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Old 09-09-2012, 09:08 AM   #1
fr0st
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Default Hood deflector... Mythbusted?

So after reading alot of info on hood deflectors, a lot were arguing that a deflector would kill the air eneterring the scoop and thus, make the intercooler hotter and you know the rest of the song..

I then went to look at shops here who put 3M tape to protect the first portion of the hood from chips and salt and crap from the road and winters we have here. I wasn't impressed and even my bro in law has one on his Mazda and it didin't look that good.

So being stubborn as i am, i went down to my stealership and bought an impreza 2.5 08-11 hood deflector. Of course the dealership told me it's a no no, that you can't put this on and it will not "cool" the turbo ..

Anyways i got home , plugged in my Cobb and checked out intake temps.. low speed, stop and go traffic, highway and my favorite " beat the **** outta it" then proceeded to install the deflector and tried it again...same temperature..even used a laser temperature gun on the IC. this thing does NOTHING to prevent air going in on a 08 + .. I can't speak for the 07 and before though.

I even used a water pressure washer to spray water on the deflector and see how it reacts on the deflector, and the water spray goes directly in.

I went on in 90 degree heat and tried every possible method to make it heat up and it was not worst having it on.

The way the deflector is built, it doesn't have a curled up tip so the air is NOT lifted from the hood and go over the windshield. it's a really there to protect the hood from chips.

Of course some will say it's not a good idea and so on but i'm keeping mine.Looks good and protect the hood and doesn't keep the intercooler from getting air at all.

I really don' t know why SOA or SOJ would not approve this thing..



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Old 09-09-2012, 09:22 AM   #2
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SOA halted sales of the leather bra for Bugeyes within a few months of initial release. The bra did push air over the top of the scoop. Continuation of this policy is either associated with habit or testing, I really can't speak for newer models.
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Old 09-09-2012, 09:30 AM   #3
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Quote:
Originally Posted by Smurftastic View Post
SOA halted sales of the leather bra for Bugeyes within a few months of initial release. The bra did push air over the top of the scoop. Continuation of this policy is either associated with habit or testing, I really can't speak for newer models.
That what i think too.. they didn't take time to test this thing out.. in the part number description they say "none turbocharged models only" and thats it.
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Old 09-09-2012, 10:12 AM   #4
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your intake temps are measured before the intercooler. so no. you are wrong.


they make hood deflectors for turbo models, but i don't know about 08+ Impreza
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Old 09-09-2012, 10:43 AM   #5
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Quote:
Originally Posted by indytruckboy View Post
your intake temps are measured before the intercooler. so no. you are wrong.


they make hood deflectors for turbo models, but i don't know about 08+ Impreza
Intercooler temp was about the same as outside temp while using the laser pointer temperature gun. with or without the deflector. Of course the IC was hotter when beating the crap out of it.. but it was pretty much the same between with or without.

Last edited by fr0st; 09-09-2012 at 10:48 AM.
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Old 09-09-2012, 10:50 AM   #6
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I find it amazing that no one in Subi's QA ever wanted to test this out

Chances are, if they do not have a substantial effect. I have a very hard time believing they screwed this up twice.
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Old 09-09-2012, 12:47 PM   #7
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Look, it isn't that hard to test out.. go around on a hot day and plan a route. do various things and stop at times to check IC cooling with a laser temp gun and your hand. Install the deflector and do the same damn route with the same temperature outside and stop at the same places and check out IC temp. i there was any BIG temp differences i would have threw the deflector on fleabay. but since it was within 3-5 degrees F difference of temp, sometimes, higher sometimes lower.. i can sincerly say it'S about the same thing. of course your IC gets hot when you're stuck in traffic, once you get moving, it cools off pretty quick. it was not hotter either way..and you could feel a little hotter on the side of the turbo ( of course)


it's doesn't take genius or an engineer to do this.. just takes 140$Cdn of my money and a few days of testing in hot weather while on vacation

lol


Of course if you put an aftermarket deflector that DEFLECTS air it will/should do something negative.. but the OEM is not a deflecor.. it's a hood protector.
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Old 09-09-2012, 05:35 PM   #8
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Quote:
Originally Posted by indytruckboy
your intake temps are measured before the intercooler. so no. you are wrong.

they make hood deflectors for turbo models, but i don't know about 08+ Impreza

That's true since the iat is part of the maf. Hmmm. Maybe I should just ditch my tmic and run a silicon pipe from the turbo to the TB. I must not need it since my intake temps are measured before it. :rollseyes:
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Old 09-09-2012, 05:38 PM   #9
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Quote:
Originally Posted by ,fr0st,
Of course if you put an aftermarket deflector that DEFLECTS air it will/should do something negative.. but the OEM is not a deflecor.. it's a hood protector.

