manimal Posted March 20, 2010 Share Posted March 20, 2010 I have done some searching..maybe not typing in the right right words. But I am looking for mods for the 2.5 4cyl. Do they use different heads like the renix and HO? Do they benefit from the same type of mods like the HO ie injectors,later manifolds,etc...? Thanks for any advice and info. -Lance BTW I have an 87 MJ 2wd 4spd. Thanks Link to comment Share on other sites More sharing options...
jteckmann Posted March 20, 2010 Share Posted March 20, 2010 For more info on the 2.5, this is a good site to check out: http://www.4bangerjp.com/forums/ Most of the available mods, however are for the 1991 and up versions of the engine, after they received multi-port injection. Us TBI guys seem to be limited. Clifford Performance makes a header for the 2.5, but IIRC the catch is that you have to upgrade to their intake manifold as well, and the Renix TBI will not bolt up to it, so you have to go with the added expense of a carb or aftermarket injection set-up on it. Avenger makes a supercharger kit, but it is for the +90's MPI version. The best mods for the TBI 2.5 are the simplest - you're not going to add much to it, instead, you need to free up and use some of the horses that are already there and being wasted. - free flowing air intake with a cone filter or K&N - open up the exhaust to about 2"-2.25" with a high-flow cat and muffler - ditch the mechanical cooling fan and replace it with an electric unit. - gearing, gearing, gearing. A stock 2.5 4sp has 3.55 gearing. General consensus seems to be that a 5sp and 4.10's are the way to go. Takes better advantage of the engine's power curve Theoretically, the Renix 2.5 should benefit from a throttle body spacer. I'm not aware of anybody that makes one - but you could use the gaskets to trace out a pattern and home-brew one. None of those things will turn the 2.5 into a powerhouse, but they will make it much more drivable and easy to live with. And for lots of people (myself included) the 2.5 is fine for my needs. But if you want real horsepower, the easiest answer on how to upgrade a 2.5 is "swap it for a 4.0". Link to comment Share on other sites More sharing options...
dasbulliwagen Posted March 20, 2010 Share Posted March 20, 2010 Ive done a bunch of those mods on my 2.5 already... the cold air intake, electric fan, gutted cat converter, and a flowmaster 50 series muffler. I have an extra 2.5 that I plan to rebuild with ported head, cam, and a header, I'm not sure on the intake yet as I don't know if I want to stay with the injection or go with the clifford intake and put on a 390 cfm holley 4 barrel. Ive been wondering though lately if a 2bbl injector from chevy pickup could be modified on to the clifford intake and tied into the factory harness..... I have some research to do! There a few of us 2.5 lovers on here, so don't get too discouraged by all the yelling voices that say to swap a 4.0. Good luck! Link to comment Share on other sites More sharing options...
jimoshel Posted March 20, 2010 Share Posted March 20, 2010 :agree: Link to comment Share on other sites More sharing options...
kro10000 Posted March 20, 2010 Share Posted March 20, 2010 Turbo! :thumbsup: Link to comment Share on other sites More sharing options...
manimal Posted March 20, 2010 Author Share Posted March 20, 2010 Thanks guys! This thing has problems, it had bent pushrods-they were replaced. Now it runs like crap i guess. I have to go pick it up still. I was paid w/ the MJ for swappin transfer cases in a friends ZJ. So I was curious about the differences. -Lance Link to comment Share on other sites More sharing options...
dasbulliwagen Posted March 20, 2010 Share Posted March 20, 2010 Good trade for a running truck! Once you get it home, go over everything, cap, rotor, plugs, wires, good gas..... youll be suprised what a difference they can make. Mine was like that when I got it... had been basically sitting for 4 years, but the owner started it every week and made sure it was still running, but it ran like crap after sitting that long and neglected, wouldnt idle. I tuned it up, put good gas in it, and I got it to idle and started driving it, the more I drove it the better it ran, up to a point, it would still buck and miss quite a bit, so then I replaced the O2 sensor and its run perfectly ever since. That engine is just about indestructable, so check it over and I'm sure youll be fine. Link to comment Share on other sites More sharing options...
