2.5 Power?

[CheapXJ]

my MJ had this:

it will have this VERY soon

it's really not too bad of a swap, assuming you have an 87 or newer recipient for the motor.

 

[Big Al 331]

Is the 4.0 easier than a V8? I know it will be cheaper, depends on where I get the parts.

 

[Ghost]

Yes that is true.....

If you have a 87 or newer. And those of us that have the 84-86 and enjoy their engine don't really have that option. It's just my opinion that with all the speed parts for the small handa and nissan and toyota crowd. it would be nice if there were companies that would cater to the jeep crowd of 4 bangers.

 

[Centrevillemx]

What u do is get a part for it called a "4.0 Liter" this strange part has shown to increase horsepower to around 190

 

[REDXJ4FUN]

Ok enough of this just swap a 4l in it. Ghost wants to know how to get a little more punch out of his 2.5. there are some nice things a about the 2.5. for one 4cly break less stuff. and its kinda good therapy when you can just stand on the gas to make a ha part of a trail yet ya dont have to wory to much.its hard to kill that 2.5 its just as tough as the 4.0.
a good cam a header and some DIY porting can realy help the little guy make some power. that along with a good intake and some 4.88 gears and you'll be quite happy. Once i get my shop built I'm going to start on a turbo 2.5 just for fun to see what i can get out of one. I've already put and avenger SC on a 2.5 and it came out nice and matcha 4.0.

 

[dodgeb1b]

thanks all you 4 bangers! i DONT want a 4.0, there like ass holes everyone has em'. i do like my 4 banger and it isnt bad when its up at highway speeds (80mph) i was looking at the MP cams, what do you guys think about them? also when i have the head off why not clean things up a bit? i dont need to win any races, i just want to shut mike up when i cant make it up his back yard
besides i have an 86, dont you have to change out the front ends to fit in the 4.0? my 2.5 is tight in there!
...I do have a fresh 400+ hp 360 in the barn... but think of the fuel bill!

 

[Big Al 331]

I've got a tired 318. I'm thinking of building it and putting it in inplace of my 2.5. Still thinking though.

 

[REDXJ4FUN]

the MP cams work pretty good and they can befound cheap on ebay.

 

[Big Al 331]

Anybody got numbers on the MP Cam? I can find it.

 

[MudDawg]

To answer Ghost... I live very near Disney...as for the info on engines...a great source are books written by the late Smokey Unich...ask questions...think about what goes on inside the engine...a little physics knowledge wouldn't hurt either.

On the quench thing...basically put, the closer you get the piston to the cylinder head around the perimeter of the combustion chamber, you increase the turbulence of the air/fuel mixture..this causes the fuel and air to be more completely mixed...the result is more power and a lower tendency to detonate (knock)..a side effect is a slight increase in compression ratio IF the engine was not originally designed with good quench in mind...most often seen in older engine designs.

Most production connecting rods are made of a iron based material..it is great for making rods used in a low RPM production engines..in cases where aftermarket forged steel rods are not available or the production cost is beyond budget..you can have your rods shotpeened...this compacts the metal making it stronger and helps eliminate stress in the metal...combined with a proper resizing of the rod and new high strenght bolts, the rod is now capable of higher RPM than when it was stock. Hesco has available rods for the 4.2 and the 4.0/2.5

 

[Big Al 331]

MudDAWG

What have you done to your 2.5? Need some good ideas.

 

[palmrose2]

I run an 88 MJ 2.5 with larger throttle body and custom made exhaust.....4.10 rear gears and I stomp V6 yotas and nissans all the time.....it can be built into a killer little motor...the archer brothers won all but three SCCA sport truck races with it.

What exactly do you use for a throttle body? I know that 88 used Renix TBI and I've looked at mine and don't think I can open it up much.

 

[Ghost]

Those that have helped thank you.....

Those that have chose to rib! BITE ME!

Mud Dawg,
I use to live in Vero Beach and have two uncles that live in Orlando. Thanks for the definitions. I do have a basic physics knowledge but it was in High School in the late 80's. What you say actually makes sence to me.

Palmrose2,
Old Man might chime in here. He bored a 2.5L TBI that was Renix. I have it now and hope to get it on a block soon.

