harddrivin1le

But those tests CLEARLY show a postive pressure build-up in the intake @ speeds above ~ 100 MPH.

Norse396

Seems to me that Ram Air is more for making sure you have good flow to the carb/throttle body. Any other benefit is secondary but nice to get anyway.

harddrivin1le

I agree with that.

I will take ANY gain in power that is essentially free.

And 100 MPH sounds "fast" to a lot of people.

Many of today's performance cars can achieve that from a standing start in less than 13 seconds....

Skeedatl

They don't change from a vacuum to a net positive pressure. The total difference is less than .5PSI...what's typical vacuum for a car -15PSI? So the difference would be just .5PSI less of a vacuum, not boost.

harddrivin1le

They were reading POSITIVE AIRBOX PRESSURES as speeds rose:

"...a manometer, or pressure gauge, was plumbed into it. With the manometer we would be able to measure pressure up to 30 millibars above atmospheric pressure.Just riding from the dyno facility to the strip was illuminating. We'd reckoned on needing 90 mph before boost would register, but at an indicated 70 mph the manometer already showed 8mb of boost.

At the strip we were able to give the big Kwakker its head, with one eye on the slowly rising column of green fluid and the other on the rapidly rising speedo. At the end of each run we logged boost pressure against indicated speed.

The results were even better than we'd hoped for. At lower speeds (under 120 mph) the gauge was easy to read and the results quite consistent: at 70 mph pressure was 8mb; at 80 mph, 10mb; at 100 mph, 12mb; at 110 mph, 14mb. From this point things really took off: At 120 mph (indicated) the airbox pressure was approximately 19mb, at 130 mph about 23mb, at 140 mph, 26mb and at an indicated 150 mph, the gauge was beginning to pump out green liquid as it bubbled over the 30mb limit.

Skeedatl

That's not 8mb of "boost". That's just 8mb higher than the bike at idle.

Your math and mine show that only .5PSI of ADDITIONAL pressure is generated at those very high speeds.

.5PSI isn't enough to change vacuum into boost. Their choice of "boost" is a poor term. Most people associate boost with pressurization. There is still vacuum, just 8mb less vacuum in you measured it in the intake.

Those differences are just differences from what is there normally. So if there is -15PSI (vacuum) there normally, the ram effect of say .5 PSI, just changes the vacuum to -14.5PSI. Not to all the way to +.5 PSI. Even with ram air at 250MPH...you will still show vacuum on a vacuum guage connected to the inside of the manifold (manifold pressure). You don't get actual "boost" from ram air...boost meaning where the intake manifold becomes pressurized like it would be say with a turbo when boosting.

My car for instance at idle has around -15PSI of boost (15PSI of vacuum, at full boost, depending on what I'm doing I I had get up to +15PSI of boost...that's a 30PSI difference. You could say that the turbo is making 30PSI but half is lost to the natual vacuum of the operation of the motor.

harddrivin1le

They were recording POSITIVE PRESSURES in the airbox!

They weren't monitoring intake manifold pressure/vacuum.

Skeedatl

But ask yourself positive pressure compared to what? Not compared to the pressure with the motor off.

Otherwise they would have had to generate about 15PSI just to offset the natural vacuum in a motor. Your math and mine both show that to be impossible.

Plus, look at the trendline of the increase. If your interpretation was correct, they saw the 15PSI (or whatever the native vacuum is) + 8mb right out of the box at what...60MPH or something? Then they go up to 170 and only see an additional .5 PSI in pressure.

So the first 60MPH they get 15PSI, the next 110MPH they get only .5 more. That doesn't make any sense. The math shows and you already acknowledged that there isn't any pressurization at slow speeds...yet by your interpretation they got 15PSI from ram air at just freeway speeds.

That's not what's happening.

They are just measuring the difference in pressure. If you do your math, or just look at mine, the numbers in mb they see pretty accurately represent what the math showed...just a difference in pressure...not enough difference to completely FILL the vacuum, plus more to pressurize.

harddrivin1le

I'm just telling you what they recording for positive pressures in the AIRBOX (via a manometer, as reported in the article).

I don't know how that translates @ the intake manifold.

The inside of an airbox of a car at rest, but with a revving engine, must register a vacuum....Right?

Skeedatl

I think they just have a poor choice of words. What they've seen is pretty much what the math showed.


