I am probally going to save up for 4.10 gear but I need to know how many rpms I will Be spinnin at 60mph (thats the speed of all higways here) My tires are 25".
I have the Auto OD Transmition.
I have searched and came up with many different answers,

Some guy said 2317.2RPM, he calculated this, and he seems to know whut he's doing.

And some other guy said that 3.73's will make you spin 3100RPM at 65mph..

My dad said he knows to install gears, When he was young, every vehicle he got he put 4.10's in. So I think I trust him lol.

City streets around here are 40km/h to 70hm/h so,

40km/h / 1.6 = 25mph, 70km/h / 1.6 = 43mph

So I am guessing they wouldnt hurt mileage much if I turn 2317 at 60mph.

 

The guy was right, 2317rpm at 60mph I used: https://www.thirdgen.org/newdesign/t...ulations.shtml

This is for a Tire with 12.5" Radius.

Findign the top speed for each gear,

30mp/h In First @ 5100 RPM.
56.7mp/h In Seccond @ 5100RPM
92.5mp/h In Third @ 5100rpm
132mp/h In Forth @ 5100RPM

Top speed at peak power is 132mp/h @ 5100 RPM..

 

ok dumb question..... how much would it cost to take it to a shop and have then put 4.10's in?

 

Well, I dunno how much this will help... but when I used to own a 1985 Fiero GT 4-speed (with the 2.8 V6/60), it had 4.10:1 gears..

sure it did the quarter mile in high 14s... but the top speed in that car was like... a hair under 100 miles an hour. It was SCREAMING at 90mph.

On the highway.. driving around 60-65 miles per hour, I was running about ~2,400-2,500 rpms.

 

how much do u think it would inscrease 0-60 times or 1/4?

What about low end? Will I be able to light em up real easy with 4.10's? Should I get posi or no?

 

Dude, 4.10s are SICK..... I mean, there is at least 400 pounds of weight difference between a LIGHT 3rd gen, and a HEAVY Fiero.

But my V6 Fiero weighs a hair under 2,600 pounds, with the VERY SAME 2.8 liter V6. The Fiero happens to put out 10 more horsepower, and 10 more pounds of torque. But my car originally had a 3.65:1 final drive, and the transmission crapped out. Rather than repair it, we snagged a 4.10:1 4-speed from a FWD Chevy Cavalier.. exact same tranny. (The engine in the Fiero is a FWD set-up.. but placed in the rear.. making it rear wheel drive).

In any case.. the Fiero is supposedly supposed to have some of the best traction of pretty much any GM car ever made.. and even with only 180lbs of torque, those 4.10s lite up those tires like it's no-bodies business.

I definitely suggest POSI if you're going with 4.10s.. otherwise you'll never get any traction... even with the 2.8.

 

Shops charge about $200-$500?
Me?
I'd seek 3:73, very good compromise.
I drive freeway, so 3:42 are great for my usage & I have plenty of pep off line with the 3.4.
I'm more concerned with longevity of project (not having to buy new cars is great!) than total 1/4 power.
That's why I swap in late model engines, it's "cheap" fix. Then add rebuilt tranny's and I'm gone. I hope this 85 Firebird will last about 15 more years (it just turned 120K miles) for quite a while.
So far chased away new cars for over two years, now.
For cost of maybe 3-4 new car payments. Labor is mine & I come cheap (for my work & cars, only)!
Last person's car work I took on, I ended up marrying the owner!
But she came with a 1968 Camaro to match my 1967 Camaro, so...... Yeah she's still a BABE, even gave me a SON (to one day take posession of the 1968 Camaro, too!).
These days, seek 3:73 & more TORQUE of the 3.4.
You'll be pleased with that combo, promise!

 

I agree, 3.73s are much easier to live with than 4.10s. Unless ALL that you're doing is regular street driving UNDER 50 miles an hour, then 4.10s are good.

 

82T/A, were those 4.10's factory? The Fiero had a transaxle, right? Can the gears even be changed in a transaxle?

 

The Fiero WAS offered with 4.10s, however, ONLY In extremely rare cases.

4.10:1 gears were ONLY offered in 1984 Fieros, and 1985 Fieros.

In 1984, there was ONLY the 2.5 liter Iron Duke. They offered three Transmission gears.