I think that's the biggest point. There are different styles, and like you pointed out, there is no lip on it like other styles. Therefore the airflow isn't lifted over your scoop.
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Old 09-09-2012, 05:49 PM   #10
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Quote:
Originally Posted by stevejones19 View Post
That's true since the iat is part of the maf. Hmmm. Maybe I should just ditch my tmic and run a silicon pipe from the turbo to the TB. I must not need it since my intake temps are measured before it. :rollseyes:
The point he was making, was that your ECU reads IAT at the MAF. The MAF reading isnt what your IAT really is.....
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Old 09-09-2012, 07:57 PM   #11
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very nice research
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Old 09-09-2012, 09:15 PM   #12
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I actually applaud your efforts to research this in as scientific of a manner as you could. In the end, I have to agree with the fact that it's a hood protector and not a wind deflector. That is evident in the design and it therefore makes perfect sense that there would be no ill effect. I think it looks pretty damn good, too. How much did it set you back?
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Old 09-09-2012, 09:46 PM   #13
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Quote:
Originally Posted by Decipher View Post
I actually applaud your efforts to research this in as scientific of a manner as you could. In the end, I have to agree with the fact that it's a hood protector and not a wind deflector. That is evident in the design and it therefore makes perfect sense that there would be no ill effect. I think it looks pretty damn good, too. How much did it set you back?
The dealer price is 145$ with tax in Canadian currency.

So i assume in the USA it would be alot cheaper.

It does add a different look to the car and i love it. As for chips on the paint, bring 'em.

The OEM deflector is actually pretty well built and comes with some 3M tape that you put on the hood at specific places and the way you install it, it doesn't damage the paint at all.
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Old 09-09-2012, 10:11 PM   #14
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Quote:
Originally Posted by stevejones19 View Post
That's true since the iat is part of the maf. Hmmm. Maybe I should just ditch my tmic and run a silicon pipe from the turbo to the TB. I must not need it since my intake temps are measured before it. :rollseyes:

based on your response to his statement, i am not sure you fully understand how the ECU uses the IAT readings from the maf sensor.\


to the OP, i applaud you greatly for taking something like this on, but i have a few suggestions/comments...

some air will make it in the hoodscoop with the deflector, but the question is how much compared to without it. this number is really unable to be quantified without a windtunnel. so the next best true way to ACTUALLY test this part out is going to be to have a post-intercooler IAT reading, and measure its time to return to its normal post-intercooler operating temps before and after installing the part. using your ECU's IAT reading is pointless since it is taken at the maf sensor pre-turbo, and using a laser thermometer is kind of pointless because you are no longer driving and the results are being skewed by too many external factors at this point.

you also would need to test the differences at various speeds because the hoodscoop tends to react differently at high speeds vs. moderate speeds.
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Old 09-09-2012, 11:11 PM   #15
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I'd have to believe the difference won't be noticeable to the daily driver. I, of course, have nothing to back that. I just can't imagine it would make THAT big of difference.
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Old 09-09-2012, 11:17 PM   #16
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Quote:
Originally Posted by tom-wrx View Post
very flawed research
flawed, indeed....need to log and post IC outlet temps

iat is meaningless as is using an ir thermometer on the ic AFTER driving...surface temp of the ic is meaningless

air temp OUT of the ic is what is the whole issue
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Old 09-09-2012, 11:22 PM   #17
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Tape some yarn to the hood and record the motion with a go pro. If it's actually deflecting air away from the intercooler, I'd expect them to be sucked up by the lower pressure air above the string. If not, they'll get pushes backwards and flap around.

I'm not an engineer so I have no idea if the above experiment is poo or not.
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Old 09-09-2012, 11:24 PM   #18
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Quote:
Originally Posted by Airplay355
Tape some yarn to the hood and record the motion with a go pro. If it's actually deflecting air away from the intercooler, I'd expect them to be sucked up by the lower pressure air above the string. If not, they'll get pushes backwards and flap around.

