Hey, if anybody's interested, I did a small writeup on the 8 3/4 swap I did recently. It's on my site..

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It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

I am close to doing this swap myself for my 71 duster, but I am waiting on some brake parts and need to order up the springs/shocks. Although, I did not go as high as 3.55 gears, I stuck with the 2.94 that originally came in the center section, as this car will probably see a decent amount of highway driving in the future

I like those 2.94's also, but there behind my big block!

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'70 Cuda AAR
'74 Duster 360
'79 MagnumGT
'79 Chrysler 300

I also like the 2.94 ratio for an "open road" car, even if it's Slant powered.
That ratio is somewhat "lazy" off the line but it sure rocks at 75 MPH!
DD

I was planning on swapping an 8 3/4 into my yellow D100 I use to commute 100 miles a day, and putting that 2.76 ratio in that.

_________________
It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

I enjoyed following your swap. Looks like you pay strong attention to detail regardless of whether its hiden or visible. I always learn something new.
BTW GunPilot, I still chuckle when I read your post over at dot com back when I introduced Bigred Its obvious that you do good work.

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Cheers!
Al T

Thanks for the kind words, Al. I guess I have forgotten which post you're referring to on .com. Was I drooling?

Edit: I found it. I hate it when I get like that , but I meant what I said.

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It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

I have an A-body 8 3/4 that I got from Lou 2 years ago in my garage. It's a 3.23 and I have a SureGrip unit that needs to go into it. I appriciate the way you think. I've been holding off until I can do it "Right". I too feel like stuff that goes back onto the car should be right even though it delays my projects sometimes. I'll be refering to your WEB page on my project. Thanks again

Mike

Somebody, please explain the theory of the gear ratio.
I hear so much about 2.94 this and 3.55 that. This is good
for low end torque, that is good for highway driving.

My son and I are rebuilding a '74 Dart Sport. It has the small
bolt pattern 7-1/4" rear end. I am looking at a Swinger donor
that has large bolt pattern rear and front disk brakes. How do
I determine what the gear ratio is in the rear end. For my son's
first car, a daily driver to school and such, what should I hope
for the gearing to be?

Jerry

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There's a difference between ignorance and stupidity.
Ignorance is not knowing any better.
Stupidity is knowing, yet doing it anyway.

Jerry the easiest way to think about gearing is this: when you are on a multi-speed bicycle you have various gears... If you are in too "high" of a gear and you try to start off from a standstill, your legs have to really push to get the bike moving, but when you get up to speed your legs only move a little bit and you go really fast: this is like having a "high/highway/cruising" gear, which would be a LOWER number ratio like a 2.94 or a 2.45 - good for mileage but slow off the line

if you are in a "low" gear on the bike, you can get up to speed really quickly but then you run out of steam as you go faster because your legs can't keep up. this is like having a "low" gear in the rear or a HIGHER numeric number ratio like 3.55 or 3.91 - quick off the line but not good for mileage or cruising.

The ratio is this: for every ONE revolution of the axle/tires (ring gear) the driveshaft (pinion gear) has to spin 3.55 times (or whatever gear you have) that is what the RATIO is. 3.55:1

You can find the ratio exactly by counting the teeth on the ring gear (use some chalk to mark the first tooth) and dividing it by the number of teeth on the pinion gear.

The two other factors that will affect your final drive situation is your tire size (diameter) and whether or not your transmission has an overdrive. Non overdrive trannys are usually outputting at 1:1 in high gear, meaning the driveshaft will spin at the same RPM as the engine in high gear. A taller (larger diameter) tire would make a 3.55:1 rear ratio better for cruising. A smaller diameter tire would make a 2.45:1 gear perform a little better off the line.

There are tradeoffs for every ratio, you need to just pick something that fits what you want to do. I would use whatever is in that rear from the donor car, a 2.94 is ok for the street, a 3.23 is better off the line, 3.55 will be good around town, 3.91 will be quick but crappy gas mileage and so on...

hope this was helpful and simple enough!

Thropar

Perfect explanation, just what I needed. Didn't know what the ratio
related to. If we do the swap, I'll probably open it up just out of
curiousity to see how everything works, and count teeth.

Jerry

_________________
There's a difference between ignorance and stupidity.
Ignorance is not knowing any better.
Stupidity is knowing, yet doing it anyway.

Looks good man Plane on having one on the back of my 78 Volare 4 door. I also want to upgrade to Wilwood Pro Street rear disc brakes. Anyone ever done this on a 78 volare? Any insight would be very helpful.