I have a '71 Chevelle with a stock 170 hp 350/TH350. I may later on put a 454/TH400 or a 406/TH350 in it. My current rear end gear is a 4.10 which is too big for the 170 hp engine. I would like to know what would be a good gear to put in now and operate and still be good to use when I go with whatever engine I go with?

I wish I had 4.11's...but I wouldnt go lower than 3.55's or 3.73's if you are performance minded at all.

If you are looking for a real difference then go with the 3.55's. The 3.73s is basically just a tire change, from a 25.5" to a 28" tire. But if you have real performance goals you might find yourself regretting making the change. Do you have your intended combo/ performance goals lined up? Maybe you could find someone in your area with an old rear end lying around you could use for a while. Plus, if you do the gear swap and the rear you have is a 10bolt your plans for some serious bbc torque might warrant doning it again. Just 2 days ago I gave away a perfectly good 10 bolt 2.73 rear to a fellow TC member, maybe you could pick one up cheap to hold you over. Just a thought!
Best of Luck,

personally, i wouldn't mess with changing the gears. i don't think 4.10's are too low in a heavy car with a 350. if it were a 400sbc or a big block and it was a stock engine, i'd run 3.55's.

The rear end I have now is a 12 bolt with 4.10 gears and a posi.

Off the line seems pretty good but it seems like once in the 4k range power starts to drop off. And that's like 60 mph or so for me.

Basicly what I want to do is have a gear installed that will work well with what I have now (bone stock 350 from a '78 fullsize) and the 406 or bbc that I plan on running in the future. Good performace throught the rpm range is the game here.

One option would be to find a 10 bolt open just throw your backing plates and drums on it (there the same). Then U would be able to cruise with your car with no problems. Once U build a motor U can always put the 12 bolt back in it. U can usually pick up 10 opens for $50 if U look around..put a wanted add in the classified section or start asking local car owners. I have a 66 10bolt that I have no use for and many other people do to out of parts cars, U kinda hate to throw them away. U wouldnt notice much of a difference going to a 3.73 gear, a 3.55/3.42 is a good all around gear. But to change to that U would have to buy another posi ( yours should be a 4series 4.10 and up) $325+ new + the gear $150-200 and labor to have it done $200-250. Another option would be to put an overdrive in the car, a stock 700 would hold up fine to the stock 350 motor.

Please consider 3.42's or if you can find them, 3.31's!!

I really like my 3.31's but I have a First Gen. car.

AND if you ever go BB, I bet 3.23's would be fine, imho..

pdq67

here is my spin on this FWIW.
If you go to a 454, unless it's really wild, anything from 3.31's to the 4.10 will be fine. With most reasonable 10" torque convertors, the convertor simply stalls higher when it has to push against a higher gear. So the net result will be less than you think.
When I switched from 3.73's to 4.10's early in my cars life, all it did was develop more of a traction problem. When it hooked good, the difference in ET was less than a tenth. MPH remained the same.
Another case in point, a buddy has a 70 chevelle with 10:1, smallish Comp solid roller, 950 holley...my old one, 10" superholeshot BM conv, also my old one and 3.31 gears. I thought he was nuts. The car runs low 11's, and has gone 10.95 in good air. And man does it love it on the bottle. 10.3 at 132. Damn it!
Ron