Economy Option : 2.15:1
Cruising Option : 3.02:1 (could be off on this)
Performance : 4.10:1

In 1985, ONLY the Fiero GT was available with the 4.10:1. However, something like less than 200 or so were actually ever made with the 4.10:1.

MY 1985 Fiero GT, originally came with a 3.65:1 final drive.
However, the entire transmission crapped out, and it was replaced with a 4-speed muncie (same tranny) from a 4 cyl Chevy Cavalier. This transmission just happened to have a 4.10:1 in it.

Didn't occure to me until it was installed and I realized how quick it was that I decided to run the numbers on the tranny casting.


Apparently, you CAN change the gear ratio, but you have to open up the transmission because the gears are inside.

 

Cool! My buddy had a Mazda MX-3, looked up the gear ratio, it was a 4.23:1. Those auto makers go all out on a FWD's "rear gear" ratio! Do you know what those gears would look like in a transaxle? Are they the same ring/pinion we're used to? If not, I could see GM asking $1000 for a gearset... ouch. Did any of those come with a posi? Is that even possible? (I know nothing about transaxles)

 

I'm actually not TOO sure about POSI in Fieros...

I DO KNOW that the 5-speed Isuzu Getrags were available with a "limited slip" option, however, these were only available in the 1988 Fieros. This includes the 1988 Fiero Formula V6, and the 1988 Fiero GT.


I've heard rumors that 1985 Fiero GTs (the quickest of all Fieros) were available with limited slip in the 4-speed, however I have never seen one. I don't know that Posi is really THAT important.. the Fiero motors all produce most of their power in the low end all the way to 500rpms shy of red-line. So, since there IS that much power down low, it's not necessary to "get up your revs" when you launch... (IE, a burnout).

Limited slip is really only useful for cars that...
A) Have poor traction.
B) Soo much power they don't know what to do with.
C) Require HIGH REVS in order to make any power.

The Fiero has pretty much the best traction you could get, it doesn't really have THAT much power (180lbs of torque), and it doesn't need high revs in order to get any power.

So... as long as you're not doing a clutch drop, and you're not driving in the rain.. it's un-necessary. (In a Fiero)

 

Okay, I see what you're talking about; good point. Also, the engine was right over the drive wheels, and the drive wheels are in the back; I imagine it's probably pretty hard to spin the tires unless you really want to, right? It's gotta be a buttload worth of traction, just from the car's design. I keep seeing the 4cyl Fieros in junkyards, never a V6. Too bad, I want that TB!

 

I see V-6s often & the TB is different.
What way?
Just slightly off and nothing in the F body seemed to line up. Same thing I ran across in the 3.4 swaps.
Just different.

 

Any idea on hwo much they will increase 0-60?

 

It's probably not worth the trouble. It'll fit, the plenums are almost the same, but you'd be better off pulling the engine and doing a complete performance rebuild... or going with a small block chevy.

Todd

 

Mike..you got a good question man. I've been considering the very same thing..whether I should run 3.73 and 4.10.. I don't get on the interstate a LOT, just to go to the movies and when I'm going to other cities...70 mph on the interstate but I usually do between 75 and 80..average traffic speed on I-95 it seems... I want 4.10 pretty bad to give the car some real pep, but I don't want to be guzzling down gas on the interstate either...3.73 isn't beefy enough but 4.10 is too beefy, why isn't there a 3.95?!

 

Hey, correct me if I'm wrong, but isn't the 10-bolt rear end in a 2nd gen Camaro / Firebird the exact same rear-end as the ones found in the 3rd gens?

If that's the case, why don't you guys just pull a rear end from a 2nd gen TransAm?

ALL TransAms came stock from the factory with clutch-locking Limtied Slip rear-end differentials. It was optional on Camaro Z28s... but was standard on TransAms. So, as long as you can FIND a TransAm in the junkyard, you can just swap rear ends. The base gear ratio was 3.08:1, but they had them with 3.73:1 as well.

Your BEST BET to make the 2.8 go fast isn't to change your rear end.... unless of course you've got 2.73:1 final drive or something.

ME? I've got a 3.08:1 Posi in my 81 TransAm, and that's what I'm sticking with.

Just add more horsepower. There are two cam-shafts available for the 2.8 liter V6/60 engine from Crane....

There is the one that improves low-end to mid-range power, and then there is the one that improves mid-range to upper rpm power.

Simple as this, if you have an automatic, get the one that improves mid range to upper RPM power.

