I'm not sure about that. I have to agree with SteVTEC, expecially after reading Norm's post I'm even more conviced Steve is correct. The radiator would have to put out a huge BTU figure in order to significantly heat up that volume of air and even higher BTU's at higher speeds. I just don't see the radiator putting out this much heat. I haven't worked the math but I can tell you, from working with customers building server environments/rooms and the required HVAC to handle the BTU's put out by their servers, that to significantly heat up that volume of air would take A LOT of heat. Also, if the engine does digest at most 10% of the air then that means the rest of the air flows through the engine compartment thus cooling it down (helping the radiator).

I'm fully convinced now that temperature is irrelevant when comparing CAI and WAI in real world driving.

If you were making more torque down low, most of the time you wouldn't have to rev up that high.

I have nothing intelligent to add to this debate other than
the fact that I like the way Tai Mai Shu used the word "myopic"

carry on...

I think that only a very SMALL percentage of air flowing onto the radiator actually makes it past that and into the engine bay. In wind tunnel tests with those streaming clouds of smoke in the airflow you can clearly see the air going around the car, not through it.

If air really was flowing through the radiator and into the engine compartment, well, there's only really one way for it to go. It can't go upwards and through the hood. It can't go through the engine block. And it can't go to the side. The only place for it to go would be downwards out the bottom of the engine bay. Then you'd see those little smoke streams coming out there, but they don't. This would also be dangerous because that much air flowing downwards would act to lift the front end of the car and it could significantly reduce stability. Not to mention the fact that it would create a very low pressure area on top of the car because no airflow would be passing over the hood.

I think it's safe to assume that this is UNrealistic and that very little air actually goes through the radiator and into the engine bay.

Plus there's the fan assembly and cowling directly behind the radiator which blows air FORWARD. Any air coming back through the radiator is pretty much going to be blocked by this. When you're in stop and go and its hot out, you wouldn't want to be blowing hot air from the radiator back onto the engine block either, would you? This would drasitcally decrease the efficiency of your cooling system. So where do the radiator fans get their air from? The only place it could be is UNDERNEATH the car in that nice little gap between the radiator/fan and the engine block. Hot air rises, so the air down there would probably be nice and cool, which is exactly what you want.

As for intake temperatures, I'm still claiming that this article from Import Tuner or whatever it was was just complete BS. The Maxima and the Accord V6 have almost identical underhood layouts. My buddy did that thermocouple test with his Accord and WAI (Short Ram) style intake and as soon as the car started moving, even just a few MPH, the underhood and IAT dropped to within 10 degrees of the outside air within literally seconds.

Just to add fuel to the fire I will say this...

I think the HAI does not help cars with the MEVI as much as a CAI.

The TQ loss with the MEVI is reduced when using a MEVI and a CAI. The effects of the CAI/MEVI above 5000 are almost the same compared to the HAI/MEVI.

So I think the CAI/MEVI is the best for both HP/TQ

Flame On

I tend to agree with everything you've written so far, except this.

The radiator fan does not blow air forward. If it did, it would create a pocket of stagnant air on the radiator when cruising at slow speeds. This stagnant air would serve to insulate the radiator, rather than cool it, and you'd over heat. At a stop and slow speeds, the fans suck ambient air through the radiator, and expel it into the engine bay. The engine block and front exhaust manifold are still much hotter than the warmed air so you still get a slight convective cooling benefit.

Try not to confuse radiator airflow with the total air disturbed by the car. The front view cross sectional area of the car is approximately 20 ft^2, compared to 1 or 2 for the radiator.

Quote:
If air really was flowing through the radiator and into the engine compartment, well, there's only really one way for it to go. It can't go upwards and through the hood. It can't go through the engine block. And it can't go to the side. The only place for it to go would be downwards out the bottom of the engine bay. Then you'd see those little smoke streams coming out there, but they don't.

Turbulence in the space between the radiator and the powertrain will do a pretty good job of diffusing the smoke streams into a faint smudge. I once built a scale wind tunnel as a project, and keeping turbulence from screwing up your observations was a major issue.

Quote:
This would also be dangerous because that much air flowing downwards would act to lift the front end of the car and it could significantly reduce stability. Not to mention the fact that it would create a very low pressure area on top of the car because no airflow would be passing over the hood.

As research for this thread I took a look under the front of my ’01 and noted that the lower surface of the radiator shroud slopes downward toward the rear. This accelerates the airflow under the car and creates a low pressure zone directly under the space between the radiator and the engine. This aids the extraction of radiator air. And would be expected to minimize front end lift tendencies.

