What should the cruising RPM be?

[Flash1034]

Howdy, Ive got a 93 W250 with 3. 54 gears, 33" tires, and an auto transmission. Ive noticed that at approx 75 mph my factory tach shows approx 2300 RPM. Is that high for cruising or about right? Where is the power band and where is max MPGs?

Thanks,

Bill

 

[Cummins Cowboy]

i don't know with that tire size but with my stock d250 tires 70mph=2000 rpm 85mph=2500rpm so to me yours sounds a bit high, i think about 1800rpm would be ideal if i only went about 60mph constantly i am sure my mileage would be mid 20's easlily

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93 D250 5sp 3. 54 gears sans muffler, ISSPRO tach, K&N filter, needs to be bombed BAD
I would rather be cummin than stroken

 

[Bob Beauchaine]

Mine runs at 1900 at 70mph. I'm running 3. 54 gears and stock tires. The NV4500HD has a slightly better OD ratio than the Getrag had. Happy Trails

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1993 250 4X2 - Banks Power Pack, BD Power Injectors, K&N Air Filter, 6 gauges and new 15% + pump. 27lbs boost unloaded. Horton fan, NV4500 5 speed and BD Exhaust Brake.

 

[J DeMaio]

Well, with the bigger tires wouldn't that make the difference in engine R. P. M. I thought when you put on bigger tires you were supposed to go with lower gears (higher numerically). This only makes sense because since there are bigger tires the engine would have to work harder with the stock gears. Just a thought, hope this helps, I'm not a real mechanic I have just read this in magazines.

 

[Russel98]

I have a 92 350 with reg tires, 5 sp Getreg
and 354 rears with a GearVendors. I checked
my rpms at 75 today and was running 1720 in
5th over.



[This message has been edited by Russel98 (edited 05-28-2001). ]

 

[paccool]

Rambill,
The bigger tires will make the speedometer read slow. If you have not corrected for the tires, the actual speed is higher than that indicated on the speedo. I suspect if you correct the speed you will be just about right on with the others.

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Stan
93 2WD extended cab, Banks Power Pack, K&N air filter, PW Injectors,rebuilt and tweaked pump, auto w/3. 54 rear with limited slip, US Gear Exhaust Brake, 3-1/2" Exhaust, Chrome valve covers and heater lines, 5K air bags, Boost/Pyro/Tach Gauges, Green/Silver, new 40-20-40 bucket seats, 151K

 

[MAX A/C]

Hi RamBill:
2300 is too high. You want to be at 1600, but this would require yet another (higher still) OD gear for fast cruising, and you may not be spinning the turbo fast enough to provide enough boost to create the horsepower required to move our big bricks through the air at those higher speeds. My truck (3. 54's 31. 5" tires) runs 1600 at 55mph, 1900rpm at 65 mph, 2200 at 75mph. There is a good discussion of fuel consumption in Issue 31, page 90. The lowest fuel consumption (brake specific fuel consumption) for our motors is at 1600rpm (which is peak torque), and this is where I get the best mpg, and so would you. For the 24 valvers, lowest BSFC is at 2000rpm. As a rule of thumb, if I cruise at 55mph, I'll get 22mpg; at 65mph, 20 mpg; at 75mph, 18 mpg; you see the pattern. Hope this helps.

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'93 W250 Club Cab, 5 spd, 3. 54, stock engine, 95K miles

 

[BushWakr - RIP]

I have a near identical setup RamBill.
While I have not had a chance to test the 75MPH reading I know that at 60MPH I'm turning about 1750RPM (thats in OD). One of the fella's noted (and rightly so) that the taller tires will result in a slightly lower speed reading than actual speed. Also you might want to consider transmission slippage in this equation too. How many miles on your rig? Hard driving, towing, when was your last transmission service, band adjust etc?


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93. 5 W250 4X4,HD Spring Pkg, Rancho 7000's, Rear Swaybar,Dual Shock Front Stabilizer,BD 180HP Injectors,31/2" Mandrel bent exhaust,BD16cm 'Hot End',Modest Pump Tweaks(lock collar still on)Star Wheel@3oclock/Timed @ 1. 37mm,K&N Air,Isspro Pyro (Post Turbo),Tach,transmission Temp,Auto Meter Oil Filled Boost Ga. , 3:54's, 4 Speed Auto, Clubcab, Aftermarket Reclining Buckets w/ctr Drop Down seat/console, Black over Silver, 22psi,285-65R-16's,American Racing Clear Coat Mags, Amsoil 15W-40HD Marine,12,000 lb. Warn Winch,KC Spots. 103,900 Kms (64,600 mi's). NOT A VENDOR,Just an end user

 

[Flash1034]

Originally posted by BushWakr:
I have a near identical setup RamBill.
While I have not had a chance to test the 75MPH reading I know that at 60MPH I'm turning about 1750RPM (thats in OD). One of the fella's noted (and rightly so) that the taller tires will result in a slightly lower speed reading than actual speed. Also you might want to consider transmission slippage in this equation too. How many miles on your rig? Hard driving, towing, when was your last transmission service, band adjust etc?

Ive got 169K on it and the transmission fluid was changed about 8 mos ago. Dont know about the band adjust. I dont know how to do that one... ?