If you have a manual, get the one that improves low end to mid-range power.

It's very simple to install a cam, especially on those engines.

Mix that with a 1.52:1 roller rocker set from Crane Cams (roller rockers are $120 bucks) and you're looking at around ~25 more horsepower. Next... replace your catalytic converters with free-flow catalytic converters or go with straight pipes... but whatever you do, don't GUT the cat, that does VERY little for performance, it creates a pressure zone in the open space where the cat is and prevents proper flow that a regular cat, or a straight-pipe would normally create.

 

Only reason I'm looking at a rear end is because I might not keep this engine. I want to soup up parts of the car that I can keep if I get rid of the engine and tranny.....which is why I'm only really looking at a rear end performance-wise..everything else I'm considering is cosmetic. I've already thought about the cam and roller rockers...but I'd have to tear down the front and top of the motor and I just dont have the tools, equipment, and knowledge to do that, and shops will charge too much. I already considered all that before..I was thinking about a Crane cam and 1.6 roller rockers and a Crower double-roller timing chain..

 

The 2nd gens rears are probably different.
Surest thing, but no true proof, is score a 4 cylinder rear axle gear set.
Those "tend" to be 3:73 ratios.
Funny they make 3.08, next 3.36 gears, so yeah why not a 3.95 is a good question.
Find an axle outta car for your gear experiment.
It'll be easier to swap complete rears once gears are set up.
PS Creating/building a rear axle can run close to One Grand.

 

crane cams makes 7 diff cams for the 60* v6 (only 2 are computer friendly) and the $100 1.52 roller rockers are roller tip only..

back on the subject of rear ends, i hate the 3.08:1 in my 83.. (100hp v6 w/ 3speed at w/ 3.08:1 rear end.. what as gm thinking??) looking around, ive seen a couple sites that sell rear ends mention that u need some kind of spacer for 4.10:1 gears.. something bout them being too wide to fit properly..


-mike (loomdog)

 

(100hp v6 w/ 3speed at w/3.08:1 rear end.. what as gm thinking??)

New EPA gas economy limit rules that penalized car makers if fleet average dipped below xx.xMPG.
Remember this was the beginning of the end of the dark days from Detroit.
Ford just released the Mustang GT using a Holley Carb. Chevy Camaro/Pontiac Firebird were GM performance leaders, new Corvette was one model year away (1984).
And Boy was I having a blast living in California!

 

4.10 gears will definately improve your low end acceleration, but it kills top speed if that is any concern. I am going to stick with the stock 3.42 gears, which are fine for me since most of my driving is in the city.

 

The 1970 Vega
Gave birth
To the 3rd Gen Fbody rear axle design.
90% of it.
Serious.
S-10 trucks four cylinders have the "3:73" gears.
S-10 trucks & Fbody same rear axle expect leaf spring perch & bolt ons for the torque arms.

 

2nd gen rears are the 8.5" 10 Bolt rear, 3rd gens are the 7.5" 10 bolt rear

 

The 4 bangers weren't the only ones to get 3.73's. I just learned the other day that early L69(305 HO) T5 cars got 3.73's as well.

 

my car gets horrible highway gassmileage because
i run 3000RPM at 75mph,
and 4450RPM at 110mph

my tires i have on it are 225/60r/15 how do i calculate my rear gear for it?

do u think my lower profile tires are bringing my rpms way up?
as i think about it, if my tires are smaller than the factory, the speedometer reads a higher mph that it really is going,, so would that mean i am going slower than 75mph at 3000rpm?

what kinda gears does this car have?

 

3000 at 75? Christ that's high! But then 4450 at 110 mph is pretty good! Were you running without Overdrive when you were doing 75??

 

You need to swap speedometer gears, www.700r4 has a calculator for determining which drive/driven gears you need to get the correct speed reading.
Now my car, non TC lockup 3.42's, 225-60 14 tires = 3k@75mph and it is a correct reading.

 

btw, its a 5 speed, final gear is .75

and when i do 75 in 5th gear the rpms are 3000
not to mention i actually goin slower cuz my wheels are smaller

 

Yeah....I think Overdrive on the autos is .75 also but I'm not 100%. Wow..turning quite a bit for 75, at least that's how it seems to me. My car's very well-mannered on the highway. At 70-75, it turns..well, my tach is dead..but it FEELS like 3500 in Drive...with Overdrive it's quite a bit less. My tires are 235-60R15 and it's got the stock 3.23 rear.