I was looking at the 88 Sales brochier and it states the 2.5 has 121 HP @ 5250 RPM and 141 Lb-Ft Torque @ 3250 RPM. I know the 91 MPI engine has more HP and Torque but this is what I was going to use as a base build up motor. The TBI set up. My thinking was to get a header, the only ones I know of are pacesetter and clifford. Use the bored TBI I got from old man. Put my stage III Mopar cam in. And bigger exhaust. Maybe a 4.0L exhaust? Would that be a bad idea? And run bigger intake and exhaust valves. And bore her out some. I would like to see a 30-40% increase in power. Is this plan doable?

 

[palmrose2]

...cam lift is .478 with 272* duration... [/B]

Are you talking gross lift or net after putting 1.5 to 1 rockers into the equation?

Do you remember what valve springs you used?

 

[palmrose2]

This is it?

 

[Beezil]

didn't get a chance to read the whole thread, so i don't know if this has been covered or not......

try mopar's engine performance manual....I read through it a bit, and theres a ton of info in there

I gave my copy to tim flowers who will be running a 4cyl.

I'm sure you've gotten ribbing on this thread, we haven't had a good 6cyl vs 4cyl debate in a while, but you won't catch me crapping on 4cyls.....no way, not after watching sewerboss(nate) give it hell with his old one over the years.....

 

[MudDawg]

Sorry, been out of town...the valve lift is .478 at the stem..the springs/retainers were purchased with the cam...I chose this cam for several reasons...the duration is pretty short...the lift is not so high as to wear the springs out too quickly...what it does is allow better cylinder fill at low to medium RPM...2000 to 5000.

The object of any performance increase is to get more fuel/air into the motor and/or increase the thermal efficiency of the engine. The parts are selected depending on the use of the engine...several factors affect WHERE in the RPM band these increases occur...bearing in mind that a normally aspirated engine setup that produces power at high RPM makes less power than stock at LOW rpm...a properly mapped fuel injection system will help with the low end softness.

A ported head with stage 1 valves (properly done!!!), header...combined with a free flowing big bore exhaust (the header will do nothing if corked up with a puny exhaust...modified throttle body (if this applies) or a intake/carb combo...(injection preferred)...cam in the 270 degree range...280 range if stickshift. blueprint the lower end. Balance the rotating assembly..Have the rods shotpeened, beams polished and HP bolts installed (Hesco has rods on the shelf, sold outright) This is the short of it....but a general direction...if used strictly for high RPM racing, the components and cost go up along with the required maintenance frequency.

 

[Eagle]

Are you talking gross lift or net after putting 1.5 to 1 rockers into the equation?

I believe the 4.0L and 2.5L, being AMC engines, use a 1.6:1 rocker arm ratio, not 1.5:1.

 

[HossHoffer]

2.5 power

I finally got back on after a screw-up by comcast on my connection. I wanted to let you know about my 2.5l. I have the engine that Tom Houston built up. With the stage II cam and headers mated up to the heavy flywheel it makes a great engine for the trail. It also has enough spunk for the ride there. I towed a utility trailer with my camping gear up into Leadville, down the front range and over the divide (Wolf Creek Pass) and had no troubles. I think there were only a couple of times I went into 3rd gear. I'm still running my stock gearing 3:11 with 29 inch tires so even with the tall gears it was a good quick trip. In fact the headwinds were more of a problem than the inclines. I originally had the carburator on but switched to the renix tbi system even before I put Tom's engine in and that made a HUGE difference. I know that there are webber carbs for it but I was able to piece together the tbi for about $50 from the junkyard. The hardest part was splicing the wiring harness together. anyway, good luck.

 

[palmrose2]

OK 1.6 to 1.

My engine is pretty fresh but stock. Which means .374" at the stem. I don't really want to dive into the bottom again but I might consider redoing the top and selling an almost new head, cam and lifters. Will a different cam and head work alone make enough difference to justifie the expense?
My previous experience was with a carbed 84 and I knew that the TBI version I am now running would make more power so I didn't change anything from stock. I found that the TBI makes considerably more power than the old 84 Chief I had but still wanted more. I opened up the air intake for a gain and installed a flexalite fan with controller for a definate gain. Gains were from about 2800 rpm up.
On the exhaust side i have the OEM manifold, 2" pipe to a gutted (not by me) high flow cat and 2.25" through a muffler out the back. I figured that was enough for 2.5Ls. Am I wrong? The only headers I see advertised are made to fit a Wrangler. Will these fit the XJ?
Still would like to know of experience opening up the Renix TB.

How fast do you spin your engine MudDawg?

Great info gents.