classic. It worked well cruising at 165 in 6th. Took a while for the engine room to respond to the throttle, but fuel consumpion was pretty good, even at those speeds the Viper was just out for a relaxin' cruise.

We were not gunning for top speed, but trying to average 155 mph over the 90 mile road course, with a standing start, and the need to slow down a bit for the narrows.

 

[RTTTTed]

Hmmm, a ZR1 transmission? Never mind the ratios, the tranny is part of the rear diff. the clutch housing has a Torque tube between the bell housing and the rear diff/trans setup. This is how the tunnel in the vette stays small ... it has NO transmission in it!

The Viper has a transmission in the tunnel and NO ancient Torque tube. The Viper is designed with the weight PERFECT as it is. The vette has the weight designed with the transmission as part of the rear differential.

They're not similar, they are not compatible. They are completely different. Since the ACR has proven the BEST, why not leave the "make it like the vette" talk for the losers? Viper is the BEST. Any vette style changes obviously would slow it down.

At Belle Isle Joe and I actually snuck in the rear tent flap and looked at the second place car in their cutaway/chopped up version. Lots of ZR1 cars there.
Ted

 

[Grant]

Hmmm, a ZR1 transmission? Never mind the ratios, the tranny is part of the rear diff. the clutch housing has a Torque tube between the bell housing and the rear diff/trans setup. This is how the tunnel in the vette stays small ... it has NO transmission in it!

The Viper has a transmission in the tunnel and NO ancient Torque tube. The Viper is designed with the weight PERFECT as it is. The vette has the weight designed with the transmission as part of the rear differential.

Assuming the ZR-1 has the same design as a C5/6, the Tremec transmission is not a normal transaxle. The diff is not an integral part (like a Porsche), its simple bolted to the end of the gearbox. The whole assembly is much longer than a normal transaxle for this reason. You could probably buy a ZR-1 trans, bolt a Viper bellhousing to it and use it.

Worst-case, if the case is different, you could probably use its gearset.

 

[RTTTTed]

I'm not able to understand why you want to take a 2nd place car and use it's transmission in the fastest car???

The ACR was designed for more than just Nurenburg, it was designed to meet emissions specs etc. If you wanted to build a car just for Nuremburg Ring it would be easier than building to ACR specs (stock Viper with slight wheel, tire, brake and aero improvements). You could add a supercharger (better than the vette one), whatever gears you wanted (not just limit it to what the vette's got), etc. Instal slicks even. Forget the vette stuff - it's not as good as the viper stuff. Maybe you could find what you want in the '09 SRT8 Challenger trans.?


Ted

 

[RTTTTed]

A friend and I were being 'bad' and snuck into the GM tent at Belle Isle. We went in the rear flap and ended up at the cutaway ZR1 car hidden in the tent. My buddy took the pics and I'm kind of ashamed to admit to having these pics .. but look ... anything you see that YOU'D want to bolt to your Viper??? Not me. Although I admit those Viper spec street tires would be OK.

You must be registered for see images

 

[mjorgensen Woodhouse]

The Vette transmission is not the same outside or inside as the 08' ACR. The gears in the ACR are integral with the 4th gear ratio so it is not as easy as swapping gears, and the shaft diameters are different so there will be machining involved. The WCGT teams cannot do this and make it work yet so I doubt anyone else id doing it yet. They can do a Gen3 trans swap out with a .8/.63 5th/6th ratio but the ACR would also need a new drive shaft to fit.

 

[Viper X]

I too have suggesting changing the 5th gear to a .80 or better and if you must, leave the damn 6th gear the same to keep the car's EPA rating (though I'd like to see it shorter as well).

If you read the recent ACR test at Auto Club Speedway in CA, you'll see where the driver ran out of 4th gear while driving and when shifting into 5th, the car didn't pull very well - we all know that.

We do the same thing here in CA at Willow Springs Raceway. Some of us hit the rev limiter in 4th gear in the front straight if you have 3.07s, race tires (shorter 18 inch tires) and a stock trans.

It sure would be nice to have a "useable" 5th gear in the ACR.

Dan

 

[Kai SRT10]

I have a .8 and .62 for 5th and 6th gear, respectively.

Some day, I'm going to change them out to a .86 and a .75

I too have suggesting changing the 5th gear to a .80 or better and if you must, leave the damn 6th gear the same to keep the car's EPA rating (though I'd like to see it shorter as well).

If you read the recent ACR test at Auto Club Speedway in CA, you'll see where the driver ran out of 4th gear while driving and when shifting into 5th, the car didn't pull very well - we all know that.

We do the same thing here in CA at Willow Springs Raceway. Some of us hit the rev limiter in 4th gear in the front straight if you have 3.07s, race tires (shorter 18 inch tires) and a stock trans.

It sure would be nice to have a "useable" 5th gear in the ACR.

Dan

 

[mjorgensen Woodhouse]

New info on the possibility of changing out the 5th and 6th gears in the 08' transmissions! If this is a mod you REALLY want to do and are serious about it we can do it to YOUR transmission. Call me if you have questions.

 

[THEMASH]

New info on the possibility of changing out the 5th and 6th gears in the 08' transmissions! If this is a mod you REALLY want to do and are serious about it we can do it to YOUR transmission. Call me if you have questions.

That is what i was waiting to hear

 

[Viper X]

Good news Mark.

Any more info?

 

[SylvanSRT]

btw top speed of new ACR's are 177 mph, the wing and splitter really limit top end vs. 203 mph for stock coupe(and vert top up)