Topic: Performance options for the 2.5

[dwtaylorpdx]

I did not want ot Hijack the 62mm Throttle body thread so I'm answering here...


Bolt on options are thin,

1. Bigger TB (Drive-ability increase more than HP)
2. TB Spacer (Same deal, moves power band to a better position)
3. Header (Depending on unit helps or hurts torque at some RPM,  and increases HP above 2500 RPM generally)
4. Fan delete (Helps overall "felt" HP by small amount, helps engine rev quicker.)
5. Less Weight = more felt HP. Try unloading  everything into your garage,
    even the tops, back seat carpet kit spare tire and mount. Mine drives like a go kart when I do this.
6. Exhaust , many options to adjust power curve, gain small torque of HP bit nothing the dyno is going to scream about.
7. Higher ratio rocker arms, gain a bump in HP but again going to be small.
8. 4 hole injectors, better efficiency and a small power bump, slightly bigger will let you work the engine harder.
9. Adjustable fuel pressure regulator. (No power just tune-ability.)
10. Adjustable map + a dyno tune to really dial it in. another small bump plus some potential drive-ability.

All of this might net you 14 to 20 HP if you tune it in.

Deeper options: Above plus,,,,
1. Re-gear to keep your engine in its power band with those great big cool tires.
2. Rebuild the engine
     a) Hesco Or Mopar cam with lifters, springs no high ratio rockers required.
     b) Have a pro do your engine, Balance, Blueprint, 4 cut valve job adds power and raises red line about 1500 rpm.
3. Flywheel - Grunt or Snap whats your poison?
     a) Inertia ring for flywheel, If your in to crawling this will help grunt over rocks etc, will slow off the line punch a little.
     c) Lightweight flywheel , if your a sand junkie this will help you out of a bowl.
4. Forced induction - Speed cost money,,, :)
5. Nitrous - Do your homework and use your head or the results will be most of the above Wink

I'm sure there is more, but bottom line is when you buy a 2.5 jeep, your buying a
small motor. There is no substitute for cubic inches of air and fuel being mixed together.

There is no magic spell that's going to add 100 HP without $$ and work.
This is not a turbo WRX you can chip 10 lbs of boost into.

Oh well my 2 bits worth....

Dave

[sharpxmen]

nice list:
I would add
- cold air intake or large(r) inlet to the air filter from outside the engine bay (also if using the stock airbox remove the restrictor)
- snorkle (probably better than the above)
- a good high flow filter (the larger the better as you can still get higher flow w/o hurting the filtering capabilities)


the programmable map - unless you run forced induction i would just put that between the O2 and PCM and use it to "trick" the PCM in targeting a richer mixture for anything over 2000 rpm and 75% internal map indication when in closed loop (this is only for the signal altering version, the one with direct output can't be used this way), for open loop just use the adjustable FPR and/or larger injectors - that way you would get both low and high rpm range improvements - but both instances will hurt mpg, so if that is important then leave it stock for closed loop.

if you don't care about mpg you can also get a programmable O2 - that way you can simulate a narrowband sensor but you can basically put in your own 0v to 1v range and alter the output to target a richer mixture - unfortunately it is a static mod, so no way of altering it based on rpm and/or map reading (your idle AFR will be the same as above idle, no way to make that specific to higher rpms)

there is a volt mod option for the MAP - basically will tell the PCM that the engine is at WOT sooner and/or that it actually gets more air in - but again when in closed loop will use the O2 feedback to target 14.7AFR so no matter what you throw at the PCM unless you use the option above it won't get more gas. What the volt mod does: the map is powered by a 5v feed from the PCM when stock, some guys replaced that with an adjustable power source (5 to 7 volts if i remember correctly, but it think the safe range is below 6v - there are some articles out there regarding this, search for adjustable map vlotage or something like that) - so in turns the MAP output is offset by the diff in the supply voltage proportional to the map reading

in the perf mods section - polished intake runners and valves - will make a big difference, never done it on the Jeep but will increase the amount of air that the cylinder can "suck" in on any engine - can be done at home with lots of patience (runners should be smooth and polished to a mirror finish, same with the valves). Polished chamber (both cyl head and top of the piston) also help against carbon buildup and also better fuel burnout.

