I need your opinion on which gears I should get.

My car has a stock L98 motor. I’ve got Hooker 1 5/8’’ ceramic coated headers and y-pipe with a single 3’’ high flow cat and Flowmaster 3’’ cat-back exhaust.

For the intake I’ve got Hawks Thirdgen ram air boxes, gutted factory air-box along with K&N air filters. I also have a 52mm BBK throttle body. I am in the process of purchasing an Edlebrock aftermarket TPI intake base and SLP intake runners. I’m going to port the intake base, plenum and runners to get as much air flow as possible.

I’m running a Bowtie Overdrives level 3 700r4 and one of their 2,400rpm stall converters. I’ve got it set up to have all the full throttle shifts occur at 5,500 rpm and to allow full throttle shifts in to overdrive.

After I finish with the intake mods I’m going to leave the rest of my motor stock for a while.
My remanufactured L98 motor (I got from A/C Delco) only has 30,000 miles on it so I’m not in a big hurry to start tearing in to it just yet. I’ve had no problems with it since it was installed and I’m happy with the way it has performed so far.

The problem is the gears – I’m going to keep and rebuilt my stock Borg Warner 9bolt rear. That’s the only part of my drive train that I haven’t gone through yet. I saved it for last until I got my motor and transmission figured out. Currently I have 2.77 gears which really zap the performance.

I’ve heard from some people that moving up to 3.27 gears would be a good move but, there isn’t much of a difference between my current 2.77 gears vs. the 3.27 gears. Although the 3.27 gear ratio was the G92 performance gear ratio option from GM for the L98 cars with the 9bolt rear.

Other people that I have talked to say I would get more performance gains from the mods that I have done if I moved up to 3.45 gears.

I’m concerned about getting traction with the 3.45’s combined with the 700r4’s low 3.06 first gear ratio and what rpm’s I’ll be turning on the highway with those gears. My car is a 100% dedicated street car so I want to pick the right gear ratio that will be best for all around good street performance and won’t hurt me too bad in terms of fuel economy.

 

I'd run the taller (3.27) gears since you drive it. My relatively stock car has 3.23s and it will easily bake the tires as well as any NASCAR. It pulls off the line just fine too. :-)

EDIT: I think you'll notice a big difference from the airplane gears you currently have. 2.77 to 3.27 is more than a 20% difference.

 

Agreed, 3.27:1

 

Thanks for the advice guys. Yeah I was worried about the 3.45's being too deep for my set up. I'll go with the 3.27's.

 

I'd had both on L98's. Go with the 3.45

If a person already has 3.27, there is no point in swapping to the 3.45. But if you have the 2.77 and are upgrading, you might as well go for the 3.45

It's only about 150-200 RPM difference on the highway (3.27 vs 3.45). It does tend to lower the mph that your 3-4 shift occurs around town (may be good, may not be.....depends what speed you drive)

The 3.45 do give a little bit more pep though. I wouldn't go for 3.73's though. They're too short for L98 cars.

 

Ah ok. What kind of rpms are you turning on the freeway around 70mph-80mph with those 3.45's?

Yeah 3.4x is about the deepest I would go with a long tube runner TPI system. The 3.73 and up gears are better suited to a combination like a mini-ram intake that can take advantage of good breathing up high in the rpm band.

 

I love the 2.73 to 3.42,Eaton posi. conversion. 3.42 is perfect for the 700r4 with OD. 1st gear is just right as far as length off the line. Your pushing more power and have the higher stall but that's usually addressed by using better tires,not chinsing on the gears. By the way your now entering into that Support cover territory we talked about earlier.

 

Thanks for the help guys. Ha ha this stuff can get confusing at times. I went on 9bolt.com and got most of the parts that I need to rebult my rear end including 3.27 gears. I also got a TA Performance girdle for the rear end too.

Ronusmc I'm probably going to take my car over to the rear end shops like you did for your car and have them install the parts. They have a shop in Livermore which is only about 15 miles from where I live.

Now that I've got all the parts that's part of the reason I'm considering moving up to the 3.45's. I haven't taken the parts to be installed by anybody yet so I could always sell or trade the 3.27 gears for some 3.45's.

