Average cruise speed??
Thread Starter
|
Freshman User
Joined: Dec 2012
Posts: 34
Likes: 0
Average cruise speed??
I have a 1986 300 I6 all stock. Has 3 speed C6 trans with 3.08 rear end. I never drive it over 65. I just feel the truck is older and why beat on it, everything works perfect. My question is was the truck designed to cruise at 70 on the interstate for long distances. This will be the first year I'm taking the truck for a few 300 mile trips pulling a 2,000-2,800 pound trailer loaded. The other trucks going with are newer and will be cruising 70-75. I'm concerned the rear end and 3 speed trans were not designed for these speeds. Pulling a trailer or just driving down the interstate should I be worried driving this fast? The truck is mechanically in perfect condition 85,000 original miles and rust free body. I have replaced all most every normal maintenance part on the truck. Fuel pump, ball joints, brakes, belts, cap wires, tires, shocks......etc only part I'm looking into getting is a trans cooler for pulling the trailer, but I don't think I would need one if I was not pulling a trailer over 2,000 pounds.
Posting Guru
Joined: Oct 2010
Posts: 1,199
Likes: 1
From: Missouri
I have a C6 and 2.75 gears and I can/would cruise at 75 mph all day long. That is kind of hard though, when the Interstate speed limits drop from 70-65-60-55 mph in the St. Louis metro area.
I have never pulled a trailer that fast, you will have to judge the handling.
I have never pulled a trailer that fast, you will have to judge the handling.
Lead Driver
Joined: Jul 2009
Posts: 6,477
Likes: 19
From: Sheffield, AL
Deer545, welcome to the forum!
My 1986 F150 [4.9L] has 3.08 gears, but with 4 speed manual O.D. At 70 mph, it is turning ~2000 RPMs and is quite happy. Your C6 is direct drive [1:1 ratio] and as best as I can figure, your engine would be spinning @ ~2800 RPMs. The engine can tolerate that, but would be noisey and return poor fuel efficiency.
Keep in mind that these trucks are shaped like bricks and as speed increases, much more power is required to overcome the wind drag. Most owners report best mileage in the 55-62 mph range.
My 1986 F150 [4.9L] has 3.08 gears, but with 4 speed manual O.D. At 70 mph, it is turning ~2000 RPMs and is quite happy. Your C6 is direct drive [1:1 ratio] and as best as I can figure, your engine would be spinning @ ~2800 RPMs. The engine can tolerate that, but would be noisey and return poor fuel efficiency.
Keep in mind that these trucks are shaped like bricks and as speed increases, much more power is required to overcome the wind drag. Most owners report best mileage in the 55-62 mph range.
Laughing Gas
Joined: Nov 2011
Posts: 1,033
Likes: 11
From: Wausau, WI
In my old '83, it had 3.00 gears with a 4-speed and 351w. The rpms were approx. 2500 at 70. No problems at all. Now with having a c-6 and 3.50s in my '86 at the same speed, the rpms are bouncing around 3000. I don't like to do it much, but still do because I know everything will handle it.
The killer for both of us is the c-6 trans. With no lock-up, the engine runs a little higher, especially against a stick trans or newer truck with overdrive. Now, if they only had a lock-up converter offered....
The 300-6 is an extremely tough engine, it'll take a lot more than that for it to give up on you. But, on the other side, it likes to stay in the lower rpms, which is kind of a give and take situation.
If it concerns you, maybe leave before the others and let them catch up at the destination. It's not a race anyways, right?
The killer for both of us is the c-6 trans. With no lock-up, the engine runs a little higher, especially against a stick trans or newer truck with overdrive. Now, if they only had a lock-up converter offered....
The 300-6 is an extremely tough engine, it'll take a lot more than that for it to give up on you. But, on the other side, it likes to stay in the lower rpms, which is kind of a give and take situation.
If it concerns you, maybe leave before the others and let them catch up at the destination. It's not a race anyways, right?
Thread Starter
|
Freshman User
Joined: Dec 2012
Posts: 34
Likes: 0
Thanks for the input everyone. I don't have a rpm gauge so I never know how hard the motor is working. I might just tell the other guys I will meet them there. Keep the cruise at 70 and hammer down.
Post Fiend
Joined: Jul 2004
Posts: 8,786
Likes: 28
From: Northern California
The national speed limit at the time our trucks were made was 55 mph. So the gearing will be set up for best fuel economy at 55 mph.
However, the 55 mph was enacted in 1974 due to the 1973 oil embargo.
Speed limits of 70 were comon in states before then, and versions of the 300-6 with C6 and Ford 9" were all designed before 1974.
So to answer the question, no it wasn't designed for our trucks to go that fast, however it shouldn't hurt things if your truck is in good condition, except maybe your pocket book.
Stopping distance is another factor to concider so make sure to keep distances so you can stop. Also be aware that in some states, if you tow a trailer, or have more than 3 total axles, speed limit is still 55 mph. Good Luck.
Trending Topics
Postmaster
Joined: Feb 2011
Posts: 3,560
Likes: 1
it'll do it no problem. the 300 runs out of breath at around 3500, but won't break anything until it reaches a much higher speed.
you have to judge the condition of your tires, brakes, shocks, etc, and judge whats safe from there. i've had my van over 85mph and its as good as can be because i maintain everything. wouldn't want to do that in my f250 which doesn't have rear shocks, has 2 good tires, and 2 i don't trust, plus a reputation for blowing the right rear - and is usually loaded beyond the rating of the brakes, and stops accordingly - i don't usually get past 60 in that truck
you have to judge the condition of your tires, brakes, shocks, etc, and judge whats safe from there. i've had my van over 85mph and its as good as can be because i maintain everything. wouldn't want to do that in my f250 which doesn't have rear shocks, has 2 good tires, and 2 i don't trust, plus a reputation for blowing the right rear - and is usually loaded beyond the rating of the brakes, and stops accordingly - i don't usually get past 60 in that truck
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
Top 10 Fords at 2026 Carlisle Ford Nationals
Joe Kucinski
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
I've run a number of fuel economy tests on a 260 mile round trip up to see my father. Initially I thought I was running 65 MPH but later discovered that the speedo was optimistic and I was actually running 62. So, with having already run a couple of tests at that speed I ran all of them at that speed. And, with several changes I finally got the MPG up to 16.
Now that the testing is over I've stepped the speed up a bit to 65+, which the engine doesn't mind at all since now I'm running an overdrive tranny. But, the MPG dropped down into the 15's. As was said, these trucks are shaped like a brick, and the wind drag is so significant that I can see a difference in MPG by changing the speed 3 MPH. And, btw, aerodynamic drag is exponential to the MPH. IOW, double the speed and you quadruple the drag.
Now that the testing is over I've stepped the speed up a bit to 65+, which the engine doesn't mind at all since now I'm running an overdrive tranny. But, the MPG dropped down into the 15's. As was said, these trucks are shaped like a brick, and the wind drag is so significant that I can see a difference in MPG by changing the speed 3 MPH. And, btw, aerodynamic drag is exponential to the MPH. IOW, double the speed and you quadruple the drag.
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
Yup. Oddly enough, people say that Ford spent a ton in the wind tunnel on the aerodynamics of these trucks. In fact, Wikipedia says "the exterior of the trucks was redone to improve aerodynamics and fuel economy." If Ford spent a ton they either didn't get their money's worth or were just checking to see that the remit they gave the designers was followed - make it like a brick.
