ACR E rearend gearing

[allan88]

I have a 2016 Viper ACR-E which i primarily use on the track. I would like to change my rear gear from the stock 3,55 to something like 4,10 (20% lower).
Is it possible to buy a complete differential unit to easily replace it, when running on small track. and if yes, where?

[steve911]

The first question that comes to mind is WHY? 1st gear will become unusable (practically speaking), Loss of top end speed and constant shifting... Bad Idea in my book. even the real pro race cars do not use that low of a gear.

[Scott_in_fl]

How small a track are we talking here?

[ViperGeorge]

Are you talking drag racing or road racing? If the later I would also say a 4:10 is a bad idea.

[Jack B]

You would have To shift to 5th at approx 120 mph

[allan88]

Thanks for the input.
We drive on 2 relatively small tracks here in Denmark, used mostly for road racing where the top speed down the long side side of the track hits about 120 mph
This is a charity race that we drive 6-7 times a year.
At present, we only drive in 2nd and 3rd gears but we want to move the gear to 4th gear with a rearend change.
My question is: Would it possible to buy a complete differential unit to easily replace the differential? Or is it possible to buy the gears only?

[13COBRA]

Thanks for the input.
We drive on 2 relatively small tracks here in Denmark, used mostly for road racing where the top speed down the long side side of the track hits about 120 mph
This is a charity race that we drive 6-7 times a year.
At present, we only drive in 2nd and 3rd gears but we want to move the gear to 4th gear with a rearend change.
My question is: Would it possible to buy a complete differential unit to easily replace the differential? Or is it possible to buy the gears only?

I don't think you can buy just a rear diff with 4.10s installed. You can buy gears though.

[Racingswh]

Best thing to do is measure speed in gear in corner and see what your proposed change is going to do. Many times by going to a shorter final drive and requiring a shift to a higher gear you are actually making the overall ratio taller not shorter so it has the completely opposite effect than what is desired. Let's do some speed in gear comparison and see what I mean.

I am going to use the 26.8" tall tire I run for this example.

At 6400 RPM with the 3.55's it goes

91 MPH in 2nd

121 MPH in 3rd

144 MPH in 4th

You say you use 2nd and 3rd now. If you move to a 4.10 your car will accelerate SLOWER off the corner in 3rd as compared to how it comes off now in 2nd with the 3.55's. Same with 4th and the 4.10's compared to 3rd with the 3.55's.
Speed in gear is HIGHER in 3rd with the 4.10's as compared to 2nd with the 3.55's and not by a small amount.

The 4.10's look like this

79 MPH in 2nd

105 MPH in 3rd

125 MPH in 4th

Here's the caveat though. If you find yourself rarely over 100 MPH most of the time and don't mind twisting the thing up tight then a move to the 4.10's will be advantageous since 3rd gear WILL PULL HARDER than 3rd gear with the 3.55's of course AND you eliminate the 2-3 3-2 shift which is worth something. For your tracks if you see this as that you wouldn't have to ever shift to second, which with the 4.10's would be traction challenged anyway, and you're going to roll the slower corners in 3rd and let the torque do it's job then 4.10's will work well. If you are always in 2nd now and rarely in 3rd except for short bursts up to 120 mph then your car will be faster if you leave it alone.

[GTSilver]

Thanks for the input.
We drive on 2 relatively small tracks here in Denmark, used mostly for road racing where the top speed down the long side side of the track hits about 120 mph
This is a charity race that we drive 6-7 times a year.
At present, we only drive in 2nd and 3rd gears but we want to move the gear to 4th gear with a rearend change.
My question is: Would it possible to buy a complete differential unit to easily replace the differential? Or is it possible to buy the gears only?

You can buy an OEM complete differential and install 4.10 gears in it. Whoever you are getting the 4.10 gears most likely can get you an OEM differential. I did that for a corvette a couple of years back due to running short and long tracks. I got it through RPM Transimissions and they have gears for the viper as well. Give them a call and I'm they can help you with what you need.
http://rpmtransmissions.com/page14.html

[Jack B]

Thanks for the input.
We drive on 2 relatively small tracks here in Denmark, used mostly for road racing where the top speed down the long side side of the track hits about 120 mph
This is a charity race that we drive 6-7 times a year.
At present, we only drive in 2nd and 3rd gears but we want to move the gear to 4th gear with a rearend change.
My question is: Would it possible to buy a complete differential unit to easily replace the differential? Or is it possible to buy the gears only?

You can easily put together a complete internal diff, however, the complete housing has to be dropped to install the new diff guts. This should be a lift only project. Call Unitrax, they are an excellent source for viper diff parts.

As I said earlier you will be close to the limiter at 120 mph in 4th gear. The 3.73 gear set might be better.
Tire size/diameter will be critical if you go to the 4.11.

[Scot@Prefix]

We can provide you a complete rear axle with just about any gear ratio you want.

We have done a lot of first gear changes to 2.66 on the gen 5 vipers as well.

[nwa_viper]

My car had a 3.91 r&p when I bought it. Great for smaller tracks with top speeds under 127mph (rev limiter in 4th). It started howling and I went back to the 3.55. I will compare lap times as soon as the temps warm up.

[steve911]

Does anyone make a 4.10 Viper Spec R&P? Not the vette styled ones with the smaller dia. Pinion Gear.

[ForTehNguyen]

4.10 is what 4 banger engines use due to lack of torque