Does a cold air intake add power on a 4.0?

View attachment 318591
Solid discussion. Thanks for your valuable contribution. If I didn't have a meaningful reply I might just ignore my question too. And btw, for not caring what I think, you sure do seem to be the one getting excited.
You should read the recent led turn signal thread. Real world experience was refuted heavily by fantasy world experience. I was told my method of install wouldn’t work and that it was a terrible idea by someone who has never done what I did nor even understood what I did. Fun stuff.

I’ll never run a “cold air intake” myself, I prefer and will always run stock but I appreciate the thread devoting detail to it and proving misconceptions wrong anyways. Dyno accurate or not, it’s pretty fucking clear to see 5 runs in a row at one power level and 5 again at a different level with only one thing changed. I don’t know how one can really argue against it unless the numbers were secretly manipulated. I don’t think they were, the thread appears to be transparent.

I am also curious why Blaine has seen the results of those mods get tuned out by the PCM over time, so that’s interesting for sure too.
 
@Jezza do you have plots for AFR on each of these runs? if the presence of the cold air intake is messing with the AFR enough (in the direction that adds power) that the LTFT needs more time to adjust, that might explain why the gains could disappear over time. And you can't just do it in reverse order because you might lose power with the stock intake and then gain it back as the PCM adapted. You'd have to do runs on different days giving the PCM time to adjust in between for each intake to get comparable results, and that introduces more confounding variables.

Overall I like your approach and I think there could be validity to your conclusions once we understand the adaptation issue. But I drive like a man twice my age so I rarely see 4k RPM or WOT and I'd rather have the filtration than 10hp I never make use of.
 
@Jezza do you have plots for AFR on each of these runs? if the presence of the cold air intake is messing with the AFR enough (in the direction that adds power) that the LTFT needs more time to adjust, that might explain why the gains could disappear over time. And you can't just do it in reverse order because you might lose power with the stock intake and then gain it back as the PCM adapted. You'd have to do runs on different days giving the PCM time to adjust in between for each intake to get comparable results, and that introduces more confounding variables.

Overall I like your approach and I think there could be validity to your conclusions once we understand the adaptation issue. But I drive like a man twice my age so I rarely see 4k RPM or WOT and I'd rather have the filtration than 10hp I never make use of.
No, I didn't do the wideband. This thing has a completely stock exhaust, so no extra O2 bungs and I don't think our sniffer has worked in 10 years.
It is my understanding however that at WOT the JTEC PCM goes into open loop fueling which on most PCMs disables the long and short term adaptive trims and references the base tables and multipliers. The purpose as I understand it is to allow for fuel enrichment under load. The factory narrow band O2 sensors can only trim air/fuel ratios to stoich which would be undesirable at WOT. All that to say I don't think the PCM has the ability to "learn" at WOT, but I don't know that for a fact. There could be programming in place for example that stores part throttle adaptive values and applies them to open loop as well.
 
  • Like
Reactions: SkylinesSuck
It is my understanding however that at WOT the JTEC PCM goes into open loop fueling which on most PCMs disables the long and short term adaptive trims and references the base tables and multipliers. The purpose as I understand it is to allow for fuel enrichment under load. The factory narrow band O2 sensors can only trim air/fuel ratios to stoich which would be undesirable at WOT. All that to say I don't think the PCM has the ability to "learn" at WOT, but I don't know that for a fact. There could be programming in place for example that stores part throttle adaptive values and applies them to open loop as well.

Exactly my understanding as well, but I was going to let people read up on JTEC for themselves and draw their their own conclusions. That being said, if part throttle fuel trims were affected which in turn changed WOT mapping (which I don't think is occurring), wouldn't that indicate the intake is having a significant effect? Then we would be back to the PCM being the issue while the intake is proven to be an improvement.....
 
Exactly my understanding as well, but I was going to let people read up on JTEC for themselves and draw their their own conclusions. That being said, if part throttle fuel trims were affected which in turn changed WOT mapping (which I don't think is occurring), wouldn't that indicate the intake is having a significant effect? Then we would be back to the PCM being the issue while the intake is proven to be an improvement.....
If the intake is adding additional air, the pcm is going to take the IAT and the Map and calculate fueling based of the pre established VE table, then checking this calc with the O2s and trimming as required. At part throttle it’s always going to seek stoich (14.7ish). WOT ignores feedback O2s (although I do believe LTFT may follow into WOT based on my experience). More air in would require the Pcm to add more fuel which would equate to more power.

