Can someone with some automotive performance expertise please step up and explain why a CAI would be an advantage? I have been thinking about this for awhile and it's really starting to bother me. It seems to me that these things are set up to be most effective on a dyno, and aren't very useful in the real world. I've also read that once you're moving at least 10mph forward, there is no air temperature difference, but that was on a site that was selling a short ram intake and had an interest in making CAIs sound inferior.

Just trying to use common sense, the way I look at it is:

- CAIs do well on dynos because dynos make the engine compartment as hot as possible, because the engine is being pushed to its limit while standing still with no air cooling or circulation whatsoever. The engine heats faster, and the air remains in once place getting hotter and hotter, except that it rises toward the top of the compartment. Thus, an air intake sticking downward, below the superheated air, is an advantage.

- But when you're moving forward, all that hot air gets pushed out of the compartment and is replaced with cool air. The radiator is more effective and the engine is cooled more efficiently. And since both intakes are towards the front of the car, all you're getting is the difference in air temperature at 3 feet elevation versus 2 feet. That has to be at most a fraction of a fraction of a degree difference. It may even be hotter near the asphalt, if the sun is intense enough to heat it like a stove top.

Other disadvantages:

- a CAI has extra bends in the pipe that are likely to be more restrictive to airflow than a straight shot to the plenum.

- the filter on a CAI is likely to get dirtier faster by being low to the ground, restricting airflow unless it's changed/cleaned frequently.

- air in a CAI has to travel a greater distance than in a short ram before it gets to the plenum. Although that extra length of pipe is in the coolest part of the compartment, it's still going to be slightly warmer than... well, nothing but air. Once the CAI bends up to the short ram's intake level, they both have to travel the same pipe-length to the plenum, during which they'll be heated equally. But with a short ram, the air is actually taking a shortcut to the plenum versus a CAI, and should be cooler than it would have been had it been rubbing up against the bends in an extra length of mildly warmed pipe.

- non-performance disadvantage: hydro-lock anxiety.

The only advantage I can see to a CAI is for that first gulp of air at launch. Then at least the car has been stopped and the engine compartment heated a little. But that's only a few seconds at idle, not redline like on a dyno, so the advantage would be much, much less than the dyno would indicate, which wasn't much to begin with.

Again, I'm not claiming to be an expert, I'm posting so that someone with some expertise will step in, because the popularity of these things is bugging me. From a purely common sense perspective, this mod makes absolutely no sense. Unless you do your racing on a dynomat.

-Jack
Obsidian '03 G35 Sports Coupe
Titanium '03 MX-5 Shinsen #532

 

JD,

Great post and it's exactly what I've been thinking too. Except it tired your typing hands out, not mine

I've always felt the same thing about ram-air systems on motorcycles. They don't work on a static dyno, so how do you prove it. I know some dyno's (or maybe just the setup) can include a ducted fan to the intake to simulate air flow, but I've never heard anyone reference this on this site and I know it's still ambiguous in the testing of m/c's.

I'm waiting (like you) with bated breath. Or bait breath, which reminds me, I need to brush my teeth.

 

I have had this same question for a while. I have done a lot searching and reading on this forum about, and it seems that just about everybody has an opinion on this. It seems that conflicting opinions both seem to make sense to me. I did come across this page:

http://www.matrixowners.com/sutra169279.html

It seems to have some good information and may be of use to you.

 

JD,
i agree with you, but i bet you just pissed off alot of people that wasted $$$$ on their cai. just give me a drop in k&n and a z tube and i'm fine!

 

Plus, take a look at where our stock intake is getting it's air from... right from the front grill.

2003.5 G35 Sedan Desert Platinum/Graphite Premium/Sport/Aero/Nav/Winter

 

Right from the front of the grill with a ram air effect!

<font color=green>GG</font color=green>

 

either a K&N drop in with the 350z tube or Stillen with the 350z tube.. End of story...

CAI is a dyno intake. There are 350z taking them off as they feel the performance go down after the install.

5 wire Grounding kit
350z Pipe / Stillen High-Flow
JUN Flywheel
Crawford Intake Manifold
Best 1/4 14.153 @ 99.19 / 2.29 - 60'

 

I got a K&N CAI on order, the new typhoon. If I feel a loss of acceleration I can always make it into a short ram intake. I want to give it a try tho.



