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Someone want to explain rear end gearing to me?

Noriaki

Lifer
Jun 3, 2000
13,640
1
71
Ok...
I think "Higher" gearing (smaller numbers) is better for top speed, and "Lower" gearing (bigger numbers) is better for acceleration...

Or something like that.

Someone want to explain to me what exact 308 gearing or 373 gearing or something like that means?

And why are bigger numbers low gearing? and lower numbers high gearing?

Basically Mathew upgraded his rear end gearing from stock to 410s (pardon moi, the 410s are in the 97 cobra, his 90 LX 5.0 has 373s) now he gets much better acceleration.

Why? What does 410 mean, and how does it give you better accel?
:D
 

Fubak

Member
Jan 10, 2001
153
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0
First of all, the numbers look like this... 3:55, 3:70, 4:11, etc.

Lets use 3:55 as an example...

The 3 is for the number of turns the wheel will make for every 5.5 turns of the drivetrain. (drivetrain = the long pole comin from your tranny to your rear-axle)

So with that said, and hopefully you understood :), the closer the ratio (4:11) the more 'off the line' torque you will have (ie. more power). The more distant ratios (2:73) are made for daily, highway, and granny driving (ie. less power).

The reason the 4:11 is better for low-end power is because it only requires the drivetrain to turn 1.1 times for every time the wheel turns. This also causes the RPMs to be somewhere in the range of 2800 RPMs at 50mph.

Did this help at all?

Disclaimer: I'm not completely sure on the last paragraph, but it will give you a good idea as to how they work. Anybody else have an input?
 

Noriaki

Lifer
Jun 3, 2000
13,640
1
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<< (drivetrain = the long pole comin from your tranny to your rear-axle) >>

LOL thanks, I know what a drive train is ;)

Ok..I think I get it.

But now I'm confused about something else.

Mike (yet another mustang owner ;) 87 GT this time) was complaining about his 308s...(3:08?)...

Why is a 3:08 much worse than a 4:10

Wouldn't 3:08 be the same as 4:12? Not that much worse that 4:10 is it?


<Edit#2: Ignore brainfart, text removed>
 

Fubak

Member
Jan 10, 2001
153
0
0
Ok, thats where I'm not exactly clear on the whole thing either. BUT I do know that the bigger the numbers, the faster it will go off the line.

I'm putting a 9&quot; Ford rear-axle w/ 3:70 gears and posi-traction in my Mustang. check out the link below...
 

Fubak

Member
Jan 10, 2001
153
0
0
4:10 is overall. No matter what gear your in, the rear-axle's ratio will ALWAYS be 4:10.
 

Noriaki

Lifer
Jun 3, 2000
13,640
1
71
Yeah I saw your sweet ride the other day :)

I didn't bother posting in any of the threads but I read your whole site :D

Yeah...but then wouldn't 3:70 be like 7 turns on the drive shaft to 3 turns on the wheels? That seems pretty week...

heheehehe *confused*

Yeah...ignore the &quot;what gear&quot; comment....read end != transmission.

Don't mind that brain fart....
 

Fubak

Member
Jan 10, 2001
153
0
0
LOL to 'brain fart'! That's a new one! haha

Like I said, I'm not completely sure about ALL this, but I understand the basics of it.

3:70 will give me a good medium between daily driving and racing. The rear-axle is your biggest bang for the buck, seriously. You could put $500 (including installation) into the rear-axle and majorly boost your @thetire horsepower :D

Personally, I can't WAIT to get that posi-traction rear-axle in there! I HATE one-tire fire w/ a passion now :|
 

Noriaki

Lifer
Jun 3, 2000
13,640
1
71
Heheh brainfart isn't my creation. But I've been using it for some time.

Yeah posi-trac is good ;)
 

ThisIsMatt

Banned
Aug 4, 2000
11,820
1
0


<< drivetrain = the long pole comin from your tranny to your rear-axle >>

Eh? Wouldn't that be your drive shaft? As I recall, drivetrain is the entire linkage from engine to wheels (tranny, drive shaft, rear end, etc).

Correct me if I'm wrong.
 

Pacfanweb

Lifer
Jan 2, 2000
13,131
54
91
Here is the correct explanation.

