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Better throttle response when air intake piece removed?

12K views 71 replies 21 participants last post by  Troy Jollimore  
#1 ·
Last night I decided to get off my lazy duff and go out to my car with the idea in mind of adjusting the right headlight. It wouldn't adjust and upon further inspection the gears weren't meshing together. On the passenger side of the car the air intake plastic tube is right there making it hard to see.

I won't go into the whole headlight deal...that's a NEW beef I now have with CarMax (to add to a couple others).

The reason I'm posting is this. Once I had the plastic inlet tube off I was curious as to what it sounded like without it. Since I have a 99 AEB I just fiddled with the throttle cable and I was right...the intake made more noise and the engine sounded a little throatier.

I figured hell, why not go for a short drive and see how this affects performance. It seemed to have slightly better throttle response and the car sounded better. However, this was late at night so the air was for the most part cool (65 deg F or so). I decided to leave the plastic tube off the car during the day today to see how the heat would affect the car's performance. This afternoon it was around 80 deg F here in Ft.Wayne.

For some reason the heat didn't seem to affect performance at all, in fact it again seemed to have better throttle response overall. I could hear the engine more, including the turbo spooling, and the throatier sound was of course still there.

Maybe someone else can shed some light on this. My reasoning for it is this. Since the air inlet is still in place cool outside air is still being directed into the engine bay there is just no restrictive tube to direct it straight into the intake. Now since the shape of the air inlet directs air towards the air box the intake is still getting fresh, cool outside air. There is just nothing to restrict the intake now.

I drove rather spiritedly around and then opened the up the hood. There was a lot of heat on the engine bay side but not so much around the intake. Of course a better heatshield could be fabricated to further shield the intake from heat but it's pretty decent as it is.

Am I just crazy or have I stumbled upon something interesting? :crazy:
 
#3 ·
P1.8T said:
ive seen this on hondas alot , but not sure if its good to do on our cars , hopefully someone can elaborate on this subject

BUMP
Yeah?

*shrugs*

I know it won't throw any CELs so it's not detrimental in that sense. I am more concerned about sucking in hot air that will rob the engine of performance.
 
#4 ·
On the B5.5 or later year B5, there is little flap on the bottom of the airbox and I'm running it without. So I have the ram air from the air duct and get some extra from other........ and I think it runs better this way. Others might say you're pulling in hot air but if you feel the difference without it, then run without it.




Josh
 
#6 ·
Ok I guess I wasn't specific enough. Here's the order of the pieces in my intake.

1. Small plastic air inlet that is screwed onto the bumper.
2. Intake tube that runs from the air inlet into the airbox.
3. The airbox itself.

The piece I removed was #2. Basically, my intake looks like this picture. Don't pay any attention to the letters, it's from another thread.

The air inlet functions to throw air in the general direction of the airbox which sucks in ambient air. Another bonus to removing this piece is that with the slush screen removed any debris will just get thrown into the engine bay and will probably fall out of the car instead of being thrown into the actual airbox.

Image
 
#10 ·
shaboinkit22 said:
hey i just tried that, didnt really notice a difference in sound but throttle response is a tad better. Maybe its all in my head idk
Exactly what I was thinking. The sound is better, but I noticed it on a late night drive without the radio playing and the windows down. During normal driving circumstances the sound is not really that noticable.

Throttle response seems better but I wouldn't be surprised if actual HP has decreased due to the medium-hot air intake temp.

However, one has to wonder if a properly made heatshield would protect the incoming air temp well enough. You'd in essence have a less restrictive, somewhat OEM CAI without having to modify virtually anything. Not to mention it'd be much cheaper than those $300 CAI that suck in hot air.

I like the idea behind the OEM airbox/intake but it still just feels restrictive. I think that this along with the COAM would be really really kickass.
 
#11 ·
ycharlies said:
you've indeed stumbled upon something! instead of CAI, it's the HAI!
Hey no need for sarcasm. It was just an honest idea that I wanted to test out and get some feedback from the community. I knew that it would suck in heat. I just wanted to see if it could be made to not suck in heat and save money.
 
#12 ·
pimpin passat said:
yeah im wondering the same thing, is the heat a problem in this factor. i want to try it atleast, but will it damage it?
Nah doesn't damage at thing I wouldn't think. The plastic piece/tube isn't even secured in place by screws or clips. It just snaps into place. You could just yank it out if you wanted to and you wouldn't damage anything.
 
#15 ·
shuPASSAT said:
Cold air or hot air they all get heated up once it goes through turbo. I don't think that little bit of temp difference is gonna change anything.




Josh
Yup. The other issue is this... if it is really less restrictive (which I don't think it is) any gain is offset by the change in temp. The other issue is whether or not you are getting as much positive pressure on the intake at say 30 mph. The narrowest point in the ducting is right above the pre-screen where that elbow fits except now you aren't generating positive air pressure off the air dam at that joint at speed. You would be pulling air from a neutral pressure source now as all the positive pressure off the dam is dispersed in the entire engine bay.

