So I recently started a project.
I'm dropping a 12a into a 78' Datsun 510 wagon.
When it's all said and done, the total weight should be around 2300lbs.
The Datsun rearend has a 3.30 gear in it. Thats a bit steep for a 12a street port IMO.
I know the factory gear ratio of an FB is 3.90. But with the added weight I would have to think that a lower ratio would be better?
I'm going to run 165/50r15 tires.
Does anyone have any feedback with experience on this?
The lowest gear I could get for the Datsun would be a 4.10. But I have to wonder what it's street manners would be like with that low of a gear??

 

4.1 is fine and pretty much the go to for fb's. 5thgear 60mph im guessing 3100rpm?

 

That's kinda what I was curious about.
I want a decent top speed, and hiway revs. But don' want it to be a total turd in normal traffic.
3100 at 60 wouldn't be to bad though.

 

I think I’d stick with the stock flywheel though.

 

Oh?
Why do you say that. From the added driveline stress??

 

If I understood you correctly, you have concern that the Datsun final drive might be too high. Adding a lightened FW might make it less friendly for street ‘stop-n-go’ driving and accelerate clutch wear.

 

Oh I'm definitely changing the gears..
The 3.30 gears are way to steep for a car that size with a 12a, I know that much.
If anything I'm going to drop to a 3.90 gear. I was more curious about the street manners of a 4.10 gear behind a 12a??
cause I can run that gear. But if that's to low, I don't want to waste my time on it.

 

Both 3.9 and 4.1 will be good. Manners on the 4.1 will be better unless you want to shave 1-200rpm off your cruising speed. Tyre size and weight you mention are close enough to an fb to go off what other fb drivers say on the matter.

 

Both 3.9 and 4.1 will be good. Manners on the 4.1 will be better unless you want to shave 1-200rpm off your cruising speed. Tyre size and weight you mention are close enough to an fb to go off what other fb drivers say on the matter.

 

Cool.
Thanx bud! I thought there would be a bigger rpm gap. But it's not that big of a jump I guess.. lol