8 3/4 gear swap

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Summers

Summers

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Have a couple of questions. Never messed with swapping out a gear set up and will probably let a reputable shop do this. But was wondering about.

I have a spooled 4.56 set up right now 8.75 rear end. I am looking to swap them out for a for 3.91 or 3.73. My question can I reuse the spool from the 4.56 or have to buy complete set up?

I am have 295/50/15 tires on the rear. Which would be a better gear 3.91's or 3.73's? Installing a mildly built 383 BB.

I will be using car for mostly street driving with occasional trip down the 1320.

Any help would be greatly appreciated.
 
Your spool will work.

From my experience, you won't notice much difference (if at all) from the 3.73s vs. the 3.91s- ET-wise. However, the 3.91s would be more fun around town, in my opinion.
 
I didn't think you could buy 373 's for a 8.75. I think 3.55 is your next choice.
 
Rob here's my opinion,

Yes you can use a spool on the street. Is it a good choice, NO. Spools don't allow the inner wheel to turn at a different speed than the outer tires does, which is what happens when you make a turn. Thus the reason for the invention of a differential. Either the inner wheel has to spin or the outer wheel has to spin when your running a spool. Not good for street use.

Since your running real short tires I think you'd be better off with a 3.55 gear. After all you said it's mostly for street use and it's a mild BB which will have plenty of torque to spin even 3.55 gears with super ease. I ran the numbers on my calculator and with 3.55 gears you'll be spinning approx. 3100 rpm at 60 mph and at 70 mph you'll be spinning well over 3500 rpm. IMO that's screamin right along. With 3.73 gears you can add about 200-250 rpm to each of those figures.
 
Also, the gear ratio should match up with the cam and converter for the intended purpose.
Wha cam do you have? (Specs?)
What is the converters stall speed?
 
Cam is custom ground 509 lift and 292 duration with 2800 stall. torker 2 intake with 750 cfm carb. 906 heads reworked and headers with 3" exhaust
 
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