If adding the intake in fact adds more air, than the fueling would be potentially lean until the PCM corrects. I don’t see a leaner mixture adding power, so I don’t believe the initial increase in power wil erode as the fueling adjusts.
 
  • Like
Reactions: srimes
This was my understanding about the Jet modules and other things like it. That after a time the PCM would revert back to it's stock tune. The only method I know fof to keep power gains is to have a new tune done to the PCM and then to load it.
So it would seem to get any true benefit from a CAI you'd need to add a reflash to keep the added increase.

As for the KN debate I've seen and read all the discussions on their use. I've got one for my 6 pack and until I can find a suitable replacement I'll have to run it.
 
IDK i dislike the term "cold air intake" and since we are not all neighbors it should be "ambient air temp intake".

super silly over simplification here but what do i need a 1200$ turbo for if i just need a 15$ shop vac hose from my A/C vent to the intake box.
if you wheel in AZ and it's 106 today , how would the engine perform with 80* air?

from the makers of the saggy corrugated out the fender snorkel brings you the hillbilly chiller.
 
Last edited:
@psrivats I found that pdf about how the JTEC PCM works. It's aimed at the Viper crowd and there are a few features here and there they are different, but the majority of it is the same.

This is actually a really good reference document. It is well written with clear information and high level circuit diagrams. Learning a ton even just casually reading it. Thanks once again for sharing !
 
If the intake is adding additional air
Which is one of my main bitches about these threads. Unless you add a turbocharge or supercharger no aftermarket intake for a TJ from anyone is going to "add additional air". That's because the air intake only flows as much air as the engine is pulling, the air intake can't add more air than the engine is pulling/demanding from it.

And with the TJ's non-restrictive air intake it's not going to happen. For those who refuse to believe it's non-restrictive, get on Facebook and find Jim Repp and ask him directly. Jim just retired from Jeep and is down in Key West Florida with his wife having the time of his life now. He was Jeep's Chief Engineer and dated from back in the CJ days. Jim is also widely known as the "Father of the Jeep Rubicon", it was his idea and he brought it to reality after convincing Jeep's bean counters to approve it. It of course turned out to be one of Jeep's most spectacular products.

He and I had lots of phone conversations starting around 2000 over a problem I was having with my previous 97 TJ that he found mentioned on the forums. Jim was also "leaking" information to me about the not-yet released Rubicon to keep the rumors down, like the air locker from Japan they were going to use. He contacted me because they were trying to find what was causing the problem, lots of '43' DTC codes and he was sending me boxes of parts to install to see if any helped. That problem turned out to be caused by a bad batch of valve springs.

Anyway, the age old issue of air intakes was alive and well even then and I asked Jim about our air intakes during one of our conversations. Basically I asked him if they restricted air in any way and he chuckled about it, saying he specifically told his staff to make it totally non-restrictive. Furthermore, as I have said here countless times, Jim said our stock factory air intake easily flows more air than the 4.0 can possibly try to pull at even WOT and redline rpms. No aftermarket air intake could possibly flow more air than the OE since it's not restricting airflow in the least... again it can easily flow more air than the engine is capable of consuming or asking for.

For those who continue to not believe what I've been saying for years about the OE air intake system and vehemently continue to disagree, here's Jim's Facebook page. Friend him and ask him yourself. Just don't be an asshole there if he replies back.

P.S. Some air intakes are restrictive. Two examples, the Camaro Z-28 and the Mustang 5.0 both have purposely restrictive air intakes. Replace them with an aftermarket no-restrictive air intake and the performance gains will be dramatic. Just not the TJ's.


Capture.JPG
 
So maybe if we just change the name of this thread we can all agree to disagree...

Does a cold air intake add usable power on a 4.0?​


I've been on a dyno more times than I can count and there is a reason we always did three pulls with the same config before changing anything. Too many variables to say any one pull was unequivocally the RIGHT and ONLY data for that config.
 
So maybe if we just change the name of this thread we can all agree to disagree...

Does a cold air intake add usable power on a 4.0?​


I've been on a dyno more times than I can count and there is a reason we always did three pulls with the same config before changing anything. Too many variables to say any one pull was unequivocally the RIGHT and ONLY data for that config.

