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Discussion Starter · #1 ·
I'm curious why the stock H2 has 6 holes in the intake tube.

Seems to me that it would negate the ram air effect if air pushed in the front can escape out the side instead of pressurising the airbox.

The H2R doesn't have this, anyone want to guess why the H2 does?
 

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Disregarding the holes in the tube, my first thought is, won't the supercharger be sucking more air than ram air will supply at most speeds?
 

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If on the bottom, perhaps to drain water?

Whether it impairs ram air function or not would depend on whether the air pressure in the area of the holes is still a high pressure area or not.

The inlet seems big enough to supply the power the bike produces.
 

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My guess is that the only reason the H2 has an induction tube from the front of the fairing is to access cooler air. I agree that any ram air effect would be negligible compared to the action of the supercharger.
 

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The ram air effect is indeed tiny compared to supercharger boost, but it's a multiplier effect.

As for the holes in the tube, at high road speeds the volume available at the front inlet (even on the H2 which only has one of them) is far greater than what the engine is capable of drawing in, including the allowance for forced induction. The small amount that overflows through those holes is irrelevant.

Why are the holes there? you would have to ask the original designers, but there are a number of plausible explanations ...
These aren't for dumping rain water; they're not on the bottom of the tube.
If the front of the bike runs into an airborne plastic bag or some such thing that plasters itself across the ram air inlet, those vent holes will still allow the engine to run.
It's quite possible that they are strategically located to quell a specific sound frequency.
 

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Possibly to draw in engine heat?I know it sounds 'counterproductive' to the idea of keeping the boost temp down.The holes are quite large and positioned very close to the head.Maximize airflow around the motor maybe?Whenever the motor is running,that tube would be pulling air across the engine.???I would imagine any air being sucked in at the duct would negate any intake air heating issue from those holes.

"If the front of the bike runs into an airborne plastic bag or some such thing that plasters itself across the ram air inlet, those vent holes will still allow the engine to run".This is very plausible also.
 

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Positive pressure from the considerable excess ram air available means air will be spilling *out* of those holes when at speed. There is so much general airflow in the area of the cylinder head that I can't see those holes from the ram air duct doing anything meaningful under those conditions. It has to be some combination of sound management and failure-proofing a blocked main air intake.
 

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I think they are there for two reasons. As a way to pull in air if the front gets some debris. but mainly to clamp down pressure in the tube to = atmospheric pressure at any speed. Or to put it another way to Shunt the ram air effect to zero.

If you cover the holes and go very fast the ram air effect will generate a pressure increase in front of the compressor that will be multiplied on the output side. The effect may be a less linear boost curve and more difficulty getting fueling right on a Dyno. With different SC gears now available getting more boost inst a problem and easier tuning is essential.
 

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"A centrifugal supercharger has the advantage of generating less heat than other designs, especially scroll-type or screw-type superchargers.[28][38] Excess heat in the intake charge can cause pre-ignition that will destroy the engine".
I think this may explain why the holes.It probably allows MORE air to be pulled in during higher loads.Even with ram functioning at higher speeds,the compressor is definitely able to suck in HUGE amounts of air.It may be the ram effect just isn't quite enough to keep up.The only effect I can see with the discharge into the airbox would be a denser air situation,not 'too much' air.The supercharger will only put out a finite amount into the airbox regardless of the inflow.The density probably has a greater effect on fueling.I mean,I'm just guessing really.As we know,the H2R has two intake ducts.

I looked up the intake duct for the H2R...unfortunately,it doesn't show the 'inside' wall of the ducting tube.Whether it has holes or not.If it doesn't,my guess is allowance of more air intake.I can't see them being to scrub off 'excess' air.Even when the ram effect is going full on.At 130+ thousand rpms,it's hard to believe the supercharger would be allowing any air to escape.

"The H2 and H2R feature a carefully designed intake to keep the supercharger fed with a large volume of cool air thus helping to eliminate the need for an intercooler "...and I did find a couple of pics of the H2R duct.It DOES have the same holes in it.So I think it's about volume.Allowing enough air into the supercharger.
 

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I think the most logical one is in case the front air intake got blocked. Think two or three tree leaves getting sucked onto it while going thru the twisties. Then the extra holes could still supply air, just not the most efficient type.

