2.5L performance

[sureshot007]

I'm sure people have already asked a billion times about getting more performance out of their 2.5L engines,, but I'm looking to take things a little further than most. I have an 86 with tbi. I just have a few rules to follow:

1) I have to run a 2.5L, so don't even bother suggesting a swap
2) Can't have forced induction, so don't suggest turbo or supercharger
3) I have already done intake and exhaust.

I'm looking for a new cam, and it seems the only place I have found one is at Hesco ( http://www.hesco.us/shop.asp?action=details&inventoryID=167924&catId=7758 ). Are there any other options for cams? I'm interested in finding a lightweight flywheel, but I figure I'll have to just mill one down. I'm also open to swapping internals, or different pistons, if it means I can raise the compression ratio a bit. Anyone mill the deck on these things to increase the compression ratio? I'm planning on port and polishing the head and intake manifold. Larger valves? Roller rockers? Are they worth it? I am not made of money, so I need to get the best bang for the buck on upgrades. Are there any tricks for tuning? I figure running hotter plugs with 8mm wires will help.

 

[gradon]

Someone here was selling a mopar stage 3 cam for the 2.5 not to long ago. If you found one, you'd have to use different springs. You could use a bored out 4.0 tb. If you're taking the pistons out, measure the deck clearance for each cylinder at tdc and then get the block shaved the amount from the piston that has the smallest deck clearance(just remember to use the same rod and piston for the cylinder they were removed from).

 

[billyjp2]

there is a great website that i used when i had my iron duke.

4bangerjp.com

 

[wolfpackjeeper]

I was not really impressed by the 4bangerjp website when I joined a few years ago.

I think it was Ghost that was selling a stage 3. I almost got it from him. I was thinking about leaving the 2.5l in my MJ and pimping it out, but decided to hold off on it and go LSx in a few years.

Gradon has the good info up there, with a good rebuild, a little head work, and a hotter cam, the 2.5l should scoot pretty well.

 

[jeepinwi]

Getting performance from that 4 banger is like polishng a turd. Save your money and put it towards a Jeep with the 4.0L engine.

 

[sureshot007]

... I just have a few rules to follow:

1) I have to run a 2.5L, so don't even bother suggesting a swap ...

jeepinwi, I'd appreciate it if you don't clutter my thread with such responses. Thank you.

 

[Sillyfast]

I don’t have any experience building a jeep or car motor but I have built a DHOC 1200cc Kawasaki engine. If you can easily get 180Hp out of pistons and cams and a decent crank I don’t see why you can’t get 200hp out of the 2.5. I realize the rev limit is much lower but its also 1300cc's bigger. I am also interested in building a cool 2.5l on the side and swap it in my xj. (has a 2.5) I am sure J and E can make some nice high compression pistons or any other reputable piston maker. I would also be interested if stroking it would produce good numbers.

On the other hand:
I also read an article in a recent JP magazine on gears vs. power adders and the dyno did show better hp numbers with 4.88 gears than it did with $$$ if go fast parts (no blower though) and 4.10 gears.

 

[JJacobs]

Apples and oranges. I don't think you're going to be able to get the 2.5L cylinder head to flow anywhere near what the bike motor does, and so on.

 

[Sillyfast]

Apples and oranges. I don't think you're going to be able to get the 2.5L cylinder head to flow anywhere near what the bike motor does, and so on.

Like I said I dont have any experience building that type of motor. I can see the flow not being there as the bike has 4 carbs. I think a nice port and polish job would help though

 

[Gaius]

Seriously, the extra HP you will get from trying to get more NA power out of a 2.5 will NOT be worth the time or money. Take this from someone who wheeled one for 7 years.

 

[sureshot007]

Ok, last time I am going to say this:

I CANNOT SWAP MOTORS DUE TO THE SPECIFIC RULES OF MY RACING GOVERNING BODY

I have to make the best of what I have. I don't care that it would be cheaper, easier, faster, better if I swapped motors (tell me something I don't already know).

If you guys would prefer, I could always trade the jeep for a subaru...

 

[Gaius]

I didn't say to swap it, I said the 2.5 is a piece of shit that does not respond well to modification, in a nice way. Then grab a engine building book, and talk to some guys who are racing the 2.5, and build it. Not too hard: high compression, more air flow, more fuel.

Good luck.

 

[sureshot007]

Believe me, I know what an uphill battle I have ahead of me. And that's the plan - I'm just looking for those guys that have raced them, to see what cams they ran, how far I can deck it, intake manifold tricks, etc. That was the point of this thread. But it seems like no one here has bothered to do such things.

 

[badron]

For sure not cheep BUT how about ditching that TBI for a port FI. I THINK this would take a new head. intake, fuel pump, computer, sensor wires and more. This is IF your class will permit it. But few mods will bring on more HP then dumping that TBI.

 

[sureshot007]

I could certainly do that. I just hate messing with the wiring on a jeep - no good ever comes of it

 

[wolfpackjeeper]

I forget who it was, but someone converted their MJ to MPI and had a running writeup as they went. I think it ended up using a wrangler engine harness and all the applicable hard parts came from a cherokee.

 

[Sillyfast]

Is swapping a MPI 2.5 against rules if its the same displacement?

 

[sureshot007]

Nope, rules are pretty open - engine has to be from same manufacturer as chassis, under 3 liters, naturally aspirated. I just happen to have 2 complete tbi, and one shortblock. I have to keep the cost reasonable.

 

[old_man]

I started off with an 85 2.5L carbed engine. I rebuilt it, shaved the head, went with oversized valves, tbi injection, ported the head, as well as port matching to the Clifford header with 2.5" exhaust. I added a 11 lb. flywheel weight. It worked great for wheeling but didn't do that well pulling the passes here in Colorado.

I went with a Mopar "purple" cam. I don't think they are available any more.

*edit*
After a quick search for 2.5l purple cam I found this

http://www.bpemopar.com/22L25LENGINES.htm

 

[88manche]

Big cam, ported/polished heads, more fuel, more air, deck the block(or head), bore the motor. Higher octane fuel, Nitrous if your class allows it. Larger valves, lightened flywheel. No power steering, manual transmission, gears, roller valve train, No A/c. Im not sure what type of "racing" your doing with this jeep, but if you can get rid of the t-case, driveline and front axle and go to 2wd, that would eliminate the rotating assembly in the front, and that would reduce drag. or convert to locking hubs. electric locking would be best if you can find them. unlock while driving, lock em when 4wd is needed. Thats about all you'll be able to do. You'll be able to do it all with a MPI motor, but carburators are more simple. You can crank up the fuel/air mixture and not have to mess with a computer.

If i could find my book, i could give you the HP/TQ numbers for a stock 2.5L carb, TBI, and MPI.

Your going to end up putting more money into this than you probably want to, just to get a decent amount of power. i wheeled one with 4.10 gears and a 5spd for a year, it SUCKED.