4.10:1 gears means 4.1 turns of the pinion gear(and therefore the driveshaft, since is bolts to the pinion yoke), to 1 turn of the ring gear (therefore the axle, since that is what ultimately turns.
Basically 4.1 turns of the driveshaft to 1 turn of the tire. That is considered a &quot;low&quot; gear, meaning it is a lower speed gear, for pulling, but works in a hot rod for acceleration.
&quot;High&quot; gears like 2.73's are because they are for more high speed operation like highway driving.
 

thedarkwolf

Diamond Member
Oct 13, 1999
8,960
89
91
I am no expert here either but the way I understood it was with 4.11:1 gearing your driveshaft turns 4.11 times per 1 revolution of the axles. That gives you a lot of off the line power but kills top end speed. My car has a 2.79:1 ratio which isn't great off the line but it cruises at 80mph easy, plan to go to 3.23:1 or 3.50:1 at some point.
 

Green Man

Golden Member
Jan 21, 2001
1,110
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0
You guys have it wrong. The ratio for a 373 gear, for example, is 1:3.73
In this example, for every 1 turn your wheel makes, the driveshaft makes 3.73 turns. For a 4.10 gear, the driveshaft makes 4.10 turns for every turn of the tire.

Does it make better sense now?
 

ThisIsMatt

Banned
Aug 4, 2000
11,820
1
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<< Ahh yes I believe you are right Matt.

Doens't help my question much though ;)
>>

I know :) but I was contributing...a little :p

Screw it all and get a 2 speed differential like the big rigs :D
 

Noriaki

Lifer
Jun 3, 2000
13,640
1
71
Ahhh ok so it's 4.10 or 3.73 or 3.08 and the :1 is implied.

Making good sense now :)

Thanks guys :)
 

SupaDupaCheez

Platinum Member
Nov 21, 2000
2,034
0
0
I have a '70 Chevelle which started as a 2bbl 350 Grandpa 'Rod' with 2:56 gears and no posi-traction. I switched out the gearing to 3:73's and posi-traction. The difference is CRAZY! 3:55-3:73 is a pretty good mid-point between power/gas mileage/top speed. Plenty of Torque off the line and good/great highway passing. 4:10/4:11's will KILL your mileage and drive you nuts at speeds over 50mph. You will probably never see 70mph (at least not for very long) and you WILL be able to SEE your gas gauge move!!! If you are looking to build a strip car then 4:10 are ideal. Otherwise go for something in the mid 3's (IMHO).

SDC
 

Sluggo

Lifer
Jun 12, 2000
15,488
5
81
Some newer cars with overdrive transmissions can handle 4.10 gears in the back.

There is also more to the equation. The height of your rear tires can effectively change the ratio of your rear end gears. For example, if a guy has a big four wheeler and gets maybe 35-38&quot; mud tires on it, he may have to drop to a 4.56 gear or lower to maintain the proper final drive ratio of his vehicle. The motor may not have the torque to turn the taller tires without the assistance of the lower gears.

If you put shorter (heightwise) tires on a car, you will be effectively lowering...(higher numerically) your rear end gears.
 

SupaDupaCheez

Platinum Member
Nov 21, 2000
2,034
0
0
Yep...forgot about that Sluggo...I stand corrected. I guess I've been thinking about muscle cars a bit much lately :)

SDC
 

Stallion

Diamond Member
May 4, 2000
3,657
0
76
Most all newer cars have an O/D tranny so 3.73 or 3.91 gears would work nicely. When I first got my Olds it had 2.73 gears. It would do 100mph at just over 2800rpm (or somewhere close, it was 15 years ago) then came some 3.42s and those were great all around gears and now I have 4.10s that are good for nothing but racing and the stop light drags. At 60mph I turn about 3500rpm and highway driving is non-existant for long periods. :( But stop light to stop light is a blast. :)
 

Noriaki

Lifer
Jun 3, 2000
13,640
1
71


<< or you can call it poor man's supercharger. >>

Actually the car might be getting a blower a some point to ;)

For now, we are going to port the heads, redo the intakes and exhaust and up the ass end gearing from 3.08 to 3.73. I just wasn't quite sure what upping the gearing from 3.08 to 3.73s did for you ;) Mike explained that it gives you more low end torque and sacrifices top end speed.

I see why he can cruise at 120kph at 1800rpm with his 3.08s now (in overdrive). I guess that will disappear when he goes to 3.73s.

Thanks for all the info guys :)
 

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