NOLA
 

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Discussion Starter · #11 ·
My guess is that the only reason the H2 has an induction tube from the front of the fairing is to access cooler air. I agree that any ram air effect would be negligible compared to the action of the supercharger.
Cooler air - For sure. It's a nice intake away from engine heat and high enough to avoid a lot of road debris.

Ram Air effect - The bikes specs are quoted with and without ram air.

H2 - 200hp without and 210hp with ram air.
H2R - 310hp without and 326hp with ram air.

Interesting to me is both those are a 5% gain so someone at Kawasaki determined ram air was worth 5%
(PS: that is also 5% that you won't see on a dyno chart)


Positive pressure from the considerable excess ram air available means air will be spilling *out* of those holes when at speed. There is so much general airflow in the area of the cylinder head that I can't see those holes from the ram air duct doing anything meaningful under those conditions. It has to be some combination of sound management and failure-proofing a blocked main air intake.
Sound management - maybe, but there is a factory air cleaner at the other end doing a fair job of keeping induction noise in.

Failure proofing - I agree it would work well as failure proofing but pretty unlikely that's why it's there.

I think they are there for two reasons. As a way to pull in air if the front gets some debris. but mainly to clamp down pressure in the tube to = atmospheric pressure at any speed. Or to put it another way to Shunt the ram air effect to zero.
Yeah, that's where I'm leaning.

With the holes in the H2 intake it is always "full" of atmospheric pressure air. Those 6 holes would bleed higher velocity air and would stop the rest of the intake pressurising.

So where do Kawasaki's ram air power figures come from?

If you cover the holes and go very fast the ram air effect will generate a pressure increase in front of the compressor that will be multiplied on the output side. The effect may be a less linear boost curve and more difficulty getting fueling right on a Dyno. With different SC gears now available getting more boost inst a problem and easier tuning is essential.
I agree, tuning for a "less linear" air pressure is difficult and would have to allow for vehicle speed along with RPM else a open loop system would get leaner the faster the bike was going. Having said that, the plenum pressure is already measured and fuel mixed to suit.

The H2R has no holes, a much bigger surface area and I have to assume a much bigger ram air effect at the supercharger end of the intake. The H2R doesn't lean out and blow-up at high speeds so it can be allowed for.

I think a lot of the power difference between the H2 and H2R are in the intake design and the fact the air cleaner is at the opposite end.
 

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"The H2R has no holes"...the H2R DOES have the same holes in it.Look on some CF sites and look up H2R air intake tube.They could only design the front intakes so far.And to make it aesthetically appealing.Any 'extra' air pulled in to feed the SC I think was designed with those holes in there.They're large.Lots of opening for air to enter.
 

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Discussion Starter · #13 ·
"The H2R has no holes"...the H2R DOES have the same holes in it.Look on some CF sites and look up H2R air intake tube.They could only design the front intakes so far.And to make it aesthetically appealing.Any 'extra' air pulled in to feed the SC I think was designed with those holes in there.They're large.Lots of opening for air to enter.
Too hard to get a picture without removal but the 2015 H2R I have here doesn't have the holes in the carbon tube.
 

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Yep...I just looked again on a CF site.No holes.Some of em show holes,some not.You have one...you would know for sure;)

Well...perhaps the H2 is the only model then that has those in there.The H2R apparently doesn't need those for increased air intake.Which is kinda interesting.I wonder WHY Kawasaki didn't simply allow for two intakes at the front for the H2.They said because of the headlamp.But ,I think they made up for the loss of air with those hidden openings.That SC on both models is pulling in HUGE amounts of air.In seconds.I think I read something like 22 liters a second,and that wasn't like flat out rpms either.I'd think any mechanism spinning that fast would need as much cooling air as possible.If it had to 'work' for it,it may not last that long.I mean,that's what I think about the holes.More cooling air to draw in.
 

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"The H2R has no holes"...the H2R DOES have the same holes in it.Look on some CF sites and look up H2R air intake tube.They could only design the front intakes so far.And to make it aesthetically appealing.Any 'extra' air pulled in to feed the SC I think was designed with those holes in there.They're large.Lots of opening for air to enter.
Don't think the H2R would have the holes - the air filter on the R is located at the front of the bike, just inside the fairing - these holes would be downstream of the filter allowing dirty, unfiltered air into the motor. On the H2, the air filter is directly before the supercharger.
 

