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Unread 09-09-2008, 11:11 AM   #1
Rob95YJ
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1995 YJ Wrangler 
 
Join Date: Sep 2006
Location: somewhere
Posts: 144
making more power with 2.5

I decided to go to a 4.0 TB and a smooth TB spacer and a homemade cold air intake. I am also going to enlarge the intake were the TB mounts and down the line maybe port and polish the head. What other items can I do to improve the power on the cheap.

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Unread 09-09-2008, 12:29 PM   #2
tawdr77
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1980 CJ5 
 
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The cheapest way to get a significant power increase over a stock 2.5l, would be to pull it out and put in a 5hp briggs & stratton engine.

Really though, I think that if your wanting a decent power gain, you should swap in a different motor. The 2.5l will nickel and dime you to death with all the little mods that will give you very little hp gains. The 2.5 is a turd, and as everyone knows, you cant polish a turd.
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Unread 09-09-2008, 01:22 PM   #3
jeepdude1987
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1987 YJ Wrangler 
 
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The 2.5 isn't a bad motor! It gets very little respect considering what it can do for a 4 cylinder. The major flaw of the 2.5L is lack of highway daily driving ability. If you need more power your best bet is a swap, but if you just would like it to be a little more driveable then that will be most of what you can do and have things still reasonable.
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[COLOR="Red"]1987 Wrangler YJ RED[/COLOR] 4.2 5-speed, NP231, BFG 31x10.5R15 AT/KO on 15x8 gambler wheels.
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Finishing a 4.0 Cyl.head swap, Just got an AX-15 NP231J combo to replace the busted t-case and craptacular BA10/5. Adding Nutter bypass. Probably more to come before it is back as a DD!
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Unread 09-11-2008, 05:33 PM   #4
jeepross
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1993 YJ Wrangler 
 
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I agree, the little 2.5 gets little respect. Around town and on trails it has more than enough power, on the highway with bigger tires, 31's it also does fine with exception of a large headwind, then I can maintain 60 miles per hr in 5th, with no hills. It came stock from the factory with 127 horsepower, which is not to bad considering other 4 cylinders out there.

I do happen to agree with people that want to do little things that do not cost much to improve what little extra horsepower they can get out of it, 4.0 throttle body, high flow air intake and cheap headers will add 10 to 15 horsepower to the 2.5 at around 300 to 400 bucks. 10 to 15 extra hp's in that motor will be noticable! while there is not much more you can do but that, while being cost effective, I think it would be worth it. So anyone that says do not invest anything for extra hp's on the engine is ludacris, the common response is, get rid of it and put in 4.0, well that is not cost effective for most people, if for 400 bucks I get a few more ponies, under the hood looks better, sounds better, then I can live with that. The biggest thing we cannot forget is how robust the engine is, I am still on mine at 310,000 kms (186,000 miles), and have not batted an eye at its reliability, starts and runs great everytime, never add a drop of oil between changes. yes, the 4.0 has more power (naturally) and is just as robust (is a 2.5 with two more pistons), but sometimes you have to give the 4 squirrels a pat on the back once inawhile as well.
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Unread 09-11-2008, 07:00 PM   #5
RedneckYJ
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1991 YJ Wrangler 
 
Join Date: Feb 2008
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Quote:
Originally Posted by jeepross View Post
I agree, the little 2.5 gets little respect. Around town and on trails it has more than enough power, on the highway with bigger tires, 31's it also does fine with exception of a large headwind, then I can maintain 60 miles per hr in 5th, with no hills. It came stock from the factory with 127 horsepower, which is not to bad considering other 4 cylinders out there.

I do happen to agree with people that want to do little things that do not cost much to improve what little extra horsepower they can get out of it, 4.0 throttle body, high flow air intake and cheap headers will add 10 to 15 horsepower to the 2.5 at around 300 to 400 bucks. 10 to 15 extra hp's in that motor will be noticable! while there is not much more you can do but that, while being cost effective, I think it would be worth it. So anyone that says do not invest anything for extra hp's on the engine is ludacris, the common response is, get rid of it and put in 4.0, well that is not cost effective for most people, if for 400 bucks I get a few more ponies, under the hood looks better, sounds better, then I can live with that. The biggest thing we cannot forget is how robust the engine is, I am still on mine at 310,000 kms (186,000 miles), and have not batted an eye at its reliability, starts and runs great everytime, never add a drop of oil between changes. yes, the 4.0 has more power (naturally) and is just as robust (is a 2.5 with two more pistons), but sometimes you have to give the 4 squirrels a pat on the back once inawhile as well.
AMEN BROTHER!!!! Mine has done more than enough to make me proud.
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Unread 09-11-2008, 07:24 PM   #6
ZeroGravity
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My 4.0 makes me proud...

