Hey! New guy here. A while ago I came across a broken down 1974 1200 GX Coupe, sitting in the back of a man's yard. I couldn't let her just rot there and I've been roaming your forum ever since.

She's got an A15 mated to her original 4-speed box, sadly I guess. I plan on supercharging it with an old 'benz kompressor I have lying around for circuit racing on the weekends, but first I beg for your much appreciated opinion -

Her old axle is kaput and I can get a mk2 escort's complete axle and diff, but the diff's ratio is quite a bit longer at 4.44:1. Think I should go for this and have it reconditioned for abuse or is there something much better for her out there?

Second, if I'm stuck with all that power, I'd love some good traction. What would the largest x Widest tire be I can fit to her with the fenders slightly rolled out? I plan on sticking with 13" wheels.

This also opens up my next question - for the rear, I can shorten the axle for deeper wheels, but what can I do for the front? Modifying chassis work doesn't bother me, but other than smaller coil-overs, I don't see another clean solution.

Thank You Gentlemen.

They are quickest in the 1/4 mile with the four-speed. But for circuit work, a close-ratio 4-speed or direct-5th gearbox might be better. The overdrive 5-speed are solely for fuel economy, they don't help power.

4.44 axle ratio is good, keeps the engine in the power band.

If you can find them, 205/60R13 will fit nicely.

Ran a Benz compressor on my A15. Recked a H150 and H165 lock rearends. With the help of nitrous after 3 seasons of drag racing, I finally threw a rod out the side of the block.
It was just all in fun.
205's fit nicely.

The torque a blower will make means you wont need gears that small. I think that a 4.1:1 from a Bakkie would be a good balance.

205's it is! I have a set of 13"s with an offset of 30 at an engineer to be widened. How wide can I make the mags themselves in front?

I'd aim for 185/195. 205s are too tight a fit. With 13s .. You might get away with it.

OK, anyone else think I should find a 4.1:1 diff, or is 4.44:1 good?

Also, I'm still not sure on how wide I can make the mags in front. Anyone got an idea? A supercharged GX deserves some traction ;)

If you want quicker acceleration, go with the 4.44. If you want increased fuel economy, go with the 4.11. It is always a tradeoff. 4.11 is the stock bakkie ratio so it is fairly mild.

For 205 tires, a rim width of 5.5" to 7.5" is specified. But 7" is as wide as will fit the 1200. +30 for best centering and allows spacers to fine-tune the look should you add flares and want to move the tire towards the outside.

Quote:

^^^^This guy is speaking from experience.
With a 4.44:1, (And some quite big wheels) I found it made 1st gear too short. Belt driven boost is all about torque. people run small gears so their engine can rev hard to compensate for lack lustre torque. (Especially on Small N/A engine with huge cams, where the engine needs to rev hard to make power)

Depends on your application. If you are racing there are special considerations. If it is to be a street vehicle, it mostly depends on your preferred driving style.

But you are correct -- it's not needed as the A15 has enough power to pull 3.9 gears. Or 3.7 gears. Or even 3.54 gears which were used in A15 sunnys here.

What do you mean by "too short"? To me that means you shift faster and more often. And faster means quicker acceleration ... even with V8 engines, 4.11 or shorter gears are used to go quickly ...

There is no wrong or right answer.