I have a stock 5.7 TPI with minor mods, 3" exhaust, headers, ported plenum, chip, afpr. I currently have a B-W with 3.27gears. I would like more low end power, and am not decided on what gear ratio would work best. Please feel free with any suggestions on the 3.42 or 3.73? I don't care about gas mileage or top mph, just about the best performance. I have checked some calculator sites, but would like some real world experience.

 

What is your current RPM @ 70MPH in overdrive???

Although I have the T5 transmission with the original 3.42, I am at 3K at 70MPH. I absolutely hate it. If I am needing to get somewhere quick (Over 70MPH) I hate it. I don't like holding the motor at anything over 3K very long. I have been looking for another transmission (T56) so I have an extra gear. My other option is to numerically decrease my gearing.

 

Low end performance? You don't care about top speed? Go for 3.73's! That's an obvious one. Just make sure you have all of the supporting mods to back up the gears. Drag springs.. Some stickier tires. A Spohn Torque Arm, panhard bar, and beefier rear LCA's wouldn't hurt either.

 

go 3.73.
Since you say you have 3.27, going to 3.42 probably won't be too noticeable.

 

With BW 9-bolt you will not be going anywhere with the 10-bolt gear ratios mentioned . If you are lucky you may find a 3:70 or 3:73 ratio made for the BW 9-bolt. Otherwise you are SOL. 9-bolt & 10-bolt parts are NOT COMPATIBLE with each other.

 

get parts here,
http://9bolt.com/

 

3.73's are great for performance, sometimes i wonder if it's a bit overkill for the street and think of going back to a 3.43 or something but then i drive it and the rush of that fast acceleration just tells me.. "nah... **** it.. 3.73 all the way!!"

 

I currently run about 2200 rpm at 70 mph. I found JTs parts and RANDY's ring and pinion have the 3.70 and 3.73 r&p. How far should i go on rebuilding with bearings , etc. right now the rear end works great with no noise or slop.

 

Hello red rock!!

Your date with destiny will come, as with all Auburn type rear units, they wear out, and are non-rebuildable!!

Start collecting parts for that date!!

One day it was a posi, the next day it was, one wheel peel!!



For the record, 3.45's are a good all around gear ratio, slightly quicker, and give good enough gas mileage!!!

I wish that I had 3.45's, then my car would be slightly quicker, and back to normal!!

 

So when you say can't be rebuilt, what parts do you mean? Posi cones, spiders, etc. I checked out http//.9bolt.com, they seem to have parts available. Thanks Clay

 

i just went from 700r4 to T5,,,i have a 3-23 posi rear...i haven't driven it on the open road yet....how will the car do with these gears on the hi-way and on take off?...are 3-23 gears good for my car?

 

With your 350, you should have decent take-off with the T5 (if it doesn't break).
I went from 4.10's to 3.42 in my Formula and I had to get used to giving it more gas when starting from a stop. with the 4.10's I would just let up on the clutch and start to move.

 

Hello red rock!!

The Auburn type can't be rebuilt like an Eaton type can, once the carrier is shot, it's shot!!

The Auburn's cones wear the carrier out, the Eaton clutch pack doesn't!!

The Auburn rear end can be rebuilt with new parts, but the carrier will have to be replaced, whereas with the Eaton type, you just replace the clutch pack, and Shazam, your on the road again, two wheel peeling!!

 

i know that the T5 is weak and with a 350 it can break...but i don't push my car really all that much ...just wanted manual ..it seems funny to me that a V-8 powered rear wheel drive car has an automatic!!....never got that...all bmw etc etc and and all real sports cars are mostly manual....even mustangs are mostly manual ..i will be carefull....thanks.

 

Thanks for the info, I'm kind of rear end illiterate if ya now what i mean!

 

The original reason is that GM offered the same 350 TPI engines in the corvettes at the time (minus the aluminum heads and other misc. things). So as a way to not hurt sales of Corvettes they only sold the 350ci irocs with auto 700r4 (which in the later years were beefed up to withstand the power that the 350's put out.) Beleive it or not, the 700r4 when modified (or even stock for that matter) can handle a crapload of torque, whereas the T-5 was weak and a t-56 is your best bet when going with a powerful engine and stayin manual.

 

I got 3.73 gears and they are perfect with a 700r4, very hard launches but still some drivability on the freeway in overdrive. If you are autocross, or strictly stop light to stop light then get 4.11's, if you plan on a lot of freeway driving then go with 3.42's. If you do a mix of everything then 3.73's will work good for you as well.

 

ok ,,but my 3-23 i'm guessing will be good with my T5?

 

I wouldn't go anything less than 3.73, but then again I am running 4.30's lol. Look at it this way the lower the gear the better the car is going to feel. I am running a T56 and the 4.30's are a little aggressive but it feels a lot better than the 3.42's that I was running.

 

It's really all about what you want. If you are on the highway much (or like keeping up with city traffic) go with the 3.42

 

Dose anybody know the difference between BW 9-bolt 7.75 and the 10-bolt 7.5/625 gear ratios???? As I stated before he is NOT going anywhere trying too use 10-bolt parts (NOTHING IS COMPARTIBLE). Only BW 9-bolt gear ratios available are 2:77, 3:27,3:45, 3:70 and 3:73 (only those made for 9-bolt). Same for 10-bolt stock & aftermarket Limited Slip carriers, they will not work in a BW 9-bolt. .