2004 Coupe, 5AT, Twilight blue / Willow int. Mtek Xenon Fog/High, Clear corners, Hypers, 18's, Aero, tint, Premium.

 

Cold air intakes make power from resonance tuning. The cold air piping acts like an organ pipe and at certain rpms the "waves" help fill the cylinders a little more efficiently than that of the factory piping. The colder, more dense air helps too, but that's not as big of change on a G35 due to the nice location and design of the factory airbox.

The diameter and length of the CAI make a difference of where it gains power in the powerband. If you change the resonance point it will change where the system ads power.
(For example, on a G20, 2.5" CAI piping will make more top end power compared to 3.0" piping which will make more mid range power, given equal lengths and similar MAF placement withing the intake piping.)

CAI tuning is somwhat similar to how a short runner intake manifold makes more power at higher rpms than a longer manifold.

Justin McClanahan
Heavily Modified 95 Infiniti G20
www.InfinitiPartsUSA.com

 

I just installed my K&N drop-in filter and Z-tube. The mod makes the car sound a little more aggressive, but I cannot honestly say it feels any more (or less, for that matter) powerful. I have not yet accomplished the ECU reset or any of the other "resets", but word is that helps to make the mod noticeable.

 

The 350z owners might feel a loss in acceleration because the throttle response is not as good as before. CAI have a delayed throttle response and SRI has a better response. Thats why you never see any Japanese make of the CAI. Most of them have a ram air tube going toward the engine compartment.

04 G35C 6mt/aero kit/nav/premium

 

Resetting the ECU shouldn't have any impact on you mods. The ECU system is setup to continually monitor and learn from any changing factors. Resetting it will set everything back to zero and it'll have to learn to your state of tune, just as if you were to change something and not reset the ECU.

Justin McClanahan
Heavily Modified 95 Infiniti G20
www.InfinitiPartsUSA.com

 

I installed the NISMO CAI and haven't felt a significant increase in power at all. What I have noticed is a significant drop in fuel economy. From what I've read when you install a CAI system without an ECU flash the ECU attempts to bring the air/fuel ratio into stock range which means that because of the increased airflow more fuel is pumped in as well causing a loss in HP and fuel economy. I'm not sure if this is correct, if it is does this mean a CAI is useless without an ECU flash or continually reseting the ECU?

 

Thats correct. Even K&N told me to reset my computer when I
installed my old K&N drop-in. Just do an easy ecu reset once or twice
a month and all will be fine.

2003 Twilight Blue 5AT Sedan, sunroof,
Graphite Leather, splashguards,
12 wire Hyper-grounding kit,
350Z intake duct, Stillen Hi-Flow Airbox
Underbody rear diffusers, Drilled aluminum pedals

 

Well, that's sorta half true. Yes the ECU will inject more fuel into the car, only if there is more air going into the cylinders (which should happen when you free up some of the breathing restriction on the car). Your car however will not run overly rich, it'll run at the same A/F ratio as before, but now only at a higher level of each. If you drive normal around town you may notice better fuel mileage, due to better breathing/pumping efficiency with the motor. However, if you get on it a lot or drive with heavy loads on the motor, it'll be injesting a lot more air, and due to the increased air coming in due to the CAI, you'll also need to have more fuel to get to the correct A/F ratio and will notice a decrease in fuel mileage. Your right foot will cause the largest differences.

The ECU does not need to be reset, it continually learns on it's own. It can even compensate for different sized injectors (within a certain percent of the factory ones) and still run well.
Example: I went from 259cc to 319cc injectors on my car even with a different motor/cam setup all with the normally factory ECU temporarily and I was still running at the a reasonable A/F ratio. Timing maps were a bit off due to the different cams and stuff, but the fuel was right on where it normally is, due to the MAF readings and the factory computers ability to learn. (I now have a custom reprogrammed JWT ECU for the specific motor/MAF/injectors/etc... that I'm running in my car)

Justin McClanahan
Heavily Modified 95 Infiniti G20
www.InfinitiPartsUSA.com