Hey all, long story short I need my truck, which in Phoenix, AZ but unfortunately I am in Parris Island, SC right now. So to fix this dilemma I'm trying to gear up for a cross country trip in this speed machine but I have a concern. The truck itself is an 88 F-150, 130k miles, 4x4 long bed single cab, and a 4.9L I6 with the T-18 4spd. No mods outside of some 32" all terrains and some professionally-done body damage. So my worry here is how safe is it for the Ford 300 to turn at interstate speeds without overdrive?

Last year I took it about 200 miles at 75mph, including through some mountain ranges, and so long as I ignored the crippling depression that came with the cost of gas, the truck did great. But that was 200 miles and this is 2,100 miles. There's no tach but if you could translate a 4.9L's RPM noise into English, it was undoubtedly cussing me out every time I went above 65. So what are yall's thoughts? Are these straight 6's safe to hold those RPMs for that long or am I just being paranoid?

 

I'd say you're overthinking it. What's the axle ratio? Easy enough to figure out your cruising rpm.

 

I had a 460 with a C6, and I thought it was over revving by the sound of engine. Turned out to be 3-3500 rpm I was worried about.

Buy a tach, wire it up, then you will know your RPMs.

 

Depending on gear ratios at 65mph
2.73 1900rpm
3.08 2100rpm
3.55 2450rpm
All give or take

 

That's significantly lower than I would have expected. I honestly have no idea what ratio I have in the rear but by those numbers I'd be good even if it was a 4.10.

Regarding the tach, I'm probably just going to buy a cluster with a tach on it, from what I've read that should be a plug and play job anyways and they go for cheap on ebay

In my line of work, not showing up on a Monday morning can turn into a nasty legal ordeal so that definitely makes me feel better about this trip

 

Those aren't right, not with a T-18. They sound a little low even with a M5OD in 5th.

 

4th gear in t18 is direct drive (1:1). 32" tire drags down rpm over stock 29" tires. There's no slippage in the system, so calculations are pretty straightforward.
65 mph is 5720' per minute. 32" tire has a circumference of 8.38', so need 683 revolutions per minute to go 65mph (divide 5720' by 8.38'). Then multiply gear ratio by wheel RPM to determine engine RPM (engine spins faster than wheels).
E.g., 2.73:1 axle gear would be: 2.73 × 683 = 1865 engine RPM

2.73=1865 RPM
3.08=2104 RPM
3.31=2261 RPM
3.55=2425 RPM
3.73=2548 RPM
4.10=2800 RPM

Mudsport is correct. Deviations from these values lie partly in tachometer and speedometer accuracy but mostly in tire size variations. By that I mean that a manufacturer's claimed 32" tire is often smaller, so you'll see a little higher engine speed, but not much.

 

If it was me I would check and top off all my fluids. Including the transfer-case and both diffs. Top off the air in the tires and Hit the road.

 

I'd just change the oil and maybe the coolant, top off the fluids, check the tires (including the spare!) and hit the road. I would keep some extra fluids (brake fluid, oil, and coolant) and a set of jumper cables in the truck. Maybe a roll of duct tape and some zip ties too. Enjoy the ride and have fun. I'd love to be able to take my truck on a long trip.

 

I agree with this. I put almost 300K miles on my 302 / C6 / 3.55 equipped ‘87 Bronco. It would run all day long @ 3000 rpm on the highway. The only issue I had was the gas gauge dropping toward “E” rather quickly.

 

I’ve put over 10k miles on my ‘95 2WD longbed, 5 speed, w/ 3.55 rear, 351 swap and with an average speed of 75mph I’m getting about 13 to 14 mpg.....

 

Lol how do you think everyone drove in the 80's? but yes you're good to go, no worries about that 300!

 

I figured just a little bit slower lol.

But overall I'm feeling pretty good about this now. It's been about a year since I last drove it so all the fluids and the battery are being changed anyways. Clutch is new, clutch and brake hydraulics are new, and the T-case is "new" from a low mileage junkyard truck, drained and filled the transmission and rear/front end when I swapped that out. Tires have less than 500 miles on them. I'm gonna book the flight tomorrow, I've gotten enough "go aheads" to put me at ease lol

 

I figured just a little bit slower lol.

But overall I'm feeling pretty good about this now. It's been about a year since I last drove it so all the fluids and the battery are being changed anyways. Clutch is new, clutch and brake hydraulics are new, and the T-case is "new" from a low mileage junkyard truck, drained and filled the transmission and rear/front end when I swapped that out. Tires have less than 500 miles on them. I'm gonna book the flight tomorrow, I've gotten enough "go aheads" to put me at ease lol, I just wanted to get some input, my work is not the most forgiving when it comes to situations that make me late

 

I believe the OP was worried about engine speed while driving cross country because of the lack of overdrive.