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Stock Bugeye differential vs a 3.9

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Hi guys. Will a 3.9 swap right into an otherwise stock BE differential? Is a 3.9 a good idea for a street car? Hit me with some knowledge here guys!
 
I have a 3.9 in my sprite with a 1275 and Datsun 5-speed. I like it. The 4.2 seems a bit too low, but in the end it comes down to personal preference and the type of driving you do.
 
I put a 3.9 in the Tunebug (out of a '74 Midget). Pops right in, no modification necessary. I'll have the 3.9, ribcase 4-speed, and Hap-bult 1275. Should give plenty of legs for decent speeds for cheap.

Can't remember what engine you're going with in your Bugeye -- that'll make a difference. The 948 especially needs the 4.22 rear end.
 
Thanks guys. I have a 1098 of unknown build. I haven't been able to drive her much since each time I do I find something I want to fix and then get shipwrights :smile:

I run out of first gear pretty quickly, so I think she'll handle the taller ratio OK.
 
All things being a compromise....
I did not like a 3.7 in my BE. It did significantly reduce
rpm at highway speeds but with my stuff it sucked for launching.
Tall first gear didn't help.
My current 4.22 makes the car such that to do
freeways....I'd rather not. It scoots pretty quickly and
is nice on corner exits. I really like it for my particular needs.
The 3.9 sounds like a good all around choice especially if it's driven routinely.
 
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