My 86 has a C6 and something like 4.55 gears (a previous owner changed it, I only figured it out because it turns so many RPMs). A year and a half ago I did about a 700 mile trip with a large portion of it on I5 in the middle of the summer. I was turning something like 3500 or 3600 RPMs for a large portion of that trip and it didn't seem to cause any issues (at least until I hit the grapevine and had to slow way down for EGT and water temps).

These engines are very tough as long as you take care of them.

 

I had an 85 f-250 with that same setup...I once drove it to Las Vegas and back which is a little less than 600 miles round trip. 65 mph seemed to be a bit fast in the Rpm dept..I felt that the truck preferred 60 mph. That was a LONG trip.

 

If you want to get decent MPG and put less strain on the engine, the best course of action is rolling at 55mph. It's hard to do, when everyone is zipping passed you on a California hwy, but it keeps the R's low and the tank fuller.

I started restricting myself to 55mph a while back and you get used to it. Just stay in the right lane and enjoy the scenery. Plus having family and friends with makes it better.

 

Yep, slowing down will increase your mileage. I while back I did an experiment with running tanks at different speeds. Never was able to drop down to 55mph though.

https://www.ford-trucks.com/forums/1...periement.html

 

With all the talk about sanity and noise at higher RPM, I would strongly suggest adding some sound insulation to the hood if you don't have the original factory blanket type thing. Dynamat makes some stuff specific for it but it is kind of pricey for what it is. In the end though, you get ALOT of noise through the hood and on a long trip that can make alot of difference. I suspect I also have some added sound insulation in the cab since mine is a lariat, but I don't really know for sure.

 

I've put a BUNCH of insulation on my doghouse and engine bay. It really helps with the sound, but more importantly, it helps with keeping the doghouse cooler so you don't have to blast the AC in moderate temps.

I installed a sticky-back reflecting insulation on the engine-side doghouse, then put the stock diesel 1/2" thick insulation, then put a saddle on the interior-side of the doghouse. I also put sticky-back insulation plus stock insulation on the engine-side of the engine bay. Lastly, I wrapped my manifolds, up- and down-pipes, plus put a turbo blanket on the turbo and turbo mount.

Even with all of that, the temps could work their way thru the saddle on long trips. So I mounted a 3" diameter flexi pipe from the grill air-inlet to the back side of the hypermax air cleaner housing, so it would push cooler outside air into the doghouse area, forcing it to blow some of the hot stagnant air down under the doghouse and out under the vehicle.

The other thing that helps me out with the engine sound is the aftermarket gearvendor overdrive, but that's a whole another topic.

 

Yes, adding the aux OD made hwy trips much nicer. Mine already had 3.54s, so it wasn't terrible at 60-65.

For sound insulation I also used some of the denim unfaced insulation you can get at places like Menards and put it in all the empty cavities in the dash. This helped with noise coming through the firewall.

I then added 2 layers of industrial rubber roofing and another layer of carpet pad to the floor. All my doors fave reflectix and denim insulation as well.

I wish I would have gotten a noise level reading prior to the insulation. You can still hear the engine noise, but it is substantially muted compared to what it was.

 

I wish I had recorded a "before" reading as well. But i think the biggest evidence for m accoustical improvement is the fact that I can actually have a conversation with a passenger in my van, without blowing out my vocal chords.

 

This is probably going off topic but I figured I'd share; I don't have pictures on what I did to my 86 (it was similar though less refined or extensive since I did it first) but this is what I did on my 97 to quiet it down:




Butyl backed aluminum sound deadening



Dynaliner for extra roof quiet/insulation

I should note that those pictures are only half way through, I basically did every bare metal surface in the truck cab (including the floor, etc)

 

HOLY! That is a ***** ton of sound deadening material! Man, the stuff id have to sell to afford all that. Bet she cruzes like a Cadillac tho.

So going forward with this. What would you guys say is some of the best ways to get these trucks running better on the highway.

From my understanding most of these trucks come with 4.10 gears. So;
4spd - 5spd swap? There is just so much conflicting information out there about flywheels, clutches, balancing etc. that it makes it hard for a guy to commit. Plus, Ive also heard the 5 speed doesn't drop the overall rpm at high speed much. Is this true?

Bigger tires, if your that kinda guy, personally I really like stock size rolling gear, I must be getting old. But this would be a solution.

Gear Vendors. Really thinking about this, but $$$

This leaves us with gears. I see some input with various ratios but dont really understand the math and compromise some info from some knowledgeable folks would be great!