I'm not trying to be sarcastic or anything here but I fully expect that any gain is completely wishful thinking. In theory it should only hurt performance. Maybe it is louder... Is that the goal? I pay alot of money to have a car that DOESN'T make a racket. Why de-engineer your car to make more noise? That seems silly. My $0.02
 
#16 ·
shuPASSAT said:
Cold air or hot air they all get heated up once it goes through turbo. I don't think that little bit of temp difference is gonna change anything.




Josh
I don't think the air lingers in the turbo that long .. and to be hypothetical if the turbo added lets say 3 deg to the air temp as it passed through it and the ambient temp under the hood was 140 deg .. end result .. 143 deg .. ambient temp outside was 80 deg .. end result 83 deg .. cooler air is denser.
 
#17 ·
You make an interesting point about the positive air pressure. But how much does the car rely on that for performance...why exactly would it hurt performance to take that away? The reason I ask is because if what you say is true, then every car in the world (not just passats) that run CAI's that aren't setup to get a positive airflow (ie, Ram Air right?) should be hurting performance wise.

Also, when it comes to pulling neutral flowing air out of the engine bay, wouldn't our cars (or any others that are turbo/supercharged) be at a natural advantage? My reasoning is this. A fast spinning turbine is going to increase pressure on the outgoing end of the charger, but that also means that it's drawing in that much more air. So in my theory, if the charger is increasing air pressure by say 4x then it's sucking 4x the amount of air and therefor creating a much larger vacuum. If this is right then pulling in neutral flowing air shouldn't even be an issue. Besides, even with the OEM plastic tubing in place, all of the kinks and paths that the air has to travel through woulld negate any effects of the positive air pressure rather quickly. To really make the best use out of a ram air type intake you 1.) have to be traveling rather quickly, about 50mph+ --- I even think there was a study done at one time about this, and 2.) you have to have a very straight, smooth and unrestrictive path for the air to flow RIGHT into the intake manifold.

Now regarding intake temps, it seems some people are saying it matters and some are saying it doesn't. I for one believes that it does. Colder air is of course denser air and you're able to pack more of it into a smaller space naturally. The MAF sensor is going to account for this and adjust fuel accordingly. You're going to be able to pack more into the turbo initially. Sure it may heat up and have to be cooled by the intercooler but the initial intake of air is all I'm concerned about here. This is because basically the more air you can have enter the turbine the more air comes OUT of the turbine and that amount of air is dependent on air pressure.
 
#18 ·
hehe just kidding. i still think more testing is required before you can confirm if this is beneficial for performance. let us know!



LateAPXR said:
Hey no need for sarcasm. It was just an honest idea that I wanted to test out and get some feedback from the community. I knew that it would suck in heat. I just wanted to see if it could be made to not suck in heat and save money.
 
#19 ·
I'll try to test it as much as I can. I believe I have an old temp probe laying around somewhere. I'll try to place it in the intake and run it back into the cabin to get some temps. I'll post them when I get them.

Oh that reminds me of something I had wanted to ask on the boards.

Where is the temp probe that the MFA uses for it's temperature readout located in the car? That doesn't use a reading taken from the MAF sensor by any chance does it? That would be interesting if it did since 1.) your outside air temp would never be 100% accurate and 2.) people like us would benefit from knowing that temp reading :)

Anyone know?
 
#20 ·
LateAPXR said:
Where is the temp probe that the MFA uses for it's temperature readout located in the car? That doesn't use a reading taken from the MAF sensor by any chance does it? That would be interesting if it did since 1.) your outside air temp would never be 100% accurate and 2.) people like us would benefit from knowing that temp reading :)

Anyone know?
Youtalking about the one that displays the outside temp? Its in behind the front bumper .. and accuracy would depend on a bunch of factors .. if your sitting still it causes many variables .. pavement temp .. radiated radiator heat etc .. but moving mine is very accurate . I borrowed a corrected digital with a remote probe from work and checked it at the 80 F range and the 30 F range .

Do a search on D-Zigner he moved his up to the intake to show those readings ..
 
#22 ·
LateAPXR said:
You make an interesting point about the positive air pressure. But how much does the car rely on that for performance...why exactly would it hurt performance to take that away? The reason I ask is because if what you say is true, then every car in the world (not just passats) that run CAI's that aren't setup to get a positive airflow (ie, Ram Air right?) should be hurting performance wise.

Also, when it comes to pulling neutral flowing air out of the engine bay, wouldn't our cars (or any others that are turbo/supercharged) be at a natural advantage? My reasoning is this. A fast spinning turbine is going to increase pressure on the outgoing end of the charger, but that also means that it's drawing in that much more air. So in my theory, if the charger is increasing air pressure by say 4x then it's sucking 4x the amount of air and therefor creating a much larger vacuum. If this is right then pulling in neutral flowing air shouldn't even be an issue. Besides, even with the OEM plastic tubing in place, all of the kinks and paths that the air has to travel through woulld negate any effects of the positive air pressure rather quickly. To really make the best use out of a ram air type intake you 1.) have to be traveling rather quickly, about 50mph+ --- I even think there was a study done at one time about this, and 2.) you have to have a very straight, smooth and unrestrictive path for the air to flow RIGHT into the intake manifold.

