The stock CJs HAVE a cold air intake. There's a rectangular hole under the headlight bucket, driver's side for sixes and passenger side for eights. A rectangular flex tube connects the air cleaner horn to a fitting on the hole. Then, in the horn, there's a vacuum diaphragm controlled by a temperature switch that closes a flapper and makes the intake draw air from the manifold stove until the engine warms up. After that the flap opens to allow air to come from the ahead of the radiator.

It's a pretty good system and cheap to do. The only thing wrong with it is that the intake, below the headlight, can be submerged in a deep mudhole. Fortunately I have a six.

Seeing that, I moved the intake to a spot on the firewall above the battery. That way it draws air from inside the passenger compartment above the glove box, which should stay dry until I have a lot more problems than the engine sucking water.

As for more horsepower, yes, cold air intake will give more power, but not a lot. There's a correction factor that any dyno operator will have, of a certain percent per degree. Rich, do you know what it is offhand?

 

Might as well save your pennies, the amount those things cost for the actual little they do they arn't worth it. If you are trying to move your air box to fit a 2nd battery or air compressor K&N sells a filter that fits the end of the stock air tube. Show me an actual dyno chart or hand calculated gas mileage under similar conditions where the thing actually does anything, not charts from the manufacturer but an independent party.

A while ago JP did a test where they did a full exhaust, air filter, throttle body, and I want to say maybe a chip (well over a grand in parts on each jeep) on a 2.5 in a yj and I want to say a 4.0 in an xj and they maybe got less then 10hp and 15 ft lbs on both jeeps. Is $100 per horse power worth it to you? If a magazine that's getting paid by the maufacturers to do the test can't pull any horse power out of the parts on a dyno think they really do anything?

If you want power start looking into engine internals and a custom chip. A cam and custom burned chip for your cam/ mods (not one out of quadratec) is probably about the same cost as the street jeeper bolt on parts collection and will give you a lot more rear wheel horse power/ torque.

If you are trying to compensate for larger tires spend the $$ on gears and the seat of the pants dyno will think you added a super charger.

 

As far as ambient air temperature...Here's what my dyno software says for my stock 22R Toyota (4 cylinder, carb'd)

Stock 22R Toyota, 1500 to 5100 RPM

Peak Torque and Peak HP (at 1,000 ft elevation)
40d F -136 brake tq, 108 brake HP
50d F - 135, 108
60d F - 134, 107
70d F - 132, 106
80d F - 131, 105
90d F - 130, 105
100d F - 129,104
110d F - 127, 103
120d F – 126, 102

 

Yeah, a little less than 6% HP increase for 80 degrees, or about .7% per 10 degrees.

A 150 HP engine with a 50 degree difference in air temp would get you about 5 HP. Might as well install a Briggs & Stratton mower engine to run the alternator.

 

You're right about the HP, Jim. But... in my Toyota truck, 5 lbs. of torque is noticeable by my seat-of-the-pants dyno! Also, in the winter time here in AZ without the AC on, I could get about 1.5 to 2 miles more per gallon of fuel. I could also run 89 instead of 91. I guess one could assume the cooler temps helped a little with performance too. With a little 96 HP stock engine, every little bit helps.

 

I've got a junkyard 4.0l throttle body and running a cone style STP filter for a 2000 Dodge Neon. (It's sized correctly to fit on the factory intake tube). It did make a difference. I would reccomend doing something similar, just don't go out and pay $200 for a K&N system. Keep it low budget and you'll be happier.:grin:
Good luck,
Aaron

 

If you're going to go to the bother of a cold air system, why not fab and install a snorkle. Kill two birds with one stone...

 

Yes, cold air is denser than hot air. It will make a difference. You might be able to shave off one, or maybe even two hundredths of a second in a quarter mile drag in a Jeep. That could put you in, our out, of the money.

It's not the cold air that makes a difference on a Jeep. Look at the air intake - YJ's use that super restrictive flat air cleaner. TJ's use that super restrictive air box.
Using a snout and K&N lets the engine breathe! You wouldn't wear a gag when jogging, why choke your Jeep?