This is another one of those subjects that will never be settled. Doesn't matter what you have as a thread name or how it's presented. Period.
 
@Jerry Bransford This is our fundamental disagreement. You say that the intake provides zero restriction at all rpms and throttle positions. I am saying it doesn't provide a meaningful restriction, especially in "normal" rpm ranges. You discount the dyno data based on talking to your Jeep engineer friend and personal butt dyno. We disagree, and on a fairly academic point. There is no reason to get upset because somebody dared question what you claim to be established fact. That's just lazy and and the height of hubris.

@Jezza , I realize the dyno fun is probably finished, but I would love to see what a manifold vacuum gauge looked like if you ever repeat the dyno process.
 
@Jerry Bransford This is our fundamental disagreement. You say that the intake provides zero restriction at all rpms and throttle positions. I am saying it doesn't provide a meaningful restriction, especially in "normal" rpm ranges. You discount the dyno data based on talking to your Jeep engineer friend and personal butt dyno. We disagree, and on a fairly academic point. There is no reason to get upset because somebody dared question what you claim to be established fact. That's just lazy and and the height of hubris.
What, you're afraid to contact Jim Repp and ask him? You fucking don't believe me so directly ask my source of information. I'm done with you and your constant arguments over this subject. :mad:
 
  • Face Palm
Reactions: reddvltj and Jezza
I went thru an experimentation phase with my old TJ while working for a real speed shop. I played with numerous different combinations, CAI, injectors and programmers (Edge, UniChip, Jet and Superchips). The least impressive was the Jet chip which caused a loss of hp. The best was The Edge Trail Jammer which netted a gain of like 7hp at the rear wheels, which is about 20hp at the crank.
The gain was seen at the upper rpm range which most of us don't normally see during daily usage.
Luckily for me, none of this came at an expense.
If I remember correctly, The Edge Trail Jammer kit was like $900.00 at the time. I would be pissed as hell if I spent $900.00 to gain 7rwhp, which would have been even less hp with an auto transmission.
In the end does it really even matter if a CAI or a programmer gives you an extra 7-10 rwhp at the rear wheel? You will never notice it anyway.
 
Last edited:
So maybe if we just change the name of this thread we can all agree to disagree...

Does a cold air intake add usable power on a 4.0?​


I've been on a dyno more times than I can count and there is a reason we always did three pulls with the same config before changing anything. Too many variables to say any one pull was unequivocally the RIGHT and ONLY data for that config.
That's why I did 5 pulls stock back to back, and 3 pulls with the K&N back to back. The data is clear. Same vehicle, same day, same conditions and back to back pulls it made more power. We can argue filtration, cost even whether the power degrades over time. One thing is clear, it did make more power.
 
What, you're afraid to contact Jim Repp and ask him? You fucking don't believe me so directly ask my source of information. I'm fucking done with you and your constant arguments over this fucking subject. :mad:
You sure are getting butt hurt over somebody daring to question the great Jerry Bransford.

I don't doubt your source told you what you said or that he would tell me the same thing. I'm attempting to discuss this topic from a point of data and facts, not butt dyno tinglings and what my cousin Billybob who used to work for Jeep said. I'm glad you are done arguing with me on this subject though. It'll be nice to have a meaningful conversation with the rest of the people in this thread whether I agree with them or not.
 
So maybe if we just change the name of this thread we can all agree to disagree...

Does a cold air intake add usable power on a 4.0?​


I've been on a dyno more times than I can count and there is a reason we always did three pulls with the same config before changing anything. Too many variables to say any one pull was unequivocally the RIGHT and ONLY data for that config.
@Jerry Bransford not sure why you 😍'd this post as it is exactly what I've been saying the entire time. Maybe you've seen the light and we can now agree? Get in here big fella. Let's hug this thing out 🤗
 
I think I’ll wade on in.
I ran a dyno at a Caterpillar dealer for a while back in the 80’s. The dyno indicated horsepower was required to to be within 10% of engine nameplate HP before release to the customer.
10% is a lot. To be fair,some of that is from deviations other than the dyno. Now this was 80’s technology, I don’t know shit about what’s out there today but I don’t think a small (3-4%) deviation or error would be unreasonable even on the same series of runs and some part of that error would be something other than the dyno.

Oops that’s not the topic of this thread.
I going neutral on the CAI thing and I think K&N filters suck ass.
 
Last edited: