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stock air box mod!!!

  #81  
Old 05-28-2007, 11:53 AM
Join Date: May 2007
Location: Sierra Vista, AZ
Posts: 77
I did the same thing to mine but I didn't really notice that much of a differance. My hole I cut though is smaller. I am going to put a K&N drop in filter in it to see if that helps anything.


 
  #82  
Old 07-14-2011, 10:09 PM
seonadancing's Avatar
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Location: Manila, Philippines
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Can somebody tell me what that thing under the right wiper do? It looks like a hood scoop but is not really connected to the engine, so is it just a hole to release heat from the engine?
 
  #83  
Old 03-19-2016, 05:53 AM
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Originally Posted by xviper View Post
Short ram intakes are generally hot air intakes, but they do work quite well as "performance" intakes. Now, the big quesion is ................. Is it better to make your intake more of a performance intake by the hole you made or does it do more harm by sucking in hot air. For every 3 degrees increase in intake air temp, you lose about 1 hp to the wheels. Air from where the stock Fit draws from should be about at road temp (a few degrees higher than ambient) but air coming out the back of a radiator once up to operating temps on a hot day can be as hot as 60 to 70 degrees. From an ambient of say, 25 degrees C, that's an increase of about 40 degrees. This would put your engine at a disadvantage of about 13 whp. Does your hole contribute that 13 hp back? No doubt you may achieve better throttle response with that hole, but that doesn't mean much if you're losing hp.
Alright, I really hate to do this, because I'm basically resurrecting a dead thread, but I'm very new to the Fit community (got my '09 2 months ago), and I'm trying to look around and get all of the information I can about mod and the like. I'm an Electrical Engineering major(3rd year) (and of course we have to take an extensive amount of math and physics, before we shunt off into our major specific classes). Anyway, how does that apply here? Well, what you are saying just doesn't make sense.

Mathematically it just doesn't add up(To be fair, my attention was snagged when I figured you were calculating with F instead of C. But even there, it just didn't seem quite right.). Anyway, when I heard this, I looked around for the SAE equation for atmospheric correction. Which is:

CF=1.18[(29.235/p)(t+459.4/536.4)^0.5]-0.18 (SAE J1349 June 1995)

In this equation P = measured inlet dry air pressure (inHg)
and t= inlet air temperature (F)

The SAE standard testing conditions are 77F at 29.235 inHg.

This is *the* equation used in a dyno.

This produces a CF value of 1. You take the CF (correction factor) and divide the HP of what your vehicle should get by that number. For example, with the '09, it is supposed to have 117 HP(new). If we take the inlet temperature and increase it by 40 degrees(and keep the dry air pressure the same), the CF value becomes 1.0432. When you divide 117/1.0432... You get 112.1549 HP

Now, you said you were using C instead of degrees. This gets you closer, but still not there. A 40C increase is a 72F degree increase, which makes the CF 1.0767, which means HP should be at about 108.665 HP. That's a decrease of about 8 1/3 HP instead of 13 HP. In our particular engine, these numbers aren't a big deal (as you are off by just under 5HP) but that does mean your figure is off by about 56%.

From this we can even try to see if we can correct your value by adding in Drivetrain losses. Using K&N's dyno numbers, the fit they used came up with 89.66whp. Compared to the listed 117HP from the crank, this is a drop of 23.93%(24%approx). Now multiplying the 108.665 listed by the same percentage loss turns 108.665 into 82.660approx. This brings the difference to 7whp(which makes sense, as smaller power generation produces smaller losses, with everything else being equal). Which brings your number to even further off, by 85.7% based on a whp scenario. Of course, this would have to assume that you calculated the drivetrain losses of the fit, and weren't just using a standard "rule of thumb", which as is evident by the result of these numbers, is a really bad habit to get into, tbh.

Now, with this being said.. The real question becomes what are the potential air flow HP gains over the temperature increase losses. Those numbers could potentially contain a negative effect, while still providing better throttle response. Which, would be adding 4.53whp(if the hole caused the airflow to match the k&n ram)while losing 7whp from the heat(if the intake temperature was increased by that much at all times). Which is a loss of 2.47whp price for the increased throttle response. Now, as was said earlier, while sitting still, the engine bay temperatures could *possibly* be as bad as the 7whp decrease, but as the vehicle begins to drive, the sheer amount of airflow running into the engine bay, vice how much of that would be entering the airbox, well, it's not going to be able to heat up the air fast enough to produce a sustainable 72F increase into that airbox. We can go into the math behind what it might be able to sustain, but I would need to look up the figures for that, or calculate them myself which could take some time for testing to ensure reliability. Also, the temperature increase in an unmodified box would need to be taken into account as well, as the box, if subjected to a constant 72F increase, would eventually equalize with the temperatures below it, and then you would have to calculate just how much heat the box can convey into the filter(as they are physically connected)as well as into the air that is moving through the box. But for the purposes of this comparison, we are rapidly approaching what would be very close to the final numbers, as the ABS isn't a very good conductor of heat, and wouldn't raise the temperature of the air in the box by much during operation. As I said earlier, my specialty is EE, and while this isn't my field.. the math is.

