Any input on the best engine RPM on a 1989 E350 cutaway used for towing a 5th wheel? From all I can find out, max torque is about 2200 & max HP is about 4000. Neither of which is a good towing RPM.

The way I'm geared right now, 3000 in drive(3rd) @ 65 mph = about 10"
vacuum. 2500 in drive @ 55 mph = about 5" vacuum. 65 mph in OD= 0" vacuum. Thanks, Elliott

 

Your combined weight must be pretty high. I've got a Winnebago Elante 33 Class A. It weighs about 16,500 lbs wet. 460, E4OD, 5.13 rear axle. I find the best compromise for speed and economy is about 55 MPH which is about 2200 RPM in OD, level road, no wind, about 12" vacuum. The torque curve is quite symetrical from about 1800 to 2800. I like to keep it in that range, but I will pull it down to 1500 on occasion, or as high as 3000 to make a shift if road conditions warrent. I have a custom transmission controller so I have complete control over gear selection and torque converter clutch application and release, which gives me an advantage over the stock programming and allows me to run it in my own particular style. With a stock transmission, I'd advise trying to run at about 55, and if the load won't allow you to stay in OD, cancel OD to stay in 3'd until conditions allow 4th. Also, if you get in a situation where it downshifts to 2nd, pull it into manual 2 until such time as it looks like you will be able to stay in a higher gear. This is just my style, and may not be comfortable for you.
Robert

 

These numbers are similar to what I do with my F350 w/460 and a 4.10 rear. This is a good compromise for all around drivability. Towing 8,000lbs, my truck is real comfortable at 60 mph, and will not down shift until 55mph. Then is screams at about 3400rpm. You can go to lower rear end gears for more engine rpms at lower speeds, but then you almost go above your power band. If you go any higher, you lug the engine and fry the trans.

Things sound about right to me.

 

Keep her @65 and you'll be ok.

 

Where ever you highest vacuum reading is will be the most efficient...in your case your highest reading is at 65 (10 inches of vacuum) in 3rd gear. Deen

 

Sorry Dean, but I have to disagree with that. I've always wondered about that theory myself, for a given load and speed, is economy better in a lower gear with less throttle, or a higher gear with more throttle? Ask a dozen people, get a dozen different answers. Here's what I've found.
I made a little "trip computer". It displays current MPG, updated every 250ms, as well as tank average MPG. I have a local hill, about a mile long, about 8% grade, quite consistant. I made several runs up the hill at 42mph. Some in 3'd gear lock up, almost WOT, 0" vacuum, and some in 2'nd gear lock up at about 8" vacuum. Can't remember the engine speeds. In any case, believe it or not, economy was about 2% better in the higher gear. I found it surprising myself. When you think of it, there are several factors involved. The horsepower requirement is the same, moving a given weight at a given speed up a given incline. In a lower gear, the engine isn't as heavily loaded, and the mixture is slightly leaner, but there are more combustion events per minute, the pumping losses are more because of a partially closed throttle, and unless it is running at peak torque, the volumetric efficiency will be slightly less. In a higher gear, the mixture will likely be richer, but there are less combustion events per minute, pumping losses are less because of an open throttle, and you are more likely to be running at or near peak torque, for better volumetric efficiency. I ran these tests both with my Class A 460, and my E150, 300 six. the results were similar. The economy differences aren't great, but they do exist, at least from my testing. I think the key here for economy, is to run your engine near peak torque when loaded, and less than peak torque when cruising.
Many newer vehicles have trip computers in them. I'd be interested to hear what anyone elses experiences are.
Robert

 

Robert, your rear axle ratio might make a little difference. Mine is 4.10 & in OD that equals out to about 2091 at 65 which is below peak torque.

Thanks for all the input. I still don't know what to do.

When we're on a trip, we are pressed for time, or we are often on a 2 lane road with speed limits that vary from 55 (Ia), 60 (mo), 65 (ok) 70 (tx). At 55 mph in od, I'm way below peak torque. at 55 mph in 3rd, I'm at 2500. If I down shift to 2nd at 55mph, I'll be way over 3000. I feel what I really need is a multi gear, close ratio trans, so that I can down shift every 250 to 300 rpm to keep in the torque range at what ever speed I have to be driving. I have an almost dead E4OD that runs at about 124 degrees while towing, 180 in campgrounds.

Don't know how it was treated before we got it.

Thanks, Elliott

 

Hi Elliot,
Oh My! Those 4.10s do present a bit of a problem with that weight! At 65MPH and that weight and frontal area you're loaded right up!
How much money have you got? You look like a candidate for the underdrive version of US Gear's dual range auxiliary transmission. Kind of weird. There's been 3 threads in the last few days that have involved this. I'm beginning to feel like I should be on their payroll, ( but I'm not, honest!). Check out their website, it might be what you're looking for. Assuming your transmission temperatures are sump temperatures, they sure sound good.
Robert

 

Elliot, those rpms you see are what I used to live with when pulling my boat with the Ford Dooley. I wasn't comfortable with the amount of rev's needed to go down the highway, but didn't want to change rear gears and lose the grunt pulling the boat out of the water. Higher gears won't necessarily improve your mileage either.

I must admit that I bailed out and bought a brand new Dodge RAM 2500 Quad Cab shorty 4x4 Cummins High Output/6 speed. I do miss the dooley's towing stability, but like the fact that it's easier to park now.

 

 

Where is peak torque on a factory 89 460?

Since it ordered as a cutaway to be customized as a trailer toter, I don't know if it would have an RV cam in it or not. It is EFI.

It would seem to that the ideal setup would be able to drive with the rpm a little over peak torque, and be able to shift up or down to keep close to that point.

Am I correct in theory?

Thanks, Elliott

 

Hi Elliot,
The Motorhome Chassis Service Guide that came with my '92 shows the torque and HP curves. I suspect that your '89 would be the same, or very close. Torque peak is at 2200, and HP is at 3600. The curve drops off significantly below about 1500 and somewhat after around 2800. Unless your engine has been modified, I don't think Ford offered any diferent cam grinds.
I basically agree with your running RPM theory. The only thing I would add is that if the engine is relatively lightly loaded at cruise, say level ground with no wind, or slight downhill grade, you could run below max torque for a bit better fuel economy, as long as you didn't go too far down on the curve. Unfortunately, the only way to get that flexability is to add more gears, and in your case, the auxiliary I mentioned should do the trick. Their site publishes a gear/speed ratio chart that you can use to calculate any RPM/Speed/Gear combination you like.
Robert

 

Hi Robert,

Yes, I've been to US Gear, Gear Vendor (feel they are mis leading) Randy's Ring & Pinion calulation page, Spicer tech suport & Eaton.
Also had a person down by Houston email me a gear chart for New Process HD 5 sp's.

Since my E4OD is dying, rebuilding & upgrading it, plus a US Gear underdrive, would give me a bill around $5000.00. Ouch!

Decisions, decisions. Thanks, Elliott

 

Put a 4.56 gear in it and you'll have more grunt to pull the boat out of the water and your rpm's will be up around peak torque while in OD.
Jimmy

 

Hi Elliot,
Funny, I thought the same thing about the Gear Vendors advertising. I did a lot of research on both company's products. G/V would have been my first choice because of the smoother shifting method, but their advertising claims are downright misleading. Didn't detect quite as much BS over at US Gear. The final decision turned out to be easy in the end. G/V doesn't recommend use with an exhaust brake.
Any way you look at it, it's going to be expensive. It would be nice to have a 5 or 6 speed manual, especially with an auxiliary, but putting that in a cutaway would be a real challenge. Decisions Decisions.
Robert