Ring and Pinion

Gu6, this is the code to my rear end.(i think). I have a 91 9ci 350, what all do i need to know to buy the right ring and pinion for my car. Thinking of getting 3.73. And can anyone tell me what this code means (gu6) its on my trunk lid.

Check out www.9c1.com or any other source. GU6 means you have a 3.42 rear end ratio with a 8.5" ring gear (9c1).

GU6=3.42 - G87 is 8.5", G89 is 7.5", G80 is Limited Slip

Note that a 9C1 won't generally have the G87 code on the SPID label or printout, but these do have the 8.5" gear. Interestingly, when I was at a junkyard yesterday, I decided to have a look at a few Caprices from the 80s - from standard 3.8/4.3 V6s to 305 V8s and the 350 9C1s - every single one of them had the 8.5" ring gear and these ran the gamut from 2.58 (GM8) to 3.23 (GU5). Must have been a Chevrolet thing, because other B-bodies of the same years all had 7.5" gears (with G89 on the SPID labels).

Thanx for all the help, BTW what exactlly did he mean by this, does this apply to my 9c1:




If your '91 has the 8½" 10-bolt, they should work. Be aware that you may need to order a "thick" ring gear if you have a 2-Series carrier. I know the later 9C1s and Impalas have the 8½" Saginaw axle, but I'm not sure about the '91s. If you haven't opened it up for an oil change lately, this might be a good time to do so.

3.42s are already decent gears for a B-Body. Changing to 3.73s will make a difference, but not a huge difference. Id there something wrong with the current gearset, or do you simply want a little more launch torque?

The car is slow, just tryin to start somewhere. I just thought gears would get me through the 1/4 a little faster. I am open to suggestions on ways i can get there faster and cheaper than gears. Thanx

The car is slow, just tryin to start somewhere. I just thought gears would get me through the 1/4 a little faster. I am open to suggestions on ways i can get there faster and cheaper than gears. Thanx

Do understand what it is that you have. Which is a 4200 pound car. While the performance of a '91 9C1 was decent, a Camaro it's not and you will need to do some mods to it to get it faster. You can try 3.73s in it, just remember that your cruising economy will take a hit with them in today's age of high gas prices. If it's dog slow and the engine is running fine, then look into possible slippage inside the transmission or a failed torque converter (such as what I'm now going through on my car). The TC is a good possibility - my car is normally a rocket from a standing stop, but since the sun shell breakage a couple of months ago there's just no get-up-and-go with it. A transmission shop definitely diagnosed it as a failed torque converter, especially with the rattling, chattering sound it makes when it's not making power. If this is the case for you, a gear change isn't going to help.

Launching a 4,200 pound barge is no easy task. There is only so much that can be done within the reasonable limits of physics that will allow a mass like that to be accelerated by rotating rubber. Start adding more power at the low end and you're likely just to experience more wheelspin and longer 60' times. Whay kind of times and trap speeds are you generating now?

You may be able to make a little more power up high with a 454 TBI unit and injectors, and a little programming. Freeing up some exhaust flow might help,too. Instead of taller gears, a new torque converter with a little more slip might do just as well, and not cost you nearly as much trap speed loss and daily driving mileage.

Thanx for all the info, all is helpful...I know the car is heavy, but i wont be racing Camaros or Mustangs, just other large cars like Caprices, Crown Vics, and Grand MarQs from around my area. Just looking for a little edge, u know how it is. I was thinkings of dropping the Throttle Body and going with a carb and intake setup, cam and maybe some heads(last). How difficult would it be for me to convert to a carb?

To convert to a carb, you'll need a '87-up SBC intake, the carb, TV cable kit, stand-alone distributor with vacuum and centrifugal advance, and a means to control the TCC for the trans. If you have to pass a periodic emission test, forget about it. You'll probably lose fuel mileage, and the timing curve will never be optimal no matter how much you play with springs, weights, advance cams, and adjustable vacuum advance/retard units.

It can be done, but the difficulties are why many people switch to the 454 TBI units instead. The 454 TBI unit has adequate flow (620 CFM) to support a 350 at over 6,500 RPM. It requires only a higher fuel pressure and tuning.

It's not hard to show what a gear swap will do for acceleration if you have access to a simulation program (QuarterJr for example) while keeping the engine specs constant. I've done this before (and posted the results several times, once on the ImpalaSS forums IIRC).

The upshot of that computer modelling exercise is that a gear swap will increase the 0-60 mph time very well.... (up to 0.5 sec improvement depending if you start with 2.56 and jump to 3.73) but it does NOT alter the quarter mile performance much at all (perhaps 0.2 sec improvement in ET in going from 2.56 to 3.73, but no real change in trap speed). The reason? The engine is unchanged, and you need a boost in torque and power to see changes at the end of the track. So a mid 16 sec car will still be running in the (low) 16s with a gear swap. It will FEEL a lot peppier on the street (0-30 mph driving) for example, but that doesn't mean big gains at the track.... and that's the mistake many people make.

You want real gains, you need to alter the engine. Plus you already have GU6, so you already have a 3.42 rear end; you won't gain much by jumping to 3.73... and your fuel economy will suffer slightly as a result. So leave it alone and spend the $500 you might have used for a gearswap on things that will help:

- a very thorough tune up
- new fuel filter
- TBI rebuild and make the FPR adjustable
- new GM / ACDelco fuel pump from an LT1 Caprice/Impala
- better exhaust
- one of the DIY cold air set ups

Your fuel economy (during cruise) won't be hurt by the above, and the car will be faster/quicker everywhere.

