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Old 07-11-2010, 10:12 PM   #1
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mpg question

so i took the jeep down the interstate we had the safari top on and it was great except that i had to kinda fight to keep it between 60 and 65..the speed limit was 70 lmao. the reason i didnt "fight" more and get it to or closer to 70 was the rpms were almost at 3000, didnt know if that was too "hard" on it and really didnt want to experiment with it. so i was telling a friend and he was like "what?! it was only around 3 at 60-65 thats great for gas mileage!" so i was wondering if thats true

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Old 07-11-2010, 10:12 PM   #2
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btw its a 2.5, forgot to add that

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Old 07-11-2010, 11:06 PM   #3
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Yea your friend was being sarcastic. 3000 RPM at 65 is quite high which means it will eat up a lot of gas. The higher the RPMs the more gas it will eat. I know when I cruise I am always above 3000 RPMs, but I do have the straight 6. There is no problem maintaining a higher RPM constantly when you are driving as long as the engine does not overheat, but that is normally not a problem. Just keep it out of the red line area on the tach and you will be fine.
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Old 07-11-2010, 11:39 PM   #4
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Crap! At 3000 RPMs with my 4.0 it feels like it's winding out... redline's at like 5200 or something but theres no way in hell I'll take it anywhere close to that. I usually shift between 2000 and 3000 RPMs and cruising on the interstate in 5th gear I'm usually around 2200 RPMs or so...maybe just under 3000 when doing 80 mph on the faster interstates.

And I agree...cruising at 3000 RPMs on the highway definitely is not good for gas mileage in a Jeep, though if your RPMs are TOO low, that's also not good because a lugging engine will suck a lot of gas too.
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Old 07-12-2010, 12:39 AM   #5
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Yes actualy it is okay and pretty good.

The engine doesn't start making good power until it hits at least 2500 rpm. These little engines can run at 3500 rpm all day long, but I wouldn't sustain much more than that.

Chart AMC 150/2.5 Compression Horsepower Torque
One-barrel carburetor 9.2:1 105 hp (78 kW) @5000 132 lbft (179 Nm) @2800
Throttle body injection (TBI) 9.2:1 117 hp (87 kW) @5000 135 lbft (183 Nm) @3500
Multi-point fuel injection (MPFI) 9.1:1 120 hp (89 kW) @5250 139 lbft (188 Nm) @3250

Torque is the one you want
I have a 1991 2.5 TBI and its actual a XJ engine designed for an automatic tranny so the rev. is super high to make power. Third gear is the god gear. I can go faster in third gear then in any other gear, i hit about 85mph at 3500 RPM flat surface. Note: i do have a 4.0L TBI and cheap old cold air 31inch tires and stock everything else.

Link with more help for the 2.5 guys to gain more power. 2.5 Jeep AMC engine
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Old 07-12-2010, 04:38 AM   #6
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Of course tire size and gearing will affect what you rev at any given speed.

my 4.0 with 3.73 gears and 30 inch tires revs about 2200 at 65 mph and you can feel the power band really kick in around 2300 or so.
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Old 07-12-2010, 05:15 AM   #7
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true gearing dose matter, especialy with tire size but he is talking about a 2.5l so 4.0 guys get out of here.

I usally keep my 2.5l jeep around 65-70 on the highway. 27-31 RPM in any gear on highway is not bad on a 2.5 infact it is where you should be for the best fuel milage in 5 th gear at cruising speed.

You should be shifting properly too for fuel econemy you want to shift from 21-24 for city driving.

JP magazine did an artical on the best MPG Jeep from MB-TJ. And do you know what that was. the 1991 Jeep stock wrangle. thats right they got 19-21 MPG. but stock is no fun. next was the 92-96 stock YJ.

I couldn't find that artical but i did find another fuel milelage one and as everyone knows the biggest diffrence in fuel econemy, has to do with your tires. the right size and inflated to the proprer PSI for street driving. link

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