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CAI calculations and retraction

 
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Old 03 Mar 2004, 12:21 pm
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Default CAI calculations and retraction

This is my official retraction of my previously stated opinion that a CAI would probably have minimal impact due to heating at the turbo and then cooling at the FMIC.

I had stated I didn't believe a 10 degree drop at the turbo inlet would lead to a 10 degree drop at the outlet, and hence a short rame with less restrictions (bends) would probably be just as good. After actually calculating turbo outlet temps based on efficiency and ambient temp, I was wrong. A 1 degree drop in temp at the turbo inlet is often around a 1.5 degree drop at the outlet! If the post intercooler temps are lowered the same amount, the difference in HP was potentialy .5 hp per degree drop at the turbo inlet.

I found a nice spreadsheet on the internet that has all the formulas for this sort of stuff.. very interesting to play with. If anyone is interested, I'll track down the link.
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Old 03 Mar 2004, 09:09 pm
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Thank you Jason, I have been saying that on our forum more then once. I am glad you found that info. , I am doing some temp test now with the rubber under the hood " remove it or not?" I will post the results this weekend. thanks again Jason. jim
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Old 04 Mar 2004, 02:07 pm
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Yes - i was one of the guys who didn't agree with you and others initially on the beneifits of CAI. I figured the real benefits were from the airflow increases of the pipe and filter, and that the heat from the turbo would make temp differences moot. I just couldn't see a 10 degree drop at the inlet having more then maybe a degree or so effect at the outlet (I use 10 degrees as i was comparing CAI to short ram with the weather strip mod). But after going through the math (I used 70% effiency and various boost levels), the effect was just the opposite of what I thought!
Here's the numbers I come up with, using just 8psi at the turbo (which would probably be around 6psi at the manifold):
inlet temp 80 -> 70 = 10 degree drop
outlet temp 200 -> 188 = 12 degree drop (I expected around 2)

i haven't calculated after the FMIC yet though - as I am not sure what sort of efficiency our IC is. But if it maintains the same temp drop (just an assumption at this point for me, I still need to research), my rough numbers show a potential 4hp gain at the crank for a 10 degree decrease at the inlet at 8psi.
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Old 04 Mar 2004, 04:23 pm
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Sory Jason but I need to do this

Somebody here posted something about the K&N FIPK system being from composite that would be better than Brand $#!%^$@. wait, I said that!

I was yelled and told that that was bull Crap...

I have to tell you that you are a real gentleman accepting this and I take my hat to you for doing this.[^]

There will be people still saying that this idea is wrong but it is nice to see that I am not alone in this issue anymore.

[?]

Ian
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Old 04 Mar 2004, 07:03 pm
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I try to make sure I'm never married to my ideas, and take my lumps if it's warranted. I figured since I debated this on the forum, it was only right to admit my mistake on it
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Old 04 Mar 2004, 09:05 pm
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Generally speaking, the charge cooler is an efficiency device.

So if the ambient side is 80 deg F and the turbo outlet is 300 deg F - the efficiency is a fraction of the temp delta. So an 80% efficient cooler has an outlet temp of:

300 - [(300-80)*80%] = 124 deg

If you drop the inlet temp by ten

290 - [(290-80)*80%] = 122 deg

Not much, right? The heat transfer efficiency will move around a little, but not much

You are more likely to pick up more power from reduced restriction in front of the turbo, and therefore less wastegate is required to make the desired boost, so lower backpressure.

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Old 04 Mar 2004, 10:39 pm
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????

In english please, 3Bar.
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Old 05 Mar 2004, 08:25 am
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MEXICANPT,

Just re-read 3BarBoost's last sentence again...it says it all. Basiclly he is saying on a CAI it's NOT the reduced air-inlet temps that are netting you more HP but rather the smoothing out or removal of the factory restrictions on the intake side. Removing the noise suppressors and enlarging/smoothing out the tube from the air-filter to the turbo is where you see the most benefit from a CAI...

Deen
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Old 05 Mar 2004, 01:24 pm
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Makes sense, thanks for the translation.
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Old 05 Mar 2004, 06:35 pm
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ok, my non turbo, stock ran 18.55 in 1/4 then the only mod was installing the 2" tubing from the hole next to the fog lite to the top of the fender well where the intake gets it't air. I then ran 18.24 in the 1/4 two different Sundays temp about the same 85* no aftermarket intake no nothing. on my turbo the intake and the hose in the fenderwell was installed at the same time when the car was new. so i believe that every little bit helps, the hose may give me 2 hp the smoothing out intake gives me 11 hp so now i have 13 extra hp, I'll take all i can get. just to show you what i mean go to the track or wherever you like to go fast and make a run. we all do it from point a to point b we go 90 mph or whatever we do now remove your rear seats go do it again you will go faster this time, I always make sure i have 1/4 tank of gas when doing a test that way i am always the same weight., inflate your tires to 65 lbs is good for .03 in the 1/4 mile et and about 3 mph. try it you will like it.
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