I'm thinking of changing the gears in my '67 Charger(a stock 383 hp re-build). Right now I have a 3.23 open rear with 28 inch tall tires and you can guess how sluggish it is. I'd like to have a bit more umph and not have to cruise around town at idle. So I'm thinking a 3.73 posi.

Question is -will I notice any big difference?

yes, will noticeable.

you'll have aprox 15% more RPMs at same speed, and also some torque increasing

Not really no. I went from 3.23's to 3.91's and it certainly gets off the line better, but it wasn't a huge difference. The biggest thing I noticed was the extra 500rpm on the highway.

If you currently have a stock torque converter, changing to a 2800-3200 stall would be a big boost, probably more so than the gear change.

well I'm saying will be noticeable, not BIIIIIG noticeable.

I jumped from 3.23 to 3.55 and I noticed.

500 RPMs increase is on certain speed not all the speed ratio... is 15% diff

I went 3.23 to 3.73 and noticed better acceleration at low RPM's. Nothing noticed above 2,500 RPM's.

it's more that I'd like to get it from idle to a usable rpm a little quicker.

I've had 323's....355's and 323's and I'd never take 323's over 355's any day. I thought running with 373's on the highway that I always needed another gear..was most likely the sound of My 3 inch exhaust. I noticed a big difference between the two.

I swapped from 3.23 to 3.91's i gained 2 tenths in the quarter and an extraa 500 rpm crusing, two tenths aern't worth it to me, i'm going back. do what the other people said and get a mild stall converter. Also i'd disconnect the vacuum advance and run 36 degrees total timing, if it were me. But everyones car is different.

Here's a little toy that will let you see the difference in RPM and speed with a gear change. http://vexer.com/68rt/speed.html

Swap to a 26" tire and see if you like it. If it's a stock build you may be working away from the torque band. Swapping on a set of tires is a quicker and cheaper solution to test it out.

I actually checked the numbers and I have a 2.94 rear end-so the jump to even 3.55's would be a welcome!

I went from 2.76s too 3.73s, it was a nice improvement, but i'll bet a converter & traction will really wake mine up, not thats its a slug now lol.

if you want to sell the 2.94 pig let me know.

I thought it was a big difference going from 3.23's to 3.91's. I found a much bigger difference going from a slightly more than stock MP converter to a 3,500 PTC. Cruising RPM also went down with the more efficient PTC converter.

I made two swaps, 3:55's to 3:91's and also from a stock torque converter to a Turbo Action #17805ST (3500) and the larger gain of the two swaps was the conveter.
I started with 3:91's than went to the 3:55's and then went back to the 3:91's with a 27" rear tire. I don't mind the 3300rpms at 65mph and the off the line grunt was better with the 3:91's.
I would suggest trying the converter swap first. If you go this route, I would suggest jumping up into the 32-3500rpm range.

Not to hi-jack the thread but I was wondering how the Mopar Performance converter compares to a stock converter? I assume the RPM stall is higher with the MP converter but how much higher and how much does the MP converter improve performance over a stock converter?

Butch

I would run a min of 3.91s with that size car and would consider 4.10s The car will spin at 65 but guess what if its street driven all your going to is blow out the cob web's Depending on the engine a 383 should have no troble with those rpm. Keep a set of29.5 tires for the highway and runa pair of 26-27s on the street. I have run 4.56s with tire that are only 28 tall and they worked fine and pulled well on the street just make sure you have a cam enough to back up the rev's