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Old 06-19-2002, 01:24 AM   #1
Shaji
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Default ram air intake vs cold air intake

which one is better, which one is worse...or is there no difference?
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Old 06-19-2002, 11:02 AM   #2
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I think I read a post here about ram air being no good for turbos...I would be interested in the science behind it though...I am currently running an AEM cold air intake on my car.
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Old 06-19-2002, 06:27 PM   #3
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hey u wouldnt happen to have a link to that post would u?
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Old 06-20-2002, 03:28 AM   #4
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can anyone else help me out?
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Old 06-20-2002, 10:43 AM   #5
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ram air is useless on a turbo... because the turbo is doing the "ramming"

the priciple behind ram-air is to use the vehicles forward motion to force more air into the engine when the valves open... thereby pressurising the air in the cylinders to a higher pressure than standard atmospheric pressure...
effectively raising the compression ratio of the engine... (well, not really, but that is the same principle)

However, pressurizing the air is the same job that a turbo or supercharger does...

hope this helps...

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Old 06-20-2002, 11:09 AM   #6
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What trboCIVIC&WRX says makes sense and I agree that the turbo does the forcing. But I don't see how using the ram air principal to pressure stack the pre-induction side would be bad. We switch to ITG and K&N filters to lessen the pressure differential across the filter to get more power, why not help push the air in instead of having the turbo have to do all the sucking. I mean we are talking fractional performance gains with filter switching, so why not tinker w/ ram air or intake scoops.

I too would like to see that thread about ram air being detrimental to a turbo.
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Old 06-20-2002, 11:54 AM   #7
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Quote:
Originally posted by zaxrex
I too would like to see that thread about ram air being detrimental to a turbo.
so would i.....
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Old 06-21-2002, 12:45 AM   #8
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Using a ram-air intake on a turbo vehicle isn't detrimental, however, it's completely USELESS. Here's why:

Once air hits the turbine in the turbo, it doesn't matter how fast that air came in, it's now under complete control by the turbo. The pressure of the atmospheric air has changed by the turbo. Therefore meaning no matter how fast or how slow you get that air to the turbo, it doesn't matter as the turbo takes over the speed of the airflow.

Ramming air into the intake isn't doing a bit of good, it's like hitting a wall as soon as the turbo starts sucking.

The only slight bit of good ramming air into the intake might be is lower air intake tempratures.. which would be a minimal amount at that. Besides, an air-filter can only flow so many CFM before it clogs itself up and cannot flow anymore air. Once again, the "hitting-a-wall" effect in play.

Jay
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Old 06-21-2002, 05:07 AM   #9
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Sorry newbie question: So a Filter like blitz, hks would be useless to my WRX? Is ram air flowing inside the engine bay? Please excuse my newbieness hehe thanks.
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Old 06-21-2002, 05:59 AM   #10
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i was told that cold air is much better than ram air. and that if you could notice a difference in power, you'll notice more of a diffeence in the cold air intake.
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Old 06-21-2002, 08:14 AM   #11
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By ram-air could he mean short ram? That kind of comparison makes more sense.

Short ram (ie Blitz, MRT, etc) vs cold air (Injen, Aem, etc)?

Erik
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Old 06-21-2002, 08:27 AM   #12
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Quote:
Originally posted by Diversion
Using a ram-air intake on a turbo vehicle isn't detrimental, however, it's completely USELESS. Here's why:

Once air hits the turbine in the turbo, it doesn't matter how fast that air came in, it's now under complete control by the turbo. The pressure of the atmospheric air has changed by the turbo. Therefore meaning no matter how fast or how slow you get that air to the turbo, it doesn't matter as the turbo takes over the speed of the airflow.

Ramming air into the intake isn't doing a bit of good, it's like hitting a wall as soon as the turbo starts sucking.

The only slight bit of good ramming air into the intake might be is lower air intake tempratures.. which would be a minimal amount at that. Besides, an air-filter can only flow so many CFM before it clogs itself up and cannot flow anymore air. Once again, the "hitting-a-wall" effect in play.

Jay
You're wrong. A turbo's compressor is a pump. Any time you reduce the pressure differential the pump needs to generate (all things being equal), you reduce the energy needed by the pump. In our case, the wastegate opens more allowing silightly better exhaust flow. This is similar to all the other flow improving mods people make - by reducing flow losses, the overall system becomes more efficient.

