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Old 03-30-2001, 01:08 PM   #1
Hashiriya
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Exclamation Front mount vs Top mount intercooler

I know that Jun, Aqua, Zero Sports, Bozz Speed, A-pro, Alpha, Cusco?(I think), and many more make front mount intercooler kits for the GC8 in Japan. Now that means there has to be benefits for it.

<FONT size="4">Now Share your opinions and knowledge for the i-club!</FONT s>

so US vendors will start making some here.

[This message has been edited by Hashiriya (edited March 30, 2001).]
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Old 03-30-2001, 01:34 PM   #2
Turk
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This is the lil I know

Top Mount= Less Turbo lag but less mid range plus heat soak

Front mount= more turbo lag but better mid range
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Old 03-30-2001, 01:49 PM   #3
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Top mount: protected from damage, shorter intake tract for less lag, limited overall size restriction due to placement, more air to the radiator for better engine cooling.

Front mount: better max airflow to intercooler, bigger overall size as well, engine will run hotter due to less flow and hotter air flow to radiator, can be damaged from road debris.

Basically, if you aren't pushing 400+hp you don't have a need for a front mount intercooler. An upgraded top mounted system with an auto water misting system and an STi hoodscoop will be more than enough for 350hp.
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Old 03-30-2001, 01:52 PM   #4
DanMan
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Each has its advatages and disadvantages. An intercooler is in essence a large heat sink. In the front of the car you can put a larger intercooler with very high surface area to volume ratio. This allows for the greatest amount of heat disipation. Also, with the large frontal area, cooling is helped by air passing through the intercooler.

However, to place the front mount on the car you need to add a large amount of piping from the turbo and back to the intake. This ads lag (less throttle response from the increased area the air needs to travel). Also, you can run into smoothness problems as the MAS calculates air flow some 10 ft from the actual engine intake. Also, with larger intercoolers there is an actual pressure drop that occurs which can also cause more lag and confuse the ECU (this can be worked around with software if neccesary).

Top mount intercoolers are good for a number of reasons. They need very little piping and are relatively cheap to make (less piping).

The front mount is really MUCH better if you are running high horsepower. But they are very hard to make and cost a good deal of money.

HTH,
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Old 03-30-2001, 03:03 PM   #5
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Yep. What WRXRob says. he is ABSOLUTLY right.

Eugene
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Old 03-30-2001, 03:56 PM   #6
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Lightbulb

The FMIC is the most efficient way to cool air as it is outside the engine bay. You can use a Water to air but I don't care for that. Lag is a factor but after you are in the boost you don't really have lag until you get into cruise mode again. I believe in FMIC and FHI believes in TMIC. Its a standard that FHI uses to make the Impreza cost efficient. If you are running 10+ psi on a stock EJ25 then its a good idea to run a FMIC, anything less will do fine with a TMIC. Of course you will make power with either one, its just a matter of what you believe is the best way to cool recycled exhaust gas. I will be running a FMIC in my RS because I will be using the EJ22T and the engine is setup differently than the EJ25. The compression is turbo friendly, therefore to make power, you have to run higher Pressure, so lag will not be as significant when using a FMIC, although it will be more than a TMIC. Of course by having lower compression, spool up is not as fast and lag is increased but that is a characterisitic of a turbo vs. a supercharger. I don't know of many people in the US with FMIC's in their impreza but its used around the world as you mentioned in your first post.
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Old 03-30-2001, 05:50 PM   #7
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Please educate me. Why would the longer ducting associated with a front mount IC cause slower spool up? The turbo itself is in the same location as for a top mount and is going to spool up the same. The longer plumbing causes greater pressure drop than a top mount which might mean a bit less power (everything else being equal) plus it takes a fraction more time for the compressed air to reach the intake which might relate to slightly more lag. But turbo spool up would not be affected by the IC location, would it?
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Old 03-30-2001, 07:33 PM   #8
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harrydog,

You're quite correct. Turbo lag itself does not increase, but intake lag increases. It takes more time for the turbo to pressurize the longer air intake tubes and the bigger intercooler. Also, the bigger the intercooler, the larger the psi drop across the intercooler, so it is a double whammy, longer time to pressurize the system, and a higher absolute pressure required to create same boost level in the cylinders.
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Old 03-30-2001, 09:26 PM   #9
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Yeah, but where are you using? For me it'll be a front mount first chance i get since i'm using primarily in the city (NYC metro). heat soak is worse than spool up. a constant 30 mph or above should negate that, but I won;t have that luxury. so, front mount for heat dissipation seems good to me. sure you'll say what am I doing with such a car in the city, but I figure if a car can handle a rally, it damn well better hadnle city hazards where I have a less than a mile between lites.

jmho,

curt
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Old 03-30-2001, 10:30 PM   #10
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Yes, but your engine will run noticeably hotter.

