I was thinking of getting gears for the Borg Warnner rear, which ratio would be best and how will it effect my times? I am currently running 2.77 gears in the 9-bolt now. It is an '89 IROC 350ci TPI automatic with 62K miles on it. It has the following mods: SLP 1 3/4 headers, no cat, Hooker catback, ported plenum, gutted MAF, gutted airbox, no smog equipment, AFPR set at 47psi, MSD coil, Taylor wires, ARAP custom PROM, 180 degree stat, cool fan turn on settings, TB bypass, and K&N filters. In the future I WANT to get an Edelbrock intake and port a set of SLP runners to help the top end.

I just went to the track last Friday the 13th and ran a 14.0 at 98.87MPH with a 2.16 60ft time. The track is at about 700ft above sea level and the time is NOT corrected, the weather was nice but a little too humid. I was running on Eagle GS-C street tires. The trans was also shifting a little too high, 5500RPMs. How would a set of 3.45 or 3.70 gears affect my times?

 

Well I am sorry to say that it would be cheaper for you to go buy a 4th gen axle with disc brakes and a full set of 4th gen wheels for what you will be paying to do this. I had a 2.77 BW unit in my 86 and could never find a gear for that carrier, but I could have one custom made and fabricated for my car. LOL $$$$$$$. I looked into this so much because that gear really sucked it out of my car. It Just wouldn't give it the RPMs the Cam intake and Converter wanted. As I stated previously that is about the only thinkg you can do unless you can find another third gen unit. THough I wouldn't give up your Disc brakes just for a lower gear.
Oh but if you can find a 9 Bolt with the 3.27 gear or lower, you can find gears for that carrier.
Good luck and if you ever find where to get them from POST it on here on every board

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89 Trans Am Turbo 3.8L All stock 43,000 miles #1053 of 1555

Past Thirdgen:
86 Trans Am w/ built 355TPI with SLP goodies and too much other stuff to List. One sweet *** car, wish I would have had a good enough Job to pay insurance on three cars so I could keep it, but for a 89 Turbo Trans Am w/ Low miles, I think I made the right choice!

 

DON'T DO 3.73 WITH TPI!!!!!!

If you want 3.73's BUY MINE

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1985 IROC-Z, nuff said :P

 

why not??? explain

 

3.73 Works fine on my TPI and it is a 305. You would really haul.

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91 z-28 305 700R4
3.73 gears out back
T-Tops and Black all over.

 

where can i find 3.73s for a 9 bolt with the installation kit?

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1989 pontiac firebird
bright red exterior(just repainted)
grey interior
5 spd
305 TBI (stock)
WS.6 formula wheels
3.73 posi rear end
http://members.aol.com/j007golden/Mikey89.html
http://www.geocities.com/firebird/myfirebird.html
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1985 trans am
factory bright yellow
4 wheel disks
16 inch wheels
305 TPI
power antenna and mirrors
t tops

 

91z4me, what RPM are you running at the end of the quarter? Also, what's the RPM like at highway speeds? I've been thinking about this too, but 3.73 seems to tall for a daily driver with a 700R4.

 

I am CURRENTLY RUNNING 3.73'S!!!
I know what im talking about

and its on a 700R4

It does NOT make you "haul *** "

It makes freeways a pain in the *** , and your quarter mile times hurt unless you can rev (with power) past 5,000 and up towards 6,000. These gears are GREAT for a carb'd engine, but you're on the TPI board, you have TORQUE use 3.42's

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1985 IROC-Z, nuff said :P

 

My 3.27's are perfect. 2900 rpm @ 60mph in 3rd gear (700R4). I think its a great all-around gear. And I also hear rumors that the 9 bolt is similar in design to a Ford 9 inch in that it has bolt-in axles and a cone-type locking differential. Mine locks turning out of driveways, chirping the inner tire ands on occasions throwing it sideways.

I'm all for the BW 9 bolt.


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Mike L.
It ain't pretty.......

1987 IROC Z TPI 350 A4 3.27 Borg-Warner.

Mods: 2300-2500 Stall Converter, Shift Kit(GM parts), TPI Specialties Stage 3 PROM, Modified Airbox w/ K&N's, homemade cold air, Relocated MAT sensor, Gutted MAF, 160* thermostat, Accel 8mm Wires, bypassed TB coolant, Flowmaster 3 chamber single 3" in/out muffler, 3" MAC mandrel intermediate, custom dual !cat Y-pipe. airfoil, ported plenum. !smog

http://www.MichaelLasiuta.home.att.net

**BOYCOTT LAPEER DRAGWAY**

 

on an automatic car i would go with the 3.45's with the3.06 first gear it'll give you a better launch ratio at the end of the track with 26in. tires should put you at 4700 or so peak hp ona stock intake tpi ona manual car with a better intake i would go with 3.70's waiting a while before i swap minne again.i paid 350 for my rear seen the car it came out of too.37000 miles on an 89 iroc(yes i got the one with 11.9in. rotors)call cfs auto in paterson,nj they will either get it for you and ship it or find a salvage yard through parts locator for it.

