Rear End for 1275

[SpriteGuy]

Currently using a 1275 Engine in my Bugeye. What would be the preferred rear end gear ratio for freeway driving?

 

[Biff]

You could use a 3.9 rear end and bring the revs down some or go for a 3.7 and cruise. But the downside with the 3.7 is you will be slower getting up to speed.

 

[Bugeye58]

With my 1275, and a 3.9 rear gear, I run about 3600 RPM indicated at 60 MPH. It goes up about 500 RPM for every 10 MPH, so you would be looking at somewhere near 4350 RPM at 75. That's with 15580SR13 Michelins on it. I'm putting 175 70 Sumitomo's on it this weekend, and I'll see what it does then.
With the 3.9, acceleration is acceptable, but I still may drop a 4.55 in, as I never go on the freeway with it anyway.
The 3.7 was in the 1500 cars because they don't rev as high as the 1275 will. And, they are real dogs by comparison. (Don't all you 1500 guys beat me up for saying that! /ubbthreads/images/graemlins/nonono.gif)
Jeff

 

[Trevor Jessie]

I think the 3.9 is a good choice (most 1275 spridgets have 3.9's). If you are serious about freeway driving then you should consider making a plung into a 5speed conversion. With 165/70 tires a 3.9 reared and a datsun 5 speed my car turns slightly less than 3000 rpms at 60 mph.

 

[Salyers890]

how to tell which is which if you have a number of rear ends sitting in your garage?

 

[ThomP]

Count the number of teeth on the ring and pinion gears; Divide the number of pinion teeth into the number of ring teeth. For instance if the pinion has 9 teeth and the ring has 41 teeth that would be 41/9 or 4.55 for a ratio. "Whiteout" works well to mark the starting tooth.