A few days ago i had my '86 Trans Am towed to the shop because of really bad grinding in the rearend. Well the shop called me today and told me the news. My rearend is messed up really bad (ring & and pinion, gears, axle, posi ect.) I just had him build up the rearend with top of the line parts including and Eaton posi with 3.73 gears. I had 2.77 gears before. What kind of changes am i looking at besides a decrease in milage and top end? Here's a little background on the car from before:


1986 Trans Am WS6
-2.77 Posi/limited slip (broken posi)
-Fresh 350 TPI with a 268* comp cam
-21lb fuel injectors
-K&N filter (in stock air box)
-Custom chip
-magnaflow muffler w/ high flo cat.

With these mods i only put down 180 RWHP and 290 FTLBS TQ would i be looking at more horse power but less of course up high? I really dont know a lot about rearends. Was the 3.73 a good choice? Im waiting to go pick up the car either today or tomorrow.

 

I forgot to mention i have a stock 700R4 tranny.

 

I'm honestly not trying to flame, but if you only put down 180/290 something is either wrong or out of tune with your L98.

My LB9 put down 212/314 almost stock. I lost that sheet, but I still have some that read ~202/312 laying around somewhere.

Have you had it tuned?

 

umm your sig says 285 hp at the crank down to 180 at the wheels??? that doesnt make sense to me. Anyways your going to notice that its real easy to break the back end loose when accelerating from a stop and turning so be careful with that. Past that it is what it is. I dont really like the 3.73's in my 1990 350 i find that it just spools up way too fast. just my opinion though

 

Well actually the motor isn't an L98. I also had the sig made before i actually dino'd the car. I asked my uncle what he though it had and he said about that at the crank. I also have a sliping 700R4 that doesn't help. The motor the guy put in said its a 300HP motor but said that its not getting what it should because of my tranny and the computer chip i recently had done. Plus i dont know if its also because of the rearend being messed up that took some power away?

 

Your car will FEEL a whole lot faster like night and day seriously. 3.73 gears are good for the 1/4 with a low reving engine and small stock sized tires. 5000rpm = ~103 mph.

I also agree you must have some serious tuning issues to sort out. Look what my LO3 put down on stock heads (in sig).

You must get headers. I doubt it will change the rwhp and tq numbers much at all.

 

Most people find 3.42 gears to be a better overall choice than 3.73s. It will give you better mileage on the highway and won't require 2500 rpm at 65 mph.

But around town I doubt you will notice much difference, mileage-wise. The 700r4 comes to the rescue with its overdrive, as long as you are not doing much more than 35 mph or so.

I find that going from 2.73s to 3.42s has actually gotten me better mileage in town! Especially since the 700r4 was rebuilt a month ago. Would you believe a change from 15.5 mpg to over 19 mpg? Freaked me out, too!

Even when it was all bone stock it never got more than 18 mpg. Now I've doubled the hp and gain more than a mile per gallon!