I did a small amount of research. According to a couple online sources, the 87 2.8 mpfi v6 car I have, has 3.42 gears. The 91 RS LO3 has 2.73?? (can't remember exactly.)

Would I have much trouble exchanging the gear ratio's/whole assembly. What about the driveshafts, should they be the same or will I have problems there.

I assume the v6 has lower ratio to make up for less power. the 3.42 would help out a mild mannered 305 tbi right. Not wanting to do a ton of engine mods as it's enjoyable to ride around in (not push around every corner). But if this swap is feasible I see no reason to not take advantage of parts I have available.

My weak point on mechanical knowledge is rear ends, (probably because I've never tore one out to have to replace. LOL) so any help on this would be greatly appreciated.

 

Direct swap-out. Absolutely identical in every way except for the ratio.

While you're changing the fluid before the install, make a point of checking the gears, so you don't get a nasty surprise. All the "research" in the world is worthless if it doesn't agree with what's ACTUALLY in your rear. The only "research" that counts, is what you see with the cover off.

You'll need the correct speedo gears too.

 

the LG4 werent exactly any more or much more powerful than the 2.8L as far as ratings show anyways, and they commonyl got 2.73 such as with my 82 t/a LG4 305 200c, in which i am currently hunting for a 3.42 to 4.10 axle for


yet the L69 alot of the times got 3.73

its wierd like that

i had a bright blue 88 s/e 2.8L auto and it was 3.42 also

its wierd like that

my little beater toyota 2wd xtracab pickup has 3.89 with the little 22RE 2.4L and auto overdrive(A43D)


so..

but yeah anyways direct swap, all the stuff is identical other than the carrier and gear set and spiders and shafts, since 87 are 26 spline and 88 up are 28

i assume youre going to swap entire axles,



good luck

 

Yep if it's a direct swap I was going to unbolt/install. I can splurge for gear oil but I didn't want to have to spend any $ for mods.

I'm pretty sure that the rear in the 87 had never been changed. Anything for that matter. Long story short I traded a totaled 95 t top 6 speed Z28 for the 87 with 42k original miles. It was 1 owner all matching paper work. It was a good little booger too. I clocked 168k and only had to change alternator (beyond regular maintenance) The head gaskets blew and city ordinance was no immobile cars were permitted, tagged or not. I drove it about 200 miles to the closest relatives. I guess the trip proved too much for it and the heads and block cracked. So I figure why not get some use from what's left.

Could I use the speedo gears from the v6? 215/65 15" tires. Same as the 91 came with, but they have been changed to the 91-92 Z28 16" wheel. I think tire size is 245/55?? I'd have to double check.

My motive for this is with the 2.73 ratio, that would be for top end correct? Well the car is governed at 110. To me that is defeating the purpose. Gear it for the top and restrict how far it can go, keeps the mini beast at bay. I was just thinking that with the 3.42 since I already have it and the car is governed, I could take advantage of what is already there. Without purchasing a chip or what not. I don't plan on beefing this up at all. Bone stock is fine with me for now. Is my logic on this way off or does what I have planned make some kind of sense.


Thanks alot for the help.

 

No that would not.

The grocery-cart ratio is for gas mileage. Those cars were the "sacrificial lambs" offered to the CAFE gods.

The car will in fact go faster, ultimately, with a higher gear ratio in it; because the grocery-getter gear keeps the motor at such low RPM that its HP output is equalled by the requirements of pushing the car at a relatively low vehicle speed. In other words, if your motor makes let's say 170 HP like its spec, but that spec is at say 4000 RPM; but your gear is such that it only reaches 3000 RPM at 120 mph and at that mph it takes 120 HP to move the car, and your engine produces 120 HP at 3000 RPM; then THAT'S AS FAST AS THE CAR WILL EVER GO. THe whole idea of "my car will do 5000 RPM in 1st gear, and according to the calculator 5000 RPM in 4th gear is 185 mph, so if I didn't have this governor I could go 185 mph", is TOTALLY WRONG.

In the real wordd, the HP requirements past a certain point (which is reached at around 40-50 mph in most street cars) increases approximately according the the CUBE of the speed change. In other words, to get the car to go TWICE as fast, you need 8 TIMES the HP. It turns out, that 170 HP with the perfectly optimum gear, will push one of these at around 125-130 mph. To get to 150 mph, you need around 300 HP. In other words, it takes ALOT of engine power to significantly increase the top speed. Which your car will never see anyway, unless you have a dry lake bed at least a couple of miles across in your front yard.

I doubt you can use the 6-cyl speedo parts with the later-model car, at least if the 87 was a Camaro; they're cable-drive, and the 91 is electronic. But you can snarf the right stuff out of a junk car of the right year.

The tire diameter is very close to the same for all the stock tire sizes for these cars. In fact, the variation from one mfr's 215/65-15 or 245/50-16 to another mfr's of the same size, is greater than the difference between the average of all 215/65-15 and the average of all 245/50-16 (regardless of what you can "calculate" by multiplying out the aspect ratio numbers and all that). In other words, the speedo gears are unaffected in the real world by which tires you've got, as long as they're stock sizes. The beauty of mass production.... make everything in such a way that as many parts as possible can all be the same.

Bottom line:
Go ahead and change out the rear, you'll like it better, guaranteed.
Get the right speedo gears for your VSS.
Forget about "top speed" because that's all nothing but a bunch of monkey-spank.
Don't worry about the tire size, the speedo will be fine as long as the tire sizes in question are stock.
ANd most important:
Look inside the rear, DO NOT assume ANYTHING about what the ratio is, because it's way too easy and likely for your assumption to be wrong.

 

I WILL double check before pulling the rear.

I wasn't saying that it would increase my top speed. I know enough that without a governor 120-130 tops. Rpms are way up there when it does shut off anyway. I was meaning that since it 's governed off at 110, the 3.42 would be a better suited match. You just explained it in mathematical terms. (170 HP like its spec, but that spec is at say 4000 RPM; but your gear is such that it only reaches 3000 RPM at 120 mph and at that mph it takes 120 HP to move the car, and your engine produces 120 HP at 3000 RPM The 2.73 just feels like it chokes (not sure if that is a suited term) the car off. I have to stay in the gas down low to get up to speed as opposed to 65-70 when it pulls alot better. I live in the appalachain mtn region and the closest interstate is a 2hr. drive away. A field day for auto cross really. I've outgrown racing on the highway. Too many lives involved. Point being though is the roads are all winding, narrow, crooked, uphill, blind curves. I would just like to use the power of the car where I need it, not where it will never be used.

Electronic speedo, thanx for the heads up.

I was figuring the tire sizes were pretty close to the same. One shows more aluminum, the other more rubber. Side by side though they are to the naked eye very close.