Would a 3.31 rear gear or 3.55 be better with a tremec 5speed? My 67 RS is a 327- 275hp stock. Currently has its muncie m-20. I want to do the gear first, which is now a 3.08 10 bolt. I am going to put a new pos unit in with the gear also. When its all done I want to have the GM 383 crate engine , 5 speed tremec , and 3.31 or 3.55 rear.

I have run a lot of different ratio's. My '55 had 4.10's, my '56 has 3.08, my '36 I ran 3.80's (9"). I am running 3.70's in my Camaro right now (9"). I believe my favorite all time ratio is 3.55. You can have so much fun with it and still be sane on the freeway.

put the motor in and tranny in first. see if lugging in first gear and what rpm at 65 mph that way you dont go to high or to low of gear.

Well again this is a customer choice. What do you want to do with the car more? cruise burnout race etc. The 5 speed will give you the overdrive and the steeper first gear too. so if you like freeway distance driving out of state etc. then 3.31 or 3.42 around town short freeway jaunts then 3.55 or 3.73. I doubt you will get too much lugging with a stock 327 since it has good lowend torque. The 383 will not be affected at any speed either as long as you keep the duration reasonable too. nothing over 280 advertised duration. I like to stay in the high 260 or mid 270 for a great high torquey street pounder. You do have the avantage of the stick shift and can dump the clutch where ever you want so that is even better for you and is more forgiving on the too much duration cam unlike a automatic trans with too small of stall convertor. Good luck with your choices. Jim -J D Race.com

What height rear tires? A 24" tire with 3.31's will run the same rpms as a 25.7" tire with 3.55's.

go to the source. drop an email or call the folks at classic chevy 5 speed. give them all the pertinent information (tire size, engine/hp and car use) and let them get you to the correct rpm range for 5th gear. we went from the 3.08 to a 3.36 and had to go with the tko-600 at .64 to obtain the 5th gear rpm band of 1800 - 2200. the only inconvenience, as we ended up on the low side of the band, is that at 70 mph, the rpms are too low to pass but that is easily corrected by downshifting for additional power. they will walk you threw the whole process.

26.6 tall tire . BFG 245 - 60-15.

try this link

5speedtransmissions.com

I run a tko 500, 3.08 gear, and a mild 383.
We'll see what happens this winter, changing cam and heads in search of another hundred HP, but at least for now, the gearing is perfect.

The 3.27 first in the 500 works very well with the 3.08 rear.

In high, this particular 383 will lug down below 50 mph no problem, and it will also pass in high from that speed or higher.

And fwiw, I'm running a built 350, 3.31, 12 bolt with a TKO-600. I love it. I cruise the highway doing 80 @ 2K rpms, and it feels aggressive enough for me on take-off. A 12 bolt is overkill for my gearing, but it should be indestructible.

67sprtcp -- are you planning on running a 12-bolt then? I only see 3.55 or 3.36 for the 10-bolt...

Since it looks like you're looking for a little more rear to help launching on hills w/ your 327, I'd go with the 3.55 and make sure you get the TKO600 when you eventually pick up the 5-speed. This will put you at about 2150 rpm at 70mph in 5th and 3350 in 4th (also 3350 with your current 4-spd). If you went with the 3.31, you'd have 2000 and 3125 respectively.

I figure if you're doing the rear gears now to make the 327 a bit easier to drive, you really want the jump from 3.08 to 3.55 (I don't think you'd feel the difference between 3/08 and 3.31 much). Honestly, before I'd go the 3.31 route, I'd consider just leaving the 3.08's in there and getting the TKO500. The deeper first gear will make it launch like a TKO600 with 3.55's, but you'll be at an even lower RPM on the highway...

Great info. If and when I get a break from work I will get something going. It would be nice to get the 5 speed first and see how it feels.

I was going to leave the 8.2 10 bolt rear in if it will last. I wont be thrashing on it that much.What do you think ? 12 bolt ?