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making more power with 2.5

12K views 122 replies 58 participants last post by  moonshinefuel 
#1 ·
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.
 
#2 ·
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.
 
#10 ·
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?
 
#3 ·
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.
 
#16 ·
The 2.5 isn't a bad motor! It gets very little respect considering what it can do for a 4 cylinder.
It's not that folks done't consider it a good motor. I had one for 7 yrs and thought it was great, still do. It just is what it is. You have to be happy living within it's performance design point. You can't really pump it up in HP a lot (if even anything really noticeable) or expect it to handle big tires. People keep building their Jeep to beyond it's capability is all, and then want more.

It's a perfect motor for a small built Jeep on or off road. I didn't swap mine out until I went to 35's, which pushed the work it had to do just beyond what I was comfortable with.
 
#4 ·
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.
 
#5 ·
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.
Robbie
 
#8 ·
But you're still the second slowest car on the road :p

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 :thumbsup:
 
#12 ·
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.
 
#9 ·
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 :2thumbsup:

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 :rtft::cheers2:

I'm going to 35's this next week, we'll see how she does then
 
#11 ·
add 2 more cylinders ???:cheers2:

just messin with ya..

4.0 throttle body?

header and exhaust?

porting for mid to high power?
 
#14 ·
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.
 
#17 ·
I think the next step is a good muffler,and if the head is off,mill it a bit to raise the compression ratio.You may have to run premium then,but that's still cheaper than a whole swap,and better for your engine than that cheap kerosine.If it costs 10% more per gallon but gives you 15% more mpg,you're actually saving$.Then gear ratio change next.Also take off the fan and replace with an electric unit.You can also try slowing down your accessories with different size pulleys to gain a few hp's and extend their life too.And if you have a distributor,advance the timing a few degrees.Good luck.
 
#18 · (Edited)
..... and none of that will make any real difference, barely noticable. This is like getting shot in the leg and someone saying "take aspirin and it will be all better". A hole bottle of aspirin won't fix the hole in your leg. Been there, done that, got dirty t-shirts to prove it.

The performance of a properly operating 2.5L either works for you or it doesn't. If it doesn't, it never will. You'll always want the next 'fix' you think will make life perfect (elec fan, pulleys, spacers, exhaust, TBs, intake, &c. yadda yadda yadda). In the end, if you get to the end, you will swap it anyway. The 2.5L is to the front end of the Jeep as the D35 is to the rear.
 
#20 · (Edited)
GEARS........if your using the 2.5 to run bigger tires and you need to change axles anyway, change the gears. i agree with LURKERYJ, no one ever re-gears to match tire size. you can have just as good power for wheelin or highway driving as you did stock if you just sort our the gear ratios. of course the 2.5 does not have the power of the 6cyl but it was never meant to.

to answer the more power question, i run a 4.0lt throttle body bored to 62mm, a 62mm helix spacer, a cold air intake, headers with no cat and a free flow muffler, use good plugs, good wires and keep the cap and rotor in good shape, i got rid of the clutch fan and run electric fans. i did all this at the same time and noticed a marked improvement in power. no it's still not a race car, it's still a 2.5lt pushing 34-10.50's, but the 4.88 gears were the best improvement.

JEEP, Live it, Love it......
 
#22 ·
GEARS........if your using the 2.5 to run bigger tires and you need to change axles anyway, change the gears.
All that does is change things back to the same revs per mile as stock. It doesn't compensate for the hugely different rolling resistance of big tires (33"+ MT styles), and it does not compensate for the mass of the tires. It takes a LOT of power to 'spin up' 400 lbs of rubber from zero to 50 mph. That's where the 2.5 will loose it. You can never add enough power to it to keep up with the work it has to do. Maybe a supercharger, but that's more costly than a swap.
 
