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Author Topic: 2.5's power curve?  (Read 5515 times)

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oakesmi2

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2.5's power curve?
« on: August 28, 2005, 12:49:08 PM »
I have read here that the 2.5 makes good power around 3,000 RPM's.
I was wondering if anyone here has a power curve for this engine.
I was most interested in finding out when the engine's power signs off on the topend?
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Offline Jeffy

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2.5's power curve?
« Reply #1 on: August 28, 2005, 01:30:09 PM »
Peak torque comes in around 3200 rpm.  Peak HP is around 4200 Rpm, I believe.  (I used to have the power curve someplace too.)  I use the whole RPM band depending on where I'm driving.  Shifting at 2000rpm's is really slow.
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oakesmi2

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2.5's power curve?
« Reply #2 on: August 28, 2005, 02:58:29 PM »
Quote from: "Jeffy"
Shifting at 2000rpm's is really slow.


What do you mean?  For normal driving on the road when do you usaully shift?
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Offline Jeffy

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2.5's power curve?
« Reply #3 on: August 28, 2005, 03:07:14 PM »
Shifting at 2000 rpm's is too early and the engine hasn't even begun to go into the powerband.  The lights is for economy shifting (which could cause you to use more gas by lugging the engine).  Typically I shift near 3000 rpm but I've been know to take it up to 5000 rpm's.  Anywhere from 3000-3500 should be alright for most situations.
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oakesmi2

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2.5's power curve?
« Reply #4 on: August 28, 2005, 03:21:58 PM »
one more.
When driving on the highway at 70 and at 55 what is your cruising RPMs.
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Offline Jeffy

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2.5's power curve?
« Reply #5 on: August 28, 2005, 06:29:26 PM »
In 4th at 70mph, I'm doing around 3000rpm.  I don't really drive at 55mph so I haven't looked.
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oakesmi2

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2.5's power curve?
« Reply #6 on: August 28, 2005, 07:16:38 PM »
Not able to use 5th?
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Offline Jeffy

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2.5's power curve?
« Reply #7 on: August 28, 2005, 07:23:02 PM »
No, I can use 5th but then I'll be doing close to 80mph.  RPM's are too low to use 5th below 70mph.

Also keep in mind I'm running 35x12.5R15's with 4.56:1 gears.
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Offline Bounty Hunter

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2.5's power curve?
« Reply #8 on: August 28, 2005, 07:46:26 PM »
I typically shift around 3K, sometimes 3500 if I pull out in traffic and need to get moving a bit quicker.

I'm about 3K in 4th gear at 70-mph with 33" tires and 4.11 gears.  5th is occasionally useable at 3K and 80mph if conditions permit.
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Offline Jeffy

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2.5's power curve?
« Reply #9 on: August 28, 2005, 08:45:02 PM »
Quote from: "Bounty Hunter"
I typically shift around 3K, sometimes 3500 if I pull out in traffic and need to get moving a bit quicker.

I'm about 3K in 4th gear at 70-mph with 33" tires and 4.11 gears.  5th is occasionally useable at 3K and 80mph if conditions permit.


LOL! only 3500?  I flog my horses and it really picks up and goes when you shift at 5000.  When it picks up the next gear it will be within the powerband so no power is lost.
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oakesmi2

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2.5's power curve?
« Reply #10 on: August 29, 2005, 09:07:22 AM »
What I am trying to do here is  be running at about 60-65 be using 5th gear and cuirse at the most effent RPM for the engine. So I was thinking if the engine's peak torque is at about 3200 RPM, I should be near that when running 70 on the highway. Btw I am going to go with 33's once my 31 BFG's are toste.  Just trying to get an idea on what gears I should be looking at.

Thanks for the advice.

mike
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Offline Jeffy

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2.5's power curve?
« Reply #11 on: August 29, 2005, 11:18:40 AM »
If you're going to swap gears, I recommend not going with anything other then 4.88's if you have a Manual.  If you look in the FAQ there is a section that addresses gearing.
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Offline Bounty Hunter

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2.5's power curve?
« Reply #12 on: August 29, 2005, 11:59:08 AM »
4.88 isn't really low enough for 33", but it's as low as you can go with the stock axles.  Not only are you compensating for the increase in tire height (causing the effective gearing to be taller), but you're compensating for the large increase in rotating mass.
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shotgun

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2.5's power curve?
« Reply #13 on: August 29, 2005, 01:29:40 PM »
Holy John Crapper.  Something's got to be wrong in my jeep or your driving on flat ground to downhill all the time.

the only time I see 70 is going downhill with a tail wind pushing. I normally run 4th at 3000Rpms and see 55-60mph. going up a regular hill  this is all I can maintain. anything relatively steep or with a posted grade will drop me to 3rd in a heart beat.  Anything over 3300 RPM and I can't feel any power in the jeep.

mind you this is an 87 4banger with 4.88s and narrow 35's ( 34x10.50 ltb to be exact.

I suspect quite a bit of blow by, but not noticable oil burning. but I think crankcase pressure is blowing oil out the dipstick as after long high rpm runs (1hr 20min.) the side of the engine is covered with oil and the stick drops about a quart. Replaced everything but the head and manifold gaskets and can't find the leak. Doesn't leak a drop just going around town.
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StefanBidi

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2.5's power curve?
« Reply #14 on: August 29, 2005, 03:24:12 PM »
The fact that it's a 87 with TBI, I don't think that's bad.  Most in here have MPFI, which is a lot more efficient than the TBI, and produces more power.  As far as I know, there isn't much upgrades for the TBI engines, they were only in production for 4 years.  Not to mention it's an almost 20 year old engine.  Probably the only thing to make it have more go, and stop leaking, is a complete rebuild.
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