So you can continue about your experiences with 10-bolt ratios but you are off the subject.

 

Yes you are right, and yes i now know the difference between the 9 bolt and the 10 bolt. The 9 bolt is a 3.70 gear and the 10 bolt is a 3.73. I see i can also get a 3.90 for the 9 bolt B-W. What I'm wondering now is to research this enough to do the swap myself or spend another 2-400 and have someone else do it? I tackled my 700r4 myself, I think i can handle it. But thanks for all the response and input.

 

Gear install can be tricky since you have to make sure the gears are meshing properly. Having never done them before, you might get lucky and get them in correctly and have no issues. My brother didn't have time to yank his rear off to have his friend do the gears so he did them himself and he got them shimmed right and had no problems. Our friend does them for about $150 and if you give him the rear he can get it done faster since he doesn't have to free up a lift. just slaps the rear on some jackstands and gets to work.

 

Hello mooch1!!

I have a 3.27 BW 9 bolt behind a 305 with a T5, and it does just fine!!



Go for it!!!

 

I have an 84 5.0 H.O with a 700r4 and 3.73 posi. and I love it, the launch is incredible. The question is when does your power come in? how can you best leverage that to get what you want, the 5.0's have better torque at 0-2000 rpm then a 5.7 but the 5.0 is all done at 3500rpm, your 5.7 will still be going strong long after that, the 3.42 will give you a more mild launch but will take off and keep going. you will get to take advantage of the 5.7's sweet spot mid to high rpm, the 3.73 will put you in your seat at idle to mid rpm, but your sacrificing your high rpm range. basicly the 3.73 will be more fun around town, but the 3.42 would do better in the 1/4 mile

 

I have a 5.0 TPI that makes power up to 4800 RPM (got it dynoed). I have 3.73 with a 700R4 and it rips all the way until 3rd gear and i'm at 4500 which is just below my power peak of 4800.. I make just a smidge more power / torque more than a stock 5.7 tpi..

 

3,000 rpm @ 70 mph just doesn't sound right. With 3.27s in mine @ 3k I'm turning only 1,750 @ 70. Do you know what your 5th gear ratio is. Mine is .63. I know some t-5 are as little as .83 but I think those are all v6 boxes.

 

Forgot to post my rpm and mph in 5th
I am at 2250 @ 70mph in 5th gear with 3.42 gears and an 88 WC T5.

 

I look at it this way...

With having such a low first gear on the 700r4 with my 3.08's its like launching with a th-350 with 3.73's.

If you do the "theoretical" math the rpm drop while shifting gears with 3.08 and 3.73 is only about 200-300 difference so I'm planning on keeping my 3.08's or moving to a 3.23 but wont go any lower unless I plan on getting a th-400 and it becomes a full out race car. Also the extra little gas mileage is nice on long trips.

just my

 

Hey guys im looking to build a fun street car and would like to go with big gears......does anyone have any recommendations?...........And does anyone know what i would need to make a complete set up?....any good sites?

 

i dont think there is a definitive answer to this. alot of people say the car will actually be faster with 3.42's since it will keep you in your power band longer

 

Just an update. I bought a used 9 bolt and completely rebuilt it myself after doing a lot of research and asking questions. I built it with a new 3.70 gear. It works great, I didn't lose much as far as rpm's, maybe around 200 rpm's at 70 mph. I kept my original rear so I could still drive it while i rebuilt the new one. I sent for new cone's from 9 bolt in Australia, took a couple of weeks, which was fine as I had the rear sand blasted and painted. All in all I am very happy with the new gear ratio. Also, I have less than $900 into a complete rebuilt rear with new bearings, cones, gears, seals, paint, and a TA performance cover. Plus I have my old rear that's in great shape with 45,000 on it. And with the TRANSGO shift kit, and 2400 stall B&M converter, It's hard to keep it straight when you get on it. All I need now is a good set of sreet strip tires for a good hook.

 

This topic has actually come up at a perfect time. I was getting ready to ask this same exact question,lol. I want to put a larger gear in my L98 car but was unsure of which to choose. I have the 3:42's in my TBI car but sometimes it "feels" like it's not enough gear for me. I guess 3:73's it is then...What RPM's should my TPI car turn at around 70-75 even during lock up? I don't want to go absolutely crazy with it though. I'd like a semblance of mileage lol.

 

i have 3.42 gears with a WC T5, and i run 2000 rpm at 81 mph. It just luggs on the highway but gets great mileage. 3.73 or closer to 4.00 would be alot easier to drive on the highway for me at least.

I know my t5 doesnt have the same gearing as anyones elses. my 5th gear is like a triple overdrive. i do get 21 mpg at 80mph with a cammed and carbed 350 that runs super rich with bad exhaust leaks that can do a 12s quarter mile

 

I have 3.73's and love the power i get.. Mileage, well, it's not my daily driver so I couldn't care less.. But regardless, highway mileage, with my 700R4, 305TPI is decent, costs a bit more than my cavalier did for a long 2 hour drive on the highway.. I turn about 2000rpm at 60MPH in overdrive

 

i went from 2.73 open to a 4th gen 3.42 posi it made a huge difference my speedo is way off so i dont know how fast im going at all

 

Like i said, I'm about 200 rpm's more at 70mph.