The new pump will easier feed the TBI engine, and it gives you the extra delivery you might need if you go beyond the above mods. This will also prevent you from getting stranded with a dead 15-year-old stock fuel pump.

The 9C1 350 for 1991 is a 195 fwhp engine, but the better exhaust + cold air will put it equal to, or beyond, the 205 fwhp rating for the 92-93 cars. The "better exhaust" is either the 92-93 9C1 Ypipe with an aftermarket muffler, or full duals with aftermarket mufflers, or headers+duals. The better the exhaust you use, the more you will need to slightly raise the static fuel pressure in the TBI FP regulator.

There are other things you can do to the engine, but the simplest things are above --- you already have a decent (but fairly mild) cam grind in the engine, it's the same one used on the L98 Corvette TPI engine but the engine is heavily restricted by the factory exhaust, and slightly too by the factory air cleaner. That's why those should be altered first. HTH.

GM high flow TBI 2"/50mm bore 1987-95 SBC 305/350/383: will this help any, with the addition of dual exhaust and an adjustible fpr?

Sure but not until the rest of the engine can move enough air to warrant going to 50mm bore throttle. The stock throttle body is large enough to move over 300 fwhp worth of air IF you had an engine with a good exhaust/cam/heads/intake.... you don't (yet) so going to a large throttle body isn't going to help.

Focus on a better exhaust, and do one of the DIY cold air setups.

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GM high flow TBI 2"/50mm bore 1987-95 SBC 305/350/383: is an intake manifold i found on ebay for $99.99

GM high flow TBI 2"/50mm bore 1987-95 SBC 305/350/383: is an intake manifold i found on ebay for $99.99

Oh, an INTAKE manifold. And the fine print in that eBay ad might be that it's an Fcar/truck GM intake manifold that's has the throttle bores machined out to 50mm dia ----- SO WHAT !!!

The comment is no different than the one I already gave -- if your engine can't use the bigger bores then it won't help make more power. AND bigger throttle bores won't help unless you are using a throttle body that similarly sized. IOW don't bother with any intake manifold with bigger bores until you have a TBI to go with it --- and don't waste your money on parts that won't make the car run any better or any faster. A bigger-bore intake won't help unless the factory intake you have is a restriction. And for a zero-mod car, it's not a problem. But the exhaust is.

Furthermore, the Fcar/truck TBI GM intake will bolt to the engine but it won't allow the distrbutor to be installed for reasons I've explained elsewhere on this forum. The intake for a Fcar/truck is different for a Caprice because of cowl interference with the distributor. The same comment applies to aftermarket TBI intake manifolds -- they all expect a small-flange long-shaft distributor to be used with them, so they won't accept a 91-93 Bcar Caprice, Roadmaster) distributor and a Fcar/truck distrib (which will fit) will have interference with the cowl when you try to install it.

Do the cold air intake / filter because it's easy/cheap and worth 5 to 10 fwhp depending on how good your fab skills are.

Do the exhaust because it the best mod you can do for the engine right now.

Tru Dual Exhaust is on the way, but thinking about adding headers, what will and wont work with my application? Thanx for all the help... btw i dont have to submit to any emission tests!!!

*bump*

These are basically tubular shorty headers that more-or-less duplicate the stock 94-96 Bcar LT1 exh manifolds. People have adapted Bcar LT1 exh manifolds to work on 91-93 LO3/LO5, so these could also be made to work on a 91-93 car.

http://www.clearimageautomotive.com/LT1%20Tubular%20Manifolds.htm

You'll also need to connect them to 94-96 style downpipes (which usually have a cat built-in) and it makes sense to use a 94-96 full dual thereafter. That means you need to add the hangers on the driver's side, as well as making room under the trans crossmember to fit two pipes. Some people section the stock trans crossmember, while others use the 94-96 crossmember + 94-96 trans tailshaft housing that mates to it. None of these are plug-n-play, and they both have their installation quirks.

The shorty headers will provide a power gain over the 91-93 cast exh manifolds but they will be louder (thinner wall metal) and they'll dump more heat into the engine bay (for the same reason). The upside is that they are cheap when compared to other headers.

Here's another alternative from the same source:

http://www.clearimageautomotive.com/budget%20headers.htm

I didn't look that closely at the differences between the "tubular exh manifolds" and the "budget headers".


Then there are the expensive alternatives... and they're full-length headers. They'll work better but they are very pricey, and frankly unless you were doing everything else "right" on the engine (cam, ported heads or replacement heads, custom tuned ECM by someone who really knows what they are doing etc) then it would not be worthwhile to buy such expensive headers because the engine just won't run up to it's potential & cost:

http://www.clearimageautomotive.com/91%20-%2093%20Caprice.htm

Since you're asking "what to use" for exhaust, then it means you don't know enough about what you would need to do to properly tune the engine --- so it would be a mistake for me to suggest you buy $800 to $1200 headers, and it would be a bigger mistake if you actually bought them.

A lot of the archives in the other Caprice/Impala forums details the installation of:

- headers
- duals
- both headers + duals

into 91-93 Bcars so you'll have to go searching for them, so that you'll have more of the details. Sometimes it's easier to just find a "friendly" exhaust shop to do the install for you, but then you're at their mercy of doing a hack-install job. That's the tradeoff between doing the research and some of the install yourself, vs letting someone else do the entire job. HTH.