I have a '91 Camaro running a 383 Stroker using a 700R4 Automatic transmission. The rear is still factory and I'm getting ready to look into upgrading the ring and pinion from the factory 2.73 to something higher. My question is this, The car is not a daily driver but is used for crusies in the summer time. It's never seen a drag strip nor ever will so my intent here is to keep the car as fuel efficent as I can while still allowing myself to get the best out of my engine from time to time. I know right now driving 65 mph I'm turning around 21-2200 rpm's which isn't real bad and I'm getting around 14 mpg highway 9 city which I'm not real happy with. What would be the best gear to go with or should I even change it? I don't want to lose much more MPG's?

 

According to the graph you got when you ran it on the chassis dyno, what is the engine's peak torque RPM?

 

Its never been dyno'd. Your suggesting I dyno it before I select a gear?

 

If you don't like your gas mileage now....you certainly wont like it if you go with taller gears. It may not drastically decrease your MPG, but it will definitely decrease it.

2.73:1 = driveshaft turns 2.73 times to make the wheels turn once.
4.10:1 = 4.10 turns for 1 wheel revolution.

Faster the drive shaft spins, the faster the engine spins.

 

Yes I'm suggesting that.

RW's point is a bit over-simplified, but a good one just the same. In most cases going to a higher # gear ratio will use more gas. THe only time it won't, is if the engine is built for high RPM efficiency (cam choice above all else), and it has a gear ratio that pins it into the idle RPM range where it can't make any power at all because it's so inefficient at tha tPRM.

Keep in mind also that you have a 2 series, non-posi, drum brake POS back there. It would be BEYOND POINTLESSLY STUPID to spend money upgrading .... that. Polishing a turd. The RIGHT choice would be to locate a LS1 4th gen rear, with a 3 series Z-T carrier and the good disc brakes, and spend your money on THAT instead.

Butt first, find out what RPMs your engine works best at, and make an informed decision instead of a stab in the dark. If you post up your combo - PART NUMBERS ONLY PLEASE, no "stock" or "mild" or "ported", along with a DETAILED description of the machine work done to it especially whether the block was zero-decked - we might be able to make a reaonable educated guess at what would work well with it.

 

If I where to go with a 3.23 gear, What you roughly think would be expected as far a gas mileage loss? Would the lowend gain be worth it going from a 2.73 to a 3.23?

 

Sorry but something for me doesn't make sence, if your cruising at 65 mph and you have stock tires your engine should be at 1630 rpm. My car has 245/50r16 and at 65 mph with my 3.23 I'm turning just under 2000 rpm.

Do you not have a lock up converter?

 

Depends on your combo. No telling without more info.

gp, he's probably just quoting whatever that pretty wavy-pointer trim option thing the factory put in his dash says... those are notoriously inaccurate, since they're not "test equipment" or anything, just trim to satisfy the desire for a "sporty" "appearance". Mostly meaningless.

 

Well, I'm no gear head but yes the tach says 2100 rpms. Now, I have a FAST EZ-EFI fuel injection system to fuel the 383 Stroker since the old TBI would not do it. My indash tach reads roughly 2200 which I know the indash gauges of the '91 Camaros are not the most accurate. However, the EZ system has it's own self tuner which I have hooked up in the car and it displays roughly 2100 which I've been told is the most accurate. So between the EZ-EFI tuner and the indash I'm around 2100-2200 rpm. Now, here's the break down of the car setup.

I'm running a 383 Stroker. My 700R4 auto has been rebuilt using a Pro-Built Automatics kit.
https://www.700r4l60e.com/store/prod...&cat=19&page=1

I'm running a Edge Toruqe convertor rated 2800-3000 stall.
https://www.700r4l60e.com/store/prod...&cat=59&page=1

My rear end is factory, From my understanding running a 2.73 gear. My tires are also the standard factory 16X8's. So, I'm not sure if this helps you make any more sense out of it, But that's what I've got and that's what it runs at. Before all this work I had just a GM crate 350 everything stock and the car would run around the 1600 rpm mark like you say at 65mph. However, Now after all the rebuilds and upgrades the rpms have shot up by 500?

 

How do you engauge the lock up on your 700r4? does the Fast Ez efi do it or do you have a switch in the car hooked up?

 

I don't have a clue. I'm not even sure what your talking about.

