460 Ford RPM's

[redtop]

I have a Ford F53 chassis with a 460 V8. I'm trying to find out whats the best rpm's to drive at to get the best mileage. I've found that if I drive at about 61 mph ( rpm is about 2500 ) my class a will climb most hills in overdrive without shifting down. But if I drive at 65 mph it shifts down a lot sooner so I'm wondering what the best rpm's would be to get the best mpg

[mpaton]

Quote:

Originally Posted by redtop I have a Ford F53 chassis with a 460 V8. I'm trying to find out whats the best rpm's to drive at to get the best mileage. I've found that if I drive at about 61 mph ( rpm is about 2500 ) my class a will climb most hills in overdrive without shifting down. But if I drive at 65 mph it shifts down a lot sooner so I'm wondering what the best rpm's would be to get the best mpg

It sounds like you maybe have a typo with those speeds. Going faster usually means it take s MORE gas pedal to make it downshift.

Secondly, it sounds like you have 2 separate goals, as the RPM for best gas milage is a different problem from the best RPM to go up hills faster, or use the least gas to get to the top.

The answer may well depend on the ECU (as different ECUs in different years don't have the same tune). It also depends on weight, especially if getting to the top of the hill fast counts.

So let us know the weight, the year, and if you can find the ECU Catch code, that will help as well.

If you look at this post
Fuel safety shutoff 1994 F53

it shows a Ford ECU with a Catch Code of MOO0 on the white decal on th eblack box which contains the ECU.

[subford]

Redtop has a 1997 F53 with a 1998 airbus home on it.

[Dwight]

Redtop (This would show better on a graph.) 1995 Ford F53 7.5L (460 CID)
Brake Horsepower 245 HP @ 3600 RPM = 360 LB-FT Torque
Maximum Torque 400 LB-FT @2200RPM = 170 Brake HP

Torque shows that the engine has the ability to hold speed very well @62 MPH.
AT 65MPH your torque drops slightly and you are meeting greater wind and road resistance causing your cruise control to work the engine harder to maintain the speed.
Because of the wind resistance at 62MPH, You could improve MPG at 55 MPH as long as you are able to stay in overdrive.

[Forest Grump]

I put a vacuum gauge in for the same reason. The more vacuum the better mileage within reason. Balance the tach with the vacuum gauge and see what u get for mileage. In some really strong headwinds in the desert I have had to avoid using overdrive altogether.

[Wanabee FTer]

I keep my R's appx 2200 to 2500 when cruising that's about 55-60 mph. Fully loaded including toad I average about 6.75 to 7.0 mpg. Not a big difference in mpg when I keep in this range. The only issue I have is running up long grades. I try to keep R's at 3500, but have gone up to 4,000 if I feel it's necessary.

[Forest Grump]

I don't think I have ever gone that high even pulling the toad up a 16% grade. I keep it around 2500 to 2800.

[Wanabee FTer]

I can't stay in 3rd gear up long grades, when the trans downshifts the revs go up to 4,000 in second, then I back off the gas until about 3500 RPM which is about 42 mph. I mostly stick to the west coast, lots of long steep grades here.

[mpaton]

I don't believe there's any harm in running the engine up to 4000 rpm or so. There's a lot of good power up there, especially with the aftermarket exhaust systems some of us have. Pulling had for a long time at 2600rpm or so may actually heat the engine up more. I suspect it depends a lot on how badly the coach manufacturer managed the airflow in front of the radiator.

Of course it certainly makes a lot more noise.

And the gap between 2nd and 3rd gear seems enormous in the mountains.
When I got my Winnebago, it had 215 tires on the front (the correct size for the chassis) and 235 on the rear. I kept the 235 on the rear thinking the gearing would help economy, but now I believe it does the exact opposite.

Closing the gear gap would mean a Gear vendors overdrive, and one of those fitted would pay for quite a lot of gas.

[Forest Grump]

I guess it all depends upon what a long steep grade is? 395 on the way to Tahoe probably would qualify. I might have a problem with tac accuracy. Anyway I keep itin third till it starts to object and then go into second and just take it easy at about 35 mph. These grades are about 8% and 8 miles long. Most other RV'S just settle in and don't pass, same with trucks (4 lane). I had to replace the radiator this year and went with a 4 core. While towing it the tow company destroyed the tranny so they had to get it rebuilt for me. I'll have to check the accuracy of the tach.

[loulong]

Quote:

Originally Posted by Forest Grump I don't think I have ever gone that high even pulling the toad up a 16% grade. I keep it around 2500 to 2800.

And what would be your speed and which gear?
2500/2800 RPM and a !%% grade

[Wanabee FTer]

Quote:

Originally Posted by mpaton I don't believe there's any harm in running the engine up to 4000 rpm or so. There's a lot of good power up there, especially with the aftermarket exhaust systems some of us have. Pulling hard for a long time at 2600rpm or so may actually heat the engine up more. I suspect it depends a lot on how badly the coach manufacturer managed the airflow in front of the radiator. Of course it certainly makes a lot more noise.

I have been thinking about making/fabricating an air dam under the front end between the radiator and front bumper to help direct air flow. The builder left a huge gap there that just lets all the air from the grill/intake dump out under the vehicle before it even gets through the radiator. I bet it would make for a much quieter ride if the fan clutch would stay disengaged when I start to climb a grade.

Any ideas where I could find plastic/rubber matting to accomplish this would be greatly appreciated.

[mpaton]

Quote:

Originally Posted by Wanabee FTer Any ideas where I could find plastic/rubber matting to accomplish this would be greatly appreciated.

I cut hardware store 1/4" plywood to fit, and then oilproofed it with 1 layer of fibreglass cloth and epoxy resin on each side.

[Forest Grump]

Quote:

Originally Posted by loulong And what would be your speed and which gear? 2500/2800 RPM and a !%% grade

Max torque is at 2400 to 2800 rpm. I am talking about 16% grades not 1% and that is in a hairpin turn. I enter the curve at about 10 mph and try to come out at 15 mph. I am between 2400 to 2800 rpms at that speed and slope. When I am in 3rd and get down to below 45 I go into 2nd and then again aim for the torque sweet spot between 25 and 40 depending upon slope.

Its not going to go up those grades any faster. Coming down is another story.