70 mph 8mb 0.11603 PSI

80 mph 10mb 0.145038 PSI

at 100 mph, 12mb; 0.174045 PSI

at 110 mph, 14mb. 0.203053 PSI

120 mph 19mb 0.275572 PSI

130 mph 23mb 0.333587 PSI

140 mph 26mb 0.377098 PSI

150 mph 30mb 0.435113 PSI

By the trend line, at 0 mph they would see 0 PSI...which mathematically makes sense. But we know there is vacuum, anywhere in the intake stream...that's how air gets in. So you don't actually see "boost" in the traditional sense...you just see less vacuum...and by the numbers, not enough to translate into perceivable gains in HP.

I didn't read the whole article...it is possible that the airbox was just part of a separate test...not connected to anything and they just take it out speeding around to see how much compression there is. That would be the only way I could see of getting actual "positive" pressures from the airbox; cause if it's connected to the motor and the motor is running...there would be vacuum (no matter what) from the motor drawing in air and any boost (like from a blower, turbo or even ram air) must first overcome that vacuum before actually pressurizing the box.

That is, if you connected a boost/vac guage to the airbox...it would read zero (since zero is typically 14.7PSI) when the car is off. When you start it it would read vacuum, rev it, more vacuum. Put a turbo on it and start closing the buy pass, the vacuum lessens until it reaches zero then starts to boost. With this ram air the numbers show that at 170MPH they were getting .5 PSI or whatever. So if without the ram air, that much thottle still made for example 15 PSI of vacuum...if they hook up the ram air, they would be making only 14.5 PSI of vacuum.

harddrivin1le

But the article clearly states they used a MANOMETER.

PLEASE read the article!

According to the article(s), they were recording POSITVE PRESSURES - in the airboxes - with a manometer, both on a dyno (via a fan) and on the road/track (via "the wind"). And the airboxes were connected to the running engines!

QUOTE from the article:

"...a manometer, or pressure gauge, was plumbed into it. With the manometer we would be able to measure pressure up to 30 millibars above atmospheric pressure. Just riding from the dyno facility to the strip was illuminating. We'd reckoned on needing 90 mph before boost would register, but at an indicated 70 mph the manometer already showed 8mb of boost.

At the strip we were able to give the big Kwakker its head, with one eye on the slowly rising column of green fluid and the other on the rapidly rising speedo. At the end of each run we logged boost pressure against indicated speed.

The results were even better than we'd hoped for. At lower speeds (under 120 mph) the gauge was easy to read and the results quite consistent: at 70 mph pressure was 8mb; at 80 mph, 10mb; at 100 mph, 12mb; at 110 mph, 14mb. From this point things really took off: At 120 mph (indicated) the airbox pressure was approximately 19mb, at 130 mph about 23mb, at 140 mph, 26mb and at an indicated 150 mph, the gauge was beginning to pump out green liquid as it bubbled over the 30mb limit.

Skeedatl

Manometers only read differences in pressure whether positive or negative, not absolute pressure. For those who are reading and don't know, manometers are typically U shaped devices and use a colum of balanced liquid, one exposed to a reference pressure, like the outside air, the other to the unknown pressure. The amount that the liquid moves compared to the known pressure, tells you the difference in pressure between the known and unknown.

So it depends on what they have the other end connected to. It could be the vacuum for all we know (with a snap judgement without thinking it through that's how I would do it). That would be the most accurate way to measure it, as whenever the throttle changes, vacuum also changes, making the actual measurement of the "ram air" impossible to determine. That you want to isolate is the contribution of ram air...that is the difference between "natural vacuum" and the vacuum after the contribution of ram air.

Hmmm, so if you connect one end of the manometer to vacuum, the other to the airbox, you would be able to isolate the 'ramming effect' pretty reliably. If you were to just put a guage on the airbox, you wouldn't be able to measure the pressure as for every throttle position, there is a difference in vacuum.

harddrivin1le

The articles CLEARLY state that they were measuring POSITIVE PRESSURES (above atmospheric) in the airboxes!

Direct quote from article (which you clearly haven't yet read):

http://www.sportrider.com/tech/146_9508_ram/

"Note that pressure, in the context of this article, is pressure ABOVE atmospheric pressure."

Skeedatl

Then I say they are very confused. Manometers don't measure abolute pressures...they may have had a 30mb manometer, which simply means that they'll measure 30mb difference.

There is no way in hell they generated enough PSI to overcome vacuum PLUS pressurize the box.

Plus how would they measure it. Vacuum is variable with the throttle...as they go faster, vacuum increases (as the throttle is opened).