It takes about a 10% increase in power to be felt with the seat of your pants. Adding the K&N and snout you will definatly feel a difference. No, you won't have a race car, but it'll have a little better pull. The negative - they are noisey, especially when cold till the IAC closes.

Snorkels and lots of ducting only add to the restrictions. Krinkle tubes cause turbulence all along the inside. If you really have to, use smooth tubes.

Some folks think ducting to the front is causing a ram air effect -- ??? On a Jeep? Get serious.

The "swirl" spacers - with Carbs and TBI they work, a little. Other FI's they don't (no fuel up there to swirl and mix. By the time the air gets down to where fuel is, it's stopped swirling.)

Adjustable MAP - no. ECM immediately compensates for it.

Bigger Throttle bodies - good for wide open throttle only, and only at the very top RPM end. Not worth the money.
Bigger injectors - The computer senses they spit more fuel, so it immediately just shorten open time. If you are running it up to 6,000 RPM, yes, bigger injectors and a bigger throttle body would help.

Matching injectors - yes - maybe a very slight increase, unless they were greatly mismatched (unlikely.) Not worth the $200.

Chips - all they are is a slightly modified advance curve, and maybe a slightly richer command. Still haven't seen one that was worth the cost. Jeep already optimized the curve to work in all temperatures and altitudes. When the aftermarket "burners" change them, something else suffers.

Exhaust - well worth the investment for a good exhaust system. Remember, "Noise" does not create power.

Cams - with carbs you can use more lift and duration. But FI you can only increase lift. Reason is more duration or overlap will cause the intake vacuum to pulsate too much, driving the MAP sensor nuts.

Instead of a cam, consider ratio rockers - cheaper, easier, they increase lift a little without increasing overlap or duration. Should help with mid to high R's.
But - I haven't found a decent source for them - anybody?

Plugs - stick with the stock factory recommended plugs - the factory has spent millions designing the heads around the most suitable plugs for that application. Who thinks the pimple faced kid at Autochina knows more than the factory engineers?

There are tons of aftermarket "performance" things - most are made to sell, not to use. They are "high performance" though - they make more money for the suppliers.

He He - And, of course - big STP stickers! They must work, you see them on fast race cars.

 

Yes, cold air is denser than hot air. It will make a difference. You might be able to shave off one, or maybe even two hundredths of a second in a quarter mile drag in a Jeep. That could put you in, our out, of the money.

It's not the cold air that makes a difference on a Jeep. Look at the air intake - YJ's use that super restrictive flat air cleaner. TJ's use that super restrictive air box.
Using a snout and K&N lets the engine breathe! You wouldn't wear a gag when jogging, why choke your Jeep?

It takes about a 10% increase in power to be felt with the seat of your pants. Adding the K&N and snout you will definatly feel a difference. No, you won't have a race car, but it'll have a little better pull. The negative - they are noisey, especially when cold till the IAC closes.

Snorkels and lots of ducting only add to the restrictions. Krinkle tubes cause turbulence all along the inside. If you really have to, use smooth tubes.

Some folks think ducting to the front is causing a ram air effect -- ??? On a Jeep? Get serious.

The "swirl" spacers - with Carbs and TBI they work, a little. Other FI's they don't (no fuel up there to swirl and mix. By the time the air gets down to where fuel is, it's stopped swirling.)

Adjustable MAP - no. ECM immediately compensates for it.

Bigger Throttle bodies - good for wide open throttle only, and only at the very top RPM end. Not worth the money.
Bigger injectors - The computer senses they spit more fuel, so it immediately just shorten open time. If you are running it up to 6,000 RPM, yes, bigger injectors and a bigger throttle body would help.

Matching injectors - yes - maybe a very slight increase, unless they were greatly mismatched (unlikely.) Not worth the $200.

Chips - all they are is a slightly modified advance curve, and maybe a slightly richer command. Still haven't seen one that was worth the cost. Jeep already optimized the curve to work in all temperatures and altitudes. When the aftermarket "burners" change them, something else suffers.

Exhaust - well worth the investment for a good exhaust system. Remember, "Noise" does not create power.

Cams - with carbs you can use more lift and duration. But FI you can only increase lift. Reason is more duration or overlap will cause the intake vacuum to pulsate too much, driving the MAP sensor nuts.

