I just went through this. Had my car painted last summer, went from a 273 that had headers, hyd. cam, 4 bbl. ign. etc, pretty much everything you could just about do to a 273. I would guess it had around 210 HP or so. Ran like a dream with my 7 1/4 with 3.55 gears non-sure. I wanted to do at least one car show with it, had plans to upgrade to 8 3/4, but was dying to run it. I had a lot of people tell me that the 7 1/4 would handle 250 to 300 HP. So I put my 340 that is darn near stock 9:3:1 comp. or so, headers, 650 eddie carb,etc.all from my 273(except the carb) I did not go crazy, but did do a couple of straight burn outs amongst other things, and on the way home CLANG!! every so often. Opened it up, 11 teeth missing on the pass. side spider gear. It is a damn shame that these can't be built to with stand more. My was so light, I was able to chuck in the dumpster at work drums and all, all by my self. Now I have a 8 3/4 with 3.55 and it still runs great, but it is probably 100 lbs. heavier....This was just about 3 1/2 months ago..