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Old 09-21-2012, 09:02 PM   #1
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97 TJ 2.5 more power?

I have a nice little 97 TJ with that good little 2.5 and a 5 speed. I love the economy I get with it, ive had as good as 26 on the highway. unfortunately it is as everyone knows gutless above 55 mph. I put a spiral throttle body spacer, that helps. I put e3 spark plugs and an accel performance coil, that helps a bit more over 2500 rpm. and I have a k&n high flow air filter in the factory air box. how can I put the most power into it for the least amount of money?

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Old 09-21-2012, 11:41 PM   #2
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There's lots of threads on this.

Bottom line is there isn't much you can do for it without a turbo or a supercharger. If you're lacking power at certain speeds, regear. That's basically all you can do.

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Old 09-22-2012, 12:08 AM   #3
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Originally Posted by PapaJammie View Post
There's lots of threads on this.

Bottom line is there isn't much you can do for it without a turbo or a supercharger. If you're lacking power at certain speeds, regear. That's basically all you can do.
What he said^^^



Some free stuff that will help is increasing your power to weight ratio. You're pretty much stuck power wise short of FI so you'll have to free up some weight...sprung and unsprung. Remove your back seat, spare, lighter wheels/tires, get a soft top if you don't have one and anything else you can think of...every little bit will help especially in town. Leaving the top on will reduce drag at highway speeds but that takes the fun out IMO.
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Old 09-22-2012, 08:20 AM   #4
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I have 33x11.5 tires on aluminium rims, Dana 35 f/r with 4:10 in both. ive read some about an electric cooling fan and colder thermostat helping is there any truth in that?
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Old 09-22-2012, 08:46 AM   #5
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Originally Posted by tallzdatank View Post
I have 33x11.5 tires on aluminium rims, Dana 35 f/r with 4:10 in both. ive read some about an electric cooling fan and colder thermostat helping is there any truth in that?
Ok, you've done a lot of stuff to your 2.5L that really didn't help except perhaps via the Placebo Effect. Really. With the type of throttle body and fuel injection the 2.5L engine uses, the throttle body spacer did literally nothing to improve performance. Spacers can work wonders under older throttle-body injection throttle bodies and carburetors but that's it. The E3's did nothing either, they only improve performance when the spark plugs they replaced were totally worn out. Really.

Your 2.5L engine's lack of performance is cause by the 33" tires which caused a major hit on performance. Their larger diameter caused a ratio change which decreased how many RPMs the engine turns at any given speed which is to say at 65 mph your engine rpms are not nearly as high with 33" tires as they were with 30" tires which substantially decreases power.

The cure for that which will SUBSTANTIALLY improve your power is to regear your axles from their present 4.10 ratio to 4.88 which is the appropriate axle ratio for 33" tires. This ratio recommendation assuming your transmission is the 5-speed manual. The 4.88 axle ratio will restore the engine RPMs back up to what they need to be to be able to produce enough power to adequately power those larger/heavier 33" tires.

While not cheap, regearing your axles (both must be regeared) to 4.88 is the only way you will see the dramatic improvement in power you are seeking. No, installing an electric fan or colder thermostat will not help.

Remember, it's your tire's larger diameter causing the problem. Their larger diameter has given them greater leverage against your engine, they are heavier, harder to turn, have an increased rolling resistance, and your Jeep is sitting up higher in the windstream from your suspension lift and taller tire height which gives increased wind resistance.

Start saving to regear to 4.88 and ignore all the rumors of improvement with all those other things you have heard which won't help. Really.
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Old 09-22-2012, 08:53 AM   #6
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I have 33x11.5 tires on aluminium rims, Dana 35 f/r with 4:10 in both. ive read some about an electric cooling fan and colder thermostat helping is there any truth in that?
No truth at all. Leave the thermostat alone, it's correct as is. Electric fans are popular is you are playing in water, they do not change power available to the wheels.
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Old 09-22-2012, 09:14 AM   #7
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Not to mention the engine computer is programmed around the engine operating at the temperature the OE 195 degree thermostat sets. When the engine can't warm up to its normal temperature, which would be a problem in colder temps, the engine would stay in a full-rich warm-up mode which would cause both power and fuel economy to go into the toilet.
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Old 09-22-2012, 02:48 PM   #8
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thanks guys, so 4.88 is the ratio I need then. boy wish I'd known that when I regeared it to the 4.10s ok well she does ok for now but I will start saving.
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Old 09-22-2012, 02:59 PM   #9
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thanks guys, so 4.88 is the ratio I need then. boy wish I'd known that when I regeared it to the 4.10s ok well she does ok for now but I will start saving.
you should have had factory 4.10s
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Old 09-22-2012, 03:31 PM   #10
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now, I know that when we put a cold air intake on my last jeep (89 yj 2.5) it helped economy, and helped power just a little. would that be a direction to look in addition to regearing?
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Old 09-22-2012, 04:15 PM   #11
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Originally Posted by 6InARowMakesItGo

