[Felsengleiskette]

Im going to switch out my 2.5 throttle body w/ a 4.0, now catalogs offer a performance 2.5l throttle body, a 4.0 performance thrtl bdy,or O.E.M parts of either engine size....which should I get to maximize gains without going to far?(like I can assume I dont want the performance 4.o,right?)

 

[khenderson]

i would go with the 4.0L throttle body as you can get it from a junk yard for probly $50. that's what i did. i don't have it on yet, but all the performance throttle bodies i've seen for my 2.5L were about 200. and i'd be willing to bet the opening on the performance 2.5 is close to the same as a 4.0.

 

[Rocjeeper]

I have the 4.0 tb on my 93 YJ 2.5. I had to swap the idle air controle plate and motor to the 4.0 tb, and plug a vacuum port. Works ok I guess.

 

[Felsengleiskette]

Will I have to then buy a 4.0 air intake to match the 4.0 throttle body ,or do I get a 2.5 version air intake?And put it on over the 4.0 tb?

 

[Rocjeeper]

The throttle bodys are the same dimentions. The manifold opens wider under the throttle body so you don't need to change the manifold at all. The intake snorkle could be left the same or a high flow kit could be installed for a 2.5 or 4.0. The 4.0 kit may be a little over kill cause the stock 2.5 will never draw as large a volume of air as the 4.0. OR swap on the 4.0 stock air intake. Try as I may, there is only so much one can do to bump up the HP of a stock 2.5.

 

[Ed in North Ga.]

The throttle bodys are the same dimentions. The manifold opens wider under the throttle body so you don't need to change the manifold at all. The intake snorkle could be left the same or a high flow kit could be installed for a 2.5 or 4.0. The 4.0 kit may be a little over kill cause the stock 2.5 will never draw as large a volume of air as the 4.0. OR swap on the 4.0 stock air intake. Try as I may, there is only so much one can do to bump up the HP of a stock 2.5.

While I usually dont troll where I dont know squat...you are in the correct ballpark-
the engine can only draw so much, and exhale so much(without supercharger/turbo help). What we do, is provide more "room" for both, to make more power, within those limits.
If you provide more available air/fuel, you should provide more exhaust ability- manys a time Ive seen people do all the special intake mods, and not even think about their exhaust..then complain because the performance gain wasent "astounding"!..more like..."just a bit `o difference".

For every reaction, there is a reaction- more fuel, more air, more exhaust-- kill one, diminish the others.

I`ll use my old 89XJ I had as a perfect example-- I did one of the first cold air induction/homemade intakes, and had access to a bored out throttlebody(which promptly screwed with my 02sensor-nother story/nother time)- I regapped the plugs, hooked everything up(replaced the 02 sensor) and whammo...power!...not much, but there....
Moved to the exhaust, completely emptied the cat, and put a downspout exhaust about midcab. MUCH more power....in the TOP end. Nice bit of power in the midrange, lost the low end(killed an 02 sensor). Ended up replaceing the cat with a (then) high flow version-ran new pipe from it out the back...Lost the high end, gained all kinds of power in the midrange...low range was a tire burner(killed another 02 sensor).
Pulled out the "experimental cat"(drillbit- 1inch- halfcat,half hole) reinstalled, BUT, put a restrictor on the end of the muffler-believe it was halfsize, but its been awhile.

power everywhere....good high end, midrange, decent lowend pull. I removed the restrictor, and felt less low end...I had reached "the point".

I provided ample intake, and "tuned" the exhaust for backpressure/lack of.
A freeflow exhaust wont work, and too mush backpressure will tarnish the highend...

Then I installed a cutout......and fried a few more 02s.

I miss that jeep.

The 2.5 isnt inherintly a bad engine, its just being asked to do something it shouldnt, and it does that well enough. It can feasabily be boosted up to higher horsepower and torque, but within limits...and those limits are somewhat small. Any increase on the 2.5 is something to talk about.

 

[Felsengleiskette]

Ed- could you talk a little more on what you did w/ the cat? I didnt quite follow...Did you pop more O2 sensors? Is there a plug in to prevent that? If Im following you so far that jeep had: cold-air/upgraded throttle body/high flo-cat(hole?)/1/2 size pipe restricter...? Did you have to re-gear that also or did you not have larger tires on it?

 

[Ed in North Ga.]

Ed- could you talk a little more on what you did w/ the cat? I didnt quite follow...Did you pop more O2 sensors? Is there a plug in to prevent that? If Im following you so far that jeep had: cold-air/upgraded throttle body/high flo-cat(hole?)/1/2 size pipe restricter...? Did you have to re-gear that also or did you not have larger tires on it?