 

IF your speedometer is reading correctly...
That would mean You have 4.10 rear end gears.

 

Nevermind.

 

I don't think so though... I've driven past those police radar station things..they radar/laser all passing cars and display the speed you're going on a big thing..it's a scare tactic..and my speedometer is always dead on with the thing. Even though my VSS is about to go out..speedometer periodically doesnt work and I throw a VSS code now and again. Wish I had a freaking tach! Then I could be positive about all of this. But according to my tach, the slowest idle speed I have is about 5000 rpms. When I tap the pedal I push past the 7 grand and bottom the needle out.

 

C'mon now, you should've known that already! That's the car I got my 3.73/posi/disc axle out of! An '84 Trans Am, engine code "G" (think "G" for "Gold"), 305/T5. Just remember, if you get this axle, you'll absolutely positively need to put the GM recall kit in for the rear calipers to get rear brakes. The recall kit is $40 from gmpartsdirect.com (do a search for posts by me about recall kit and you'll find the part #), order the parts individually instead of getting the recall kit and you'll pay over $200.

And Nixon, you're right, those signs that display your speed -are- a bunch of crap. Know what those are about? They're taking a traffic survey. Each road, every now and then, goes thru a survey to determine if the speed limit is adequate. So say the posted limit is 40. They do a survey. Everyone sees this automatic radar "this is your speed" sign, gets paranoid, pictures the whole police squad parked behind a bush just Waiting to pull them over- and they slam on the brakes. They slow down to 32 MPH. Say everyone does that. Well guess what? In a year or so, you'll see the speed limit on that road drop to 30 mph. And nobody will want to do 30 mph; they'll keep doing 40. And then the cops will pull 'em over. And then the town makes money. Great, huh? So now, I speed when I see those signs. 'Course, I make sure there's no cops around

Oh, here's a good one: Few months ago, they had one of those signs on a road I travel at least 4 times daily. The frickin' sign was placed in the middle of a hill. Radar travels in a straight line. So guess what? As I'm going up the hill, speeding, at 60 mph, the little sign read low #'s, until the beam was straight at my car. So as I'm coming up, it would read like 20, 25, 40, 52, and when I was "level" with the sign, then it would read 60. So their little survey would come up with an average of 40 mph. I can't wait to see what the limit drops to.

 

btw the 4.10 ratio reply was for rsrick

 

Dammit Tom, I coulda swore you got that axle from a 4 banger.


Those tires wont noticably affect your speedo. They are very close to stock. There is definitely something wrong with those RPM's being so high though........

 

**** man I wont even shift till 2500-3000, thas no big deal when redline is 6500.

most time Ill drive around in 4th gear about 2500 rpm everywhere. car sounds better and 5th gear is a real dog at that low of a speed.



4.10 gears sound like fun, I dont drive very far much, once ina while Ill get on the eway and get across town fast but still, if 60-65 was only 2500, oh **** big deal. now if it was like 4500 then I would worrie.

I know a guy with a 3:73 posi but its for an 80s olds cutlass. But a 4.10 sounds better.

hmmmm 4.10 with a T5 sounds very inteesting, not to mention a 5th gear.

 

Someone up above posted that 2nd gen TA's all got limited slip differentials. That is not true. A lot of them did, but i have run across several TA's with open differentials. Also, I believe that the 2nd gen rear end is wider than ours, along with all the other differences.

Hey tom, around here, they don't even bother with the 'your speed' signs. They just arbitrarily decide that the road people have been driving 55 on for the past 50 years probably, is now not safe to drive above 40 MPH on, even though there are no more houses or businesses than there was 10 or 15 years ago. One week the signs get changed, the next week, the cops are out there writing piles of tickets to fill the city's coffers.

Oh yeah, the 3.73 gears came with 4 cylinder cars, but those didn't get positive traction or 4 wheel disc brakes. The only 3rd gen to get 3.73 posi disc brake rears was the 1984 L69 305 H.O. with a 5 speed. I don't think that ratio was available in 1985, but I could be wrong. That means that them beez a pretty rare find. (lucky dog!)

