720 gear ratio vs. 521 gear ratio

[hacked521]

whats the difference between a 720's gear ratio and a 521's gear ratio if there is one, oh and another question whats the highest horsepower you would trust the stock axles with? ahh too many questions, are the third members interchangeable between models?

[datzenmike]

The 521 with a J13 motor had an H-190-AL rear end with 4.875 ratio. L16 equipped 521s had the same rear end but 4.375 ratio.

 

720s came with H-190-ML diffs and ratios of 3.364, 3.70, 3.889, 4.11 and 4.375

 

They also came with a C-200 axle with 4.11 and 4.375. The C-200 will never swap into the H-190 diff. All the H-190 720 gear carriers will swap into the 521 but the input (drive shaft) yoke may vary so check.

[hacked521]

i dont care for what the input, driveshaft yoke is going to be. I have to have a shop make a new driveshaft anyways. Which would be the best setup for top speed with an L20b and a 5 speed?

[datzenmike]

The lower the numbers the higher the top speed.... but you have to have enough power to push the wind out of the way. I've seen vehicles that would go faster in 4th than in 5th. It's called power limited when top gear revs drop so low that the motor isn't making enough hp to push through the air at that speed. Also the 5th gear overdrive ratio must be taken into account as well. The '80-'83 280zx has a very high overdrive and coupled with a 3.70 or 3.889 may be too much for the L20B.

 

Is this a stock L20B?

Do you plan to carry any loads in the back?

Will most of your driving be in town?

 

If YES to these then don't go too much lower than 3.889/3.70

[hacked521]

the l20 is getting a turbo thrown on it...and later on a ported and pollished head. almost none of the driving will be done in town. and deffinately wont carry any loads. haha

[kirky]

If i was to put a H190-ML diff in the rear of my 521 with L13 (stock) engine what would be the recommended gear ratio to use? The truck currently has 18" wheels with low profile tyres and the standard 4 speed. I could do with a bit more legs on the top end as im doing 70km with high revs and currently its just way to slow for longer journeys.

[wayno]

Just try the 388 gears, I drove from washington to florida with about a 1000 lbs. of hanggliders and camping equipment and was able to go fast. After I got back into town and started working again(loaded truck) I had to go back to the 437 gears, the truck(clutch) just couldn't handle the starting and stopping with the weight. I have a L20B with dual SUs, a early peanut head with 260Z valves, the intakes ported to match the intake manifold and a header wayno