you should have had factory 4.10s
it had factory 3.73 and 3.07. it was a 96 made for the 97 model year. one of the first 50 off the line its a sport TJ with a 2.5.
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Old 09-22-2012, 04:53 PM   #12
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Whatever it came with, it didn't come with 3.73 and 3.07. The '97 TJ SEs that were made in '96, as mine was with its 3/96 build date, came with 4.10 when they had the 5-speed transmission.
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Old 09-22-2012, 04:59 PM   #13
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well then somebody before me changed it up. I counted the teeth myself. so if regearing to 4.88 is what I want do you know a good brand e-locker that I could buy to do that. I figure since im running open diffs now if im gonna go through that again ill put lockers in while im there.
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Old 09-22-2012, 05:02 PM   #14
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Your rear axle is too weak for a locker, go with just a front locker until you can upgrade the rear axle. Do you live where you need a selectable locker? I.E. do you have to drive on icy roads during the winter?
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Old 09-22-2012, 05:16 PM   #15
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I live in Montana where it snows till June some years. so if I wanted a rear locker should I go with Dana 44s? I have a friend with an 80 grand Wagoner with Dana 44s I could raid his engine is blown its in his pasture.
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Old 09-22-2012, 05:17 PM   #16
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His Wagoneer axles are set up for leaf springs and your TJ is set up for coil springs... it'd take a lot of work and fabrication to get his axles installed into your TJ.
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Old 09-22-2012, 05:25 PM   #17
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I have a degree in metals fabrication. its what i do I know they're leaf springs. but 3 hours of fab work could save me $2000 but Dana 44s are the way to go if i want rear lockers right?
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Old 09-22-2012, 05:30 PM   #18
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His Wagoneer axles are set up for leaf springs and your TJ is set up for coil springs... it'd take a lot of work and fabrication to get his axles installed into your TJ.
Not so ballisticfabrication.com sells all the tabs and axle brakets to put any axle under a tj and for cheap prices, so you could stay coil springs :-) and retain you control arm suspension....
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Old 09-22-2012, 05:37 PM   #19
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I'm fully aware there are premade axle bracket kits available, I have first-hand experience with that. It's still not an easy job to convert from leafs to make it TJ ready especially given that the Waggie's axle widths are not the same. I'm not going to trivialize the work involved in converting a Wagoneer axle to work in a TJ.
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Old 09-22-2012, 05:40 PM   #20
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I totally spaced on how wide wagoneer axles are... Well just run full size axles lol....
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Old 09-22-2012, 05:48 PM   #21
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I have a friend who put um under his yj, and have welded new conversion brackets on axles before, its not so bad. I'd have to make new fender flares but thats about all.
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Old 09-22-2012, 05:49 PM   #22
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That's good you can do that though there's a lot more work in converting them to work in a TJ than you experienced when you installed them into your friend's YJ.
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Old 09-22-2012, 06:11 PM   #23
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but it seems better than buying new axles at almost 1200 a pop.
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Old 09-22-2012, 06:13 PM   #24
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You only need one axle, the rear.
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Old 09-22-2012, 11:49 PM   #25
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You only need one axle, the rear.
but I have to regear them both right?
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Old 09-23-2012, 01:15 PM   #26
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but I have to regear them both right?
if you're asking if both gear ratios need to match, the answer is yes
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Old 09-23-2012, 01:21 PM   #27
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then if both ratios need to match, it seems to me that it would behoove me to replace both axles with a Dana 44 that was already geared how I want rather than just the rear end and regear the front. also while im doing it put in lockers. just do it all at once.

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