For #9 actually you can make more power with that than #8 assuming you have enough air and the injectors won't start squirting at higher pressure. 
Both 8 and 9 probably for best results (or at least new injectors if not design III ones)

good job putting the list together 

[C.Redbeardd]

most of these things "i hear" dont apply to the 90's? Just checking, Im just having trouble figuring out what works on the 90 YJ's as they seem to be different than the 2.5L's in the 91 to 95's.

[dwtaylorpdx]

On my YJ the guy who did the head only polished the exhaust ports,
he found the intakes need to be a little rough, (Think sand blasted texture)
it maintains the turbulence and atomization in the intake air stream.
I noticed this on some Roush Racing heads a while back too so I trust his point of view.... :)

I've run an Inovate meter on several jeeps, and I've yet to find one that
maintains the mixture where it needs to be, most run a bit rich,  The computer
does not seem to have a real fuel "curve" its more like 4 or 5 steps. I suspect Chrysler
cheesed out and did a really brain-dead table. And the minimum responses I see
from the computer imply a rough digital response not a fine analog response.

If you do all the mods it gets even worse, The adjustable MAP sensor will at least let you
tweek it closer to ideal, won't be perfect but its a jeep not a F1 car :) :)

Good point on the air filter, let me add that.

Dave

[dwtaylorpdx]

most of these things "i hear" dont apply to the 90's? Just checking, Im just having trouble figuring out what works on the 90 YJ's as they seem to be different than the 2.5L's in the 91 to 95's.

If it was me, I'd start crawling around in the Fiero forums.

The GM iron duke was a 2 to 2.5 liter 4 cyl with a TBI injector.
Don't give up too quickly on it. I think prejudice over the years
poisoned the well for these engines.
There are still folks who think a carb is going to perform better
and be less maintenance.

If you look at the design, its a spray nozzle at the top of the Air intake.
The injector "eggs" are mostly all the same, so one from a larger engine
will flow more fuel. GM/Delphi built most of the systems, a few days in
the u-pullit yards may yield a larger bore unit.  Another possibility might be a 2
barrel manifold (Clifford) with a aftermarket replacement TBI unit to fit the 2bbl
manifold. Youd probably have to run a Howell computer and work with them to make it
work. But its not rocket science, the Howell is just the GM computer with their code in it.
I have not looked at the TBI computer, It might be interesting to see if Jeep just bought
it from GM....

The last option, (My favorite) is a SDS engine management computer with a MPI
manifold and 4.0 throttle body. Easy and under 1500 bucks to convert to a totally
tuneable simple system. (I'm headed there on my rig.)

Good luck.

Dave

[dwtaylorpdx]

Updated Version

Bolt on options are thin,

1. Open up the intake,
    a) remove the restrictor tubes in the pipe.
    b) use a good air filter.
        i) I use a K&N
        ii) At least use a good clean filter.
    c) A external cold air intake / Snorkel seems to show benefits as well.
2. Bigger TB (Drive-ability increase more than HP)
3. TB Spacer (Same deal, moves power band to a better position)
4. Header (Depending on unit helps or hurts torque at some RPM,  and increases HP above 2500 RPM generally)
5. Fan delete (Helps overall "felt" HP by small amount, helps engine rev quicker.)
6. Less Weight = more felt HP. Try unloading  everything into your garage,
    even the tops, back seat carpet kit spare tire and mount. Mine drives like a go kart when I do this.
7. Exhaust , many options to adjust power curve, gain small torque of HP bit nothing the dyno is going to scream about.
8. Higher ratio rocker arms, gain a bump in HP but again going to be small.
9. 4 hole injectors, better efficiency and a small power bump, slightly bigger will let you work the engine harder.
10. Adjustable fuel pressure regulator. (No power just tune-ability.) This can compliment 9 a lot.
11. Adjustable map + a dyno tune to really dial in after the above mods. another small bump plus some potential drive-ability.