Quote:
I think it's safe to assume that this is UNrealistic and that very little air actually goes through the radiator and into the engine bay.

Per above, maybe 10% of the total airflow impinging on the frontal area of the car. But it still has to be sufficient to carry away the heat rejected by the radiator and A/C.

Quote:
Plus there's the fan assembly and cowling directly behind the radiator which blows air FORWARD. Any air coming back through the radiator is pretty much going to be blocked by this. When you're in stop and go and its hot out, you wouldn't want to be blowing hot air from the radiator back onto the engine block either, would you? This would drasitcally decrease the efficiency of your cooling system. So where do the radiator fans get their air from? The only place it could be is UNDERNEATH the car in that nice little gap between the radiator/fan and the engine block. Hot air rises, so the air down there would probably be nice and cool, which is exactly what you want.

I’ll check which way the fans do run and then get back (rather than present as fact something that’s not much more than a hunch at this point). But in the meantime, it just doesn’t make sense to have a fan fight against the naturally occurring high pressure zone that’s on the front side of the radiator even at the low speeds where a fan is most needed. Particularly a fan driven by a relatively small electric motor. At some relatively low speed the effort of the fan would be exactly balanced by the car-velocity-squared pressure effect on the other side. Result? Zero air velocity through the radiator and very poor cooling and A/C performance.

Norm

Well from looking at the fan assembly on my 4th Gen, it looks pretty much like it blows air forward. About 99% certain. The only time you need the fan at all is when you're stopped, or moving at extremely low speeds. Anything above that and you'd probably have enough air flow over the radiator that you woudln't need it.

But anyways, what does this have to do with Intake Air Temperatures?

My bro in his Accord V6 did measurements like this that pretty much prove that intake air temps are not an issue with the different intake styles. The Maxima and the Accord have almost identical underhood layouts. So if anybody wants to prove anything, just go and measure your IAT while stopped and then while moving and see what the difference is.

I think you'll find that under hood temps do not remain at 130F or whatever BS the import tuner mag article stated, but instead go back down to ambient or nearly-ambient temperatures.

If you're not 100% absolutely sure of the direction that the motors turns either, that makes this train of thought nothing more than speculation without logical basis. Motor direction is what I'm waiting to see for myself.

What this has to do with IAT is the effect on underhood temperature that pulling air through the radiator first (and heating it up) vs drawing relatively cooler air up from the ground.

More details are needed re your V6 Accord measurements. Like were there any 'leaks' around the radiator support near the intake inlet through which it could draw cooler air than is average for the engine compartment? Ambient temperature that day? Wind? Location of the IAT sensor?

Norm

This is splitting hairs

I would believe my friend and his measurements on his Accord V6 (he too is an engineer like myself) more than some dumb HonDUH Tuning article, which publishes more BS than anything.

I'm going to borrow a thermocouple from work for the weekend and I'll try to run some experiments, even though I only have the stock airbox. I'll just make some underhood temp measurements and I'll report back after that.

It's simply pointless and a waste of time/energy to continue debating every single factor that could affect IAT when all we're wondering about is what the IAT really is. Just go measure it for crying out loud and call it a day

I'll report back over the weekend.

SteVTEC - hope you haven't been taking all this too personally. I'm as open to the liklihood that there's some BS in the Honda Tuning article as I am to the possibility that there's a grain of truth in there somewhere. So can we agree that they may be on to something, but that their specific numbers may well be suspect?

I didn't mean for the discussion to actually cover all the details I listed in my last post, only that they be recognized as having effect.

You're right about going out and getting the data, given that you have the means to do so (not all of us do). I suppose that I could unplug the IAT sensor in my '79 from the manifold, plug the hole, and let it read underhood temps and thereby add to the collection of this knowledge, but those measurements aren't too high on my list of priorities.

My viewpoint on this discussion (and engineering in general) is that knowing as much as possible about the 'why' and 'what's happening' leads to a better understanding. Comes with practice. A few more years worth, in my case vs yours. No flame intended, OK?

Norm

First off, when you see the smoke trails, the reason that you do not see it coming out under the car is because by the time it goes through the radiator, the smoke is so diffused from hitting everything under the hood, it couldn't possible stay as a stream of smoke.
Next, yes there is front end lift from the air going into the grill and out under the car. Why do you think race cars have front spoilers to divert any air that isn't going into the grill, to go around the car. This minimizes front end lift.
And, you should put try to put your hand behind your fan. The last I checked, the fan never ever blew forward . If it blew forward into the radiator, when you go at speed, the fan would be fighting positive air pressure and be useless. Fans ALWAYS draw air front the front towards the rear, whether or not they are in front of the radiator or behind. Not to flame you, but at least get the basics correct.

