Ram air on the M...a waste?

[ace996]

So I took apart the airbox looking for some 'free' ways to increase flow. While the top of the box was off, I really considered the design and have some doubts about the efficiency of the 'ram' effect with the stock box and with the aftermarket scoops. I love the lower scoop (fog-light location) and the intake at the kidney grills, surely they will allow some 'ram' effect but the top opening...the driver's side nostril, I believe, is the problem.

My thought is that the driver's side hood nostril will let any additional ram air pressure out of the box. I don't see that opening creating any positive pressure for the intake, just another place for air to be ingested at high rpm. I really wonder if the hood nostril inlet was closed-off that airbox pressure would be higher at higher speeds.

Your thoughts?

[Sticky]

Not a waste, I feel a difference as soon as it cools down (night).

[BimmerRob08]

I'd guess it would be best if a BMW engineer that designed the air box could comment on why they designed it as such. But I think and this is comming from my turbine technical back ground. Massive airflow injested will create high pressure as we all know. But for example, when the turbine engines are starting up, decelerating, and at lower rpm's the compressors have to "bleed" off some of the air that is originally injested from the intake. Only at higher rpm % do the bleed off valves close to allow full consumption of the airflow. So I'm thinking that the concept is the same here where at lower speeds/rpm's the air is allowed to flow without being backed up in a closed airbox. at high speed/rpm's where the engine needs all the air it can get, the airbox probebly allows the max air flow by creating a vacuum at the hood opening by suction. I don't think the M3 airbox was designed to gather air and compress it but to allow the maximum airflow across the filter. Just my technical guess but I cold be wrong. Maybe on a dyno one should seal it off and see what happens.

I do wonder why BMW built to inlet scoops and two opening at the hood although one is functional. I know there is a V10 M5 kit and the engine uses both air scoops/hood outlets but I wonder if BMW have another idea down the road??

[ihyln]

The top nostril or vent, the drivers side in particular, is actually a vent. I noticed this one day when a leaf got sucked into the lower intake and with the way it was stuck I realized that it's simply a vent and not another intake

[lucid]

Originally Posted by BimmerRob08

I'd guess it would be best if a BMW engineer that designed the air box could comment on why they designed it as such. But I think and this is comming from my turbine technical back ground. Massive airflow injested will create high pressure as we all know. But for example, when the turbine engines are starting up, decelerating, and at lower rpm's the compressors have to "bleed" off some of the air that is originally injested from the intake. Only at higher rpm % do the bleed off valves close to allow full consumption of the airflow. So I'm thinking that the concept is the same here where at lower speeds/rpm's the air is allowed to flow without being backed up in a closed airbox. at high speed/rpm's where the engine needs all the air it can get, the airbox probebly allows the max air flow by creating a vacuum at the hood opening by suction. I don't think the M3 airbox was designed to gather air and compress it but to allow the maximum airflow across the filter. Just my technical guess but I cold be wrong. Maybe on a dyno one should seal it off and see what happens.

I do wonder why BMW built to inlet scoops and two opening at the hood although one is functional. I know there is a V10 M5 kit and the engine uses both air scoops/hood outlets but I wonder if BMW have another idea down the road??

This is a plausable explanation. But with the turbine design you are referencing, there are valves that control flow. Are there any valves in the M3 intake system? To the best of my knowledge, there aren't. It could be that flow at the hood opening simply reverses direction when the engine demands more air and the cylinders suck/pump more air in. I've been meaning to stick sensors in the intakes and driver around collecting data, but haven't gotten around to it. Maybe during Thanksgiving break...

I sounds like for whatever reason the single functional hood opening gave them what they were after. Making the other one functional as well might have produced undesired results.

[ace996]

Originally Posted by Sticky

I feel a difference as soon as it cools down (night).

I suspect that what you feel is the cool air making the difference, if it were the scoops then you'd feel it all the time.


So it's raining a bit here in NY today and I took the car out. I noticed that any water surrounding/on top of the hood nostril was forced up/out of the opening, as there seems to be decent positive pressure from the box whilst at speed.

It stands to reason that the grill-scoops would help combat any negative pressure created at high rpm/load but I have a suspicion that they would work better if there wasn't a "leak" out the hood. I feel that the scoops are not so much a 'ram-effect', adding power, but work by reducing the vacuum of the airbox at high rpm/loads.

I would think that the best "intake-mod" for the car would be a scoop (something similar to an STI's hood scoop...obviously much smaller or a NACA duct which would be much more visually appealing IMHO) that would allow the hood nostril to actually function as a positive pressure influence on the box, instead of a negative pressure producer as itsits now.

Even a small lip at the rear of the opening would help reduce the vacuum-effect.

Now where did I put that fiberglass and resin...

[PunjabiM3]

Originally Posted by ace996

I suspect that what you feel is the cool air making the difference, if it were the scoops then you'd feel it all the time.


So it's raining a bit here in NY today and I took the car out. I noticed that any water surrounding/on top of the hood nostril was forced up/out of the opening, as there seems to be decent positive pressure from the box whilst at speed.

It stands to reason that the grill-scoops would help combat any negative pressure created at high rpm/load but I have a suspicion that they would work better if there wasn't a "leak" out the hood. I feel that the scoops are not so much a 'ram-effect', adding power, but work by reducing the vacuum of the airbox at high rpm/loads.

I would think that the best "intake-mod" for the car would be a scoop (something similar to an STI's hood scoop...obviously much smaller or a NACA duct which would be much more visually appealing IMHO) that would allow the hood nostril to actually function as a positive pressure influence on the box, instead of a negative pressure producer as itsits now.

Even a small lip at the rear of the opening would help reduce the vacuum-effect.

Now where did I put that fiberglass and resin...

Hate to say it, but I am sure the BMW engineers have a lot more knowledge in this area than yourself or just about anyone on this forum. If using the hood scoop/vent as a ram-air or not having it altogether would have yielded 5 or 10 more hp, I am sure they would have designed the intake in that fashion instead.

[Sticky]

Originally Posted by ace996

I suspect that what you feel is the cool air making the difference, if it were the scoops then you'd feel it all the time.


So it's raining a bit here in NY today and I took the car out. I noticed that any water surrounding/on top of the hood nostril was forced up/out of the opening, as there seems to be decent positive pressure from the box whilst at speed.

It stands to reason that the grill-scoops would help combat any negative pressure created at high rpm/load but I have a suspicion that they would work better if there wasn't a "leak" out the hood. I feel that the scoops are not so much a 'ram-effect', adding power, but work by reducing the vacuum of the airbox at high rpm/loads.

I would think that the best "intake-mod" for the car would be a scoop (something similar to an STI's hood scoop...obviously much smaller or a NACA duct which would be much more visually appealing IMHO) that would allow the hood nostril to actually function as a positive pressure influence on the box, instead of a negative pressure producer as itsits now.

Even a small lip at the rear of the opening would help reduce the vacuum-effect.

Now where did I put that fiberglass and resin...

No, I wouldn't. When its 95 degrees out the air being "rammed" in isn't exactly cold.

I feel more of a difference when it cools down with the scoops and filter than I did without them. The scoops aren't really a low end mod they really kick in at freeway speeds.

[GT3 Tim]

Originally Posted by ihyln

The top nostril or vent, the drivers side in particular, is actually a vent. I noticed this one day when a leaf got sucked into the lower intake and with the way it was stuck I realized that it's simply a vent and not another intake

That has happend to me several times. Mostly with "hay trucks". lol. I will be driving then all of the sudden there is some straw poking up throught the hood vent! lol. They all come from the intake track and get stuck "on their way out" of the intake track in the hood vent.

Under full load, who knows....maybe it sucks a bit from the hood vent. I dunno.., However, the idea of "pressurizing" the intake track is a joke if there is an opening in a lower pressure area (the hood vent). You may be able to hold a slightly higher than nominal pressure in the intake track, but with that hood vent open, I doubt you could even measure it.

Now, block off the hood vent and I bet you would see some pressure in there. It would be a worthy experiement for somebody that has the equipment. I wish I did, I would try it.

[ace996]

Originally Posted by PunjabiM3

Hate to say it, but I am sure the BMW engineers have a lot more knowledge in this area than yourself or just about anyone on this forum. If using the hood scoop/vent as a ram-air or not having it altogether would have yielded 5 or 10 more hp, I am sure they would have designed the intake in that fashion instead.

Yep, and they've designed every part of the car for ultimate performance, right? The extra cats, the rubber suspension bushings, the charcoal filters integrated into the air-filters...all are compromises...just like the nostril on the hood.
I suspect that the engineers that you so fondly speak of had to incorporate those hood nostrils on the car for visual purposes, as it is one of them are faux.

I've been around the block enough times to know that a hole in an airbox is not optimal. Thanks for your thoughts, though.

[GT3 Tim]

Originally Posted by lucid

It could be that flow at the hood opening simply reverses direction when the engine demands more air and the cylinders suck/pump more air in. I've been meaning to stick sensors in the intakes and driver around collecting data, but haven't gotten around to it. Maybe during Thanksgiving break...

You are prolly correct. Thinking of what you said, I had a thought....

If you installed a one-way valve (or louver!), the car could suck air through the hood vent if it needed to. But when the ram effect of the two front intakes (or scoops) starts to have a positive pressure effect on the intake tract, the louvers would not allow that air to escape through the hood vent.

I would be interested to see your pressure data when you get around to it.

It would be interesting to see a baseline (stock), one with stock config but with scoops, one with stock config but with hood vent blocked, and one with scoops and hood blocked.

I bet if one way louvers or something similar was intalled on the hood, you would see a larger pressure gradient in the intake tract at speed. The scoops may add to it. That would be a good way to see what the hood vent does at speed, and what the scoops do also (in stock form and with blocked (or in effect, louvered) hood vent).

Worth a shot.

BTW, copyright on the louvered one-way hood vent idea!

[ace996]

Originally Posted by GT3 Tim

If you installed a one-way valve (or louver!), the car could suck air through the hood vent if it needed to. But when the ram effect of the two front intakes (or scoops) starts to have a positive pressure effect on the intake tract, the louvers would not allow that air to escape through the hood vent.

Great idea and similar to what Audi did it in my past 2001 A4 1.8T. There was a spring-loaded flap that kept the airbox sealed unless intake vacuum was strong enough to open it. The cheap "free" intake mod was to remove the spring and flap and let the air freely flow...the turbo did all the "ramming of air".

Great idea, though, and if it could be hidden under the nostril it should...in theory...work to great effect.

[lucid]

Originally Posted by GT3 Tim

You are prolly correct. Thinking of what you said, I had a thought....

If you installed a one-way valve (or louver!), the car could suck air through the hood vent if it needed to. But when the ram effect of the two front intakes (or scoops) starts to have a positive pressure effect on the intake tract, the louvers would not allow that air to escape through the hood vent.

I would be interested to see your pressure data when you get around to it.

It would be interesting to see a baseline (stock), one with stock config but with scoops, one with stock config but with hood vent blocked, and one with scoops and hood blocked.

I bet if one way louvers or something similar was intalled on the hood, you would see a larger pressure gradient in the intake tract at speed. The scoops may add to it. That would be a good way to see what the hood vent does at speed, and what the scoops do also (in stock form and with blocked (or in effect, louvered) hood vent).

Worth a shot.

BTW, copyright on the louvered one-way hood vent idea!

I am sure they would have used a valve if there wasn't something else keeping them from doing so. Or maybe there is some kind of a primitive valve and we don't know about it. It is hard to think why they wouldn't want slightly more air/combustion in the cylinders. Maybe emissions related. We would need to see some data to know that the hood opening is indeed acting like a vent though at least some of the time. Leaves getting stuck there or what people observed when the car is stationary is not evidence. I'll try to get around to collecting the data soon...

