S/C SRT-10 Owners - Rear Axle Preference/Experience

[ViperInBlack]

I would like to hear from current S/C (in their SRT-10) owners and which rear axle they are running and what went into their decision-making.

There are essentially three popular rear axel options with an S/C SRT-10
a. 3.07 factory
b. 3.55
c. 3.73

Three opinions are often disputed:

1. If you supercharge, your best bet is 3.07. Go deeper and you transfer power too quickly during hard acceleration on the streets

2. That is not accurate, and many use 3.55 with their S/C and feel that the power is transferred in a more predictable fashion

3. 3.55 is fine but not if you track the S/C car

(4. A fourth opinion comes from my personal mechanic. He prefers, and installs, 3.73 and S/C but admits it can be a handful.)


Am wondering about those who have 3.55 and S/C, their experiences, how often they track the car (or is it completely street use)?

Much appreciated,


Alice & The Viper Blog

 

[TedK]

I understand that 3.30 is also available........possibly a good middle-of-the-road approach.

 

[BigCarrot]

I went with 3.33's which are a bit harder to find. I think they're perfect. Makes up for the 19" wheels and then a little. Unitrax runs across them from time to time.

 

[onerareviper]

Believe it or not, I found my GTS easier to control with 3.73's vs. 3.07. Given, my whip is 'only' 430 RWHP, but I think my experience could correlate to a higher HP car/SRT10. Here's my take - When I had the 3.73's, and the Viper's tail stepped out, I eased off the gas and it straightened out immediately. With the 3.07's, this is not the case. I have to be much more cautious when letting the rear end get loose, because it takes longer for the car to respond - 'hook'/'straighten'. That being said, the rear tires did brake traction quicker with 3.73's, but it was very controllable and could be prevented with throtle input and clutch modulation. So in conclusion, with a steeper gear the tires will break loose earlier, but I find it easier to control/correct the car when it happens.

 

[GR8_ASP]

So Alice, since your mechanic prefers the 3.73 and Paxton combination one wonders how many he couldd have possibly installed. I mean how many supercharged SRT's are there in the Atlanta area?

Also, unless your mechanic has had substantial seat time with each option his opinion would be second hand.

And not to forget that tire choice is not independent with respect to gear ratio. Going with 18's is nearly a .3 ratio impact.

 

[BigCarrot]

Alice, in most cars 3.73 would be great! That's just not the case with Vipers. I don't know if it's the gearing in the tranny or what, but I don't think you'd be happy with them at all.

 

[ARMORGOD]

Like the combination in my car. Power is a bit excessive from a standing launch. On the highway (at cruising speed) it is very responsive and reasonable and they (blower and 3.55's) make a great combination. Have not tracked the car since doing the blower, but will some time this summer.

 

[ViperInBlack]

I doubt that my mechanic has done more than 3-5 such installations. There would unlikely be much of a market for S/C Vipers in Atlanta...although you would not get much wheel hop sitting in the parking lot that they call I-285.

Crockett's compromise of 3.33 makes a great deal of sense, and it is interesting to here that re-gaining control is easier on the 3.55 vs. 3.07. Admittedly, the 3.07 is a nod to the EPA people in the first place.

Alice & The Viper Blog

 

[Art 138]

DLM suggested I leave the 3.07s for street use when I recently got my SC upgrade.

 

[DSR207]

Quote:
DLM suggested I leave the 3.07s for street use when I recently got my SC upgrade.

Great advice...Unless you're getting sticky tires to go with the 3.55s. This might help
web page web page

 

[MAVERICK]

If you look at Mike's links above and do the math, a stock SRT rear-wheel torque in first gear is:

450 ft-lb x 2.66 First gear ratio x 3.07 rear end gear = 3670 ft-lb

So, if you swap in a 3.55 rear differential gear, peak torque at the rear wheels in first gear is now:

450 ft-lb x 2.66 x 3.55 = 4249 ft-lb

This is a 16% increase in rear wheel torque without touching the motor. That's the same as keeping the stock gear and modifying the engine to increase its torque output to 598 ft-lb (Take away 13% for driveline losses and you get 520 ft-lb).

520 ft-lb x 2.66 x 3.07 also = 4249 ft-lb

You will gain 16% more "pull" in every gear with a 3.55 gear swap. One of the best "bangs for the buck" you can do to your Viper.

With a S/C and 3.55 gears there are traction limitations, and if you can't get the increased power to the rear wheels then you're spinning your wheels while slower cars are moving ahead of you. The solution that I found is to run sticky enough tires for the gears. I replaced the stock Michelins which were breaking loose in 1st/2nd with Kumho V700s and now they really hook.

Another point with the S/C 3.55 and sticky tires is that you can race and beat most cars on the road without even going to boost since you have so much power to begin with.