DodgeFan01 Posted March 22, 2010 Share Posted March 22, 2010 Another 2.5 lover here, I am interested in the same things! Mine is an 88 2wd with manual steering. I actually picked up a power steering gearbox a few years ago, but I haven't installed it because I am afraid of losing more power. I would love to upgrade to an electric fan, but I have no idea where to start or what to buy, as well as the cone filter, lost there too. Let us know what you decide to do! Adam Link to comment Share on other sites More sharing options...
jteckmann Posted March 22, 2010 Share Posted March 22, 2010 Ha! I did the same thing - I have a whole power steering assembly sitting in my garage, and haven't put it in because I'm afraid of the power drain. I may go ahead and do it anyway, since it's my DD, and parallel parking the thing is a pain. My best guess is that adding the ps and ditching the mechanical fan will cancel each other out, and it will just drive like it did before. For the electric fan on mine, I just purchased the smaller Hayden(?) universal model at the local AutoZone. Cost about $65 and came with all the wiring and mounting hardware. I wired in a toggle switch on the dash so I can turn it off/on manually. It's worked fine for me - doesn't take much to keep the 2.5 cool. Pretty much the only time I have to run it is when I'm sitting in stop and go traffic. Anytime I'm at speed, the natural airflow keeps the engine at normal temp. If you search this site, or look through the DIY thread, there are a few good write-ups on how to use the electric fan from a Ford Taurus - cheap and plentiful at local junkyards. AFAIK, that mod works on both the 2.5 and the 4.0 - you may just have to do a little extra trimming when mounting it to the radiator. For the filter, your best bet is also home-brew. I'm not aware of a company that makes a complete set-up specifically for TBI 2.5 MJ's or XJ's. Easiest thing to do, IMO is to get a decent cone filter, and then fab up the ductwork yourself. The other thing is to grab the airbox from a 4.0 at the junkyard and swap it in place of the 2.5 box. It's slightly bigger - so you may need to relocate your washer fluid or radiator reservoir to get it to fit. But K&N makes a drop-in filter that fits the stock 4.0 box. Gearing seems to be the way to go. From what I've read, the 2.5 likes to be in the 2500-3500 range, and can rev at 3000 all day long. The 4sp, 3.55 combo seems to be a real dog, especially at highway speeds. Tire size makes a huge difference. I moved from the stock 215's up to just 235's, and I was having to feather the clutch a lot more just to keep from stalling out at red lights. Right now, I'm just waiting for one of my driveline components to fail, so I can justify the expense of upgrading to a D44 with 4.10's and a 5sp. :brows: Link to comment Share on other sites More sharing options...
dasbulliwagen Posted March 23, 2010 Share Posted March 23, 2010 First thing I did was the PS swap. I didnt notice any power drain at all. I noticed a touch of gain with the cold air tube, and a touch of gain with the electric fan, and a lot with the 4:10 gears, but when the AC compressor kicks in you notice a momentary drag on the engine and then back to normal... don't worry about a PS drain, it really only pulls a lot of power when you are turning at slower speeds, going straight it don't matter at all. If you do notice anything, it won't matter because youll be soo happy you don't have to force the wheel anymore! Link to comment Share on other sites More sharing options...
DodgeFan01 Posted March 23, 2010 Share Posted March 23, 2010 Lol, no doubt, at least I'm not the only one. It sure would be a world of difference to have PS! It's good to know that you didn't notice a difference once installed. I too am thinking about the gearing, I have the 4 speed in there right now but I bought an AX-5(?) 5 speed a while back, just haven't installed it yet, but I guess I should wait to throw it in until I can get some 4:10s. I am running 235s with no problem, I can even get a squeel out of them if I want to! The other thing I have been thinking about is putting a turbo on it(I think I'll eventually post a question on this as well). I have a 84 Dodge Daytona that has a 2.2 with a turbo on it stock. I know some of the later years(88, 89) have a 2.5 option with turbo, so I'm wondering how different the 2.5 from the Daytona and our 2.5 is and if I could fit a turbo set up from the daytona on to the jeep. That would be Sweet! Although I know one big difference is the daytonas are ohc. Link to comment Share on other sites More sharing options...
Backroads Posted March 23, 2010 Share Posted March 23, 2010 Is your 2.5 a TBI? I'm wondering how that would work, or if its even possible to turbo a TBI style engine. If its possible, I'd be pretty interested to give that a go! Link to comment Share on other sites More sharing options...
kro10000 Posted March 23, 2010 Share Posted March 23, 2010 The 2.5 Daytona is a completely different motor from the jeep 2.5, its an OHC motor (Mitsubishi IIRC), whereas the Jeep 2.5 is essentially a 4.0 minus 2 cyl... Link to comment Share on other sites More sharing options...
kro10000 Posted March 23, 2010 Share Posted March 23, 2010 I can't see any reason why you couldnt turbo a TBI motor, remember there were factory cars that had turbos with carbs, although I can't remeber a factory turbo TBI, If i were to do it Id swap on MPFI Link to comment Share on other sites More sharing options...
