Do ram air products really work on a BMW?

[tomjonesBT33]

Folks -

First let me say that I know ram air has been proven to work on some car setups, particularly the older muscle cars which came this way from the factory.

I’m interested to hear your thoughts/experience with ram air or scoops that are marketed for our BMWs. BMW is damn good at squeezing power from their engines, so the fact that Z4s didn’t come with an air scoop leads me to think that it’s not very effective. Otherwise I’d expect that they would have implemented something like the RPI scoop on our cars from the factory.

At $130, I’m not willing to try it as I feel that money is better spent on basic maintenance items to keep the car in top notch running condition.

If it does work then $130 is a no-brainer.

Thoughts/experiences?

[Sergio19]

Yes and no...

The factory air horn behind the grille is actually a small restriction. You can remove it for free and get the same gains as the after market "scoops". The restriction is only 2inH20 or 0.07PSI so not much!

Proper ram air has a shape that allows the air to slow down after it enters to build pressure. You also need to be travelling 150mph to get even 0.4PSI out of it.

From this page: https://www.musclecardiy.com/perform...se-horsepower/

[pokeybritches]

This is my setup on my 3.0i. I had to retune the intake manifold tables in the ECU to account for the higher airflow, so I know it works.

[tomjonesBT33]

That’s a nice setup pokey. True cold air intake.

[Vanne]

Originally Posted by Sergio19

Yes and no...

The factory air horn behind the grille is actually a small restriction. You can remove it for free and get the same gains as the after market "scoops". The restriction is only 2inH20 or 0.07PSI so not much!

Proper ram air has a shape that allows the air to slow down after it enters to build pressure. You also need to be travelling 150mph to get even 0.4PSI out of it.

From this page: https://www.musclecardiy.com/perform...se-horsepower/

Sory bud, thats incorrect.

following .. (pulls out shitty manual)

Pram=0.5x P x V^2

Pram obviously being ram pressure in PSI/Sft^2
P being sl air pressure in slugs..
V^2 is the speed in feet/sec

so lets take a look see.
P = constant (depending on alt, but lets assume SL) 0.0023769

V^2 at 150 mph is 220 feet/sec (close enough for government work)

anyways, plug it all in at youll get somewhere around 57 PSI/square feet. which is actually a considerable amount, obviously depending on what your surface area is and what restrictions you have going to your inlet. (this has been talked bout a lot before on this forum)

And again, dependant largely upon the surface area of the intake. Which ours is actually super small. The scoop, increases that surface area by a bit, which is why it works.

at any rate, lots of variables, so many in fact that looking at a single part of those variables is useless (The intake restrictions). nothing for nothing staying NA, esp without a tune.



Bored as hel isolation, otherwise I Def wouldent have bothered. Lol

[racerbruce]

pokey and Vanne....
YOU'RE.FREAKING.ROCKET.SCIENTISTS!

[Sergio19]

Intake modifications should focus on 1) coldest possible air and 2) lowest possible restriction. Forget ram air.

#1 is already done from the factory.

#2 is close, I measured 14inH20 and it's possible to get it down to 7inH20 by removing the scoop, charcoal filter and MAF screen.

The 06+ ECU can absolutely compensate (up to a point) assuming the MAF section remains unchanged. It also has wideband O2s for closed loop fueling even under WoT. My logs show it's right around 13.0 AFR so why mess with it.

[Michael9218]

What Pokeybritches has shown above is definitely NOT a ram air intake. Any difference he has found is likely due to less restriction from the cone filter and routing.

His setup has merely moved the cone filter further into the high pressure area in front of the radiator. Air is free to move around that cone filter.

I am also skeptical of gains to be had by air intake scoops like rpi. I made a larger scoop and sealed it to the kidney grill, but doubt it really does anything when you consider the rest of the path the air has to take before getting to the throttle bodies. Measuring air pressure at the TB’s would be the only way to verify efficacy.

If one were to take a CSL air box and route the 8” intake tube straight out to the front of the car with a large trumpet opening, say 12”, then maybe at 150 mph you would see an increase in air pressure at the TB’s. But then you would have to consider the aerodynamic drag introduced by this ram air. Gains in HP may be more than offset by drag. The fact that you see no development and use of this type of intake on road race cars, and even no rules time attack cars, answers this question...