They're simply a bit confused.

harddrivin1le

So everyone who conducts these tests are confused...

But you aren't.

Skeedatl

What we have is a few givens here.


Running engines make vacuum everywhere in the intake stream; that is in the intake manifold, through the throttle body, MAF, and the air box.

If they in fact measured pressure, ABOVE atmospheric, then they would have had to generate pressure to offset that vacuum PLUS more pressure to actually get the positive reading.

Lastly...vacuum changes with throttle...so the faster they go (assuming RPM's go up), the more vacuum is generated. Thus they would have had to make EVEN MORE pressure.

Nope...I don't buy it. The math doesn't support it, logic doesn't support it...they couldn't even MEASURE it...they're simply confused.

What the math and logic do support is that they have a 30mb manometer, one end connected to vacuum, the other to the air box, and they were able to isolate the contribution of ram air. Given their speeds and the differences in pressure they noted...they're close enough to the mathematical model that I would say they were fairly accurate. The only atmospheric they're measuring...was the atmospheric conditions inside the box...that is the differences in conditions inside the box compared to another vacuum source.

But NO WAY in hell and I going to believe that they actually generated boost...they simply have their terms confused.

harddrivin1le

1) The dyno results and the road/track results were very similar in terms of what they measured for POSITIVE PRESSURE in the airboxes.

2) They recorded SIGNIFICANT HP gains...roughly 2.6 rwhp for every 10 mb increase in pressure for the Kawasaki.

http://www.sportrider.com/tech/146_9508_ram/

harddrivin1le

1) The dyno results and the road/track results were very similar in terms of what they measured for POSITIVE PRESSURE in the airboxes.

2) They recorded SIGNIFICANT HP gains...roughly 2.6 rwhp (2.1%)for every 10 mb increase in pressure for the Kawasaki.

http://www.sportrider.com/tech/146_9508_ram/

3) Have you ever stood in a 100 MPH wind? Inhale all the air your lungs can take in and there will still be a net positive pressure in your nose and mouth.

Skeedatl

I think they aren't "confused" as must as their wording is confused. They call something "atmospheric" when it's not what people would consider "atmospheric". They call something "boost" when it's not really boost.

If I conduted a test like their's, used a manometer, hooked one end to vacuum, the other to the air box, I believe I would have gotten the exact same numbers...fairly accurately representing the contribution of "ramming" from ram air, while isolating any changes in vacuum due to throttle position.

If I just left the other end to the atmosphere...as soon as the car started the other end would refect the vacuum (water on the atmosphere side would be pulled down).

Now there is an obvious problems I see comparing the air box pressure with "outside air". Vacuum in the airbox changes with throttle, ram air changes with speed...2 variables that are not measurable independantly. You only get 1 reading trying to measure both. You have to isolate one.

If they infact measure airbox to outside air...they wouldn't be able to tell what was ram air and what wasn't.

harddrivin1le

They were gaining 2.6 rwhp (~ 2.1%) for every 10 mb increase in (positive) airbox pressure.

1) The dyno results and the road/track results were very similar in terms of what they measured for POSITIVE PRESSURE in the airboxes.

2) They recorded SIGNIFICANT HP gains...roughly 2.6 rwhp (2.1%)for every 10 mb increase in pressure for the Kawasaki @ its power peak.

http://www.sportrider.com/tech/146_9508_ram/

3) Have you ever stood in a 100 MPH wind?

Skeedatl

1) They don't get positive pressure in the air boxes, just an increase in pressure (compared the what is normally there) in the air boxes and a small one at that. If they say positive pressure compared to normal atmospheric...aka boost, they're full of sh!t.

There is NO ram air capable of overcomming 15PSI of vacuum. Even at 500MPH, you get about 4.5PSI of pressure from ram air.

2) Injen get's the same dyno increases from their CAI when parked...HP increases from ram air in cars is from cold air, not pressure.

3) Sure 100MPH seems gusty...but there is a difference in pushing aside air vs. compressing it. You get pushing aside of air at any speed, but compression doesn't really start to happen until Mach .5...and even then compression in relation to speed is such that in order to get any decent compression at all, you have to be FLYINNNNNN.

NO automotive ram air...hell even an aircraft ram air...can overcome vacuum...that is develop so much pressure as to negate vacuum and pressurize.

With ram air you just get a tiny bit less vacuum...to the tune of .5 PSI at a zillion MPH.

harddrivin1le

You keep saying the same thing while dismissing ACTUAL TEST results.