WBKrazy Posted March 23, 2010 Share Posted March 23, 2010 I can't see any reason why you couldnt turbo a TBI motor, since the injector(s) are between the TB and the turbo on TBI motors, the injectors are constantly under boost as well. if your running 10lbs of boost, that 10psi is pushing against your injectors. a TBI typically runs around 13 psi max, so if you subtract the 10 psi boost pushing against them, its like you have 3 psi fuel pressure... not anywhere near enough fuel pressure to support boost..... Link to comment Share on other sites More sharing options...
DodgeFan01 Posted March 23, 2010 Share Posted March 23, 2010 Oh yeah, the 2.5 from the daytona is not TBI, it is MPI. Hmmmm :hmm: Link to comment Share on other sites More sharing options...
kro10000 Posted March 23, 2010 Share Posted March 23, 2010 The same could be said about a carburetor, youre only pushing about 6 psi then, itd be the same principal with MPFI, youd still have all that boost pushing "against" the injectors Link to comment Share on other sites More sharing options...
kro10000 Posted March 23, 2010 Share Posted March 23, 2010 With a carb the jets are between the throttle plates and the turbo as well, not trying to start a fight but that doesnt make sense to me :thumbsup: Link to comment Share on other sites More sharing options...
jimoshel Posted March 23, 2010 Share Posted March 23, 2010 It may not make sense to you but it works. Anytime you can cram more air into a cylinder, with the corresponding proper amount of fuel your going to get an increase in horse power, and or increase d engine efficiency. Link to comment Share on other sites More sharing options...
kro10000 Posted March 23, 2010 Share Posted March 23, 2010 Youve got me confused, i am saying a turbo tbi would work, read prior posts Link to comment Share on other sites More sharing options...
jteckmann Posted March 23, 2010 Share Posted March 23, 2010 It's definitely possible to turbo or supercharge a TBI. When I go to car shows with my father-in-law, I see a bunch of the hot rod and muscle car guys running aftermarket systems on their TBI GM V8's. You just need a pressure bonnet with a relief valve that goes over the TB. I've always thought supercharging would be the way to go - so you don't have to deal with splicing into the exhaust system, and you get the power right from the start. I'd imagine turbo-lag would be kinda a pain to deal with when driving on the trail (for an off-roader, a DD not so much) If I had an MPI 2.5, I'd be saving my money up for a kit right now. I definitely think it's possible with a TBI - get one of the aftermarket kits for the 2.5, get a pressure bonnet somewhere, and fab up an adaptor to the Renix TBI. I've also thought that if you went with Clifford's intake/header set, threw on a Holly TB, and then bolted a supercharger on that, you'd probably be able to build quite the screamin' 4-banger. These are bullet-proof little engines, and IIRC, AMC used to dominate while racing a 2.5 Comanche. But there's the rub. Building it is one thing - building it on a reasonable budget is something else. You could throw $5K into a 2.5 and have an awesome engine, but it's be comparable to a fresh 4.0 that somebody dropped maybe $1K into, tops. And with the lack of aftermarket support, you'd constantly be running into headaches the 4.0 guys don't have to deal with. But that's all part of the fun. It's the same motivation that drives guys to swap in diesels and all other sorts of stuff - doing it for the enjoyment and pride of building something different. Link to comment Share on other sites More sharing options...
jimoshel Posted March 24, 2010 Share Posted March 24, 2010 Being a 2.5 and a turbo believer I am interested in any and all thoughts on the subject. As jtechmann pointed out the biggest drawback is the lag response. Altho the newer models have come along ways in overcoming it. Wastegates, lighter weight, etc. I have a 2.5 I just completed overhauling and a half dozens turbos on the shelf awaiting a use. However I am hesitant about putting a used unit on the engine and believe I will go for a new one, Right now I am comparing spec sheets on several diff models and reading what I can about the opinions and experiences of others. The engine ,with turbo, is going into a '88 SB MJ I am building for serious off roading. Any and all thoughts welcome and appreciated. Jim Link to comment Share on other sites More sharing options...
Yesterday's Danish Posted March 24, 2010 Share Posted March 24, 2010 I'll be watching this thread. I was thinking of swapping out my 2.5 for a 4.0, but I kinda wanna keep it and do something fun and different with it. Link to comment Share on other sites More sharing options...
mnkyboy Posted March 25, 2010 Share Posted March 25, 2010 the mitsubishi 4g54 sohc in the starion/conquest was TBI and turbo. IMO the easiest way to turbo a 2.5L would be a draw though set up with a carb, but the best way would be a blow through setup and MPFI which is how I'm planning top do mine as soon as i can get converted to MPFI. Link to comment Share on other sites More sharing options...
kro10000 Posted March 25, 2010 Share Posted March 25, 2010 Id never do a draw through setup, theyre horribly inefficient, seeing as they superheat the fuel coming in Link to comment Share on other sites More sharing options...
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