Instead of a cam, consider ratio rockers - cheaper, easier, they increase lift a little without increasing overlap or duration. Should help with mid to high R's.
But - I haven't found a decent source for them - anybody?

Plugs - stick with the stock factory recommended plugs - the factory has spent millions designing the heads around the most suitable plugs for that application. Who thinks the pimple faced kid at Autochina knows more than the factory engineers?

There are tons of aftermarket "performance" things - most are made to sell, not to use. They are "high performance" though - they make more money for the suppliers.

He He - And, of course - big STP stickers! They must work, you see them on fast race cars.

I am not as familiar with the Jeep stuff, but I agree with almost all of Rich's comments. Especially the aftermarket performance things are made to sell and many times you are buying "hype" with NO published data to support their claims. And, that the engineers who designed these engines most likely know more than any backyard mechanic hacking up a stock intake system.

I would not mess with rocker arms ratios!! - that is almost Voo-Doo science!

I would look at camshaft profiles.

I would NOT buy a K&N system until someone shows me some certified data on it's performance gains vs. cost.

Performance exhaust systems will almost always give you the biggest bang for the buck! Coupled, with a proven cam profile and you can gain a nice number in torque and HP at a reasonable investment.

That's just my worthless opinion

 

WOW !!!
you guys are amazing
thanks so much for all your input and info
i'm just trying to help the TJ run efficiently
with gas prices the way they are
and this Jeep being a driver i'm just curious about upgrades
not really trying to build a race car or power monster
the manufacturer can say a lot and like you said...
maybe the magazine is being paid to promote the product
i just figured i'd check it out with you folks first to see if there's
any validity to these "upgrades"
i'm usually willing to spend some dough if it works and it's worth it
but no need to waste hundreds on crap
thanks again to everyone
- chris

 

I would look at camshaft profiles.

For the I6 the OEM cam is about the best one you can install on a Jeep. To do otherwise would start to move the power and torque band around to where you might not like them. When I repalced my engine... I used an OEM spec cam without regret.

 

Don't know how it would apply to the I-6 but I had a ZJ with the 318 (5.2l) and I did a few things all at once so I don't know what helped the most, and what didn't do anything.

1. Throttle body spacer ($20 new)
2. Removed air restrictor on front of Airbox (10 minutes, Free)
3. Factory replacement K&N ($40)
4. MSD Ignition ($250 new, pick them up cheaper on Ebay)
5. Thicker plug wires as recommended for MSD ($60)
6. Gapped plugs out a little (Free)
7. Flowmaster muffler ($90 installed(maybe less restrictive, but more for the sound))

All in all about $460

Never Dyno'd before and after to give a honest answer, but Seat of the pants felt better. And according to the onboard computer and crunching miles per tank and gallons used I brought my milage up from about 16 to 22 on highway trips. Around town I had a hard time keeping my foot out off the floor so I can't attest too much to City Mileage. I figure the MSD was probably (hopefully) the biggest improvement.

 

I can't give any real data on the K&N and snout, I no longer have dynos, but when I put it on my Rubi I could feel the difference. I've put them on some of my customers too - all have told me they can feel it. 8-10% or you don't feel it.

Try something - blow out the engine compartment with an air hose - blowing out the loose dust.

Then try yours down the street for a short ways without any ducting, snout, airbox or filter, just the open airhorn. You'll be able to feel how much yours is restricting it now.
If you like that increase in power, get the K&N.
The K&N and snout won't cut that newfound power any.

There's lots of propaganda out by their competitors saying the K&N's terrible, it "doesn't work," "plugs too easy" etc.
1. Plugs too easy? Theirs let the dirt on through rather than getting plugged.
2. "doesn't work? Run a white paper town or rag down your snout. Look at how much dust collects on the inside of the snout (that's just what got caught on the sides, lots more went into the engine.) Then try it with a K&N - clean!

3. But - since a little oil gets sucked off the filter - especially if you use too much, it will spoil a MAF sensor (Mass AirFlow.) Fortunately Jeeps don't use those MAFs, they use MAP sensors (Manifold Absolute Pressure) instead. They are relativly impervious to the oil vapors.

