Differential Ratio....3.45 or 3.54

[tzoid]

Don't laugh at this question...it's taken me a year to find a Viper tech that'll come to my house and remove my 99 GTS diff so I can send it to Unitrax to have the gears changed. Doing it over the winter when downtime isn't critical. Which ratio is the most favored....3.45 or 3.54? Just used for pleasure type driving and to improve my mood when I need a boost...never raced except when someone wants to mess around on an open stretch of road. Does it really make a difference between these 2 choices? Jon B...your responses to questions in the past seem to qualify you as the resident expert...what's your opinion? Thanks for your thoughts...sign me "cold in Pittsburgh, wish I was in Palm Springs".

 

[Kid97GTS]

I just got my gear swap done at Unitrax last month (the invoice said 3.55, but I thought the Dana ratio was 3.54 as well). Anyway, I'm very pleased with the performance of the car. It doesn't feel anywhere near as rough as the 4.54's I have on my Chevelle, and it has much more perceived pickup with the lower gears, and still cruises nicely in 5th at 45-50, with 6th offering plenty for the freeway. Better yet, I still won't have to shift out of 4th in the 1/4. Only negative I've experienced is the increased urge to punch it to feel the increased thrust! There is a graph available on the Viper web page (maybe SoCal club page) illustrating the increased thrust of the gears below about 65 mph. Anyway, I think 3.54(5)'s are just right, with enough oomph and enough gear to cruise at high speeds.

 

[tzoid]

Thanks for the feedback....did you take the car to Unitrax or did you R&I the diff and send it there? If you did the R&I, how long did it take. Thanks again....

 

[Kid97GTS]

I dropped the car off at Unitrax and picked it up about 7 hours later.

 

[Tom Welch]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Kid97GTS:
I dropped the car off at Unitrax and picked it up about 7 hours later.

<HR></BLOCKQUOTE>

Tzoid, don't spend your money on gears unless it is one of only a few mods you intend to do. Your transmission will love you for leaving in the 3.07's. As you develope more power(which maybe you don't intend to do) you will want to gravitate back to the 3.07 to utilize the torque. Your car has more torque than hp and the torque band expires at only 4400 rpm. to shift at 5500 rpm is wasting valuable torque and TIME. These are not small block chevys, they don't need rpms to operate at their peak, so please don't confuse the two.

Just my opinion, but i run 11.40's with 3.07 gears in a viper with only exhaust! With nitrous the same car runs 10.40's at over 137 mph, and there is no way i could finish the quarter mile with any other gear but 3.07's without shifting into 5th(overdrive) which will SLOW YOU DOWN.

Don't take my word for it though, ask some of the other tuners that make mega hp. Ask Norm Kroener, HMS 650R owner, he runs 3.07 gears in the 10's and money is not an object for his choice of upgrades.

just my $.02

tom

 

[bad viper]

I had uNITRAX DO THE 3.45 FOR ME.Perfect
for drag strip applications stay in 4th. Good for
Silverstate run about 57-5800 rpm in 5th at 165 mph

 

[Paul Fischer]

I ran 3:45's in my GTS. You get out of first faster but spend more time shifting after that. I'll leave my next differential stock since the torque of the car is what I've learned to use on a road track rather than revs (had to unlearn the BMW thing). For gooseing it on the freeway I don't think there's any benefit though 6th gear is available at a pleasingly low speed.

Consider putting in a differential cooler as well if you are doing anything but light street driving.

 

[Kid97GTS]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Regretful:
I hear what Tom says about running a maximum effort 1/4. You don't want to have to shift into 5th.

How about for fun on the freeway -- racing in 4th gear from 65 mph? Seems like a 3.54 or 3.73 gear would give you much better acceleration in 4th gear until you had to shift into 5th. By that time the race is long over.

<HR></BLOCKQUOTE>

Remember that Tom is running 130+ trap speeds in the 1/4 - no wonder he'd have to shift out in a lower gear setup! If you are running trap speeds under 130, I doubt you'd have to shift out of 4th, even with 3.73's, but check the tables on the VCA tech page to be sure. Also, assuming you can hook up (which is a big assumption on street tires), I have a hard time believing that lower gear ratios will give you a worse et. You have to shift into 4th anyway with the 3.07's, so crossing the line at an rpm closer to 5000 rpm will yield a greater overall time at maximum tq/hp througout your run. It makes more sense to cross the line at your rpm sweetspot, rather than having just shifted into 4th. Of course, the equation is skewed when you are passing through the traps at 134, in which case you'll likely be at that point in 4th with stock 3.07 gears. Anyway, I'll have some empirical before/after numbers after my next trip to the drag strip

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