They picked up ~ 2.1% in terms of peak HP for each 10 mb increase in (positive) airbox pressure.

Skeedatl

That is easily explainable by CAI. Injen got the same results PARKED. And with any CAI the HP difference increases with RPM...just as it does with "ram air".

That's simply cold air at work...not ramming air.

If they pressurize the airbox on the dyno...that's not what happens on the road. If they pressurize the airbox to say .27PSI to replicate 125MPH or whatever...they're actually putting in .27 PSI, plus the vacuum of the motor...another 15 PSI.

Nope.

TLGator

I haven't read a single post in this thread. I'm just here to make the following observation.

Every thread either started by or involving harddrivin1le ends up being pages and pages and pages long.

If you're harddrivin1le I imagine you think to yourself, this happens because I have a special ability to create thought-provoking and complex conversations.

A casual observer like me comes to an entirely different conclusion, which I'll keep to myself.

End of random observation. Carry on, mates.

harddrivin1le

Again:

The airbox pressures they recorded on the dyno (via a fan) compared VERY WELL with those they subsequently recorded on the road/track. So that kills your "that's not what happens on the road" argument. It IS what happens on that road and they PROVED it (by getting comparable readings on the manometer).

The fact of that matter is that "Ram air"produces a small, net positive pressure in the airbox.

You'll never ACTUALLY READ any of those articles, so you'll never know that.

And the intake temps were THE SAME during those various tests. The engines were ALWAYS seeing "cold air." Where do you think the "hot" air was coming from (on motorcycles, with intakes exposed DIRECTLY to the outside air????!!!!!!!!!!

The only real difference was THE PRESSURE in the air boxes!!!

Skeedatl

So what you're saying is that at 60MPH, ram air produced 15PSI, enough to overcome vacuum and then a little extra? Then going from 60MPH to 170MPH, only gets you 15.5 PSI?

LOL. Use your little formula to show how that is possible. It ain't. They're measuring DIFFERENCES between vacuum, not absolute pressure compared to the outside air.

NO WAY IN HELL can ram air overcome engine vacuum in any car or bike...NO WAY IN HELL.

NO ram air generates 15PSI or ANYTHING even close to it.

With your claims...if you disconnected the ram air from the motor, calibrated a pressure guage to read zero when parked, then went cruising down the road you would get 15PSI at 60 MPH and 15.5 PSI at 170MPH.

That's what you're saying if you go along with the claims that they're able to pressurize the airbox on a running car or bike.

That is unless you now want to claim there is no vacuum in an airbox of a running car or bike.

And after all of this...how to they take into account throttle position in controlling vacuum. If they weren't measuring differences in vacuum, they simply couldn't measure the effect of ram air. Everytime the throttle is moved, so would the "guage" no matter what speed yer going.

harddrivin1le

Have you read the articles yet?

Do you know what air "stack up" is?

A given engine can only inhale a given quantity of air (cfm) @ WOT.

Skeedatl

The motor doesn't ever see the stack up. The pressure difference is the same old pressure difference. Whether the vacuum extends only to the throttle plate, or to the airbox...there is still no "ram".

That is unless you remove the filter and everything else (like the throttle plate )...but that would be bad.

harddrivin1le

How do you know that?

(I'm not claiming that I'm CERTAIN that it does...)

That bike probably requires ~ 450 cfm of air @ WOT....

Have you read the articles (in their entirety) yet?

Seeing "100 MPH" in type is one thing. Standing face into a 100 MPH wind is quite another....

Skeedatl

You are simply moving the stack from the front of the car, to farther inside the airbox...that doesn't do anything for the motor.

You aren't getting "compression", you're simply moving the line of vacuum closer to the throttle plate. You could just remove all the plumbing before the MAF and do that.

Skeedatl

But I just did have one of those DUH moments...the stack obviously explains why they could pressurize the air box.

harddrivin1le

The airbox is essentially connected to the intake manifold and there is little in the way of pressure drops between those two items under WOT....

The Kawasaki bike tests indicated a oeak positive airbox pressure of ~0.5 psig and the ~2.1% gain in rear wheel HP is on the order of what one might expect from that amount of positive "boost."

harddrivin1le

EXACTLY....

But it DOES do something for the motor...~ 2% in terms of RWHP for every 10 mb increase on that bike engine.

Skeedatl

The TB is a point of restriction for a motor even at WOT. In order to "fill" the intake, you would have to take it to WOT and keep it there...plus have a TB that can easily out flow the motor.

