You can find the "emperical data" in any physics book or class. The air spends less time in the intake...less time in the intake means it spends less time exposed to conductive materials...less time exposed means it's temperature's rate of climb will be slower...slower temp rise means it will be denser by the time it gets to the combustion chambers.

No one's denying a temperature drop. This has been covered at least six times now.

First, not all race applications use a sealed box because some applications don't place the filter in such proximity to the engine and some simply don't worry about it due to abient flow (indy applications are great examples). Second, no one has yet to say that sealing the filter from the rest of the engine bay isn't beneficial.

They weren't. It simply wasn't a concern with the FC...have you ever heard one with the intake box removed? How would you know if the hood wwas down? You likely wouldn't.

It was a concern with some cars...my MKIII Supra, for example. An open element with a straight intake (they have a resonator in the stock plumbing) is ridiculously loud.

Where?

See, I like it when people try to prove things they don't know with other things they don't know. Just because you have a theory doesn't mean you're right. :)

By the way, a short ram intake with a sealed box around it will have a shorter intake duct. Are you aware that your later arguments contradict your earlier ones?

Didn't say all of them did. But you said emphatically that they didn't.

Why did you use pot metal when you designed the door handles on the FC? Oh, wait, you didn't design the FC. Were you even alive in the late 70's when they did? How do you have any clue what was and wasn't a concern?

To quote you "You, sir, are simply not reading."

If you want to contest my statements feel free, but let's try actually actually using our mind from here on out, shall we? Or, is this just a test to see if the rest of the forum is paying attention?

The stock air system on any car is mainly used for noise muffling.

My first modification was to just slap a K&N on the end of the AFM. I didn't build an box around it or anything. I knew this was going to let heat from the engine compartment soak into my intake charge. I wasn't too worried about it because I was planning on doing the CAI into the fender well soon (of course it is now a year later and I am only halfway done with the project).

With a stock exhaust you can easily tell the difference in sound. Even more so now that I am halfway done with the CAI and have removed the stock air tube shit and replaced it with a more free flowing tube a couple weeks ago. It sounds mean as hell under the hood and more mean with the hood shut.

Now that I have removed the air pump silencer it sounds mean as hell under the engine compartment. :D

I prefer the CAI project over the box. It moves the filter OUT of the engine compartment as opposed to just blocking out the Hot air.

I think its time to close this thread, just going round and round now.

Physics isn't generally "theory". Some is, but this is very basic stuff.

How so? By saying that it'll spend less time in the intake tract exposed to energy conductive material? Same concept holds true, but you'll be starting out with air at a higher temperature to begin with with the breather closer to the engine.

That's another aspect that is only beneficial to an intake assembly...the shortest path possible to the throttle body. Again, shortest distance between two points is a straight line...another reason why a straight tube fed by ambient air would be superior.

You emphatically implied they all did. I doubt that was your intention, nor was it mine to suggest they all didn't.


Logic. If intake noise was such a concern with the assembly, mazda would have gone through much more effort. The stock assembly really isn't that much quieter than an FIPK or CAI...the stock assembly is actually kind of noisy by most standards.

~no, I don't have proof that it wasn't a concern, but seeing the steps taken by other manufacturers, including Mazda, at the time to reduce intake noise and how none of those steps were taken with the FC I just find it highly improbable that it was important to them.

Read what I quoted. You were still stating that a rebuilt air box was supplying colder air to the motor and no one said otherwise...actually, it'd been stated half a dozen times by myself and other members that it was, in fact, supplying colder air.

It's not a contest. No one here can tell me why having an airbox is better than a very simple, straight tube fed by cold air...yet people are hung up on these boxes...maybe if your goal was to retain a somewhat "factory" look or if you were just doing it for kicks (a la my twin turbo project) I'd understand why but it'd never be justified as the best method for performance.

A straight path fed by ambient air...I just have a hard time seeing how that can be beat.

if it bothers you, then check something else out. Some of us have nothing better to do and the discussion only hold promise.

You really call this a discussion?

This is completely wrong. Manufacturers go to great lengths to suppress intake noise because at WOT is can generate as much noise as the exhaust. It can be just as difficult to get the intake noise to meet the drive-by noise levels that cars must comply with as it is with exhaust noise.

If you don't believe me look at this picture. That's the air chamber that sits in the front wheel arch of a '94 WRX and leads to the airbox in the engine bay. It's purpose it purely noise suppression and it's responsible for about half of the pressure drop though the entire pre-turbo intake system. It's pretty obvious that noise was a major design consideration at the expense of flow. This is an extreme example but similar devices are not that uncommon in modern cars. The chambers teed into the intake duct of lots of airboxes (including the FC's) are there for the sole reason of reducing intake noise.

