FatfreeGTO

I'm going to be ordering a new rear end for my car and I'm curious about engine longevity gas mileage etc with the gear ratio selection. I currently have 3.23s

I have a LY6 and a 4l80e 27" tall tire, going to order a Strange S60 rearend

3.54 rear gears put me at 2550 rpm at 75mph

3.73 gears put me at 2700 rpm at 75mph

I don't have a stall yet but somewhere down the line I will have around a 3000-3200 stall.

My TQ peak was 4600 rpm which is 3.54/105mph and 3.73/96mph.
HP peak was 5300 rpm 3.54/120mph 3.73/114mph
And my stock cam has me limited to 6000 rpm max for now

So basically I know the rpm difference is pretty minimal and probably won't matter either way but I'm wondering which route people think I should go? Not sure if spinning this engine for extended periods is bad at 2700 rpm or not.

V8Rumble

iTrader: (9)

Just personal opinion here, but I'd lean toward sticking with the taller gears (3.23, etc.). With the way that gas prices have been climbing lately, you might be sacrificing a tenth or two in the quarter - but being able to drive your car more than once a month would make up for it! (I've all but settled on 3.90 gears for when I can afford my 9" Ford, but I have the T-56...) I don't think that the 3.54 gearset would be different enough for you to notice much (if any) change, & I personally wouldn't want to spin my engine to near-3000 just to go down the highway...

Stu Cool

iTrader: (13)

How are you calculating the RPM? Using this calculator:
http://www.csgnetwork.com/multirpmcalc.html

I get 2437 rpm for 3.73 with a 27 inch tire and a .7 final drive ratio

Pat

BLK95-Z

iTrader: (2)

If it stays cool 2700 rpm isnt going to hurt it. I drive a couple hundred miles a week all expressway with a stalled 4l60e/373 geared ls1, my cruising rpm is about the same.

FatfreeGTO

The fuel issue is something to think about but this car is mostly just a weekend car anyways so I'm not too worried about it. Also the S60 rears tallest ratio is 3.54, but your right I probably won't notice a big difference between the current 3.23 and 3.54.

The 80e has a OD ratio of .78 so that is the difference. I was using the http://www.f-body.org/gears/ calc but that is a neat one you posted. I like how accurate it is down to the single rpm.

I haven't had a single problem yet with overheating but I also haven't gotten very much time behind the wheel to be absolutely sure. Does your 98 feel like its buzzy at that rpm or are you comfortable?

BLK95-Z

iTrader: (2)

By buzzy do you mean loud? It does have a definite drone to it but Im running a dumped bullet off the y-pipe so its pretty loud anyway. If Im going to burn all that gas I want people to know my car has some *****

Im totally confortable cruising in a loud car at a higher rpm but that may just be me. I dont know how it would be with full exhaust.

If its just a toy/weekend car Id set it up for how you want it. Unless you plan on going on the power tour i wouldnt worry to much about fuel milage. Chances are itll still be decent anyway.

gMAG

iTrader: (1)

I tried the calculator, but it didn't show what the final drive gear ratio was for a 5-speed?? As a result, it's showing 300 rpm different (higher) than the actual (mine-2050) @ 70mph.
There's nothing wrong with spinning the engine @ 2700 rpm's, but it will be more fatiguing, louder, and gas consuming.
Gas could be $6 or $7 in the future.

Stu Cool

iTrader: (13)

There are two calculators on that page. In the bottom one you can specify the actual final drive ratio.

gMAG

iTrader: (1)

Thanks, Pat. I see it now.

FatfreeGTO

I think I'm just going to order the 3.73's, thanks guys!

tta656

iTrader: (5)

im not understanding,your going 3.73 but want lower rpm while cruising..i would try and do 3.08,pretty sure that was the gear a buddy went with in V6 GN and didnt loose alot of proformance

FatfreeGTO

My main concern was I wanted to know if the 2700 rpm while on the freeway was going to be bad on the engine. The tallest gear I can get with the rear end I'm ordering is 3.54.

I found out the vehicle my engine came from would have had 3.73 and a 30" tall tire resulting in 2450 rpm @75mph. So that isn't all that much lower then where I will be at.