All of this might net you 14 to 20 HP if you tune it in.

Deeper options: Above plus,,,,
1. Re-gear to keep your engine in its power band with those great big cool tires.
2. Rebuild the engine
     a) Hesco Or Mopar cam with lifters, springs no high ratio rockers required.
     b) Have a pro do your engine, Balance, Blueprint, 4 cut valve job adds power and raises red line about 1500 rpm.
3. Flywheel - Grunt or Snap whats your poison?
     a) Inertia ring for flywheel, If your in to crawling this will help grunt over rocks etc, will slow off the line punch a little.
     c) Lightweight flywheel , if your a sand junkie this will help you out of a bowl.
4. Forced induction - Speed cost money,,, :)
5. Nitrous - Do your homework and use your head or the results will be most of the above Wink

[chardrc]

If it was me, I'd start crawling around in the Fiero forums.

The GM iron duke was a 2 to 2.5 liter 4 cyl with a TBI injector.
Don't give up too quickly on it. I think prejudice over the years
poisoned the well for these engines.
There are still folks who think a carb is going to perform better
and be less maintenance.

Good luck.

Dave

jeep stopped using the iron duke long before they went to tbi.. the tbi 2.5l in jeeps are the amc 2.5l like the mpfi 2.5l just different fuel injection obviously.

thanks for the hint that fieros used tbi.. since the jeep tbi has same injectors and other similarities to gm tbis... looks like the fiero tbi has a more open design (how the injector is mounted and what not)

great idea on making this thread should help stop some confusion.

[dwtaylorpdx]

Updated Version (1.1)

Bolt on options are thin,

1. Open up the intake,
    a) remove the restrictor tubes in the pipe.
    b) use a good air filter.
        i) I use a K&N
        ii) At least use a good clean filter.
    c) A external cold air intake / Snorkel seems to show benefits as well.
2. Bigger TB (Drive-ability increase more than HP) (MPI Only as far as is known.)
3. TB Spacer (Same deal, moves power band to a better position) (MPI spacer common, need ID of a TBI version)
4. Header (Depending on unit helps or hurts torque at some RPM,  and increases HP above 2500 RPM generally)
5. Fan delete (Helps overall "felt" HP by small amount, helps engine rev quicker.)
6. Less Weight = more felt HP. Try unloading  everything into your garage,
    even the tops, back seat carpet kit spare tire and mount. Mine drives like a go kart when I do this.
7. Exhaust , many options to adjust power curve, gain small torque of HP bit nothing the dyno is going to scream about.
8. Higher ratio rocker arms, gain a bump in HP but again going to be small.
9. 4 hole injectors, better efficiency and a small power bump, slightly bigger will let you work the engine harder.
10. Adjustable fuel pressure regulator. (No power just tune-ability.) This can compliment 9 a lot.
11. Adjustable map + a dyno tune to really dial in after the above mods. another small bump plus some potential drive-ability.

All of this might net you 14 to 20 HP if you tune it in.

Deeper options: Above plus,,,,
1. Re-gear to keep your engine in its power band with those great big cool tires.
2. Rebuild the engine
     a) Hesco Or Mopar cam with lifters, springs no high ratio rockers required.
     b) Have a pro do your engine, Balance, Blueprint, 4 cut valve job adds power and raises red line about 1500 rpm.
3. Flywheel - Grunt or Snap whats your poison?
     a) Inertia ring for flywheel, If your in to crawling this will help grunt over rocks etc, will slow off the line punch a little.
     c) Lightweight flywheel , if your a sand junkie this will help you out of a bowl.
4. Forced induction - Speed cost money,,, :)
5. Nitrous - Do your homework and use your head or the results will be most of the above Wink