Sounds like everyone is saying that stepping up to 3.45's would be a good performance move. I've just been getting so many different stories on which gear ratio would be better between 3.27's and 3.45's so its nice to hear from people that have made the swap before.

 

At 70 mph, you're looking at 2200 vs 2400 RPM.......(To be specific, it would be 2289 RPM vs 2415 RPM.....A difference of 126 RPM)

 

Ive been running 3.42s for over 5 years now and take 1 1/2hr road trips to and from family about twice a month. Its mostly around town but just using it that way tells me I made the right decision.My tachometer dose not work but I can tell when a engine is winding out and with my 3.42s and 700r4 in OD. cruising at 70mph is not a problem. I look at it this way,if there are some traction problems off the line than add better tires with suspension up grades like lower control arm relocation brackets, etc. This is just my personal opinion and the one I took years ago when I went through this same discussion with the shop doing the rear end work.
http://rearendshop.com/index.html
By the way I always ask for a drive on lift and if they don't have one be sure they know were the proper lift spots are for our cars using a swing out lift.I tell that to any and all even if Ive been there before.

 

I put 3.54s behind my 700r4 and love it, if your going to be doing 75 to 85 all the time do the 3.27 or leave in the 2.77 and supercharge it!

 

I say you leave it alone. Unless you have 2.73s or non posi. I changed my camaros to 3.73 and was sad at my gas mileage. I don't know why I thought THAT was a good idea.

 

I'm not going to switch to 3.73's. I am still keeping my long tube runner tpi set up so thats not needed. If I had a mini ram I may condsider that.

I've got 2.77's now which is the 9bolt equivalent of 2.73's for a 10bolt rear.

With stock style tpi systems 3.4x is the deepest that you really need to go to. steeper than that and you will have a serious traction issue. The motor will be out of the torque and power band to.

 

yaj15,
I just read through this thread again and noticed no mention of what Posi. unit you have.Unless I missed something than if no modifications have been done to the stock differential than you may have the 26 spline carrier(posi.unit) 2 series, with 26 spline axles.I don't know much about 9 bolts but in order for me to run the 3.42 (including the 3.27) you will need a 3 series carrier.That means replacing the 2 series posi. you have for the 3 series carrier/posi. and preferably upgrade to 28 spline unit including 28 spline axles. Thats exactly what I had to do when I did my upgrade.
I beleave there is a way around that with thicker gears,but I don't know if there available for the 9 bolt.(some will tell you not to run the thick gears but I do not know "exactly" why.)

 

The 9 bolt didn't have 26 spline axles, but the 2.77 does use a 2 series differential that must be swapped for the 3 series when going to the 3.27 or 3.45 gears. There are no thick gears for the 9 bolt that I know of.

 

So that obviously means the 1988 Iroc-z came stock with 28 spline axles.Is that right ?
Could have saved myself $250.00 in axles if GM would have done that with my car.

 

As far as I know all the thirdgen Borg Warner 9bolts came with 28 spline axles. The 10bolt rears didn't get upgraded to 28 spline axles until 1989 or 1990 I think. I'm not entirely sure on that though. I know all the 1991-1992 Z28's got the upgraded 10bolt rears with 28 spline axles.

The 9bolt axles also were press in they didn't have c-clip retainers like the 10bolt rears do either. So I don't think a 9bolt axle would work in a c-clip style 10bolt. You could always by a c-clip eliminator clip kit though.

There were some other differences as well that made the 9bolt a little stronger than the 10bolt. The 9bolt is no where near the strength of a GM 12 bolt aftermarket rear but, it is a little stronger than the GM factory 10bolt rears.

 

Here's a link showing some of the carriers/posi./locker units that Eaton is carrying. Mine is the one that says Eaton Posi. Differential over it = http://www.eaton.com/Eaton/ProductsS...ials/index.htm
Here it is in detail =
http://www.eaton.com/Eaton/ProductsS...als/PCT_339923
There is a locker that is a little less expensive but I cant think of witch one it is.
Thats great on your axles,and I'm sure it is kind of a bummer knowing that a new/rebuilt carrier is necessary. I just came up with a idea. Call the Rear end shop in Santa Rosa and ask for Dan (owner) and tell him what your plans are than ask him about a rebuilt Eaton Posi. could be allot cheaper considering a new unit is around $500.00.