I'm not an engineer so I have no idea if the above experiment is poo or not.
****ing genius!!! Give this man a medal and a cookie!
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Old 09-10-2012, 12:24 AM   #19
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The deflector could just be acting like a springboard for anything that hits it?
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Old 09-10-2012, 05:38 AM   #20
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Quote:
Originally Posted by Uncle Scotty View Post
flawed, indeed....need to log and post IC outlet temps

iat is meaningless as is using an ir thermometer on the ic AFTER driving...surface temp of the ic is meaningless

air temp OUT of the ic is what is the whole issue
So to you, if the IC surface temps is at 75 F then the air inside is alot hotter?? If i beat the **** out of the car and check out the IC temp on hot and cold side, i get 95 / 75... if i get the same with or without the deflector i can assume i'm not losing 100 WHP here. if the IC would be hot as **** or even a little bit hotter, yeah i can relate to that.

You guys are right on the post IC temps sensor... i thought the IAT was on the hot side would would have made sense my last turbo car was a Mazdaspeed Protege and the IAT was close to the air filter.. but Mazda was on a budget building this car so relocating this would cost $$$

I thought Subaru did this correctly and logically. the IAT should be on the post IC

Still, i used a ir thermometer to look at it myself. I assume on an STI with a bigger IC it can only be better if on a WRX not enough air will make it to the IC like some say here.. but you have to be logical on this.. the deflector is about 1/4" from the hood surface and marries that hood shape pretty well. It's not like it's going to remove(if any) 50% of the airflow to the IC.

I'll take a pic today and show a few angles on how it's installed so you can picture the air going in the scoop.. I can understand how air can be diverted by bumps,ridges diffrents shapes and likes, but there is no much there to make the air diverted o begin with.

As for performance wise, i took on a friends 2011 wrx with a cat back from a stop to 60 mph and i have a 225hp with a stage 1 cobb AC we were equal all the times we tried it out.So either he's a bad driver or or the Cobb stg 1 does it's job and the deflector doesn't remove any performance. i had to find something for my ass dyno to reference to.


Last edited by fr0st; 09-10-2012 at 05:48 AM.
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Old 09-10-2012, 05:51 AM   #21
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Quote:
Originally Posted by fr0st View Post
So to you, if the IC surface temps is at 75 F then the air inside is alot hotter?? If i beat the **** out of the car and check out the IC temp on hot and cold side, i get 95 / 75... if i get the same with or without the deflector i can assume i'm not losing 100 WHP here. if the IC would be hot as **** or even a little bit hotter, yeah i can relate to that.


the temperature of the upper surface of the ic is irrelevant

what is the temp of the LOWER surface???


the temperature of the air coming out of the ic outlet is, really, the ONLY relevant temperature to be discussed here.

all the rest is f00-f00
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Old 09-10-2012, 05:53 AM   #22
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Quote:
Originally Posted by Airplay355 View Post
Tape some yarn to the hood and record the motion with a go pro. If it's actually deflecting air away from the intercooler, I'd expect them to be sucked up by the lower pressure air above the string. If not, they'll get pushes backwards and flap around.

I'm not an engineer so I have no idea if the above experiment is poo or not.
Thats a great idea ! I got my Gopro here.

I'll check that out.
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Old 09-10-2012, 08:42 AM   #23
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This IS a stellar idea. OP, please report back with your findings. I'm also looking forward to the other pictures too. Nice work thusfar. I can appreciate that you didn't just slap this on and not consider the impact it might have.
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Old 09-10-2012, 09:23 AM   #24
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Quote:
Originally Posted by Uncle Scotty View Post
the temperature of the upper surface of the ic is irrelevant

what is the temp of the LOWER surface???


the temperature of the air coming out of the ic outlet is, really, the ONLY relevant temperature to be discussed here.

all the rest is f00-f00
^^this

The surface temperature of the intercooler isn't necessarily a good indicator of how well it is working. It would be even better if could get an ic inlet and outlet temps and then use the differential to determine if the deflector is having any effect.
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Old 09-10-2012, 09:33 AM   #25
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Quote:
Originally Posted by V3rtigo View Post
^^this

The surface temperature of the intercooler isn't necessarily a good indicator of how well it is working. It would be even better if could get an ic inlet and outlet temps and then use the differential to determine if the deflector is having any effect.
Its not precise as having 2 sensors in and out of the ic i concur but surface temp surely has an impact as you can feel it hotter on the turbo side and it gets to ambient air temperature on the engine side.

Anyways ill get some stuff this evening ready and should be able to posr something on youtube with variable speeds with me gopro cam tapedbto the hood

Lol
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