Need advise on gearing/mph highway use

marty79

marty79

Well-Known Member
Joined
Nov 24, 2013
Location
Newton, NC
So my 89 2500 5.7 has 4:56gears, th400 and now that its driving I have to go to Boone to pick up a motor. My concern is (new to this setup) at 45/50mph its sitting at roughly 2200/2300rpms ...holy crap. Motor runs good and everything is pretty much new but :
What's a safe speed for this 4hr round trip on the motor and mpgs? Thank you for advise and help!
 
I suppose my dual exhaust doesn't help with it sounding harsher than it is?
 
Best mpg will probably be 12 at 50 mph. It will get worse over 50 mph. Life span of motor will be about 100k. But on the bright side gas prices are coming down and at $ 2.40 a gallon it's relatively cheap.
 
moldman05 said:
Best mpg will probably be 12 at 50 mph. It will get worse over 50 mph. Life span of motor will be about 100k. But on the bright side gas prices are coming down and at $ 2.40 a gallon it's relatively cheap.
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Ok so from ur response everything sounds normal then...thank you
 
What's redline? A 5.7 chevy is good to go at 4000rpm pretty much indefinitely. Heck, a low tech inline jeep 4.0 lasts a lifetime of 2500-3000rpm driving. Mine runs 3000rpm at 80mph and is happy as can be.
 
jeepinmatt said:
What's redline? A 5.7 chevy is good to go at 4000rpm pretty much indefinitely. Heck, a low tech inline jeep 4.0 lasts a lifetime of 2500-3000rpm driving. Mine runs 3000rpm at 80mph and is happy as can be.
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Well thanks guys, good to know its normal lol. On the bright side I guess towing my rig should be super easy with it!
 
General rule of thumb I always see is 2500rpm at cruising speed (55mph) with no OD. That said, I'd much rather be rolling a couple hundred rpm too high than burn up a trans that's constantly hunting for gears.
 
marty79 said:
Well thanks guys, good to know its normal lol. On the bright side I guess towing my rig should be super easy with it!
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I wouldnt say super easy, but as long as you stay at that speed itll be fine. Id keep my out for a 4l80 to swap in at some point though.
 
UTfball68 said:
That said, I'd much rather be rolling a couple hundred rpm too high than burn up a trans that's constantly hunting for gears.
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Very true!
paradisePWoffrd said:
wouldnt say super easy, but as long as you stay at that speed itll be fine. Id keep my out for a 4l80 to swap in at some point though
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Well ill most likely sell the 14bolt since it has good off-road gearing and buy/trade for dually rear end with 3:73/3:90ish..that would be ideal but that's down the rd
 
One more ?, my cooling system is all new so it should be fine at higher rpms with 160thermostat (its carbed) for several hours or any better recommendations for upgrades
 
If it works for 15 minutes, it'll work for 15 hours.
 
Another option would be running a larger tire. It probably came stock with a 215/75/16 load E or something similar. Heck, put a 285 on it and see what it does. Stay with a load E though. My Yukon with the 3.73 tow package gearing and stock 265s (?) pulled 2200 at 80 in OD. I threw a set of 315s on it one day just to see how they ride before I put them on the Jeep and on flat interstate hauls it knocked the rpm down to under 2k at 80. Hurts with the stop and go driving but in a normal week where I'll see 1000 miles of drivetime, I may very well be saving a few bucks.
 
Jody Treadway said:
Did it come factory with 4.56 gearing? Seems odd for that combo
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Yeah its got the service bed remember, and it says chassis is 2nd and some other stuff on the door so I guess so
 
It has 225/85 r16 load E now
 
It is going to take your current combo to tow a trailer with a vehicle
 
I hope it has a good transmission cooler. That torque converter is going to make some heat since it's non-lockup.
 
moldman05 said:
It is going to take your current combo to tow a trailer with a vehicle
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Really...Tahoe pulled pretty good with 3:55 at 6400lb load on flat ground so I figured 3spd with 3:73 or even 4:11 would be plenty..considering I don't climb Boone mt anymore. Pretty much gonna be towing to Marion, Gulches, Kentucky and maybe Uwharrie. Well, we'll see how things turn out on this Boone trip...if it don't kill me on gas and such then ill keep it and just run 33s maybe.
Still gonna get a dually rear end for it though, then later on go 7.4 to make a nice healthy tow rig ...that's the plan anyways lol
 
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