[tomjonesBT33]

Originally Posted by Sergio19

The factory air horn behind the grille is actually a small restriction. You can remove it for free and get the same gains as the after market "scoops". The restriction is only 2inH20 or 0.07PSI so not much!

Why would BMW place this plastic cover in the air intake’s path if it restricts air flow?

[Michael9218]

Water intrusion....

And I’m not sure how much it really restricts airflow at speed. The area the intake draws from is under high pressure as the air bunches up in front of the cooler stack.

[pokeybritches]

Originally Posted by Michael9218

What Pokeybritches has shown above is definitely NOT a ram air intake. Any difference he has found is likely due to less restriction from the cone filter and routing.

His setup has merely moved the cone filter further into the high pressure area in front of the radiator. Air is free to move around that cone filter.

I am also skeptical of gains to be had by air intake scoops like rpi. I made a larger scoop and sealed it to the kidney grill, but doubt it really does anything when you consider the rest of the path the air has to take before getting to the throttle bodies. Measuring air pressure at the TB’s would be the only way to verify efficacy.

If one were to take a CSL air box and route the 8” intake tube straight out to the front of the car with a large trumpet opening, say 12”, then maybe at 150 mph you would see an increase in air pressure at the TB’s. But then you would have to consider the aerodynamic drag introduced by this ram air. Gains in HP may be more than offset by drag. The fact that you see no development and use of this type of intake on road race cars, and even no rules time attack cars, answers this question...

Call it what you'd like, but the gains are absolutely there with an OTR (over the radiator) setup. The MS45 ECU uses several "intake manifold" tables which have difficulty accounting for large increases in airflow (any ESS twin screw owner will tell you they have misfire and hesitation issues at WOT). The fact that I was getting misfires and had to retune the tables to compensate is a testament to the increase in airflow. The low end and midrange power on my non-intercooled centrifugal setup was within 10 whp of an ESS TS2, based on dynos that ESS themselves released to advertise their kit, and we both used similar Dynojet dynos running WinPEP 8. This was despite the pressure ratio of the twin screw being 1.6 vs 1.1-1.2 for my centrifugal setup. Of course the top end was much greater with the centri supercharger. The ignition timing and E85 account for some of the power, but so does the improved intake design.

Whether you can call it a ram air system is moot IMHO. Placing the filter into an area with high dynamic pressure might increase the static pressure in the intake tubing when the throttle body is closed, and then again it might not. Mass flow and temperature are ultimately more important. Higher pressure at the filter and reduced restriction will increase flow. The heat shield and filter location help prevent heat soak. I normally see IAT at the MAF sensor (located just before the supercharger inlet) 2-3 deg higher than ambient, no matter how hard I drive the car.

I got the idea to develop an OTR intake from LS Holdens, where OTR intakes are a popular mod that provides ~20 whp gain. This isn't just forum BS - I've seen these cars get tuned independently on the dyno and show real power gains of 20+ whp.

Instead of measuring pressure at the TB, why not monitor MAF voltage, since that's ultimately what's important? I'd expect the pressure would vary wildly at an ITB on a Z4M due to the intake manifold design.

[Michael9218]

Originally Posted by pokeybritches

Whether you can call it a ram air system is moot IMHO.

You’ve given a very good analysis on the benefit of a cold air intake...but the OP was asking about ram air intakes. Something that someone with a forced air induction system would have no interest in. You’re mechanically pressurizing your intake charge. Ram air alleges to do the same thing as your supercharger to a lessor extent by capturing free air flow and ramming it into the intake, thereby creating a pressurized charge...Which is bogus, IMO.

[couchflyer]

Originally Posted by tomjonesBT33

Why would BMW place this plastic cover in the air intake’s path if it restricts air flow?

Attachment 2287936

I believe so that the Z4 M wouldn't be faster than the M3.

[Sergio19]

Water, dirt and bugs mostly. Definitely a restriction though, 2inH2O measured at WOT.