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87 trans am 350,L98 aluminum heads,LT4 hot cam,slp runners,slp 1 5/8 headers,3in.y-pipe,edelbrock base,hi flo cat,air foil,afpr,as&m ported plenum,t-5 tranny w/centerforce clutch and a 3.27 9bolt(11.9in. brakes),ed wright's fastchip,relocated iat sensor,tb bypass,accel supercoil,hollowed maf,slp 3in. catback,a/c delete(she's on a diet,get me down to 3200 like a rustang and watch her go!!!!!!!!!!!!!!!!

14.10@97mph w/2.01 60'

slp catback is finally on!!!
fastchip prom is in.OH!MAN!
FLOWMASTER S.U.C.K.S

 

Ive come to find that in other posts you have had, You are a complete IDIOT!!!!

 

I'm running 3.73's in my car with a ZZ4 and TPI. Forgeting about the motor, the gears work well with the 700R4. Being there's no juice or anything I'll come through the traps at about max rpm in third gear which is what you want. I don't drive the car everyday though. I have a non-lockup convertor and I'm at about 2250 or so at 55mph. With a lockup convertor you'll be slightly better. Not awful but not what I'd want personally for an everyday driver.

 

Well, I too have the poopy 2.77 gears in my car (booooo hissssssss..... Exactly what in THE Fock was GM thinking?????????). I am counting the days until my fourth gen 10-bolt with 3.42s gets here .

I have heard pretty much every angle you can get about this issue and I agree that the BW 9-bolt is a bit stronger than a 10 bolt. It has pressed bearings on the axles with no c-clips and the carrier is beefier than a gm 10 bolt. But the cost of parts for the BW 9-bolt is absolutely ludicrus. My price (employee GM discount) on the series 3 carrier (3.27 or higher gears) is nearly $700!! Then another $250 for gears (3.70s are the only ones available as of yet...) and plan on doing some searching for shims since they are all discontinued. I didn't even bother looking for side bearings but they are likely discontinued as well. The pinion bearings are $45 a piece (my price). I have been told that you can get some shims from other diffs to work, if you have access to them....

I know of a guy that is trying to get a hold of 3.73s and 4.10s for the BW rear but he is still working on it. He also is trying to get series 3 carriers.... I think. If you do a search on this subject you should see him around here. His name is Miles and he goes by '88 427 Camaro' or something like that. My guess is the price will still be entirely too high for parts for this rear end type.

I just can't pay that kind of money for a rear end at this point and if I could, I would go the extra few hundred and get a Ford 9 inch or a GM 12-bolt.

If you look around in junk yards and call around a bunch you should be able to locate a third (later years) or fourth gen 10-bolt that has 3.42s in it. Even if you can't find the right gears, you can always buy the used rear end, some new gears, a carrier and a full bearing/install kit for the price of just the carrier for the BW 9-bolt. Plus if you get lucky, you can find a rear end with the 11.9" rear disc brakes that the fourth gen and some third gens have.

As far as the ratio dilemma..... I feel that a 3.73 gear is a good ratio to run on a car that is more a strip car than a street car. It isn't THAT crazy of a gear, but it will keep ya from keeping up with traffic on the freeway unless you like getting about 10 mpg and wearing out your engine. The 3.42 gear seems just about right to me. The thing that we have with the th700R4 is that crazy low first gear to bail us out if we run a highway type gear. Hell, the 2.77 gear in my car doesn't seem to stop it from blowing the tires off of it every time I get on it...... So with that lower first gear we can afford to run a 3.42 gear, gaining all of the streetableness of the lower gear, and still get nice performance out of the hole. I think a 3.55 would be even closer to perfect for most of our cars...........

Of course, if all you want to do is run 1/4 mile all the time, a higher gear like the 3.73 will give you what you want.

Keep in mind that I have heard quite a few guys that put 3.73 gears in their cars talk about wishing they had 3.55s or something a bit lower than what they have, as they end up almost needing to shift into fourth at the end of the 1/4 mile.........

my $.02

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1987 GTA L98 MD8 GH3
355 '97 Vortec 4-bolt block, TRW(suck) forged pistons 10:1 CR, TFS 23*, LT4 Hot Cam, Ported plenum and intake, SLP Siam Runners, Edelbrock TES, gutted Cat, Flowmaster, K+N cone, AFPR, TB bypass, AirFoil, !AIR, !A/C, !EVAP, ARAP, 2300 stall, Hotchkis STB.

 

I have 3.73's in my car. They were installed by the previous owner. I checked the rpm, and tire size, and calculated the ratio. He told me they were in there, I just wanted to make sure. I like them. I have never ran the 1320, but the car feels good. My MPG sucks at about 20, but with 116,000 miles, I can't ask for much more. I do have the 5sp. and on my recent trip to Indy, I could run 85mph, and still keep the rpm reasonable. This is just another setup. 3.73 might not work very well with a 350.



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Joshua Johnston
1991 Z-28
Flowmaster
K&N
305 / 5spd. (Temporary)