AUSSIROC

iTrader: (1)

I currently have 2.77s and barely get out of 2nd down the strip. I am considering either 3.45's or 3.73's for the BW 9bolt. Where can i find a formula to work out the best rear end ratio so i can pull 5500-6000 thru the traps in third gear with stock-ratio 700r4, stock converter, and stock height wheels and tyres??

Thanks in advance for the help!

Also, if i can sort this out, what kind of et/mph can i expect factoring in that my present best with 2.77s is 14.19 at 95ish mph???

AlkyIROC

For the 9 bolt, you better see what ratio you can find first. 3.70 fas a factory replacement ratio. Anything else around that or deeper is aftermarket and there isn't much available if any.

You'll also need to replace the carrier (posi). The 2.77 is a 2 series. 3.27, 3.45, 3.70 need a 3 series. Good luck finding a new one or a used one that's not worn out.

Sonix

iTrader: (1)

https://webdisk.ucalgary.ca/~jmknopp...eed%20calc.xls

Right click, save-as. It's an excel file. That's my personal favorite RPM/gear/speedo calculator, because I made it.

89gta383

iTrader: (5)

With my 3.73's, 700r4 and 9-bolt, I turn about 5400-5500 thru the traps on motor and 64-6500 on the bottle. You would need 4.10's to go thru any higher. I shift at 6500 from 1-2 and 6-6200 from 2-3.

1320_Guy

iTrader: (3)

Gears arent the only thing you need to know, dont forget about tire size and converter slippage.

Orr89RocZ

iTrader: (20)

if your lucky i have seen some 3.90s floating around for 9 bolts. that could work well for yah

AUSSIROC

iTrader: (1)

Thanks, i'll check it out!


Thanks everyone else, appreciate it. The best thing about having a BW diff is that parts are readily available. Cool sounds like the 3.73s sound good.

Cheers!

Orr89RocZ

iTrader: (20)

i guess parts would be available in australia since its an aussie rear! haha hope it all works out well for yah

AUSSIROC

iTrader: (1)

Yeah Thanks! Its good for that!

What approx times can i expect with 3.73s if i currently run 14.2's at 93-95ish??

atc3434

iTrader: (4)

Are 3.73's really the right gear for a TPI motor. Perhaps I'm not farmiliar with your setup, but judging from your times, you've got a pretty typical TPI motor, a monster on the bottom (good ET's) with no top-end (slower MPH). My experience with my own L98 motor was that it was pretty well out of steam by about 4800-5000rpm, I can't imagine bothering to pull to 5500rpm. I think you'd find a 3.45-3.55 rear end would be about the best for stock intake style TPI. Some of the aftermarket designs pull beyond 5000rpm ok, but stock, I would refrain from going to crazy with the gears. Now converter with 3.45's and stickie tires would be a nice improvement in ET.

flaming-ford

iTrader: (7)

that was my thoughts also for what it's worth

i planned to go 3.43s in my 10 bolt and my mildly modded tpi setup.

Orr89RocZ

iTrader: (20)

i wouldnt think 3.73's would be best for TPI intakes as like said above, they are out of steam by 4500+rpms. modded runners/base may have power to go near 5000 but thats about it.

what is your setup to need to pull thru 6K in the top end? thats pretty high rpm, unless you have a cam/intake setup that is making power to that rpm i dont think its a good thing for your motor. But sounds like your mostly stock by your times so far.

AUSSIROC

iTrader: (1)

I have considered the slightly lower gears (3.42's). A lot of people seem to think they are the better choice. I might match them up to a mini-spool and have some fun!
I like revvin'! thats all! :Lol: However, with stock cam, intake and heads i just want the best ET improvement with whatever gears would match the best. Although the motor would prob prefer only revvin' to 5k (less strain).
I wanna see consistent 13's. I believe they should come with a gear change..
Gonna happen?

Thanks!

Orr89RocZ

iTrader: (20)

could happen with gears ona good weather day and good traction.

i think 3.42's would be a better match on street tires or sticky tires up to 26 inches tall.

AUSSIROC

iTrader: (1)

Yeah, i would hope to gain at least 2 10ths with gears. The gear change should up the rwtq by a good amount (torque multiplication).

Orr89RocZ

iTrader: (20)

i think i did almost .15 from 3.27's to 3.42's. thats not as big of a difference like 2.77's to 3.42's is tho

AUSSIROC

iTrader: (1)

Thanks, that gives me a good idea. 13's here we come!

Cheers!