Here's the motor info:
http://www.ebay.com/itm/Chevy-383-47...item43abecde9b

 

Well the 700r4 uses a lock up feature that locks the converter up when the ecu commands it to, it basically make it a 1:1 raito with no slip between the flywheel and input shaft of the trans, thats why if you look up torque converters to buy for a 700r4, you will see lockup and non lockup, I use a lockup one cause its not a track car and take advantage of its uses to lower my rpm's on the highway. Just to make it clear all 700r4 came with a lockup that I know of, maybe some real early ones did not but I have never seen one. So the link you posted of you converter says its a lock up one, so if its not hooked up then I think you should.

 

After reading this you actually have answered one of my problems with the 600 rpm increase which has been killing my fuel economy. I just got off the phone with fuelairspark's tech support. They informed me that a kit is required for a 700R4 when using there FAST EFI systems. No one ever told me that from all the people who has been working on this car. It's no wonder after driving down the highway the center console felt like a stove.

 

Glad I can help, anyways I still think your off with those gears, If I had to make a bet I would say you have 3.23,3.27 or 3.08 in there, best way to check is take off the rear end cover and write down the numbers on the ring gear, plus you can do a nice oil change to boot, if you haven't changed the gear oil yet. Then just divide the numbers to get your gear size.

 

That's kinda too much cam for anything resembling "good" gas mileage. It's going to need 3.42 gears AT LEAST to let it get up into a range of RPM where there's any dynamic compression AT ALL, without which it's impossible for the engine to produce power. Meanwhile, I'd expect that as it is, it's probably pretty soggy off the line (stock motor would spin the tires, this one won't, kind of thing) but comes on like a banshee above about 3500 or 4000 RPM, once it gets up to RPMs where it can actually work right.

What exhaust?

Yes you need to get your TCC working ASAP. FAST supports that, all you need to do is hook it up and program it. All 700s have it, except when people buy "special" "racing" converters that leave it out; not likely in your case.

 

FAST told me to buy this: http://www.jegs.com/i/TCI/890/376600/10002/-1?CT=999

I just ordered today so will have next week and hopefully this will take care of one issue. I have about 1000 miles on the motor, TC and trans so I'm hoping that not having this working properly hasn't damaged anything. As far as the exhaust the car is setup with 1-5/8 Hooker shortys, Magna Flow Cat, and Magna Flow exhaust system for my model year Camaro.

The car itself I wouldn't say is a dog off the line. It certainly blows away the GM 250hp 350 crate that was in there. The issue I have is the non posi rear causing the rear to light up back and forth. There are times when you get on pending on speed and rpm that the car does seem a little doggish. The thing is I can handle the fuel economy I'm getting now, I just don't want it to become worse. Most my miles are highway and if the overdrive wasn't kicking in like it should I will see some MPG gain. With that there will be room to lose MPG with a gear change which the engine builder and Pro Built Auto recommended was to go with a 3.23 gear or 3.42. Thats what was recommended by the engine builder himself.

 

Yeah 3.42s and a functioning lockup will make a world of difference.

 

You had made mention earlier to locate a better for end from a 4th gen LS1. I noticed on Hawks Third Gen they sell used LS1 rear end assemblies with or without TC for $500. Is this a fair price and is this what you are talking about?

http://www.hawksthirdgenparts.com/ca...ectprices.aspx

I don't want to spend a fortune on a rear end put wouldn't mind throwing $1K into it if that's reasonable.

 

Yup, that would be the one.

 

And these just bolt right up without any alterations? Or nothing major I should say?

 

Right, nothing major.

Your wheels will stick out and look kind of poseur; if you're into buying wheels, just get ones to fit 4th gen. Or, go get yourself a pair of 4th gen stock ones.

Other than that, the only other kink is the parking brake cables. There's a cure but I don't know offhnad what it is. Prolly available somewhere on the brake forum.

 

I believe the LS1 rear is longer so wheel offset is different, anyways I like 3.42 for a more street car and 3.73 but the 3.73 is a little more od a hot street car. With 3.73 and my stock tire, engine should be turning about 2300-2400rpm.

You can do the math yourself to figure out what works best for your driving habits. If you don't know a 700r4 overdrive is 0.70, heres a cool calculator for you.

http://www.ringpinion.com/Calculator...x#Transmission

By the way I feel that your car would be very happy with 3.73 with that cam and stall your running, it would put the motor right at the sweet spot on the highway but at the expense of less mpg.

