1990_RS350

Hi I have a 1990 Camaro RS and i dropped a 350 in it a lil while ago and its got nice lil mods on it... I dropped it in with my uncle and he told me eventually i'm going to want to put a posi on it because the engine will throw out the open wheel rearend... I wanted to go ahead and get posi anyway but theres things i want to know... what would be the best gear ratio? can someone educate me on why a 3.73 gear ratio is better than a rearend with a lower ratio... then i see people that swap out there rearends and before the swap they have drum brakes then after the swap they'll have disc brakes whats with people changing the brakes? does that really matter... any comments would be appreciated... thanks

camarorsssss

iTrader: (2)

What are your goals with the car? Are you looking for quicker launches or higher top end? Do you drive it on the highway mostly or just as a weekend/fun car? The higher gears you go like 3:73, 4:11 ect the faster you launches will be but you will lose top end and gas mileage, so its really up to what you are looking to do with the car. you can always go for something in the middle, like 3:23 or 3:42.

1990_RS350

yeah... i want a quick launch but a good top end too... so i guess middle would probably be better huh? but its mainly my everyday streetcar... haven't brought it to the drag races yet so i don't really know what i'm runnin'. but what about the brakes? does that really matter? i want it to be fast... and eventually i want it to be just my project car i work with through the years after i get a truck when i go in the army. i'm shootin' for fast and sexy.... bring it to car shows and race... ya know? but for right now its just my everyday car that i work on... but yeah... about the brakes?

JamesC

iTrader: (5)

The simple answer is that the more speed you generate, the more stopping power you need. Much of the braking power comes from the fronts, so bigger discs there would be quite helpful. Discs in the rear (such as PBR's with their 11.7 rotors and single piston alum calipers) would be the ticket.

JamesC

1990_RS350

ah... thanks... could i take a posi off of an 80's 5.0 stang? i don't really intend to... theres alot of that in my area's classifieds section of the paper and i was wondering if that'd be ok. what do u guys recommend would be the better gear ratio? for street and drag but not reeeeeeal bad on gas... but 3.73 won't be that much worse than 3.23 right? but anyways... just askin' questions for u guys to throw awesome ideas out to me.... thanks!

camarorsssss

iTrader: (2)

I'm not really sure about the mustang rear end, I know the ford rear is stronger and better, but you will almost certainly have to make modifications for it to work and it will probably end up costing more than its worth especially since they are going to be used rear ends. I would say if you can find a 89 or later rear from a camaro or bird with the pbr disc brakes, posi and 3:42 gears then you would be good, but im not sure what gear ratios came in the later year rears, you would have to do some research. 3:73 is a good ratio if your using the car more for drag strips, racing or just a weekend car, but if your doing highway driving and or drive the car often 3:73 may be a little high., but it really is a matter of preference i think. I am actually in the process of going to a 3:23 posi rear from my 2:73 non-posi rear.

1990_RS350

what does it mean to have a 9 bolt or 10 or 12 bolt rearend? what are the bolts for? just wondering... i don't have too much knowledge of rearends... haha... basically just what they do... could anyone answer that one for me?

JamesC

iTrader: (5)

Number of bolts holding the cover on the diff. Check the following pic of a 10-bolt for reference:

https://www.thirdgen.org/forums/atta...-89-guides.jpg

JamesC

1990_RS350

ah.... thought so...

Mikz86TA

iTrader: (4)

Identification by the bolt number is common. But there is 2 10-bolt apps for GM....one is like your F-body one which has a 7.5 (earlier)/ 7.625 (later) sized ring gear and the truck type 8.5 ring gear. Theres more but you kindof get my drift. Some are represented soley by the ring gear size or just a model number. Ford 8.8 = ring size, 7.5 = ring size, 9-inch = ring size. Dana 44 = model, Dana 60 = model. Most of the time the larger the ring gear size the stronger the diff. Thats why 5.0s Mustangs have the 8.8 and 4 bangers have the 7.5. They actuall look real similar to the untrained eye. Diff cover shape and size along with bolt #s are usually the quick way to ID a diff. Common on F-bodies is the 7.5/7.625 10-bolt which has a round but square-like cover. Other performance models have the Borg-Warner (austrailian) 9-bolt. Has a disticntive odd-looking cover, fewer of them and hard to get parts for. But stronger. 92 Firehawks had a Dana44 I believe it was which is the strongest of them all. Used to be availible through GMPP and pricey. Moser, Strange and Currie all commonly have the GM 12-bolt which is very strong and used orig on HD truck apps. That along with Ford 9-inch models are made now to 'Bolt-In' to our 3rd and 4th Gen F-Bodies. 9-Inch rears are strong, used in all types of racing, multitude of parts options and one of the most well-known diffs. IDed by no removable rear cover, the entire front of the pumpkin (3rd Member) comes out as one unit with the carrier and gears. It can be 'set up' outside the car and poped in. That alone made it popular. Racing teams can have one housing and multiple pre-setup 3rd Members availible if a quick gear change is needed. If you can get over the fact it is a Ford diff, it is generally cheaper than the Dana44 and 12-bolt apps.

camaronewbie

For a reference - I swapped in a rear from a 2002 LS1 car (4th gen). It has the LS1 rear disc brakes and 3.42 posi gears. I have a 350, mild cam, headers, carb. I get about 17-19 mpg on highway at 70mph - in town just sucks, but it's too fun to not put my foot in it at least a few times when I drive.

