The side port version of the Cool Cowl permits the windshield to fold down. The top port version does not.
Why Didn't The TJ Get a Stock "Cold Air" Induction?
- Thread starter TJRick
- Start date
James Brewer
Member
You keep trying to make the arguement but you don't supply any data that shows the 4L tj engine would perform better or even differently...I say route an external air intake and drive 5000 miles and report back
I’ve had an ARB snorkel on my last 3 Rubicons and can say without a doubt, there was zero improvement in performance or fuel economy. The only thing it does other than give me piece of mind when traversing deep water is it causes the air filter to get dirty faster
I confess I have not read all 7 pages of this thread but I think if adding a cold air intake made any significant difference especially in MPG it would have been done at the factory. If such a simple fix would have helped the factory meet their MPG mandates, they would have been all over it.
Speaking from experience a 2.5l YJ with a stock intake can ingest exactly 6.4 gallons of water from the San Gabriel River in 1.7 seconds with the throttle wide open.
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LONGJP2
TJ Expert
Yes, that's me. Made it through with no ill effects, but I wouldn't do it again.
The hotter air would contribute to better economy. In the '90s I experimented with a Geo Metro, one of the mileage hacks for them at the time was to make a fuel heater out of a copper pipe large enough to splice into the radiator hose, and to wrap copper tubing around that then solder and wrap with insulation. This was used to pre-heat the fuel. It made the car a bit more of a dog as far as acceleration, but you could easily attain 80+ MPG. The heated gas was expanded, thus would burn more completely vs the same gas that was cold and dense.
Same basic principle applies to the air charge... cold dense air has more power in combustion and hot thin air will net better economy.
Unfortunately that's not really true. The physics are the same but the PCM/ECU and how it measures/reacts to changes is not. Some cars adjust for air temp, some don't. Some can identify higher/lower octane fuel and adjust timing accordingly. Some can't. Some detect knock or even have factory wide band O2 sensors. Most don't. The JTEC PCMs in most of our Jeeps are pretty "stupid" with fairly low resolution.
Oh shit, where is the Popcorn? I cant wait to see how this argues out! 
Be aware that I like cold air intakes in general and have one on my Jeep. But while some may say the answer is a one size fits all "they are pointless on a Jeep" I will say that it's not worth the effort for most and can be dangerous for most (engines) as well. Jerry's advice is correct for 90% of TJ's out there. It's not for 100% though. Arguing the physics of it vs the practicality of it are to separate arguments that must be combined in a nuanced way.
the difference in density between 100°F and 170°F air at sea level pressure and the same humidity ratio is about 12%, so in theory the engine should be able to draw in that much more air mass at a given engine speed and throttle position. That's the physics of it.
There's an IAT sensor so the ECU is doing something with it, and even if it didn't, the air mass ought to push the mixture lean and induce a response in the STFT via the O2 sensors. But we don't really know how much more heat the charge picks up after the IAT sensor. Probably much smaller than the original difference at the air filter at least.
I swear there's something that feels more crisp about my TJ when I drive it on a cold morning with sub-100 IAT's vs a 105 degree day with IAT up around 170. I can't blame the fan because I still feel it at highway speed. I'm not sure I can tell any difference in WOT performance, but I don't really go WOT because it doesn't feel any stronger than about 60% throttle anyway (which leads me to believe the throttle is no longer the restriction once I get that far, hence why larger TB's are useless).
The best I can come up with is that due to the density, I may just be reaching the same mass flow at a slightly smaller throttle position. As has been touched on earlier in the thread, a more consistent IAT makes more consistent emissions, and that's probably why Jeep did it.
There's an IAT sensor so the ECU is doing something with it, and even if it didn't, the air mass ought to push the mixture lean and induce a response in the STFT via the O2 sensors. But we don't really know how much more heat the charge picks up after the IAT sensor. Probably much smaller than the original difference at the air filter at least.
I swear there's something that feels more crisp about my TJ when I drive it on a cold morning with sub-100 IAT's vs a 105 degree day with IAT up around 170. I can't blame the fan because I still feel it at highway speed. I'm not sure I can tell any difference in WOT performance, but I don't really go WOT because it doesn't feel any stronger than about 60% throttle anyway (which leads me to believe the throttle is no longer the restriction once I get that far, hence why larger TB's are useless).
The best I can come up with is that due to the density, I may just be reaching the same mass flow at a slightly smaller throttle position. As has been touched on earlier in the thread, a more consistent IAT makes more consistent emissions, and that's probably why Jeep did it.
I agree, I'm not trying to make my jeep faster, and it has plenty of power.
I do like the system that @jscherb created. That would further enhance the stock system, in that you can easily add a dust pre-filter... or a snorkel if you needed to drive submerged...
ejay
TJ Addict
Previous owner installed a K&N system...I want to get back to stock. Any resource for parts? Looking on ebay and other online offerings I haven't found a reliable source.
look in the for sale section, there are always Jeeps being parted that may have what you need
MountaineerTom
LJ Enthusiast, Retired USAF Weapons Loader
Supporting Member
Ride of the Month Winner
Daveysjeeps.com
If it’s not on their page, do a parts request. Everything isn’t shown.