[808MGuy]

Originally Posted by ace996

Yep, and they've designed every part of the car for ultimate performance, right? The extra cats, the rubber suspension bushings, the charcoal filters integrated into the air-filters...all are compromises...just like the nostril on the hood.
I suspect that the engineers that you so fondly speak of had to incorporate those hood nostrils on the car for visual purposes, as it is one of them are faux.

I've been around the block enough times to know that a hole in an airbox is not optimal. Thanks for your thoughts, though.

On that train of thought, if the one functional side didn't do anything, why make one functional and one not. Just make both cosmetic only to save money on ducting. It obviously there for a reason. What that reason is will be hard to determine without actually being part of the design process. The beauty of engineering is that there is never only one right way to do things. The ultimate goal can be accomplished multiple ways.

[Ronin13]

As Pencil stated earlier in the thread, he observed a vacuum at the top vent under full engine load. So, it appears to serve a purpose to support top end CFM requirements.

[lucid]

Originally Posted by Ronin13

As Pencil stated earlier in the thread, he observed a vacuum at the top vent under full engine load. So, it appears to serve a purpose to support top end CFM requirements.

That's for a stationary vehicle (with some artifical airflow directed at the front it sounds like). We don't really know what happens in a real situation at high speeds when the front facing intake really begins to influence the dynamics.

[lucid]

I figured this diagram should be posted on this thread. Thanks to GregW for finding it.

[GT3 Tim]

Originally Posted by HIS4

On that train of thought, if the one functional side didn't do anything, why make one functional and one not. Just make both cosmetic only to save money on ducting. It obviously there for a reason. What that reason is will be hard to determine without actually being part of the design process. The beauty of engineering is that there is never only one right way to do things. The ultimate goal can be accomplished multiple ways.

I agree that the hood vent is there for a reason. Without testing, we cna only speculate.

I speculate that it is of benefit at low speed only. Once the car reaches a given velocity, the ram effect of the front lower intake prolly supplies more than enough air. Being as the hood vent is in a relative low pressure area, I would think it "leaks" air at speed.

Again, just speculation. I look forward to the test data.

Interesting note from a previous poster about the Audi system. Seems like he need something similar. I was thinking a simply "louver" system would work fine. Of course, given the system would pressurize (per se) if the hood vent was closed.

Let the testing begin!

I wish my car was not in the shop...I would monkey around with it and start to prototype something up....just for the hell of it.

[ace996]

Originally Posted by GT3 Tim

I speculate that it is of benefit at low speed only. Once the car reaches a given velocity, the ram effect of the front lower intake prolly supplies more than enough air. Being as the hood vent is in a relative low pressure area, I would think it "leaks" air at speed.


I was thinking a simply "louver" system would work fine. Of course, given the system would pressurize (per se) if the hood vent was closed.

I wish my car was not in the shop...I would monkey around with it and start to prototype something up....just for the hell of it.

Tim,
Ever monkey around with that louver? I may try to apply a flapper...like what's used on an inside/outside exhaust duct on the inside of the airbox, where the hood vent meets the airbox to achieve that "one-way" valve.

Or a rubber plate to cover the hole and have smaller flappers...or louvers...cut into it.

Be good,

TomK

[McLuVan]

this maybe stupid
but.....
since it can get very hot in there, the cold air will get hot
so it constantly flushes the system to insure that there's only cold air getting fed to the engine?
maybe?

[ace996]

Originally Posted by McLuVan

this maybe stupid
but.....
since it can get very hot in there, the cold air will get hot
so it constantly flushes the system to insure that there's only cold air getting fed to the engine?
maybe?

not stupid at all, shows you're thinking...good point and it could be valid...

[montreal red]

Originally Posted by McLuVan

this maybe stupid
but.....
since it can get very hot in there, the cold air will get hot
so it constantly flushes the system to insure that there's only cold air getting fed to the engine?
maybe?

yes i was thinking this too.. i think you may be right the vent is to let the hot air out and ensure that the air box always has a good amount of cooler air in it. definitely a valid point.