Cruising speed and rpm?

[TeamAL2.5]

What is your top highway speed and rpm?

My deuce is just ticking the 45 mph mark and doesnt make it over 2100 rpm. another local owner here says his trucks are cruising around 52-55 mph. Does anyone have any suggestions of things to check?

 

[WillWagner]

Mine will do 55-56 at rated RPM...2600, but I don't like that. I cruise about 48 to 50 at around 2200 ish. Sounds like your RPM is OK. If it won't pull past 2100, maybe there is a filter issue or it isn't getting full throttle...or the dash stuff is wrong.

 

[Chevytruck]

have you checked your filters?

if not i would start with that before digging deeper in

good luck!

 

[TeamAL2.5]

they're all new. truck was the same way before i changed them.

 

[stumps]

What is your top highway speed and rpm?

My deuce is just ticking the 45 mph mark and doesnt make it over 2100 rpm. another local owner here says his trucks are cruising around 52-55 mph. Does anyone have any suggestions of things to check?

After fuel filters, the surest and quickest killer of power is dragging brakes, and mismatched tires on the rear axles.

If your air assist cylinder has a leak, it can apply braking pressure all of the time, which will be more than enough to pull your top speed down. If your tires are mismatched, they will fight each other which will wear down the larger diameter tire, and kill your gas mileage and top speed.

-Chuck

 

[Big CASE]

are you in high rang ?
I have 395s i can top out at 75mph at 2700 rpms
tho I like 60 62 about 2250 2300

 

[Burgerboy13]

are you in high rang ?
I have 395s i can top out at 75mph at 2700 rpms
tho I like 60 62 about 2250 2300

Do you have any braking issues at those speeds and with big tires?

 

[Big CASE]

no alls good

 

[wsucougarx]

I would try using a GPS to track your actual speed and compare to your RPM's. One of my trucks says I am doing 45 when I am actually at 50

 

[cranetruck]

are you in high rang ?
I have 395s i can top out at 75mph at 2700 rpms
tho I like 60 62 about 2250 2300

Careful about overevving these engines.

This image shows fairly accurately speed vs rpm with 1100 tires. Figure about 8% less speed with 900s.
(Yeah, it's running a bit warm here, but I was pushing it and with the semi-permanent radiator cover...)

 

[Divemaster920]

Cranetruck....now thats a BIG Blind spot.

 

[cranetruck]

That's my "heads up display".

 

[GoHot229]

I must have a faulty something-or-other, because I'm reading 15-1800ish RPM's at 50 MPH, it seems I'd be closer to 2200 or so? Mabe time for a new tach and spedo.

 

[mkcoen]

Flat terrain I keep the needle buried (so between 60-65mph) at 2200rpm. Drops to around 50mph at 2500rmp as soon as I hit a hill. The flat speed was confirmed by the wife traveling behind me. I know it's not as acurate as a GPS but that system has worked fine for me since the 70's.

 

[ivbeenrokd]

Mine will top out at around 55-57 running a full 2500 rpm, but I really don't like to drive it that hard. I wouldn't mind trading my 12.5/20's for some 14.5/20's or 15.5/20's just to get a little higher top speed.

 

[stumps]

Come on guys, your speedometer and your tachometer are hard geared to each other! The relationship (ratio) between them is fixed by the gear shift and transfer case lever positions.

Unless you have broken speedometers, and or tachometers, or have some custom gear ratios in your transmission, you are going to have 56MPH (indicated) at 2600RPM (indicated) in 5th gear.

If you put larger tires on your deuce, you increase your potential ground speed, but you will still show 56MPH on your speedometer when your tachometer says 2600RPM in 5th gear.

If your deuce is set up as the manufacturer intended (tires, injectors, governor, etc.), you aren't going 65MPH! 65MPH would require an engine speed of 3017RPM. Your poor little MF engine will have been on governor long before it gets to that speed! If you ever successfully get your MF engine over 3000RPM, you are setting the stage for throwing a rod!

-Chuck

 

[cranetruck]

Well, my speedmeter is corrected for the larger tires with the appropriate adapter (on the transfer case).

 

[SCSG-G4]

In my strong running deuce 2200 RPM's is about 48-50 MPH, and since it will only drop to 2100 RPM going up the longest hills I encounter in SC, while pulling the MKT, I'm happy. The speedometer says it's going 4-5 MPH faster, but the interstate mile markers (10 mile average) tell the real story, which also agrees with the total miles traveled (130 miles in three hours - some on back roads).

 

[TeamAL2.5]

Amen stumps! Lol so any thoughts why I can't get this thing over 2100? My throttle rod from the pedal to the ip arm has a smooth curve in it but i believe that isn't an issue. When you depress the pedal you can feel and hear the point where that spring on the rod starts depressing and then there is probably another 1.5 inches of travel past that point. So I'm under the assumption it's getting full throttle. However, is it possible for the return spring to pull against that governor spring and not let the arm travel all the way to a full position?

 

[stumps]

I must have a faulty something-or-other, because I'm reading 15-1800ish RPM's at 50 MPH, it seems I'd be closer to 2200 or so? Mabe time for a new tach and spedo.

In 5th gear, with the transfer case in high, the ratio between RPM and MPH is:

2600RPM/56MPH = 46.43 RPM/MPH or

56MPH/2600RPM = 0.0215 MPH/RPM

So 50MPH, is about 2300RPM. 2200RPM is about 47MPH, and 2500RPM is about 54MPH....

-Chuck