 

Exactly: 4th gen wheels have about 1½ - 1¾" more backspacing.

 

I did some searching on this subject earlier and saw there was a length issue. The few cars that had pics on here with the extended rear I thought looked bad with the tires sticking out past the fenders so I'm not sure that's for me. I just bought a set of 16X8 Chrome Iroc style rims for my car about a year ago and the last thing I want to do is spend even more on rims. Someone suggested on another forum board to keep my rear and just purchase a Eaton housing? Not sure what that is but said it's good and will give me posi. Then suggested as you to dyno the car and with that setup run a 3.55 or 3.73 gear pending on the dyno results from the specs I listed. They suggested just reusing most of the old components as the axles and such to help keep the cost down since the most important critical piece is the posi housing, ring and pinion. Would this sound better?

 

most third gen v6 cars came with 3.42 rear gears.thats what i have.same strength as the v8 cars.my car turns 2200 rpm at 72 mph with a 700r4.

 

My RS was actually a 305 model and never had a V6. Based on the gearing chart listed here on Thirdgen it says the '91 Camaro RS with 305 700R4 had 2.73's.

 

Do you still have the RPO code sticker in the glove box? if so and your rear is original then you will know for sure. My RPO is GU5 which is 3.23, not sure if the Camaro is the same RPO but if so GU2 is 2.73.

 

The Eaton posi costs over $500. http://www.summitracing.com/parts/ETN-19599-010/

All you get by buying the 6-cyl rear is MAYBE the better gears. Won't be posi; won't have better brakes.

This is one of those things where you're either in or you're out; there's not much "Ima do it halfway".

You will end up spending more than you are imagining trying to turn a 6-cyl rear into what you deserve for spending all that money. And you'll STILL just have antiquated drum brakes.

All around, in this day and time, a 4th gen rear is the core to start out with.

I agree these cars look AWFUL with the little pizza-cutter stock 8" wheels stuck out in space like will happen putting them on a 4th gen rear. Very poseur especially from behind.

My suggestion for dealing with that situation is, sell the chrome rims (which IMO aren't appropriate for these cars EITHER, there not being A SINGLE ATOM of chrome anywhere else on them, ANYTHING chrome looks like it fell off an alien spaceship and got stuck by accident, but of course that's JMO, you may think otherwise) and get a set of 4th gen or Vette wheels. Even just stock ones. You'll need a pair of spacers up front. But you should be able to do all that wheel stuff pretty much revenue-neutral, and have wheels that fit the styling of the car better than anything chrome ever possibly could besides.

 

I never said anything about putting a V6 rear end in my car. I said I was told to upgrade my current rear and asking if that was a decent solution. From what I've been reading most people say the 4th gen rear ends are not any better then the 28-spline 90+ rear ends in the 3rd gens. Everyone notes that you get disc brakes and possibly better gears if you can find the right rear end. The disc brakes I could car less about since I don't race or run the car at a drag strip. All the used ones on Ebay i've been scrolling around looking at they want anywhere from $300-$600 and thats not including the rough $100-$200 freight. The other issue I have from most of these wrecks is I don't have a clue as to what I'm getting and it could be damaged or whatever. From what I can tell it's going to cost about the same to buy a used 4th gen rear then to maybe just rebuild mine. Then you have the length issue that will cause more hassle and possibly more money in order to get that looking correct.

 

i was suggesting to swap in a v6 rear end like i did.like you said the forth gen rears are the same except for being too wide.the 89 to 97 disk brake rear ends have basicly the same brakes anyway.posis can be added.

 

Thats a nice motor. I dont think its possible to make that thing fuel efficient!

 

I basically have the same setup but I don't know your cam specs for your rpm range. My car has 3.08's which are nice for highway and descent for town. I don't get nearly the gas mileage you do but I run right around 2300 rpms at 70 mph. I get about 13mpg highway/8mpg city and that isn't horsing on it. with the 3.08's and the tall first gear of the 700r4 makes it like launching on 3.42's in a th-350. My car has plenty of power to break the tires loose at 35mph, 70mph, and higher (I don't know the speed because I was sideways but when I looked down after I let off and got her straight my speedo said 85mph) with the 3.08's.

 

My fuel mileage is slightly less on the highway but around the same in city. I posted a link to the guy who built my motor with the exact specs several posts up.