3.73 or 4.10?

[DBossMan]

I need to get work done on the 3.54 D60 in my 72 Crew. I am considering moving to 3.73 or 4.10 while they've got it apart.

I'm building the truck for towing a vintage mustang. It will see 3 or 4 trips each year, with mostly highway driving. Right now, the thing is a dog. I will be rebuilding the 390 this fall.

Any thoughts about 3.73 vs 4.10? I know the 4.10 would probably be better for towing, but I'm worried it will have the 390 screaming at 70 to 75 mph.

Thanks.

[71-F-250SC-72-F-250C]

I have 3.73 in my truck, and I keep off the highways as much as possible. It starts screaming at 60. It cruisies at about 50-55. But, my truck has a 360 in it which might be a little different.

Stephen

[willowbilly3]

My crew has 3.73s with a 390/4 speed. Tires about 31-32 inches tall (stock) It pulls decent and runs down the road effortlessly at 70-75. That's about 2700-2800 rpms at 70 by my estimation. I pulled my 96 F-150 supercab 2300 miles home and it run 70 on flat ground like nothing was behind me. Now coming up over Dillion and Vail passes was a different story. At that elevation I was in low gear grinding along at 20 mph for miles, wouldn't quite pull third. It definately needs more gears. If I had a NV4500 5 speed it would make a big difference. And if I had one laying around with a 500 caddy engine bolted to it I would perform blasphemy.

[DBossMan]

WillowBilly3... your tires are a little taller than mine (which are 30.6" tall 9.5 by 16.5's) so you're RPM's are not far off what I am seeing with 3.54's. My RPM's have always seemed a little high, but I have confirmed the ratio. Perhaps my speedo is off a bit.

Have you done anything to your 390 to boost power?

I've only towed once, pulling a small block mustang on an open trailer, and the 2V 390 in my crew was great from a stand still, but a dog from 45 to 70. On the slightest incline, I'm losing speed big time.

I'm planning on a rebuild for the 390 this fall. Plan to go with the basics: RV cam, 4v intake and carb, headers, etc. Perhaps a 3.98 crank. Hope to have a torque monster when I'm done.

[willowbilly3]

WillowBilly3... your tires are a little taller than mine (which are 30.6" tall 9.5 by 16.5's) so you're RPM's are not far off what I am seeing with 3.54's. My RPM's have always seemed a little high, but I have confirmed the ratio. Perhaps my speedo is off a bit.

Have you done anything to your 390 to boost power?

I've only towed once, pulling a small block mustang on an open trailer, and the 2V 390 in my crew was great from a stand still, but a dog from 45 to 70. On the slightest incline, I'm losing speed big time.

I'm planning on a rebuild for the 390 this fall. Plan to go with the basics: RV cam, 4v intake and carb, headers, etc. Perhaps a 3.98 crank. Hope to have a torque monster when I'm done.

My 390 is a stock 2bbl. 1970 car engine. Not exactly the most powerful 390 I ever drove but it does ok. I'd like to get some headers for it. I do have duals with turbo mufflers now.
Is your truck a 4 speed or auto? I think the 4 speed trucks pull harder. The C6 probably slipd a couple hundred rpm and robs 20-30 horsepower at cruise.

[68F250]

DBossMan, I calculated with your 30.6" tire diameter what the rpm's would be at 70 and 75. This is assuming you have a manual trans.

Ratio - RPM - MPH

3.73 - 2870 - 70
3.73 - 3070 - 75

4.10 - 3150 - 70
4.10 - 3380 - 75

I run the 3.73's but with a C6 and 33" tires and it seems like a good compromise between pulling and cruising.

[Sharkdance]

1970 F250 2WD
360 - C6 - 3.73 gear and 31X10.50 - 15" BFG tires
Nice combination for me. I drive it like a manual valve body though.
Tow what ever I want and cruise 80MPH all day long. (Without the trailer of course)
At somewhere over 80MPH the tach runs from 3500RPM - 3900RPM, but the FE likes it there.

Sharkdance

[OLEYELLERTRUCK]

3.73 is a nice all around gear, 4.10's are alot, especially if you do any highway.