 

i've been reading a lot about these cold air intake kits today
aFe kits claim on their website to gain up to 50 more horsepower !!!!
that sounds completely ridiculous to me
while the others ( K&N, AEM, etc... ) claim only 10-13

 

I've seen these adds too. I think the one you speak of is for the 7.3l Powerstroke. It's also a combination of their Stage 2 cold air intake and 4" turbo back exhaust together. Is the claim true? I don't know, but I have seen a few comparisons/tests and the AFE is considered #1 in the diesel world.
Aaron.

 

50 more from just under 200?
Over 25% - no way. They must be running for President!

SCAM!

 

i wrote their tech. department
and asked them for more info.
and some solid numbers
that apply directly to the jeep tj 6cyl application
we'll see if & when they get back to me
let you know
- chris

 

50HP? Here's some random thoughts. What's the stock HP of a TJ.. about 190HP? Under what conditions/rpm, etc., is that 50HP created? If you're investment could lead to a 25% increase in HP under all conditions, sustained load, etc, that would be great! However, I'd bet that 50hp is measured under very controlled experiments. How likely are you to see that percentage gain in the bush?

However, remember one other thing about colder, denser air... and a TJ, and that's the little thing called Electronic Fuel Injection. The cylinder can gulp more air if it's being rammed in, or if it's denser. There's no disagreement with that. However, the EFI is also going to monitor the air/fuel ratio and attempt to trim it to the magic 14.7:1 mix to produce an optimal plasma charge.

If more air is gulped, the mixture will appear lean, and the EFI will attempt to enrich the mixture. When you sit down and think about it, it's not really that efficient to attempt to throw more air down the throat. Also, the engine is a tuned system, it gulps more air and it has to exhaust it. Are the exaust ports and valves able to do that quick enough? If you start mucking about with the cam, valve sizes, etc., then you've disregarded the EFI's effect and thrown it all off. Then, of course, you've got to move all that spent plasma through the exhaust system. It's got to be more free flowing. The costs now are rising to do the system right.

Can the EFI respond quick enough, remember it's always one cycle behind when it trims fuel. It also trims fuel in steps. If the mixture is thrown out of the EFI steps, that causes havoc with the logic of the ECM. In some cases that can happen (not always).

If the gain is not across the board, then it's periodic, depending on engine load conditions. If that's true, you'd pay a premium for peak performance during peak conditions. That's a whole lot of money that could be spent elsewhere and give a better return on the invested dollars.

 

i'm not saying that i agree or believe in all of this mumbo-jumbo
that's just what they're claiming
and i'm sure, if at all, you're right about the PERFECT conditions
but 50hp is ridiculous !
i'm waiting to hear back from them
if they reply at all
we shall see...

 

i'm not saying that i agree or believe in all of this mumbo-jumbo

Agreed! I just find it important to comment, and perhaps throw out another way of thinking about the topic.... no disrespect intended or meant! Sometimes another Jeeper will be searching on a topic such as this and come across the post and gain something from it.

I'm looking forward to their answer and how it is framed to put the best light on the product. IMHO, you can dress a pig up in anything you want... but deep down it's still a pig. That's not much different from many of these products that are hyped. Once you take all the marketing window dressing off, they're still a pig, pure and simple. But it's fun to hear how the marketing and sales guys dance around some pretty pointed questioning.

 

so here you have it !
they just got back to me
apparently the 50hp gain doesn't apply to all their products ( or any )
this info seems more believable
but doesn't seem worth the $$$
case closed !
thanks again everybody
- chris

 

RRich....good write up...

I agree with just about all the points....and speaking from personal experience...keep the cam stock...but ratio lifters could be good....more air in without changing the duration....FI can handle that better....

But what I do take issue with on the pros of CAI is the MPG gains. Sorry guys, but I don't buy it. MPG is a function of fuel used to propel your vehicle per mile....if we all agree that the computer is controlling the air/fuel ratio, then reducing the intake restriction is NOT going to change the air/fuel ratio. In other words, if nothing else changes, how in the world can increasing the air flow improve the MPG? The fuel pumped in depends on the amount of air...once the system goes closed loop (O2 sensor controlling), changing the air filter is just not going to change the MPG....