#27 ·
Going slower just means you get more time to enjoy your jeep. :thumbsup:
 
#28 ·
I am not after a corvette. I have had my hot rod a '78 c-10 short wide lower 5/7 with a 383 stroker running 11:1 compression, ported and polished heads, headers, and 4.10 gears with posi track and I got rid of it for my Jeep. I understand there is no replacement for displacement. But what you are failing to understand is that I know that the 2.5 is not going to equal the HP or torque of a 4.0. Hell I don't care if it does. I just want to make what I have better, without spending a lot of money on it and getting some improvement in the power department, and yes I have regeared to 4.88 and am not going bigger than 33's.
 
#31 ·
wow, some of us seem to have lost track of the original question,

"What other items can I do to improve the power on the cheap?"

the answer to that question i have posted above, and i did all of it for less than $400.00

having owned a CJ with a V8, a tj with a 4.0 and 2 yj's one with the 4.0 and one with the 2.5 i feel very confident in my ability to "advocate pumping up or not" of your 2.5

i am agreed that the best route to power is a 4.0, but if you just want a little more behind the peddle without the money/work invloved in a swap or buying a whole new jeep then the things i mentioned before will help you out.

JEEP, Live it, Love it.........
 
#32 ·
I love my 4 pissed off gerbils.

They get me where I need to go on teh road and off.

I too am looking for a few things that might make it pull a little harder. I am running steel rims.. that aluminum rim idea seems like common sense but i have never thought about it before honestly. Maybe some day.:thumbsup:
 
#35 ·
little extra power

[/B]I have a 2.5 in my 93yj with 31" i got more power by removing the muffler and running a prybar into tha cat. and hollowing it out then i called JEG'S and got a 2 1/4" cherry bomb and had a local shop bend out a 2 1/4" tial pipe and the power was verry noticeable, the cost was $25. cherry bomb,$ 75. tailpipe,:thumbsup: give it a try
 
#36 ·
hey guys

i m a new owner of a 2.5 TJ '01 and i would like to increase a little bit the hp. I already changed the air filter with a K&N. Could you plz propose me a reliable TB?

I found this one http://www.4wd.com/productdetails.aspx?jeep-sid=4&plID=0&partID=5550 however i don t know whether is suitable and the most important reliable for the mod i intend to make. I need the best possible.

Thank you in advance.
 
#37 ·
welcome, you have a TJ (round headlights and coils) this is the Yj section (square headlights and leafs) hop on over the TJ section im sure they can help you.
 
#38 ·
Comparing the 2.5 to a dana 35 is kind of bull**** IMO. There is no reliability issue whatsoever with the 2.5 when compared to the 4.0. Yes i understand the money issue, but you knew you'd get a rise out of people with that one. The fact is the 2.5 is a very good motor for what it was designed to do. Don is right though, it has a limit, period and the mass of the tire will eventually exceed the 4 bangers ability to spin it.

Basically, other than tuneing it up and re gearing. you can either throw stupid amounts of money at it, do an engine swap or adjust your driving habits to fit what you have. IMO I dont think anything bigger than 35s is realistic on the 4 banger when it comes to highway driving. Mine is comfortable at 70 but thats it. Much more tire and i would be pushing it up hills. My rpms are good, the power just isnt there.


Nothing wrong with doing simple cheap stuff to coax a little extra out of it but realize you arent going to make a real difference unless you go to superpower on it, turbo, supercharger. And thats big money to waste on that engine. The 4.0 is always so highly touted, but even the 4.0 is underpowered IMO and that will not be my choice when i do upgrade unless i literally got everything for a song. Whoop! theres another can of worms, but Jeeps are notorious for being underpowered and always have been.
 
#40 ·
try putting in an inertia ring, read this http://www.4x4wire.com/tech/clutch/inertiaring/ it shouldn't cost a lot its just labor intensive.

i also have to say the best thing i did to my jeep was put in a 4.0 there is no comparison on and off road.

i bought a whole Cherokee for $500 and sold the body and axles for $200 (i could have gotten more but i just wanted it gone) then i probably spent about 200 for all the little odds and ends to get it running. thats not bad but it was a lot of work.
 
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