That being said, I'm not going to run out and buy a ram air intake, though I might make some more modifications to the stock intake.

Kevin
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Old 06-21-2002, 09:54 AM   #13
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Thumbs up inatakes and thermodynamics

Here is my take on the intake situation. Your ram air intakes take air from in the engine bay, that is warm air. A cold air intake takes it from the fender well, with a signifigant lower temperature then the ambient air around the hot engine. This makes all the difference. When noting efficiency and power gains it is easy to see that a lower intake temperature leads to more efficiency and power. Using a basic carnot cycle to show what happens, this makes the low end temp lower, leaving more of a difference between the high and the low temps, and better power/efficiency. The whole priniciple of the air intake system is to keep temps low. Thats why you have an intercooler. Basically, you want the coolest air, and most pressurized, oxygen packed, air flowing into the cylinder so you can burn more fuel for more power. CAI is better. I think, granted I've only taken introductory thermodynamics and heat transfer.

~ken
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Old 06-21-2002, 09:57 AM   #14
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Quote:
Originally posted by Red Rocket


You're wrong. A turbo's compressor is a pump. Any time you reduce the pressure differential the pump needs to generate (all things being equal), you reduce the energy needed by the pump. In our case, the wastegate opens more allowing silightly better exhaust flow. This is similar to all the other flow improving mods people make - by reducing flow losses, the overall system becomes more efficient.

That being said, I'm not going to run out and buy a ram air intake, though I might make some more modifications to the stock intake.

Kevin
I was just going to say the same thing...

Picture what would happen if you had ram air hooked up and you disconnected the compressor from the hot side. As you went faster, the compressor wheel would actually start to spin by itself from the "rammed air" going through it.

So then hook the compressor back up to the turbine. Now the hot-side has to work that much less to get the compressor wheel spooled up, which has two effects. First, the amount of backpressure at the turbine would be reduced since it doesn't have to work as hard to spin the compressor up, and second, you will get full boost faster, allowing the waste-gate to open sooner, which allows air right past the turbine.

-B
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Old 06-21-2002, 02:19 PM   #15
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Would it be safe to assume that in 1st and 2nd gears, most of performance gains (however large or small) from an exterior scoop for ramming air to the filter side of the intake would be from a cool air source (not engine bay)? Then at higher speeds, >3rd, you get the benefit of the cooler air source plus any contribution of the pressure stacked air column?

Switching gears now

Since turbos donít have this direct harmonic thing to worry about (with the fan being in the way and all) the following has no bearing, but I read Pop Sci this month and there was a piece explaining how the new Lamborghini model made sick power. Air coming through the intake has some velocity to it as it get sucked into the engine. When the intake valves close, the air in that column hits a dead end and rebounds. They can variably modify the length of the intake tract (like a slide trombone, I guess) to make use of the "resonating" air and pressure fronts to force a bit extra into each of the cylinders.
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Old 06-21-2002, 05:05 PM   #16
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Quote:
Originally posted by WRXTACY
Sorry newbie question: So a Filter like blitz, hks would be useless to my WRX? Is ram air flowing inside the engine bay? Please excuse my newbieness hehe thanks.
blitz and hks are just filters, they utilize the stock intake system.
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Old 06-22-2002, 12:47 AM   #17
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Another thing to consider is if you plan on using a front mount intercooler, if i'm not mistaken (correct me if i'm wrong) but if you go with a cold air intake, and in the future decide to go with a front mount, you have to junk your cold air intake and go to a short stack, since the intercooler piping needs to go into the hole where the Injen/AEM intakes go into.

Jay
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Old 06-22-2002, 01:17 AM   #18
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OK, lets get our terminology straight here. A "Ram Air" intake is an external scoop that catches air, using the forward motion of the vehicle to pressurize the charge - like the big intake above the driver's head on an F1 or IRL car. A "Short Ram" is entirely different - don't know where the "ram" part came from (some marketing guy, perhaps?) but the "short" part come from the fact that it's basically just a filter bolted directly on to the throttle body, or in the case of a turbo car, directly to the turbo. Where the air is super hot - not so great.

Ram air might be a bit beneficial for reducing lag, but thats it. The computer will only let the system make so much boost - 13.7psi or whatever. It's not that the turbo get to make 13.7, then you could add in a few fractions of a PSI from the Ram Air. What is measured and controlled by the computer or MBC or whatever is manifold pressure - so the ram effect has no effect on boost and therefore power.

