3.89 or 4.11?

[metalshapes]

I need to get the limited slip diff rebuilt thats in my '28.
And since its being worked on anyway, I think I should change the R&P as well.
I normaly like the final drive to be a little tall, but this time I might have over done it a bit.
Right now it has a 3.55, 7.50X16 rear tyres, and a T5 5speed.
The engine loves to rev, 283 SBC with a aluminum flywheel and a VS57 McCulloch blower.
1st gear feels a little tall, but I could live with that.
In 5th gear the car is slower than in 4th. ( thats probably because when I shift to 5th the boost drops with the revs, and it cant build it back up )
My question is: will I notice the difference between a 3.55 and a 3.89 gear, or should I go from the 3.55 to a 4.11?
I know I should have given more information, but the car has no tach and no accurate speedometer.

[thirtytwo]

if your motor lags that much with the 3.55 i would probely step to the 4.11 sounds like the little 283 would like that better, where is the split though? i know there are usally three carriers for differnt gear ratios , i think usally there is a 3.73 and lower gear carrier ,but i think they do make a couple of ring gears that are special intermidiate???

[metalshapes]

I think thats just for the Chevy carriers.
My '28 has a 9" out of a '57 full size Ford, and I am pretty sure one carrier does the trick for all the different gears.

[Deyomatic]

Alex, go to this site if you want to play around with the math end of figuring out which ratio you want.
If you have an OD in that 5 speed, I'd go with the 4.11. From what I hear, you can tach that 283 out pretty far. From what I've read, my Eclipse has a 4.15 axle ratio, but that is 4 less cylinders-and a torqueless POS! Just something to think about.

http://www.richmondgear.com/101032.html

[thirtytwo]

looks like your right thats what i was messing with before this early ford stuff, just looked at a catolog that seems to be a gm or dana dealthey only list on diff for a ford , sorry

[metalshapes]

Thanks guys.
Deyo, that calculator is fun!
I Googled the T5 and all I could find were the specs on a Mustang tranny, OD on that was .80
My tranny is out of a IROC / Z28 , and if thats the same, then 4.11 might not be enough.
Should I go for a 4.56 or is that getting a little crazy?

[Deyomatic]

Just for reference again, I THINK my Eclipse has 2 OD gears, a .8? and I think a .68. A 700R4 has a .70 OD. I think that when I use that tranny again, I'm going to try for a 4.11 or lower, depending on what the vehicle is.

Just make sure you have the right tire diameter in that calculator and if what it says for the 4.56 gears seems alright to you, go for it.
I personally feel "guilty" if I'm driving faster than 75, even with the 75 MPH speed limits. It is from years of conditioning in East Coast 55 and 65 MPH highway zones. http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif So for me, a really low gear will be fine, because I won't ever want to sustain a high speed. The real fun is getting there!

[gettingreasy]

A buddy of mine had a T-5 outta a Iroc that wasn't OD, it had pretty close ratios from 1st to 4th but a wide ratio change from 4th to 5th. It was in a heavy Chevy pickup with 3.73s and cruised just fine with a 350. I think you could get away with 4.11 with a 283, another freind of mine had 4,10s with a 283 in a 54 chev p/u and cruised REAL nice, but it had a 3 speed in it. Sorry for the rambling just throughin out some facts for you.
-Jesse

[John Copeland]

There is a significant difference between a 3:55 and a 3:89, without question. Although the 4:11 is streetable, your pushing the envelope, if you plan on hitting the freeway. If your talking about stop light to stop light, and your going to stick close to town, buy all means try a 4:56 or 4:88s, you'll have a blast!

Shoe

[burger]

Metalshapes,

For more info on your tranny, check out my t5 info site (a lurker provided me with the info... credit will be given where it is due):

http://home.earthlink.net/~edmurder/t5s2.htm

If you're into computer software & playing with the numbers, check out CarTest:

http://www.cartestsoftware.com/cartest4.5/

Download the DOS version at the bottom of the page, as it is free and the Windows version isn't.


Ed

[Flatdog]

That little 283 needs more gear.Myself would run 456 with the T5 and 16 tires.Ran a 283 for years 411 no OD never felt over geared.Made sweet noise on highway.

[C9]

Most OD's are 30% over.
Looking from here, it looks like the 4.11 would be a nice gear for in-town and spinning up the on-ramps and once in 5th things should be pretty smooth.
What will help in the mileage dept is to gear the car so the engine is at max torque output at cruising speed.
With naturally aspirated engines anyway, an OD will be a little different, but the big thing is don't lug it.
Install a vacuum/pressure gauge and select your highway gears from that.
My 88 Mustang GT pulled a higher vacuum in 4th than it did in 5th on some of the long desert upgrades and flats when traveling at 70-75 with a resultant mpg improvement.

As far as noticing the difference between the 3.55 and the 3.89 - you will.
To make comparisons figure the gear ratios as a percentage of one another and you'll be able to predict the rpm drop - or rise - at a specific mph with a gear change.

As a fr'instance, the planned for 3.50 in my 32 is 5% taller than the 3.70 - assuming I did the math right and I think I did.

If you go with the 4.11's and it's not quite where you want to be, you can do a little fine tuning with tire diameter.
Figure the difference in tire diameters as a function of percentage as well.

Regardless of how well the 4.56 or lower diffs may run on the highway once in OD, you may - probably - find them too short for easy in-town driving.

[ELpolacko]

I agree with the 4.11 gears too.

Forte's parts has some pretty good break downs on T5's and Tremec transmissions. Unfortuneatley their web site seems to be down today. Forte's Parts Connection (http://www.fortesparts.com)

I have used the calculators available at Randy's Ring and Pinion, Calculators (http://www.randysringandpinion.com/calculators/calculatorsind.html) and by punching in the numbers using a 4.11 gear, 28" tall tire, 75 MPH and a .68 trans ratio you come out with 2500rpm.

If you remember my Dad's little coupe, it has a stock 1965 283 with factory power pack heads and a FourJet carb. We have the stock power glide trans and a 1949 Mercury rear end with 4.10 gears in it. That puts us up in the 3700 rpm range, while a bit high on the scale but is tolerable. It still gives us 15 miles to the gallon! When I took this car from Phoenix to Bakersfield I got slightly better mileage than Ronnie did in his 27 Touring with the nailhead and overdrive. And I had the AC on http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif

[Rocky]

I had a 64 'vette with a '66,350 hp 327 and 4.11 posi. It had a non O.D. Muncie and I drove it on the interstates all the time with no complaints.. If you don't mind a little interstate rpm's go with 4.56's...In 5th gear it'll feel about like it does now in 4th if 4th is 1 to 1. In 2nd and 3rd, it'll feel like pure sex.

[metalshapes]

Thanks guys.
I am going to go for the 4.11 gears.
If that will bring up the boost enough in 5th gear, cool...
If not, oh well...
I'll report back about this after its all back in the car.

[safariknut]

I would probably weigh in with the 4.11's.I think the 4.56's would be too whiny around town.I have 4.56's in my 57 Safari with an M-22 and the thing is a nightmare around town.Forget about highway driving!I can make 4th gear starts with no problem at all and that old Poncho really doesn't like to rev very much.JMO.
Ray