[sharpxmen]

On my YJ the guy who did the head only polished the exhaust ports,
he found the intakes need to be a little rough, (Think sand blasted texture)
it maintains the turbulence and atomization in the intake air stream.
I noticed this on some Roush Racing heads a while back too so I trust his point of view.... :)

hmm, for peak performance i disagree (maybe mpg) - at peak the power is given by the capacity of the engine (how many cubic inches or liters), the amount of fuel, the Volumetric Efficiency (VE) and the BSFC for that engine (Break specific fuel consumption - this is how much fuel would be used to make 1HP, and it is in fact the efficiency of the engine)

EDIT: I didn't explain this one - VE is the capacity of 1 cylinder vs the amount of air that is admitted in that cylinder when the intake valve is completely closed at the rpm at which the engine provides peak power - so if you have a 6 cyl 3 liter engine, 1 cyl has 0.5L and at the end of the intake cycle at peak power rpm and wot the air that was admitted was only 0.4L the  VE is 0.4/0.5=80%. At idle for example if you suddely open the throttle the VE will most likely be over 95% as the piston speeds are like 10 times less than at peak power rpm so the air has more time to be "inhaled". The less restrictions in the intake mean more air into the cylinders at high piston speeds (high rpm) and same with polished intake runners and 4 or even 5 valves per cylinder.

polishing the intake (and larger intake, high flow air filter and cold air inlet to the filter for the same purpose) will improve the VE which in turns means more oxygen mass for the mixture and results in the capability of burning more fuel which means more power (see BSFC) - polishing the exhaust is beneficial but negligible if you leave the intake unpolished - this has been proven and dynoed many times (i'm not saying that polishing the exhaust won't give any gains but not as significant EDIT: for the same reason the intake valves are larger than the exhaust valves)

for getting better mileage out of the vehicle your mechanic might have been correct but not so much for peak power.

I've run an Inovate meter on several jeeps, and I've yet to find one that
maintains the mixture where it needs to be, most run a bit rich,  The computer
does not seem to have a real fuel "curve" its more like 4 or 5 steps. I suspect Chrysler
cheesed out and did a really brain-dead table. And the minimum responses I see
from the computer imply a rough digital response not a fine analog response.

Jeeps with 2.5L engine use a narrowband O2, that means they will cycle really fast between rich and lean based on O2 feedback - your guess is correct, looks more like a digital, pretty much 0 or 1 for lean and rich or more specifically above and below 0.45v which means 14.7:1 AFR and the PCM will switch the opposite way as soon as it sees the signal above or below that - it will never be spot on at 14.7. the average AFR would be 14.7 though, and the PCM will re-learn the required duty cycle for injectors after a computer reset to minimize the adjustments between rich and lean (keep in mind that this is only in closed loop)

If you do all the mods it gets even worse, The adjustable MAP sensor will at least let you
tweek it closer to ideal, won't be perfect but its a jeep not a F1 car :) :)

adjustable MAP vs. programmable MAP - here's what imo is the deal with these 2:
most of the time the Jeep PCM is in closed loop so that programmable MAP won't do any good (the only reason you want one is to compensate if you have forced induction and you stock MAP reading will be otherwise limited to 1 bar) - when in closed loop it won't matter what the MAP will say, the PCM will readjust the injector duty cycle based on O2 feedback - seems an expensive mod for little gain (most you will get out of it will be to trick the PCM in going in open loop sooner) - same thing can be achieved with the volt modded MAP, $300 for the programmable MAP, $20 or so for the volt mod - no brainer there. I guess i'm not sure if that's what you meant by adjustable MAP (the voltage modification or programmable MAP, i might have misunderstood as i thought you meant programmable so my bad if you meant the volt mod one).

I believe that either Split Second or some other company sells a sensor conditioner to alter O2 output and give you the ability to tweak the mixture in closed loop.