 

Well, here's some more fuel for the fire, . I installed 4.10's in my 90 RS a year ago August, along with an Eaton clutch-type posi. Since installing them, the biggest drop in fuel mileage for me was around town, especially where speed limits are less than 40mph. I believe this is mostly due to the fact that below 40 the torque converter stays unlocked. With 235/60 R15 tires, I am turning 2200 at 60 and 2600 at 70 (www.f-body.org/gears). Around town I still get 18-20 mpg, and on long trips back and forth to school (400+miles), I get between 26-29 mpg, thats mixed interstate and 2-lane 60 and 70 mph speed limits. So, if your car is in good shape and tuned well, you should see similar results.

 

On the same thought, those of you worried that lower gears will limit your top speed, let me just say that if you are running a stock 2.8 or 3.1, you will run out of power before you hit the rev limiter in top gear. For example, IF my car was able to hit a redline of 5500 in overdrive, it would be traveling 149mph, not likely with a stock 3.1, in drive you would hit 104 at 5500. Wouldn't it be fun to remove the ol' speed limiter and install a shift valve for wide-open shifts to OD! Or better yet, a 5 or 6 speed manual

 

even with 4.10 I dont tihnk my top speed would be possiable.

I got no speed limiter.

with stock rear end and t5 it says my tops speed at 5500 rpm would be 227mph, if the road was long enogh and I could stay awake long enough and carry enough gas, maybe after a week or so 5th will wind out.

with the 4.10 gears my top speed would drop to 173, still too fast.

Im sure a 2.8 would start to poop out around 140.

I know ive been near 120, held it wide open many time till the other guy gave up, probably at 110 when it pooped out like every car on the road past the 80s.


more and more you talk, 4.10 are a smart solution for the 2.8 andeven better if ya got a T5 T56.

ok so now who has the best price on a 4.10 posi to replace my open wheel 3.42???

 

oh yea, why is everyone including me saying 4.10, its GM thats 4.11

I asked in the trans section aobut a low budget open wheel to 4.11 posi

sound like a real step in the right direction, we all know the v6 has the peep, just needs some help planting it.

good runnin stock thridgen on 75-100hp NOS shot with 4.11 posi. no major mods needed. anyone wanna guess on 1/4 times

2.8
3.1
3.4

 

Are we talkin stick or auto? With a good driver and good tires I might be inclined to say high 14's? at least low 15's with a 2.8 (I didnt think 3.1's were much different performance wise, maybe 1/4 or 1/5 sec quicker?

3.4 would have to hit high 14's with a good exhaust, headers, intake, 4.11's, and a 100hp shot. Definately with a cam.
160 hp
+100 (NOS)
+20 (?reasonable estimate for exhaust/headers/intake?)
+10 (Cam, rockers)
290 at the flywheel

and when you add in the gears, I would believe maybe a 14.9 or so.

Remember though, I was dropped a lot as a child, and frequently crashed my bicycle in the ditch so I could be possibly be wrong.

What do you all think?

 

.....I've been saying 4.11 for the past year now!! I only started saying 4.10 cause everyone else was!

 

eh, its ok to call it a 4.10, its just like rounding...no one ever pays attention to that last digit.

If you have a 2.8 engine, you might as well round it up to 3.0...If you have a 3.1, why not just round it up to a 4.0? 3.4's are close enough that you might as well just call it a V8

 

well, 4.10 vs 4.11 is a little different between 3.1 and 4.0. The fact is, the gear set is listed both ways. Richmond Gear lists it as a 4.10 Summit part # RMG 6903221. Randy's Ring and Pinion lists it as a 4.11 no part # on website. So, it depends on who you are talking to, but its really not worth arguing about.

 

Agreed. I just think 4.11 sounds cooler!

 

If you had 290 Flywheel Hp, you should be able to turn a lot more than 14.9 in the quarter. I believe that I am somewhere in the mid to high 15s with my nitrous shot on my 3.1 liter, depending on how much bottle pressure I have. I have never taken it to the track, so i am not positive. I arrive at that by comparing how I did against cars that have been to the track and have a timeslip. I can beat a truck that ran a 10.4 in the 1/8th, so that is where my guess is coming from. If I am getting roughly 215-220 flywheel HP, and have 3.27 gears in the car, and can run high 15's, I would say that a car with 75 more HP, and 4.10s should be able to run mid to low 14s in the quarter with any kind of traction at all. That's just my 'educated' guess.

 

Thats what I thought, but I was being conservative just to be safe. I was think 14.9 at the very least.