In the start, I had basicly drilled a hole in the cat, but ended up gutting it completely to see if I could get a bit more flow...thats the problem, according to the Jeep Techie who diagnoised it- it had too much exhaust flowing too fast, and appearenty-according to him- that fried my bevy of 02 sensors. The replacement cat (junk yard special) I used, i went back to the drilled hole method, and put a cast iron cutout right before it-- ride around town at 35/55 with the cat, opened it up on the freeway (which killed 02 sensors, but slowly).
The throttle body was bored out just a hair- enough to remove a line, no-more....shouldnt have even mentioned it, but it was there.
Most all of this was on 235s- towards the end I was on my 31s-

strangely enough, with the 31s I got better gas mileage, but lost alot of the low end...cruiseing around at 2000RPM at 75+ mph....I have no idea why the tranny didnt fry over time.

I did check up on that old jeep last year- i have *access* to run state VINs, and sure enough, that sucker is still registered and running around Atlana somewhere....it did, for some *unknown* reason, fail its first smog test a year after i sold it....bet that guy was suprised when he found all the special stuff...

There is....a way....around sensors in the renix jeeps. Most sensors are variable...the 02 sensore puts out a signal in ohms, the MAP uses a voltage that converst ohms....the computer eats ohms for breakfast/lunch/dinner...very little actual voltage is "used", as mch as ohms.
Wise man say: check how they modified the MAP sensors, and apply it to everything else...if an 02 sensor puts out sayyyyyy(non-true example)...5ohms when its truely warmed up and running well...whos to say where that 5ohms comes from?
suppose...just suppose...you supplied it with 5 ohms, instead of a stupid platnimum tip?....... ....just stiring your mind alittle...think about it. If a MAP sensor puts out 5 volts when happy.....

theres alot you can do....

alas, we also dont have smog cops here....so, I can get away with alot. I havent really dug into the MJ , since its my DD and I cant lose a day at work fiddleing with it....but the EGR went by by awhile back....and that cat is looking reallllyyyyyy old.....

 

[Rocjeeper]

O2 sensors produce voltage. Ohm is what resistance in an electrical circuit is measured in. The two are very different. This wise man says don't F with your sensors. Other than that I'll be nice and stop there, but its not easy. :flipoff:

 

[Ed in North Ga.]

O2 sensors produce voltage. Ohm is what resistance in an electrical circuit is measured in. The two are very different. This wise man says don't F with your sensors. Other than that I'll be nice and stop there, but its not easy. :flipoff:

oh, please, dont be nice....
but I`ll give you a better hint. Influencing the resistance (ohms) of an electrical circut can affect the output voltage....or input for that matter.

and no...it isnt easy....but it is possible. <-(without flippoff)

 

[Rocjeeper]

There is....a way....around sensors in the renix jeeps. Most sensors are variable...the 02 sensore puts out a signal in ohms, the MAP uses a voltage that converst ohms....the computer eats ohms for breakfast/lunch/dinner...very little actual voltage is "used", as mch as ohms.
Wise man say: check how they modified the MAP sensors, and apply it to everything else...if an 02 sensor puts out sayyyyyy(non-true example)...5ohms when its truely warmed up and running well...whos to say where that 5ohms comes from?

Well then maybe you would like to rewrite this paragraph because as I read this I think, maybe it's just me, you have no clue what you are talking about.

 

[Felsengleiskette]

Well ummm... chit. you both just flew right over this tiny brain of mine then...Must of rolled over a few too many times.Or smoked 2 much hippy hay cuz all this stuff 'bout ohms my god will the holes make car go vvroom!!!! or what?!lol

 

[Ed in North Ga.]

Well then maybe you would like to rewrite this paragraph because as I read this I think, maybe it's just me, you have no clue what you are talking about.

naaa...think I`ll leave it as is- its self explanatory. When you can get the mileage I got through normal means, you got something better. I like what I did- it worked.
Think- if you can add resistance..you can control available voltage. 0 resistance is full voltage(el~leano)...adding resistance decreases voltage-the signal-(rich)
I homebrew- if you wanna call me on it, thats your right. But I`m happily clocking 30+ mpg in my MJ now with almost no mods...and got better in the XJ with the mods...all with a little time and thought..and homebrew. Renix jeeps are easy to fool. The computer is part way retarded right out of the factory- you just have to give it the right information.

so ponder this- an 02 sensor that reads low (for lean mix) and a map sensor with a variable pot switch that thinks it reads High vacuum, a coolant switch thats bypassed,with no cat. Cold air intake, no heat riser....

tell me why it worked....