Want to improve MPG? Reduce drag and keep the engine running properly.

 

In other words, if nothing else changes, how in the world can increasing the air flow improve the MPG? The fuel pumped in depends on the amount of air...once the system goes closed loop (O2 sensor controlling), changing the air filter is just not going to change the MPG....

I'll disagree politely with this. Along with propelling the vehicle, the engine uses it's power to pump in the air for the next explosion. So, the power from a power stroke propels the vehicle, but it also uses some of that power to do other stuff, like turn the fan, overcome the alternator drag, AND pump in the air. Theoretically, if you reduce the drag on the incoming air, the motor doesn't have to use as much of its power to pump the incoming air in, and therefore needs less OVERALL power output to propel the vehicle. And as a result, the vehicle will go the same mile on less power output required from the motor. So, an increase in MPG.

Why do you think MPG goes down when you turn the AC on? More engine drag.

Pete

 

The MPG probably wouldn't change enough to measure, unless something was really wrong before.

"IF" it did change at all, it would probably be because with less air restriction, there would be a little more oxygen available, but the O2 sensors would sense it's lean, and add the correct amount of fuel for it. But that may be at a slightly more efficient RPM. But it could work the opposite way too.

The lower restrictive intake isn't noticed (power-wise) till mid to upper range anyway, especially under load. It only will help when the engine is trying to injest lots of air and couldn't before. Picture walking, then jogging, then running with a mouthful of cotton.

For me all it does is give a little more "oomph" on hills. Off roading at low R's you'd never know the difference.

But - when it's cold and the IAC is sucking more air, it makes friends think there's a big vacuum leak. The stock systems do a good job of muffling the noise.
He He - I told a couple of kids it was my jet engine! I think they believed it.

It's really quite a science getting all the different things and places working together.
Often just modifying one can be detrimental without the others. It's a combination of theory and trial and error. What "should work" doesn't always. Armchair racer rumors abound.

 

And - another thing I like about the snout and K&N. Airbox is gone, leaving space for a Sanden compressor for on-board air. Behind that it still left enough room for an extra battery for 24 volts for the welder.

 

Absolutely true, Pete. It's one reason diesel engines can idle all day on a sip of fuel - no 'pumping loss' but a gasoline engine has to work hard to pull air through the idle opening in a carb or FI air meter.

But I'd bet $40 against a donut hole that it's impossible to measure the fuel useage difference in the real world. Probably couldn't even find it on a dyno. At small throttle openings, where most engines spend most of the time, there's so little air being ingested in relation to the capacity of the intake system that the difference has to be miniscule - with the huge restriction at the throttle plate, a little difference upstream doesn't matter.

Wide open, when the engine is sucking a lot of air, the difference might be measurable, but immaterial since we don't run Jeeps there.

 

it's impossible to measure the fuel usage difference in the real world

Actually Jim, it is possible. But you'd have to have a lot of good metering that would give you real time information. It's called a Trip Computer. Back in the 1980's Sears used to sell them for Carbed systems. It was a about $200 and quite the system. It would give you real time fuel usage. The problem is how small/detailed can you measure?

With today's systems, you could measure the usage under similar conditions. Then, once you find the metrics, you could easily compute the payback for the dollar invested in the modification. Of course you'd have to figure in the cost of the metering sensors, the computer it's connected to, and the labor for installation, etc.. Then you'd soon figure out that the modification would likely NEVER pay you back for the investment made....hence, it's really not an investment.

Now send me that $40... Ok, I'll settle for the donut hole!

 

Donut holes are very tasty if you wash them down with a root beer.

 

Donut holes are very tasty if you wash them down with a root beer.

Rootbeer helps make life worth living! Rootbeer floats are things that will help you cement your family ties together. Go out and make/buy your loved ones a rootbeer float (french vanilla is yummy) today! You won't regret it! :givemebeer:

Put down that wrench and take 'em all out for a Jeep ride to A&W (Or the rootbeer joint of your choice!)and enjoy a great evening!

There... now it's Jeep oriented!