 

A used Gearvender isn't that hard to find. I found mine on car-part.com for $250 with the controller and cables. The CRUCIAL thing to obtain when hunting for a used Gearvendor or other aux OD, is make sure you get the TAILSHAFT HOUSING! Lots of yards just assume the housing is just the stock housing from the original tranny, but no, the gearvendor comes with a custom housing and without that, you might as well give up.

But I'd say the best thing to bring down noise, increase MPG, and bring the RPM's down on my IDI was the installation of a Gearvender. Best investment on my van hands down. Probably even better than my turbo install.

I did a quick search and found these Aux OD's on car-part.com:

1987
Transmission Overdrive Unit Only
Ford Truck F150 4X4,AOD 87F150 $50 Auto Parts Pros USA-FL(Lakeland) E-mail 1-863-665-7278 1-800-685-9332 Request_Insurance_Quote
2187
1988
Transmission Overdrive Unit Only
Ford Truck F150 4X4,AOD 000 $50 Auto Parts Pros USA-FL(Lakeland) E-mail 1-863-665-7278 1-800-685-9332 Request_Insurance_Quote
2187
1988
Transmission Overdrive Unit Only
Ford Truck 150 4X4,AOD F150 $50 Auto Parts Pros USA-FL(Lakeland) E-mail 1-863-665-7278 1-800-685-9332 Request_Insurance_Quote
2187
1989
Transmission Overdrive Unit Only
Ford Truck 150 4X4,AOD 892821 $50 Auto Parts Pros USA-FL(Lakeland) E-mail 1-863-665-7278 1-800-685-9332 Request_Insurance_Quote
2187
1989
Transmission Overdrive Unit Only
Ford Truck F250 7.5L,MT-F250 4X4,WHT,2DTK,3/89,OFF&TAG A 9DK451 $Call Aumiller's Auto Parts, Inc.-ELITE USA-PA(Halifax) Request_Quote 1-800-692-7463 / 1-717-896-3994 Request_Insurance_Quote

 

You could also change our your 4.10 for a 3.55. But I looked into this. Doing a gear swap isn't the easiest job for a DIY mechanic, and here in Los Angeles, the cheapest tranny shop that would change it out for me was $1000. I didn't want to spend that, and I'm pretty sure the lowest bidder gear swap job would have terrible longevity issues, so I shelved that idea.

That's why I went down the gearvendor path instead.

But I figured out a cheap workaround to swap out my original 4.10 to a 3.55. A while back I obtained an E350 for really cheap. After checking the axle code in the driver's door, I found out it was a 3.55. I just changed out the axle and leafs from the donor van to the clubwagon. If you can find an axle at a yard, I would definitely do that instead. I had to torch some of the nuts to get that thing swapped out, but eventually it worked out really easy. And my driveshaft didn't need modifications.

 

I'd get in mine and drive coast to coast tomorrow with no worries. If you have caught up on maintenance and fixed any hackjobs and neglect or abuse from previous owners there's nothing to worry about. I tow with mine 500 miles each way at ~70 MPH for vacation each summer, it just works. In a couple weeks I usually put 2000+ on the truck. I've taken it up to Canada, I did have a failure but it was my creative rear fuel tank mounting for the 38 gallon tank. A ratchet strap held it up fine until I was home and mounted it more securely. I'd be nervous doing the same trips in a new truck as everything is fragile and there are so many single points of failure.

I've done a shorter trip of around 2 hours with the speedo buried and running on the governor most of the way (before I added overdrive). I learned about the importance of injector hard line clamps on that trip as one injector line had no clamp and it cracked. Not a big deal, just leaked until I got home and sourced a replacement and new clamps. This would have happened locally at lower RPM just the same. This falls under fixing PO hackjobs and neglect.

3.55:1 gears and a ZF5 is the way to go. Mine turns about 2000 RPM at 70 MPH. Downshifting is required for hills particularly when towing, and it's EGT limited while towing. A double overdrive would be nice but the torque isn't there for it and I suspect EGT would be too high without a bigger turbo and an intercooler. 4.10 and no overdrive sucks for highway driving, but just slow it down. My engine runs fine at 3300 RPM for hours but it feels "happy" in the 2000-2500 range. Run it where it feels right.

 

I drove mine from BC to Ontario in 5 days towing a 1996 camaro on a car hauler and my bed was full of stuff.. like 1500 lbs in the bed this was in 2015. Trans went in the mountains but after i had it fixed the truck did it no problem. Then 3 months ago i drove back to BC from Ontario with the truck filled with stuff and a utility trailer full as well truck handled it no issues.