You're convincing me but I'm not quite there yet. 2-1/2 HP is so small, how do you measure it? Can't do it on a dyno. Plus as small as it is, that's a lot to get from .5PSI of "boost".

Skeedatl

Hmmm, I dunno. With that, 500mb (or a 7.25PSI turbo) would build 100% more power? 100 or more HP from a 7 PSI turbo on a bike?

EddieXo

wow i feel like priting this out and going to the can... LoL

harddrivin1le

http://www.sportrider.com/tech/146_9508_ram/

"At peak power the ZX-9R was producing an extra 2.6 bhp for every extra 10mb of pressure fed into it by the fan. Peak power was up from 123 bhp to 131 bhp, an extra 8 bhp over atmospheric pressure."

They picked up 8 HP via a 30 mb positive pressure in the airbox.

That's a total increase of 6.5% above peak HP without ram air.

That's ~ .43 psig of positive pressure yielding a 6.5% gain in peak power.

That's consistent with what one might expect would from a (lame a**) blower providing the same amount of positive (boost) pressure @ the intake manifold.

kilrb

Hey, Skeedatl, I am no engineer, but when I showed my engineer buddy the lengthy article you posted at the beginning of this thread (by Dave Rodabaugh), he suggested the following. I don't know if it helps or not. BTW, his comments are referring to Rodabaugh, not you.

"I don't think the author of that write-up understands the physics of a moving vehicle. The things he said are true if you're talking about fluid flow in a pipe, but the moving vehicle is just a little different.
For instance, the diverging, converging cone argument. Yes, it's true that if you have air moving along a pipe, if you make the pipe bigger (diverging cone) the static pressure will go up because the air will slow down. However, we're talking about a moving vehicle. The shape of the nozzle in increasing air pressure is irrelevant (although some shapes are more efficient than others). Picture this, a car/motorcycle is actually not moving, but the air is moving around it at 100 mph.
Does the air not slow down when entering the air box? Why yes it does. It was going 100 mph, but now it entered the air box and is now not moving relative to the speed of the vehicle.
Then there's his comment about air compressibility. He's wrong on this.
Air is just "considered" incompressible under 0.5 Mach for the sake of simplicity in calculations. And he's also applying this wrong. Air is, in fact, compressible and you need to treat it as a compressible fluid.
I do it all the time at work. What this >0.5 Mach incompressible flow assumption is used for is in aerodynamics for the calculation of drag, not pressures in a pipe. It's the phenomena that the Cd changes with speed and very complex calculations are involved in quantifying the compressibility effects on drag. This has nothing to do with ram air at car speeds.
The effects of ram air are small, but they do exist. It's just this
guy's confusion of setting up his boundary conditions for his control volume internally to the air intake scoop, and not outside the vehicle.

Skeedatl

The air moving in a pipe is exactly what is happening with ram air...air is diverted through a closed environment...the mathematics for pressure work the same for air as they would for any fluid...just the constants are different (which I noted in the calculations). All of the calculations treat it as compressible, and in fact show the amount of compression, which was later verified in an article posted by 1LE, but like Rodabaugh, the amount of conversion taking place is so small that you can call it incompressible until the difference it large enough to be "worth discussing".

It's compressible for the sake of description, my math shows that there is "some" compression going on...but for the sake of description, the amount of compression is so small, that it doesn't make any difference in terms of HP.

It's like measuring MPG. If you get 30MPG or 30.1MPG...it's not going to make a difference. Not that .1MPG is "non-existant" but rather because there are so many other variables that .1MPG is within "uncertainy" in calculating MPG.

At any speed you can move air molecules closer together...but there is a point in which the pressure difference is so low that it doesn't matter. Rodabaugh's argument is that in automotive applications, cars as so slow, that the tiny amount of compression that does occur "doesn't matter" in terms of generating horsepower...that is until you're driving so fast that you are talking about speeds no one goes, especially on the street (where you see ram air applications like the WS6). In that case, you see HP improvements along the lines of ANY CAI, like the Injen CAI.

harddrivin1le

Cold Air PLUS ram air is superior to just cold air.

And Rodabaugh should read those bike articles.

http://www.sportrider.com/tech/146_9508_ram/

~ 0.43 PSIG of POSITIVE AIRBOX PRESSURE was good for an 8 HP (6.5% gain) on that Kawasaki @ ~ 150 MPH.

That's not bad for what essentially amounts to free power.