My pod filter is clearly audible over my exhaust, which is far from quiet.

Have you measured the pressure drop through the components of the stock intake system to ascertain that? It sounds more like an assumption...

The FC's stock airbox has been proven on a flowbench to be very restrictive. In pretty much all stock airboxes the filter itself causes a very small amount of restriction compared to the box itself (and a tiny fraction of the restriction of the whole system), and simply dropping "performance" filter into a stock airbox will do nothing for performance. In the WRX mentioned above the filter accounted for just 2% of the intake system's total restriction. Even if filter restriction is halved, that's an insignificant improvement.

This is ridiculous. Makenzie71, please stop spreading misinformation.

Even though this is a heated discussion my thoughts are this. Temp shielding is not going to stop heat soak. You can however cut a hole in the sheetmetal to vent air into the box you make and in my opinion that would help you cool down your charge. But if its a 80 degree day and your under hood temps are 180+ then your not really doing a whole lot. And this just goes for us turbo guys. You NA guys shouldn't really loose any sleep about performance gains or losses because of heat soak because it will never be a noticable difference.

That was my only good reason for doing it over a full CAI. I didnt want to bother relocating stuff on that car. Two of the four FC's I've owned have had full CAI, and I wouldnt do it any other way from now on. For people who dont have the capacity to do the mildly simple CAI work, the air box is still a good option.

As far as the other stuff goes, I did spot some misinformation, but I dont really have a desire to go back and prove it wrong. The bottom line is: an airbox will be an improvement over the stock box, but not quite as good as a CAI. The air box is still a good mod for those who arent very good when it comes to modifications.

well this was a fun read.
I just got my prelude kit off ebay to make the fender well CAI
I'm curious to see what kind of intake temps it will make.

Heres a link to some research that was done many years ago:
pistons or rotary
pistons or rotors, same theory. especially when the rotary has strong pressure waves throughout the intake. so tuning the intake's length will make a notable difference in the performance of your car.. (specifically for NA's)

If I'm not mistaken... mazda already did this with S5 cars. Just convert to VDI.

thank you, my canadian friend.

I am not 100% framiliar w/ the VDI system, but i was trying to reffer to the actual length of the intake (filter element to the throttlebody).

Agreed... It's getting rather bothersome that Makenzie seems to think he's the new self-proclaimed guru of every subject, and somehow everyone else is always wrong.

That being said. Cold air boxes are a nice alternative for those that don't want to build a CAI that pipes outside the engine bay. It's easier and can work effectively. I've built 3 custom CAI's for 2nd gens, all of then with custom pipe that goes outside the engine bay to draw in cooler air. I'll never do anything different, but a cold air box is definitely a good alternative still. Much better than the stock air box and much better than a cone filter just sitting by itself in the bay.

I agree in theory with what you're saying, HOWEVER, a proper cold air box will draw from the fenders/headlight/outside of engine bay. If done properly you can achieve results nearly identical to a "cold air intake". It's just a matter of design. :) The air entering the intake is constantly refreshed with ambient temperature air drawn from outside the engine bay.

I should have mentioned before, my temps with the cold air box sit within 5-6* of ambient when the vehicle is in motion (only time you really need air flow, unless you're in a revving contest ;) LOL) A fenderwell intake tested as 4-5* above ambient. That difference can be negated.

Regardless, I'm glad I'm not alone in my opinion of the matter.

Everyone needs to stop the petty bickering and post some picks. And as for Makenzie, you need to stop being such a Know It All, Let people do what they want.

Come on, keep the pics coming.

Thank you AaronCake and NZ!

I was reading this thinking, when is someone gonna shut this guy up? :)

I just wanted to see some custom air boxes, instead, 5 pages of lousy bickering. What a waste of a good thread.

Holy shit!

Some people need to whine less!

This was a GREAT thread, whats wrong with discussion on a forum hmmm? We all learned something.

Plus I found my cold air box pictures by searching ;).

too bad makenzie stopped posting in here :(

I had a dream last night after watching a nascar race... heres what it was of:

http://members.shaw.ca/jono24/rx7/cai.JPG

I know, I know, ram air doesnt work. I just thought, with the charcoal cannister and cold start system removed, you could run a 3" pipe straight off of the TB, through the wall of the bay, and out the fender. Just run a smallll scoop outside to pull in the air. you could weld it in so its all flush, you could paint it over stuff too... never seen it done, thought it would be neat.

would require a new attatchment off the tb, no elbow!