3.73 would really throw you in your seat, but less gas mileage. For a daily driver with some affordable fun (gas mileage affordable), 3.42 gears would be the pick.

FYI The stock 3rd gen wheels stick out about 1.5 inches farther on each side of the rear with the 4th gen rear, as they were slightly longer. And you'll have to have 16in wheels for a LS1 rear (to clear brakes). But no rubbing problems with Eibach lowering (1") springs.

Glad to type ya some help on the swap, when you get there - just PM me

1990_RS350

awesome... thanks man!

Stephen

iTrader: (12)

The Mustang rear would take a lot of fab work. They are leaf sprung whereas our are trailing arms, coil springs, panhard bar, and the torque arm. A Mustang was OLD simple technology.

duckmanquacker

the 80's 5.0 mustang he refered to would be a 4 trailing arm set up but still way too much work to install, the 4th gen swap would be the best for simplicity.

Stephen

iTrader: (12)

Ah...Yeah, 4th gen rears are direct bolt-ins, except for the wheel bs. If you are doing aftermarket wheels anyways, that's not an issue.

duckmanquacker

yeah I forgot about the backspace issue.

Stephen

iTrader: (12)

I think the bs isn't really an issue, to me. I like the way the factory rear wheels fit, with the wider rear end.

duckmanquacker

did you have any change in your stability?( good bad otherwise)

Stephen

iTrader: (12)

Not my car, but a local club member's. I'll ask him.

I don't expect to notice any difference, except for any gear change, or drums to discs. Although the rear end itself is wider, the offset of the wheels didn't really change the track width by much, or enough to make a noticeable difference.

89formula350b2l

iTrader: (11)

i'm dropping in a LT1 rear end and keeping my stock formula wheels, but getting a set of 4th gen wheels for MT drag radials.....you could do that if you do the swap....

Stephen

iTrader: (12)

Apparently, he DID notice a difference...

"actually i think i did notice a bit difference...i could tell the rear was a little wider and maybe a little more stability but its hard for me to tell cause i need to replace my shocks anywayz."

1990_RS350

with the 4th gen rear would the wheels stick out further is that why u are saying i couldn't use my stock rims?

Stephen

iTrader: (12)

Look again.

I posted a pic of that blue Camaro, with a 4th gen rear, and stock 3rd gen rear wheels. They do sit out farther, but do not stick out.

1990_RS350

yeah i got ya... i think i'td look a lil cooler with wider tires though... like drag radials... ha

Stephen

iTrader: (12)

But like me...Not everybody likes drag racing. Don't get me wrong, but stomp the gas, feather the gas, turn what? 4 degrees left & right? Aim straight, 10 seconds, let off the gas. yippee...

Versus 40-60 seconds of gas, brake, turn, gas, turn, brake, turn, gas, brake turn, turn, turn, gas...I like autocross. Our cars were built with handling. A farmers pick-up truck can run straight for quarter mile.

Feniks9174

Is there a general rule to follow about which cars came stock with a posi unit? I've saw someone mention finding an 89 or later rear with a posi, but I know my 91 RS has an open rear. Were the posi's factory installed only on Z28's and IROC's?

I'm starting a new project on an 86 Z28. I haven't taken delivery of the car yet, so I don't know what it's situation is, but the first thing I'll need to do is put a Posi in it if it doesn't already have one. It'd be nice to know where to find one.

Stephen

iTrader: (12)

GTAs had posi & disc brakes standard, but in the 9-bolt rears.

1LE Camaros all had posi & disc.

Zs had drums or discs, depending on years. Not positive on on Zs=posi. I'm sure someone will chime in.

JamesC

iTrader: (5)

No. My 85, while it originally had four-wheel disc brakes, did have have limited slip. The 86 that I swapped in from another IROC not only had discs but a posi.

JamesC

1990_RS350

i'm guessin' all RS' had open wheel rears... because most the RS stock rears I've seen were open... and i'm lookin' to get a NICE rearend... because i can tell this new engine i dropped in my baby is gonna throw me in my seat and make all the blood rush to the back of my head with a posi... hell it already throws me kinda with the open... i just can't wait to get it fully restored and bring it to shows... so far its restored.... hmmm... if engine counts... 2% maybe? haha...