Why not just do the top mount upgrades I suggested above? FMIC's suffer from heatsoak as well, a sprayer is a more cost effective solution.
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Old 03-31-2001, 04:37 AM   #11
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Better air, but more rocks and water...
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Old 03-31-2001, 10:03 AM   #12
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Interesting...

Well do you all think US vendors will start making FMIC sets for the WRX or RS?
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Old 03-31-2001, 10:04 AM   #13
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You can see right through my FMIC, So I don't know how it will decrease the radiator's effieciency?
Zee
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Old 03-31-2001, 11:31 AM   #14
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An FMIC will definatly decrease radiator efficiancy. But, you can always upgrade the fans and radiator. I have run them on Hondas and had no issues at all.

Even with that said, I still plan to stay top mount, over time the front mount takes a lot of abuse. This leads to reduced efficiancy for both the IC and cooling.
I think an STI or BPM top mount will do me with a water sprayer.

Ken
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Old 04-02-2001, 06:06 PM   #15
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In a previous thread which I can no longer find, I recall some people arguing that the addition of an aftermarket IC in and of itself would show no power gains.
In Autospeed's continuing series on enhancements for the WRX, they cover aftermarket IC's. The top mount unit from BPM is a bar & plate design which gives 40% better heat sink capacity than the standard unit as well as less pressure drop.
Even more impressive, the top mount bolt on replacement unit from AVO is also a bar & plate design and it has been proven to reduce an otherwise stock WRX's 1/4 mile time by 0.3 seconds and increase the trap speed by 4 mph. It gives 1/3 less pressure drop than stock.
These figures are for the previous generation WRX but when the IC's for the current version are available, they will most likely give similar results.
These units are not cheap but these gains are significant and reliability will actually be increased if anything.
I'm convinced that with an exhaust change and maybe one of these IC's, I can get as much power as I was hoping for without any ECU changes and keep engine durability as good as stock.
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Old 06-25-2012, 02:23 PM   #16
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Default both maybe??!!

could you in theory do both a top mount and a front mount?
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Old 06-25-2012, 02:41 PM   #17
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Quote:
Originally Posted by rexsubie46 View Post
could you in theory do both a top mount and a front mount?
Holy old thread.

Yes, you could run both, I'm just not sure why you'd want to. You would be increasing the volume of the system. FMIC+mist is plenty cool.
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Old 06-25-2012, 04:54 PM   #18
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Quote:
Originally Posted by rexsubie46 View Post
could you in theory do both a top mount and a front mount?
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Old 06-25-2012, 06:06 PM   #19
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Quote:
Originally Posted by rexsubie46 View Post
could you in theory do both a top mount and a front mount?
Well.... not in the way you are probably thinking LOL

But you could do a Top mount Watercooled intercooler which requires a Front mount Heat exchanger. It makes it look as though you have both hahaha. I actually had a guy ask me why I had 2 intercoolers at a Subie meet in So cal.... I didnt have to say anything because the rest of the crowd laughed enough that he knew he was being a Newb.
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Old 06-26-2012, 09:44 AM   #20
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Here is a related question....

On a normal stg 2 2.0L
tbe
up pipe
GS 3 port
tune

I am running the wrx stock tmic, would upgrading to a sti tmic be better at all or just save the monies for something else?
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Old 06-26-2012, 10:30 AM   #21
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depends what you get that sti tmic for.
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Old 06-26-2012, 03:29 PM   #22
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Quote:
Originally Posted by UK-Wagon
Well.... not in the way you are probably thinking LOL
Sure you could. Reverse manifold setup, run through the tmic first. Not saying its a good idea, interesting concept though.
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Old 06-26-2012, 03:42 PM   #23
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Originally Posted by super_usdm View Post
Sure you could. Reverse manifold setup, run through the tmic first. Not saying its a good idea, interesting concept though.
The gains would be minimal as you cannot cool past the lower temp boundry of the gradient, ie. the outside temp. There is no such thing as a >100% efficient air to air intercooler.
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Old 06-26-2012, 03:48 PM   #24
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Not to be Johnny Law, but FMIC/TMICs are illegal in some states, so you may want to consider that when making your decision. Here in good ol CA, you get pulled over and have to go back to stock if you are caught with an illegal intake/intercooler/exhaust.

I like TMIC's for the reasons stated above and to keep a relatively stock appearance. I had an APS TMIC on my bugeye and it made a nice difference with the "stage 2" stealthback system.
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Old 06-26-2012, 04:04 PM   #25
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The only time you "need" a FMIC is when your turbo is big enough, to need a bigger IC core that can be fitted under the scoop, as for heat-soak there's ways around it that work good enough to not have any Heat-soak issues even with the TMIC... Water sprayer, turbo blankets, header wrap, hood vents, insulation... Any of them will help, do all, and your TMIC efficieny can be as good as a FMIC...
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