IF you need to engage the boost you can do it in 3rd gear and the car will literally explode forward .... and whoever is next to you will just give up because they know that you have something pretty powerful under the hood.

 

[SRTRICKY]

If you look at Mike's links above and do the math, a stock SRT rear-wheel torque in first gear is:

450 ft-lb x 2.66 First gear ratio x 3.07 rear end gear = 3670 ft-lb

So, if you swap in a 3.55 rear differential gear, peak torque at the rear wheels in first gear is now:

450 ft-lb x 2.66 x 3.55 = 4249 ft-lb

This is a 16% increase in rear wheel torque without touching the motor. That's the same as keeping the stock gear and modifying the engine to increase its torque output to 598 ft-lb (Take away 13% for driveline losses and you get 520 ft-lb).

520 ft-lb x 2.66 x 3.07 also = 4249 ft-lb

You will gain 16% more "pull" in every gear with a 3.55 gear swap. One of the best "bangs for the buck" you can do to your Viper.

With a S/C and 3.55 gears there are traction limitations, and if you can't get the increased power to the rear wheels then you're spinning your wheels while slower cars are moving ahead of you. The solution that I found is to run sticky enough tires for the gears. I replaced the stock Michelins which were breaking loose in 1st/2nd with Kumho V700s and now they really hook.

Another point with the S/C 3.55 and sticky tires is that you can race and beat most cars on the road without even going to boost since you have so much power to begin with.

IF you need to engage the boost you can do it in 3rd gear and the car will literally explode forward .... and whoever is next to you will just give up because they know that you have something pretty powerful under the hood.

Thats some very useful information....Only thing I'd be worried about is what people are talking about in other threads about the hydralock situation.

Off topic...beside your Viper I see you have a Ferrari 360...looks AMAZING..is it yours? Props on the bad ass rides!

 

[Viper X]

Hi Hemotox,

My car is at Unitrax as I write this with a blown hyrdaloc and broken 3.55's. I'm replacing them with 3.07s and should have the car back for the weekend. I'll post again after driving the car with the new taller diff. I liked the 3.55's, but eventually added taller tires for a reduction in overall gearing and more traction. If I decide to keep the 3.07s, I'll probably put shorter tires on the rear to put the gear ratio up a bit numerically.

My feeling right now is that if I could get something in the 3.33 range, this is what I'd go for with the S/C. 3.55s were great with headers / intake and tuning, but a bit low for the S/C. Unitrax will have something in the 3.33 range available in the fall. They'll be five cut, polished and hardened. As Dan Cragin said in another post, and this has happened to me several times, it seems some of the 3.55's available are going through the hardening on the ring gears, metal through the hydralock and boom, big trouble.

Good luck,

Dan

 

[Paul Hawker]

3:55's make the car more throttle responsive with or without supercharger. For driving rapidly in street conditions it is a very sweet package. The down side, is that with the more rapid boost gain, the car can easily overpower the available traction with stock run flats.
The stock gear allows the engine to work efficiently, and really puts the power down more controllably. This gear really works well on road tracks, and makes shifting less frantic. This gear is also strong and quiet.
It boils down to kind of a fun factor. The 3:55's are a blast. Really get your attention, and require significant concentration. The 3:07's, while putting down the power, do not have the same fun factor. The boost comes on slower, and the car may actually be quicker, but there is something about lighting up the tires with just throttle that brings out the little boy on a tobaggan in us.

No way would I put a 3:73 in a blown snake. Don't think the engine would have a chance to do the work it is designed to. Go throught the gears so fast, it would be almost impossible to control the torque. Probably feel like driving on very slippery street.

 

[MaxedGTS]

DLM suggested I leave the 3.07s for street use when I recently got my SC upgrade.

DlM told me the same thing a long time ago. He said to wait till i get used to the power then maybe change the gear.
Max

 

[ViperInBlack]

We got a bit off-track from the original question.

1. I already drive a 3.55 equipped car
2. I was actually asking whether those SRT-10 owners with S/C and 3.55 were comfortable with that decision.

 

[BigCarrot]

Alice, since you already have them, I'd just leave it like it is. If you don't like it, move down a notch. It's not super expensive.

 

[onerareviper]

To build on what Carrot said:

1.) Try the 3.55.

2.) If you don't like them, trade someone the entire diff. that wants 3.55. You will make money on the deal, and swapping the units will take a pro only a couple hours or the backyard mechanic an afternoon.

 

[Janni]

Thank you Paul, ViperX, MAVERICK, ARMORGOD, & ViperSRT for your experiences and educated opinions. I'll consider all you've said and let you know what I decide.
Hemotox

I must have missed that response while I was reading the scolding of others to stay out of this discussion and to stay on topic.