Stephen

iTrader: (12)

Yep. Except for B4Cs, but the only thing RS about them, were the badges!

My wife almost FORCED me to swap her 3.08 peg leg, in her '90 RS, for the 3.73 posi, from the '84 Z28! Not that she had to ask me real hard though! LOL

1990_RS350

man... i'm runnin' with the baby 2.73. about how much time u think it'd take me to take a bolt in posi rearend and bolt it into my camaro... and take the drums off and put discs on... is there anything else special i'd have to buy for the bolt in rearend besides the rearend itself?

RPOL98

I figure it must be only the manual trans guys that are crying about the 2.73 rear end. with the ridiculously steep first gear of the 700R4, you can do smoky burnouts, whiplash launches regardless of what gearset you have in the rear end.

randomguy121

ohnestly i would talk to a place that specialises in rearends and mods. if you go to a ford 9" loke most you automticly have a problem with driveshaft length and lugnut spacing im assuming. some years of camaro/ firbird came out with kick @$$ rearends with rotors. you might ask them what to look for......... thats what im fixing to do is my rearend. i haft to talk to them about possi trac vs a mini spool and whats best so i can still drive it on the street. hopefully ill find good advice here hahaha good luck

1990_RS350

nah i'm runnin with an auto tranny... i just know that the lil 2.73 is nothin' compared to the kick of the 3.23 or higher... why would i wanna brag about open one wheel burnouts and leaving from a dead stop with ONE wheel? it won't be as good as posi

Stephen

iTrader: (12)

My 3.27 posi roasts the tires pretty easily. Even at 161,00 miles! Once the car is moving, like 25+mph, it is harder to break the tires loose....if the tires are warm, I rarely get a 2nd gear chirp. If the tires are cold, the 2nd gear chirp is pretty easy. Even got a 3rd gear chirp, once!

kenf729

iTrader: (3)

Just to give you an idea, I found a 3.23 posi rear with disk off an 87 IROC, the hardest part of the swap or most time consumming was the E-break cables up in the tunnel, (very little room to work) all in all you should be able to swap the rear end in a weekend very easy, one tip is to calculate the gears needed for correct speedo readout and pre order the parts.

Ken

Shagwell

..well, atleast you said auto cross, not asscar. Straight line is easy? try 10.5 outlaw. 2500hp, factory front suspension, factory firewall(no engine set-back) and a 33x10.5w tires on the back. - They want to go anywhere but straight.

- pre 88 10-bolts were 26 spline axles instead of the later 28s. Factory axles are weak enough, I wouldn't chance the little ones with much power. - as for gearing, it all comes down to your engine's power band and the intended use of the car. Low gears(numerically higher) will give you a quicker launch, but you'll top out sooner. - Steeper gears tend to be harder to hook up as they try to bring the wheel speed up faster. Most tires are controlled spin, especially street tires. Low gears make it easier to control wheel speed, thus easier to control spin.

Stephen

iTrader: (12)

Asscar is even worse...Straight, turn left, straight, turn left, straight, turn left...for the next hour. No thanks. At drag racing is over quickly. 10.5 outlaw isn't exactly the same as drag racing a street car. Just like Funny car, Top Fuel, etc. Not nearly the same.

9-=bolts are stronger than 10 bolts, but (according to those you talk to) weaker than a 9 inch, others say they are equal. Thing is, 9 inch parts aren't cheap, and there isn't near the choices. I'm lucky enough to have 2. If I break one, I can be going again, in no time. Just swap them out, the fix the broken one, if I want to. I'd probable just get a 4th gen rear, if I broke bot my 9 bolts.

flaming-ford

iTrader: (7)

a 9 bolt is a ton weaker than a 9in, your talking the difference of a 7.625 ring gear compares to a 9in gear. I think you're were getting part of your response backwords 2 no offense.

9in are a much more common rearend than a bw 9bolt. the 9 bolt is the 1 hard to get parts for, and they are also pricier (300$ for a gear set).

as for fourth gen rears i think the extra 3 inches in length is a definite turn away for me. they just won't look right with factory rims anymore, easily correctable with a different rim but, still.

anyways i have a factory drum 3.23 posi 1989 iroc-z.

btw if you're not having problems with factory brakes i wouldn't swap them out. Now the fronts are a whole different story though. you have to remember 60%+ of braking is on the front on a rear wheel drive car. the factory front brakes (other than 1le's) are truly pitiful so upgrading is definetly a smart choice

Stephen

iTrader: (12)

Well, you can see the pic I posted in this thread, of a blue Camaro, with a 4th gen rear, but the stock wheels. I think they fit perfect. Not a lot of dish, but that's the same as stock. The 3" is total width, so only 1.5" per side.