Now regarding intake temps, it seems some people are saying it matters and some are saying it doesn't. I for one believes that it does. Colder air is of course denser air and you're able to pack more of it into a smaller space naturally. The MAF sensor is going to account for this and adjust fuel accordingly. You're going to be able to pack more into the turbo initially. Sure it may heat up and have to be cooled by the intercooler but the initial intake of air is all I'm concerned about here. This is because basically the more air you can have enter the turbine the more air comes OUT of the turbine and that amount of air is dependent on air pressure.
And that's why you realize people cut their airboxes and add additional inlets . . .
 
#23 ·
Ambient temp probe is infront of the radiator, near the bottom of the radiator.

Intake temp probe is in the throttle body.

IMHO, the turbo adds more than 3 degrees F to the intake air temp... When driving aggressively, I see IAT temp variations of 10 degrees C or more (>18F) when logging data with my vag-com. ...of course once the SMIC heat soaks, the IAT stays high.

I've done about 1/2 of D Zinger's "IAT displayed on the MFD" mod. I think I'm going to tap into the intake stream on the snorkel hose to take data.
 
#24 ·
Jesstzn said:
Youtalking about the one that displays the outside temp? Its in behind the front bumper .. and accuracy would depend on a bunch of factors .. if your sitting still it causes many variables .. pavement temp .. radiated radiator heat etc .. but moving mine is very accurate . I borrowed a corrected digital with a remote probe from work and checked it at the 80 F range and the 30 F range .

Do a search on D-Zigner he moved his up to the intake to show those readings ..
Ahhh....very cool. I'll make sure to do that search. I've noticed myself that the outside temp goes up when sitting still. I've never seen a car that doesn't do that. Nice to know where it's located though.

Guess I'll be hooking up my own thermal probe. Stay tuned for details, I'll soon find out exactly how hot that intake gets.
 
#25 ·
LateAPXR said:
You make an interesting point about the positive air pressure. But how much does the car rely on that for performance...why exactly would it hurt performance to take that away? The reason I ask is because if what you say is true, then every car in the world (not just passats) that run CAI's that aren't setup to get a positive airflow (ie, Ram Air right?) should be hurting performance wise.

Also, when it comes to pulling neutral flowing air out of the engine bay, wouldn't our cars (or any others that are turbo/supercharged) be at a natural advantage? My reasoning is this. A fast spinning turbine is going to increase pressure on the outgoing end of the charger, but that also means that it's drawing in that much more air. So in my theory, if the charger is increasing air pressure by say 4x then it's sucking 4x the amount of air and therefor creating a much larger vacuum. If this is right then pulling in neutral flowing air shouldn't even be an issue. Besides, even with the OEM plastic tubing in place, all of the kinks and paths that the air has to travel through woulld negate any effects of the positive air pressure rather quickly. To really make the best use out of a ram air type intake you 1.) have to be traveling rather quickly, about 50mph+ --- I even think there was a study done at one time about this, and 2.) you have to have a very straight, smooth and unrestrictive path for the air to flow RIGHT into the intake manifold.

Now regarding intake temps, it seems some people are saying it matters and some are saying it doesn't. I for one believes that it does. Colder air is of course denser air and you're able to pack more of it into a smaller space naturally. The MAF sensor is going to account for this and adjust fuel accordingly. You're going to be able to pack more into the turbo initially. Sure it may heat up and have to be cooled by the intercooler but the initial intake of air is all I'm concerned about here. This is because basically the more air you can have enter the turbine the more air comes OUT of the turbine and that amount of air is dependent on air pressure.
What it really comes down to is pretty simple... the potential gain here would be so minimal that it's really moot. There is however a greater potential for loss. Doing a series of real tests would be interesting however. In regard to a CAI being more productive despite it not drawing directly off the air dam? It makes gains in other aspects. Larger inlet diameter, larger surface area, less frictional loss in the piping etc... it doesn't mean it isn't a loss to not have positive pressure on the inlet it just means that the loss is mitigated by gains.
I'm also talking hard theory here. Without doing a full analysis on volume of air over time, air temps, volume drawn at given RPM ranges etc... you won't get a concrete answer. VW however did this work to the tune of hundreds of thousands of dollars. The result? The airbox that has piping directly to the airdam. I wouldn't do it.
 
#26 ·
been wanting to experiment with mine....the late-model b5.5's have the intake pipe inlet covered up in the grill..thinking about making a scoop or something to pull in the air from the grill and shield the inlet from the hot radiator core. The secondary air inlet mod (flapper) might be cool to try as well.

you should log MAF and inlet air temp before and after, that will tell you if you've "improved" anything