So what you really want is cold air, ram doesn't really help, and those short rams suck in all sorts of hot air.

That being said, it is my understanding that the Subie WRC cars employ ram air using the (vacated - they run FMIC) hood scoop. I would guess this is done to get good cool air nice and high up on the car - it wouldn't be a good idea to hit a deep water splash at speed with a CAI sucking in through those brake ducts at the bottom of the front bumper!

Last edited by chmoorewrx; 06-22-2002 at 01:28 AM.
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Old 06-22-2002, 01:58 AM   #19
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Ram air doesn't need a forward facing scoop. If the car didn't have a scoop in the hood alreadyyou could take air from the high pressure area at the base of the windshield like the early trans-am racing series Z-28 and Boss mustang.
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Old 06-22-2002, 05:58 AM   #20
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Actually, a Injen, AEM, K&N Typhoon intake's are Cold Air intakes.
The Blitz and HKS are short intakes or POD intakes, all of them are really not ram airs at all. Even though we call the shorty's short ram, and the fender CAI just a CAI. Yes colder air coming in is better, but some
people say that for a turbo, since our air is cooled by an intercooler that the intercooler cools the intake charge.
also they say a short sytle is better, because a turbo should in theory have the shortest path for taking in air, also if you upgrade
your TMIC,or get an FMIC to a more efficient unit, then it really
shouldnt matter on the type of CAI, or Pod Intake.
basically if you upgrade, the shortest intake should be better
for the turbo efficiancy than a longer route, of course this can depend on your mods and so on. plus if you ever get an FMIC
you will probably have to cut your Injen, or just use half of the K&N or the AEM. save the money and get an upipe for the same price. if you can install it yourself, then get a better intercooler
or just start out with any of the vendors like Cobb, Turbo-XS
or vishnu, all of those are great product,s and give good bang for the buck.

just my 02
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Old 06-22-2002, 06:19 AM   #21
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Simply put, if you plan on running a Front Mount Intercooler, get a Blitz SUS intake.. The big big big power WRXs are running the Blitz SUS, minus the Cobb WRX which is using the APS unit, which looks like a good unit too. If you plan to run the top-mount intercooler, i'd stick to AEM. I have a friend with an AEM, it's really nice, and the throttle response on his car is WAY WAY better than my car with the stock intake.

Jay
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Old 06-22-2002, 11:13 PM   #22
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AEM has a short ram coming out. it stays in the engine bay. do you guys think it would perform well?
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Old 06-23-2002, 01:46 AM   #23
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Quote:
Originally posted by AK_2002_WRX
AEM has a short ram coming out. it stays in the engine bay. do you guys think it would perform well?
it will pretty much be the same as other ram airs. So it will perform the same if it gives you any additional performance at all.
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Old 06-23-2002, 11:56 AM   #24
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Since the intercooler provides the majority of the cooling, it seems to me that a water spray kit would provide a better option for cooling intake charge. For instance, my car feels like it has more power on cool rainy days.

JC
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Old 06-23-2002, 12:19 PM   #25
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Default thermodynamics?

Theory to practice time.

Theoretically, The fenderwell is the best source of cold air, and sucking "hot" air from the engine compartment is bad.

In stop and go traffic, the engine compartment may heat up a bit. But as far as when you start moving, the ambient temperature where the short rams draw their air is not very much hotter than ambient. But it doesn't matter, not in a turbocharged car. Heres why.

The turbo, spinning at hundreds of thousands of RPM heats up. And it compresses the air. Both of these heat the incoming intake charge- 200+ degrees farenheit at times.

Now heres some more theory. The higher the temperature of the intercooler, or intake charge, the faster it will transfer heat out to the cooling air. The relationship is linear, as far as I know. That also goes the same for colder air entering the turbo- the colder it is, the more heat it absorbs.

So now that you've sucked in all that nice cold air, it's doing a very good job cooling down the turbo. It still comes out and goes through the intercooler at roughly the same temperature. And even if it is higher, the rate at which heat is drawn out in the intercooler will be higher, further narrowing that difference.

And this only matters when you first start off from a stop. A fairly long stop. The rest of the time, engine compartment temperature ~ ambient.

Practice - let the interCOOLER do its job better- invest in a water spray kit for those long stops and enjoy the increased throttle response of a short ram.

Chime back with any feedback you have, I'd hate to be acting smart and be all kinds of screwed up here.
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