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Unread 09-11-2008, 07:39 PM   #7
j33p3r4x4
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If your going to port and polish the head take the block in and get it bored .30 over
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Unread 09-11-2008, 07:47 PM   #8
Matt_vs_YJ
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1989 YJ Wrangler 
 
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Quote:
Originally Posted by Ringwood View Post
My 4.0 makes me proud...

But you're still the second slowest car on the road


It's all good though, I'm ok with being the slowest. My Jeep has never left me stranded cause of engine trouble. Even after my first engine blew a ring, it still got me to work for at least a week
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Unread 09-12-2008, 03:34 PM   #9
OneCleanYj
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1992 YJ Wrangler 
 
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Agreed here too, the 2.5 doesn't get as much respect as it deserves. When I was moving this past weekend I had no problem maintaing 40-45+ on the steeper grades going up Highway 50 into Tahoe. That was with a 6X9ft trailer loaded with my bedroom, tools, detailing equip, couch, etc. Didn't even make the old girl sag much

I'm in the process of polishing my old cyinder head and intake, eventually I'll swap them onto my new motor. I've already done some to my current intake manifold and noticed a small gain, even before my 4.0 TB.

Be careful though, you can easily puncture a water jacket or ruin a valve seat if you're not careful. I'm using various bits and sandpaper to do mine, mainly cleaning up the casting marks to make a smooth surface. The bowl is definitely trickier, but doable. Don't focus on removing excess material, just smooth out those casting marks IMHO

Edit: I'm also averaging damn near 20 MPG, and even got 16 towing on I-80 at 65

I'm going to 35's this next week, we'll see how she does then
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Unread 09-20-2008, 09:08 PM   #10
Rob95YJ
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1995 YJ Wrangler 
 
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Quote:
Originally Posted by tawdr77 View Post
The cheapest way to get a significant power increase over a stock 2.5l, would be to pull it out and put in a 5hp briggs & stratton engine.

Really though, I think that if your wanting a decent power gain, you should swap in a different motor. The 2.5l will nickel and dime you to death with all the little mods that will give you very little hp gains. The 2.5 is a turd, and as everyone knows, you cant polish a turd.
First of all easy on my "TURD". I am looking for cheap to free mods so I am not worried about bieng nickled or dimed to death. It will not cost more than $300 dollars to do what I want, so I can not see changing the whole drive train to get rid of an engine that I trust to take out in the middle of nowhere beat the s**t out it and it brings me home. Not to mention gas at over $4.00 a gallon. I can fill my 20 gallon tank and play all day. Can you?
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Unread 09-20-2008, 09:14 PM   #11
ghost183
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1992 YJ Wrangler 
 
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add 2 more cylinders ???

just messin with ya..

4.0 throttle body?

header and exhaust?

porting for mid to high power?
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Unread 09-20-2008, 09:15 PM   #12
Rob95YJ
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Quote:
Originally Posted by j33p3r4x4 View Post
If your going to port and polish the head take the block in and get it bored .30 over


WHY PUINCH IT OUT? My engine has 105,000 miles and still has great compression. I only planned on pulling the head smoothing out the casting and gasket matching everything. If I bore it out I have to pull the engine take everything apart buy new pistons, rings, seals, gaskets and do a complete rebuild.
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Unread 09-21-2008, 04:03 AM   #13
lowflare
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1993 ZJ 
 
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Location: Thompson MB
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Not the most powerfull thing on the road but even with 31's I can maintain good hwy speeds. It is a little slow out of the gate but with 200,000+ miles on it it still runs like a top. I plan on the 4.0L tb swap also. Alittle extra power can't hurt.
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Unread 09-21-2008, 12:19 PM   #14
rip_1986
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1992 YJ Wrangler 
 
Join Date: May 2008
Location: n. manchester, in
Posts: 111
my stock 2.5 has 130,xxx on 33's with stock gears and can run down the highway 65 mph @ About 1900 rpm in 5th gear. hills drop me down to about 55 mph depending on grade. but come tax time it will get a 4.0.
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Unread 09-21-2008, 07:01 PM   #15
lurkeryj
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1997 XJ Cherokee 
 
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Posts: 538
dont bother getting a 4.0, the problem is no body gears their axles after adding big tires to the 4cyl and thats what kills it the most.
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