Anyway, I'll get off my teaching pedestal, lol. Thanks OP for the picture. I might potentially do what you did, just to make it look stock and avoid problems if I were pulled over.. but.. eh. I don't know. Anyway... thanks!
 

Last edited by SoCalGSXR; 03-19-2016 at 09:36 PM.
  #84  
Old 03-21-2016, 10:36 AM
Myxalplyx's Avatar
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In an nutshell, it's approximately -1whp loss for every +10F increase in air temperature?

Something else I read -->
Assuming the pressure stays the same...
Correction factor (Cf)
Temperute in Celsius(Tc)

Cf=1.18((Tc+273/298)^0.5)-0.18

So at 25 degrees C, the CF is 1 (STP or around room temp)
Equations: Dyno Correction Factor and Relative Horsepower

So its ~1.11% hp per 10degrees F temp change (no humidity or pressure changes)

Read more: How much does temperature affect H.P? - Corvette Forum
BTW: I suck at math and science.


I'm very interested to see what modifications you do to your Fit (Power wise) and the 'why' you choose that specific modification.
 

Last edited by Myxalplyx; 03-21-2016 at 10:40 AM.
  #85  
Old 03-21-2016, 12:25 PM
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Location: Portland Or
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Dyno sheets before and after or it didn't happen.. LOL

If the system is restrictive enough,,, free air flow will give more power back than lost by the hotter air, but if your going to test it, you have to be on a chassis dyne with a wind machine, your air through the engine bay has to be at a controlled speed that matches the wheel speed. Few shops have these, they cost a lot and most dyno customers are not educated enough to know its necessary. Your stack of 1/4 mile slips are the best evidence..
 
  #86  
Old 03-28-2016, 06:45 AM
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Location: San Diego, CA
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Originally Posted by Myxalplyx View Post
In an nutshell, it's approximately -1whp loss for every +10F increase in air temperature?

Something else I read -->


BTW: I suck at math and science.


I'm very interested to see what modifications you do to your Fit (Power wise) and the 'why' you choose that specific modification.
The losses you experience would be very dependent on the exact vehicle setup, but primarily that would be dependent on the exact drivetrain. The CF tells the division factor for the power produced. From there, exactly how much power the engine is capable of making must be taken into account. For example(leaving inHg @ 29.235inHg):

With our setup, in perfect conditions (77F) the CF is 1. The numbers produced are accurate.
However, at 87F our CF becomes 1.0109. Basically 1.1%. Taking this and dividing our (new) HP of 117, we get 115.73. So basically, just over 1HP from the crank. From there we factor in the drivetrain losses (23.93%approx) and that is 88.04. So down from 89.66 to 88.04, or about 1.62. So your number is off by a little bit still. We should lose **roughly** 1.62whp per 10F, which can be further affected by other factors present in the condition of the vehicle. Like engine health, oil condition, etc.

The big take away here, is that this equation gives you the ability to estimate the effects of things you do. If the math doesn't add up here for a gain in something, you would be very foolish to do it anyway, as you can almost certainly expect the results of a dyno to come in slightly lower(as the exact condition of *everything* will take its toll).

Right now, for my modifications, I'm just looking into CAI, turbos, and the potential for airbag suspension. Not sure I will get into all of it, but I'm having alot of fun playing with the numbers at the moment, lol

Yeah.. I'm an engineer. Numbers make me giggle.

Originally Posted by dwtaylorpdx View Post
Dyno sheets before and after or it didn't happen.. LOL

If the system is restrictive enough,,, free air flow will give more power back than lost by the hotter air, but if your going to test it, you have to be on a chassis dyne with a wind machine, your air through the engine bay has to be at a controlled speed that matches the wheel speed. Few shops have these, they cost a lot and most dyno customers are not educated enough to know its necessary. Your stack of 1/4 mile slips are the best evidence..
Absolutely. In our particular case however, if the intake temperatures did go up by 72F/40C(at all times), then an potential gains from this mod would be lost. But of course, that isn't likely, and would require a temperature check to figure out the numbers. I'm considering getting a stock box to cut, and wiring up my Arduino to begin polling the information to see exactly what the temperature does before and after.

Regardless of everything here, if you want extra throttle response, go ahead and cut it. But you might potentially lose power. Especially if your filter is more restrictive than the kn CAI.
 

Last edited by SoCalGSXR; 03-28-2016 at 06:50 AM.
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