 

There isn't an Eaton Posi available for the 9 bolt. The only thing that is available for the 9 bolt is the Borg Warner cone type differential and a very expensive German made differential.

 

Ditto. The 9-bolt is its own beast. 10 bolt stuff does not interchange at all.

I also agree with the 3.27:1 gear ratio choice. I've had two 3rd Gen's with 2.73's, and 2 3rd Gen's with 3.27's (one of them I swapped from 2.37 to 3.27). The 2.73/2.77 is great for highway gas mileage, but pretty gutless at launch. The 3.27, IMO, is the ideal gear ratio for a TPI car with a TH700. First gear is so deep on the TH700, that a higher gear ratio is kind of useless without some kind of crazy rubber to hook up in first. The only time I would really recommend going 3.45 or 3.73 would be for a T56 swap. I had 3.27s behind my last T56 (a '93 style with the tighter ratios), but it still wasn't enough. Next time I'll be putting 3.45s behind it. If I was building a '94-up T56 with the .5 overdrive, I'd go with 3.73s.

You'll like the 3.27s. Lots of pep, and 24mpg is still very achievable. If you want more pep around town, just bump up the stall speed on the converter.

-cal30sniper

 

Thanks for your real world input. Yeah I thought about getting 3.45's too because they came on the LB9/T-5/G92 cars. Then I remembered that the LB9's with those options were rated at 300 pound feet of torque from 1989-1992.

The L98 cars from that same period came with 3.23's or 3.27's depending on if you got a 10bolt or a 9bolt rear. Those L98 motors were rated at 340 pound feet of torque in 1989 and then 345 pound feet of torque from 1990-1992.

With the mods that I have I'm am going to have at least 400 pound feet of torque (probably more) and with the 700r4's first gear there is no way I'm going to get good traction with 3.45's. Then on the freeway I don't want to be turning high rpm's on the freeway with 3.45's - that would cut in to my fuel economy too much.

My new BMR torque arm in addition to the hotchkis lower rear suspension package that I alread had really helped out in the traction department. That BMR torque arm made a real difference. The rear in my car has never felt so planted. Even in regular driving going over rail road tracks or bumps don't upset the rear end like they used to when I was using the stock components.

Yeah I bought most of the stuff that I need from 9bolt.com. I just have to contact that rear end shop and get it installed. I'm really satisfied with my 2,400 rpm stall converter and bowtie overdrives level 3 700r4. The 3.27's should help that out a lot.

I just bought an Edelbrock intake base, stock plenum, and SLP intake runners. Along with my 52mm thottle body I sent all that stuff out this week to have it port matched. So all the intake, exhaust, and trans mods are really going to help out with those 3.27's.

 

That's going to be a nice, completely streetable, and quite peppy setup. You should really also look into getting the tuning equipment to take advantage of the new engine parts you're putting on. You'll pick up a little just by bolting them on, but a lot more by properly tuning for them.

Another note on rear ends. The taller the gear you run (tall being 2.77, short being 4.10), the stronger the actual ring and pinion setup is. It's not much, bet every little bit helps.

My GTA was a factory L98/TH700/3.27 9-bolt car. It's a perfect ratio for the factory engine. My mom's '86 Vette has the L98/TH700/2.5* gears in it, and it's nowhere even close to the acceleration of the GTA (even being 5-600 pounds lighter). You'll be very happy with the setup you have planned here.

-cal30sniper

 

I did a extensive search including 9 bolt.coms web page does not show a complete rebuilt 9 bolt , 3 series ,carrier.(that does not mean they don't,and worth a call.)
I did find this = http://www.ebay.com/sch/i.html?_trks...at=0&_from=R40
As far as your gear selection is concerned, the power and torque you are putting out will allow you to take advantage of 3.23 gears. I LOVE my 3.42s but that's because my 5.0 does not have the power/torque necessary to make the 3.23 jump of the line. Heck we have a guy on here that is running 2.73 and getting fast track times because he has the power to make them work.
Maybe the "Rear End"shop has a 9 bolt rebuilt 3 series posi for you. Give them a call.