 

[ViperInBlack]

Crockett:

Excellent point. (BTW: I already own an unused 3.07 ring and pinion) If I find the 3.55 not to my liking once/if S/C is installed, then I can simply switch back, and it is true, this is not an expensive undertaking. Unfortunately, my mechanic is not a "drop off on the way to work" location so it takes some planning.

It is an interesting observation that with 3.55 control is regained more easily. In a non-S/C car, the 3.07 in this City was not a good experience.

Again, thanks for the input.

 

[Shelby3]

Everyone but Alice:

I had 3:73's in my GTS with 700 RWHP and it was not a good thing. Too much shifting and too little traction. Now have stock 3:07's and love them. Would never do the gear thing with a blower again. Gears are much better suited to NA cars.

 

[ARMORGOD]

With all of this blower/gearing discussion I think that there are two important points to keep in mind:

#1 Moving to 3.55s (or any gear in that range) will allow you centrifigal blower to come on to boost quicker than a stock 3.07 geared car. Sure the car will be harder to handle down low, because it will be so much more responsive. But if the driver modulates the throttle and rolls it on, instead of stabbing the pedal to the floor, it is a very workable set-up. Bottom line - any centri. blown Viper will get into it's boost quicker with 3.55s. Say the Roe unit was available - I wouldn't do that particular blower along with gears - way too much punch down low. But I think the 3.55s can bring a lot to the Paxton. A stickier alternative to the stock tires would make it even mo-betta.

#2 When swapping gears it's always a give and take. My decision with the 3.55s factored in the effect it would have on all driving conditions. The give is that the car can be a hand full down low. But the take is getting 6th gear back as a useable gear. This is true even on a blown car. Cruising down the highway, with the engine spinning at around 1500 rpm, the Paxton blower isn't giving you much extra power at all. And on a 3.07 car, 6th gear is a joke. With the 3.55s I can truely use 6th on any 70-75mph freeway.

Just throwing that out there as my .02 for any new owners that may be considering one, or both, of those mods.

 

[VIPER D]

Hey Alice


I have about 700 rwhp with 308 gears until I got rid of those run craps, I could not hookup in 1st or 2nd gear, it would even spin the low end of 3rd gear. Since I got the bfg's and 18 inch rims only now can I use 2nd gear. How on earth can anyone with 373 gears,700 rwhp and run craps hook the car in 1st or 2nd is mind blowing.


I think that if you keep those horrable tires and get the blower then at the very least go with carrots sug. and go with 333's. But that might be pushing it.

The only way I can say use the current 355's is if you change the rims and tires to bfg drag radials


good luck, my future my s/c sister


vd..

 

[Kelly06]

Best repeat topic I ever read

 

[Viper X]

After driving with 3.55s / Paxton for over 3,000 miles I just went back to the 3.07's. After only 300 miles on the 3.07s, I'm having my Quaife geared at 3.07. Needless to say, this would be my recommendation to you. You'll probably like the 3.55's for a few months and then get tired of trying to make them work.

If you keep the 3.55s(or anyone here with 3.55's / Paxton) and want some traction, I have a set of Nitto drag radials that have two runs on them and about 60 total miles. These are the 305x45R18s. They are 28.8 inches tall and will really make the 3.55's work well on the street or at the drags. They reduce your overall gear ratio to about 3.37 which is very effective with this setup. They fit on 18 x 10 or 18 x 11 inch rims - which you'll need to buy.

Let me know if anyone is interested. I'm going to keep the 3.07's, so I'll be picking up a set of Nittos in the 305x35ZR18. These are 26.42 inches tall, shorter than the stock 27.4 inch Pilot Sports.

Good luck,

Dan

 

[Skip White]

You have a handfull with the 3.55's in a modded car. but it really is something we need. As we increase our skills, and stickier tires become available, this is a good gear. I really think the 3.33 is all around best, on an average. This subject has come up so many times. If this were a drag racing fourum, for cars at the track, it's an easy subject, but on the street, there are many factors, such as, tire size and grip, passanger in car, heavy occupants, road surface quality, mods on car, DRIVING SKILL, etc. There is no question the car is geared a bit tall in it's oem form. But if you can't shift the car fast enough and at the right rpm, the oem geared car will in fact pass you up. One more thing few have thought of, if you have been having good luck with those short runs involving first and topping out in second, you may find your self running out of rpm, and having to go to third, and that is a very slow gear to shift into. Now you have to extend the race to make up for the huge loss in time going to third. This is the first thing I noticed when going to the 3.55

Skip White

 

[VIPER D]

Ben just came back from the track and proved my point! He has 355 and ranout out gear towards the finish line. Also he just couldd not make traction even with wide drag radials.

take a look

http://vca2.viperclub.org/forums/showflat.php?Cat=&Board=UBB21&Number=531638&page=0&view=collapsed&sb=5&o=&fpart=1

vd..