I checked the fan blade shape, and you're right, the fan does blow air rearwards. Not *all* cars are like this, though. A car I used to drive did actually have the fans blowing the air forward. I assumed the Maxima would be the same but I guess not.

I read the article too and found it very interesting. A couple of things I don't understand though.

-How does under hood temp change drastically while moving - when fabricating a custom intake I was looking for a place to run it to the front of the car. There is absolutly none unless you disconnect a light, or remove the radiator, the radiator covers everything. Also, when I installed my Y-pipe I noticed that the bottom of the engine bay is pretty much covered by protective plastic, so where is all this air coming from?

-Is the size of the throttle body note worthy. No matter what size or length intake you get it will have to pass through the throttle body. I would think that a porportional pipe would flow the same. IF you turn on an outside water faucet (the faucet represents the throttle body, and the hose represents the intake piping) wouldn't a hose attached to it fill up a bucket of water at the same rate whether it was two feet long, or if you cut it in half? I would think that the bends in the pipe would be more of a concern.

-What I feel would hold an intake back most would be the filter and availability of air. This is why closed hood dyno's should be performed. If the hood is open regardless of underhood temps (which I agree with Honda Tuning, because the whole debate from the RSX community is that with the large open ports found on the front of the RSX, HAI intakes will pull in cool air just like CAI once you start moving, that was not true for the well ventalated RSX, and it definatly would not be true from the all encompassing radiator, and undercar covering that I have seen on the max.) you have given the intake a huge source of air. Since air flows from it's least restrictive source, I'll bet most of it comes from over the hood when HAI are dynoed (but HAI's would be pulling air in from the small cramped space of the engine bay, where hot air is circulating, (put a blanket over your head and breath))
This is the exact reason why I think the CAI starts to cough in the high end. It is encompassed by the fender well (try breathing outside, and try breathing outside with a helmet on)

I personally think that the CAI is the better choice, and dyno's of the HAI's are so that they pull in the same temp air as the CAI, but have a much larger source (the size of the open hood, vs the samll space of the fender well) this is why I think they pull better at higher RPM (there is more available air). If your going to dyno a CAI vs a HAI with the hood open, arrange the CAI so that it will have as much available air (so it's outside of the fender well.) I'll bet the HAI would still be a little better since it has no bends, but in the real world the intake temps are going to be different, and colder always means better.

Any thoughts?

In real world conditions (ie: sitting at a stoplight) a CAI outshines a pop charger hands down. It's getting cold air from the moment you hit the gas until the moment you stop. A pop charger on the other hand is drawing in all the hot underhood air until the car finally reaches a speed at which air flows in fast enough to reach the intake. Loss of low end TQ on a hot day with a Pop Charger is more then noticieable.

Dynos may be able to prove the benifit of any high flow intake over stock but are usless at comparing CAI with Pop.

Also this trend of turning HAI's into "hybrids" does nothing but add a fancy pipe that may increse throttle response at best. It still faces the same problems of any other pop charger being that it resides inside the engine bay and not the fender well.

Are those Lexus IS300 rims on that 3rd gen?? It looks tight!!!

Did you use the Lexus center cap?

Yea, polished IS300 rims. I used the Lexus center cap but removed the "L"

The center also had to be bored out some

You guys are all debating how the temp diffferences are small when comparing the CAI to HAI. The HAI will flow a bit better, but I'm still convinced that a CAI on a MEVIed Max, or any 5th gen Maxima is better. It's interesting how an MEVIed Maxima loses a bit of mid-range torque when compared to the fixed manifold, and how the diference between the CAI and HAI becomes much less when the MEVI comes into the picture. The MEVI seems to be making the HAI's weakness a little more apparent. They both have the pluses and minuses.

Consider how the ECU deals with the incoming air. With a HAI, it always has to adjust to the varying temps. Can the ECU, or the motor, adjust to the varying air temps just as quickly? One of the CAI's greatest benefit is that the intake air temps are consistent, and I'm sure that the ECU and thermodynamics of the motor can better deal with the consistant air temps from a CAI than from a HAI.

I converted my car from a CAI to HAI. One thing I still miss about the CAI was the total predicability of the car. With the HAI, if I floor it below 5000 rpms, it's a wee bit vague, but I'm like, wait till I hit 5000 , then I'm gone. This is with the fixed manifold.

DW