Would you change rear gear?

[68Stepbed]

Originally Posted by Sawlog

350, bored .040. 5.7in stroke
Dart iron eagle heads 165cc runners. 67 c.f. chambers
.221-221@.50 duration. .470 .470 lift lsa 108
Th400 tranny, 2000 stall.
31 10.50 rear tire.

OK, it sounds like you have a slightly hotter than stock engine. The heads should be good for building low end torque, but add just a tad of compression. The cam looks like it would be a good mid range power setup while still making decent torque in the 2500-3500 rpm range. Seems to be a good setup for a stout street cruiser.

Your kicker is the tires. Is your truck 2wd or 4wd? Those 31's are going to make your 3.07's feel like 2.73's. If you ever plan to run a smaller tire, the 3.07 gear would still work well, but if you plan to keep the same size tire, I would suggest a 3.42 gear to make better use of the rpm range of the engine. A LSD like an Eaton would also be beneficial to keep from one-wheel- peeling all the time.

Also, FWIW, the 3.07 gear is a 3-series gear, and 3.42 is considered a 4-series gear, but you can get a gear made for a 3-series carrier.

[Sawlog]

It dynod at 333hp @ 5300. 388 tq @ 3700

[halfstep]

Gear it.
My 2 cents:
- You'll get more "go" from beginning to end.
- Doesn't sound like you got this truck for family trips.
- You've already invested in reasonably high performance modifications to your engine and transmission and with that cam your 3.07's are a bit low.
- Chevy high performance vehicles of this era (67-72) ALL started with higher numerical gears. Small blocks 300hp and up, 3:73 std. , Big blocks 325 and up 3:42 or 3:55 std and our trucks are heavier are less aerodynamic.
- 3:73 gears were a common option of our trucks and I believe std. with 6 cylinder trucks.
- These trucks will never get great gas mileage no matter the gear. I have a similar set up to yours (well modified sbc, th400 with ati stall) and when I switched from 3:07 to 3:73 posi I experienced NO DIFFERENCE in gas mileage or highway drone although I was "tach'ing" more rpms. BIG DIFFERENCE on launch and anytime I hit the gas - especially on the highway.
Around 3K i am on the early side of my torque curve and the engine is very happy. I think you will be too. Unless you have fuel injection and advanced timing controls, regularly operating your carburetor engine outside of your torque curve is not efficient. I did pick up 2 mpg in tuning...after the gears!
- As far as drone, etc. if that's an issue - get better mufflers or run resonators in front of your existing mufflers, and/or insulate the cab.

[Sawlog]

Originally Posted by halfstep

Gear it.
My 2 cents:
- You'll get more "go" from beginning to end.
- Doesn't sound like you got this truck for family trips.
- You've already invested in reasonably high performance modifications to your engine and transmission and with that cam your 3.07's are a bit low.
- Chevy high performance vehicles of this era (67-72) ALL started with higher numerical gears. Small blocks 300hp and up, 3:73 std. , Big blocks 325 and up 3:42 or 3:55 std and our trucks are heavier are less aerodynamic.
- 3:73 gears were a common option of our trucks and I believe std. with 6 cylinder trucks.
- These trucks will never get great gas mileage no matter the gear. I have a similar set up to yours (well modified sbc, th400 with ati stall) and when I switched from 3:07 to 3:73 posi I experienced NO DIFFERENCE in gas mileage or highway drone although I was "tach'ing" more rpms. BIG DIFFERENCE on launch and anytime I hit the gas - especially on the highway.
Around 3K i am on the early side of my torque curve and the engine is very happy. I think you will be too. Unless you have fuel injection and advanced timing controls, regularly operating your carburetor engine outside of your torque curve is not efficient. I did pick up 2 mpg in tuning...after the gears!
- As far as drone, etc. if that's an issue - get better mufflers or run resonators in front of your existing mufflers, and/or insulate the cab.

I don't have any issues with drone. My truck is pretty quite until I open it up.thanks