 

3.27 9-bolts are pretty common. You might find it easier to just grab a 3.27 off craigslist (that's where I found mine), and have it rebuilt by your rear-end shop. A lot of the L98 cars, and all the L98 GTAs came with 3.27 9bolts. Plus, you'd have your stock 2.77 rear if you ever wanted to go back. Win Win situation.

I plan on doing the same thing when I outgrow my 3.27 9-bolt, only I want to find a Dana 44 to replace it.

-cal30sniper

 

Looking at a 3 series posi carrier from 9bolt.com from Australia for 547.00 shipped
Gears are available from Motive and Yukon in all original ratios {2.73 - 4.10}for about 200.00 if you shop.
Bearing sets are available from Yukon, Motive, 9bolt.com and others at about 200.00 also.
Setup cost will vary, probably about 300.00
If you already have a good housing,axles, and brakes, you are half way there.
ronusmc, did you look in the carrier parts section?

 

I just typed in 9 bolt posi or something along those lines.
$ 547.00 and I'm sure its a completely rebuilt unit.
That should do it.
I still say call Dan (owner)at the Rear End Shop (Santa Rosa)and talk to him about you plans. He may have just what your looking for at a better price.
I'm interested in what he has to say.Also he should offer a warranty if you buy from him.

 

My shop charged me $450 to swap out my carrier, gears, install new bearings all of which I purchased from 9bolt.com back in 2002. I switched from the 2.77 gears and carrier to the 4.10 gears and carrier. The complete gears, carrier and install kit from 9bolt.com (Which used to be a guy named Miles) ran me a total of $800 not including the installation of $450. So to do the complete swap ran me around $1250. I am I running a Turbo 350 trans hooked up to a 383 sbc and a 4500 stall converter. I keep an extra rear-end in the garage with 4.45 gears and a 3500 stall for any highway driving I need to do. I can drive it from Joliet, IL to Chicago which is about 35 miles at 65-70mph with the engine spinning at around 3500-4000 rpms. but my engine was made for racing anyway. So cruising at the rpm is very easily comfortable at that speed. It's not like I would cruise at those speed over an hour or more. but for such a short trip of about 40 miles, that is very doable. Kind of wished that I had a 700r4 that was built to handle that engine and then I could cruise to places like Michigan or longer, but my gas mileage is not that great, but then again my '02 Dodge Ram get close to the same mileage anyway. About 12-15 mpg city and about 18 hwy mpg.

 

I would go with 3.45s. I like that ratio. I don't think that it's too much gear for an L98 at all. My IROC has 3.42s with a T5, which has about the same 1st gear ratio as a 700R4. My TPI Corvette had 3.55 gears with the ZF 6 speed, which also had a 1st gear that's similar to a 700R4. Neither of those cars had traction problems, and both were a boatload of fun to drive.

 

Thanks for the info guys. Yeah I plan on getting a tune after I get my parts back from being ported.

Yeah I've learned that too. The high gear ratios (2.77) have thicker gears so they are stronger. It's not by much but yeah every little bit helps.

I'll make a call over to the rear end shops to and see what they have to say.

I recently got engaged so that and work has been more of a priority over the past couple of week.

Hopefully I'll get the parts back from being ported in the next couple of weeks. Then I can see about when I'll be able to have a chance to install the parts.

 

Sorry it's taken me a while to get back to this thread. I didn't have luck finding a 9bolt rear with the gear set I wanted late last year.

I also got married earlier this year so my car took a back seat to that as well.

I got a good deal on here for a 3.27 gear set and 3-series carrier. I'm going to install the 3.27's since I'll be doing a lot of highway driving.

I'm also speaking with another group member about buying a 9bolt housing that is missing the ring & pinion and 3-series carrier - but it has every thing else; backing plates, axles, bearings etc.

If that doesn't work out I can take the parts that I have to a rear end shop and have them rebuild it.

The rear end is the last part of my drive train that I'm going through. It's the original rear end and with 199,000 miles on it I know it's over due for some attention. I didn't want to change anything with my gears until I finished working on the engine and transmission combination so I could match the rear gears to those components.

I've got a level 3 700r4 from Bowtie Overdrives with a 2,400 rpm stall converter. I really like this trans and converter set up but, that higher stall really isn't matched to well with the 2.77's - especially at low rpms like others have said here.