[dwtaylorpdx]

My engine builder has built engines for a lot of front name formula car race teams, he's not just a mechanic...
He was also the engine tech for a Nascar and Winston team for several years.
Left it when his wife got tired of not seeing him 10 months a year 

The way he put it, the value for labor was not there for polishing or full porting.
He feels (Especially for street engines) That a good valve job, light port relief,
re-cut guides and good valves give you 90% of the benefit for 20% of the work (Cost).
He also thought the engine, cam, head crank combo would not exploit a full polish
at the RPM's I'd be running, I requested he build it to a 6500 rpm redline with some
margin for stupidity. He thought we would be talking another 4 or 5 HP and the cost
would go from 1800 to about 3000 bucks. So economy affected the performance
calcs for me...

I use the voltage adjuster on the MAP to just tilt it a tad closer to center to help make the off idle
performance better and it seems to help the engine lug better without fouling out. I know the ECU
is supposed to go off the MAP in closed loop, but I'm not convinced they are not trimming some value
based on the throttle position vs the map because the voltage trim works in closed and open loop...
Unless my $$ dollar meter is screwed up :) lol. um I mean 

What I found with my Inovate (Lm-2 dual channel not the dash unit) was that it
wasn't averaging 14.7 It was running lean at some rpm's, rich at others kind of a
sawtooth pattern (averaging) and generally not being near as tight as a plain
old toyota corolla motor which stayed really solid at 14 to 15 most all the time...
I tried a couple different O2 senders as well as MAP sensors and temp sensors to
see if it was bad sensor, noise or something odd, I put a O-scope on the signals
as well and they looked clean...

I haven't popped or the split second yet, because I'm still fooling around with it...
Time will tell, that or I'll go full stand alone and ditch the Mopar ECU
Cause then I'd have to add forced induction 

Good talking...

Dave

[C.Redbeardd]

So im just checking, and this may be a dumb question, or it may not, but it is possible to put a larger throttle body into the 1990 2.5L?

[sharpxmen]

I use the voltage adjuster on the MAP to just tilt it a tad closer to center to help make the off idle
performance better and it seems to help the engine lug better without fouling out. I know the ECU
is supposed to go off the MAP in closed loop, but I'm not convinced they are not trimming some value
based on the throttle position vs the map because the voltage trim works in closed and open loop...
Unless my $$ dollar meter is screwed up :) lol. um I mean 

i obviously misunderstood - yeah, that makes more sense $ wise (the voltage adjuster) - one thing i'm not sure about (and maybe you or someone else knows) is if you don't reset the PCM will it re-learn the trims or just use the curve learned 50 cycles from the last reset? - that could make a difference if let's say you reset the ECU, let it learn with the normal voltage on the MAP and then adjust the voltage a tad higher - will it give you a bit more fuel due to the offset in voltage and not readjust the trims? this is just by logic, i have no idea if it would work this way or not - that could explain the better response in closed loop (aside of going in open loop earlier)

i think your guess was right - by my understanding the PCM is using both tps and MAP to estimate the amount of air and also the IAT readings and rpm for some adjustments in fuel as well as ignition advance.

[FourbangerYJ]

So im just checking, and this may be a dumb question, or it may not, but it is possible to put a larger throttle body into the 1990 2.5L?

The bigger TB is for 91-02. Same for the injectors.
You can do the E-fan.

[chardrc]

So im just checking, and this may be a dumb question, or it may not, but it is possible to put a larger throttle body into the 1990 2.5L?

short answer its not possible... long answer is that you may be-able to find something simi compatible in a gm tbi system but the chances are slim(aka this is speculation) and it would be way more involved than for the mpfi systems (91+) (aka totally different)...

[sharpxmen]

The bigger TB is for 91-02. Same for the injectors.
You can do the E-fan.

and apparently the TBI has an adjustable fuel pressure regulator from the factory, so some fiddling with the fuel pressure might increase the perf a bit but at least a cold air intake should be added as well.