Need Rear End Advice...got 3.42 Zelex-Torsen...will it kill mpg and the tranny?

The short version is I bought 3.73 auburn for my T/A....since the T/A is a M6 now I have a spare 3.42 Zelex-Torsen.

My Camaro has the 2.73 gear open diff in it now. If I swap in the 3.42 rear how much gas mileage will I lose? How much 1/4 mile time will I gain.

The car dyno'd 132rwhp and 220rwtq but it has 225,700 miles on the original tranny. Will the new rear add strain on the tranny and kill it?

------------------
91 RS Camaro 305TBI w/198,500 miles

99 TransAm

72 Vette

 

I went from 2.73 to 3.73 and lost at most 2mpg. I seem to be the odd man out with mpg as my actual ratings are much higher than most. I still get 22mpg city and 28-31 hwy depending on my speed.

I haven't and most likely won't 1/4 mile my car but the off the line jump is great, and if you go with 3.42-3.73 it tends to stay in the RPM sweet spot for power at WOT.

It does however add some stress as it has to turn the driveshaft 3.73 times to turn the wheels once completely (correct me if I'm wrong about the way the measure it) vs. it having to spin them 2.73 per wheel revolution. This means the motor works harder and revs up more and the tranny spins more to go the same distance.

------------------

 

My car is also one of the MPG freaks, it's best is 31.5mpg and it's gotten 28mpg+ more times than I can count. In town it's more like 24mpg I can live with losing 2-3mpg, I can't live with lossing 10mpg and getting 14mpg in town.

Thanks for the advice!

 

when i switched rear gears it didn't affect my highwya mileage at all. i went from 2.73 peg leg to 3.54 posi.
around townit was worse because i started launching from every traffic light

later
tim

------------------
91 Camaro RS-LO3,Auto
New Times Coming Soon!
Check Out The East Coast F-Body Nationals Home Page
www.geocities.com/njspeeder
My MAFB.ORG Home Page
www.mycar.net/mafb/registry/detail.cfm?id=299
DSI Racing Home Page
www.geocities.com/foff667

 

yeah i was just gonna say that...i bet the fact that you like to show off your new gears at every chance yo get will lower your mileage. i really don't have any experience to speak of as far as this goes, but i don't think it will be a huge deal.

-Brian

------------------
1991 Camaro RS - ultra blue metallic, t-tops
GMPP 350 HO crate engine - 454 TBI, MSD ignition, SLP exhaust, everything is new
700R4 - 2,400 stall converter, vette servo, shift kit
z28boy.cz28.com
Central New York F-Body Association
z28boy@twcny.rr.com AIM - "Z28 Boy"
Daily driver - <A HREF="http://members.fbody.com/z28boy/grandprix" TARGET=_blank>
1998 Pontiac Grand Prix GT</A> - 2 door, black

 

You should get better mileage in town, BUT you will probably get worse as described as you play with your newly found right foot. Less pedal is needed to drive in the city with lower gears, but most end up using more!

 

If I drive my 3.42 zexel easily. I get 26mpg on the highway with cruise set at 72. In town I can't seem to keep my foot out of it no matter how hard I try. Launch is much improved and highway driving is unaffected.

------------------
91 Camaro RS 5.0L Black Convertible 700R4
** Added so far **
*GM Wonderbar,Alston SFC's,spohn LCA's and Panhard rod
*Turbo City Inj Spacer
*Dual Snorkel Air Filter
*March Performance Pulleys
*GM 3.42 Gears with OEM Zexel POSI
*Edelbrock headers
*3" High Flow Cat
*3" Dynomax Exhaust
*Walbro 255 lph Fuel Pump
***Future 330hp Vortec Crate with LT4 hotcam and 454 TBI

 

I just got my Richmond 3.42's with the Zexel-Torsion Posi. Lost no highway mpg, town is a little less, like one mpg less. As for the performance gain, I'm still beaking them in, but it definitely feels like it has more get up and go.

------------------
89 RS parts car
Daily driver 91 RS auto LO3 70k, 14x3 K&N Open element, cat-back delete.
Coming soon: 350, headers, loudmouth exhaust.

 

Later this week we start rebuilding the front suspension, after that the rear goes in.