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Ram air on H2R is part of the extra cost/performance. It is already a bike with everything you would add as far as full exhaust, CF intake tubes and cams. I believe Kawasaki would have also fine tuned fueling on a track by logging wideband O2 like the Woolich package can. On H2 with those holes in the intake tube it is physically impossible for there to be any ram effect. Any positive pressure building in front of the bike will immediately vent to atmospheric exiting those holes. I would say 5% difference between them at top speed due to ram air sounds very reasonable.
 

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Discussion Starter · #17 ·
Nah, you miss the point...
The H2 is also quoted as having a 5% ram air power increase and like you, buggered if I can see how as I also expect those holes ensure it has zero ram air effect.

H2 - 200hp without and 210hp with ram air.
 

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The holes won't vent ALL pressure. They are small compared to the INLET of the ram air duct.

I beg, I plead, for the people who question this, and think that they are venting ALL ram air pressure to atmosphere, to do the following experiment.

Obtain a paper cup. The one from the last coffee you bought at Tim Horton's (or Starbucks) will do just fine.

Punch a hole in the bottom. 4 - 5 - 6 mm diameter or thereabouts will do but it doesn't have to be anything fancy. Stab a screwdriver through the bottom, or something of that sort.

Now take the cup and hold it upright under your kitchen sink. Turn on the water. Note that some water accumulates on the bottom of the cup, and the faster you run the water, the higher the level of water in the cup. Water spurts out the hole in the bottom, but if you are running the faucet full blast, eventually the cup fills up and water overflows over the top because it's being fed in faster than the hole in the bottom can drain it. That's the situation with the stock ram air duct (math proving this will follow).

Now, punch a smaller hole in the side about halfway up. A 2 mm hole will do.

Repeat the experiment. There is essentially no difference. The cup can still fill up. It takes a wee smidge more flow from the tap to do it to make up for the leakage ... but it can still fill up and overflow. At that point of overflowing, the laws of hydrostatics mean that there is NO difference to the pressure at the bottom .. it takes a little more flow to keep it full to make up for what's leaking out that hole on the side.

Now ... Math proving this.

We have a 1.0 litre engine that spins near 12,000 rpm (200 revs per second) and it draws half its displacement per revolution from the intake plenum (so 100 litres per second of air in the plenum), but near as makes no difference for what we are talking about here, the plenum is pressurized to 2 atmospheres (in reality the heat of compression takes some of this away but let's be optimistic and say that you have a perfect intercooler) - so the engine pulls in 200 litres per second = 0.2 cubic metres of air normalized to atmospheric pressure. (Or somewhere near that number - Close enough for what we're about to do.)

The front of the ram air opening - viewed from straight on the front; I realize that it is actually bigger but is at an angle - is an irregular shape but it is somewhere near 40mm high and 75mm wide (actually a little more than that if you count the way the fairing around it funnels in towards the opening). That is 3000mm2. That is 0.003 square metres.

At 300 km/h you are passing through the air at 83.33... metres per second.

So the volume of air that the facing-straight-ahead projection of the ram air opening is "intercepting" is simply 83.333 x 0.003 = 0.250 cubic metres per second. That's more than the engine is drawing in. Not by an enormous margin (there is something to this "engineering" thing!) but it's more.

Now, I don't have access to those holes at the moment and I don't recall offhand how big they are. Going by memory I think they're 10 - 12 mm diameter and there's 6 of them. If they are 12mm diameter that's 678mm2 area, about a quarter of that of the ram air opening. There is not going to be much pressure drop across them, so only a small part of the flow will be going that way rather than through the main ram air opening.

If you are insistent on having ALL of the air going in the ram air opening go into your engine, this situation is really easy to fix. Take a piece of duct tape and stick it over the holes. You won't even see it with the bike assembled. If it makes one iota of difference to a top speed run I'll be a monkey's uncle!
 

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Discussion Starter · #19 ·
Great post but still leads to the question:

Why did Kawasaki put those 6 holes in the H2 intake?

I understand your 6mm / 2mm hole experiment (although I would never drink Charbucks) but what happened to the "path of least resistance?" I think your experiment needs a coffee filter put over the bottom of the cup too if we are replicating the scenario because it's not just the diameter of the inlet, there is also additional resistance.

I also understand that the total volume of the 6 holes is far less than the intake opening (maybe it's 20%) and maybe the holes are there to tune the intake effectively "smaller" under high speed air entering.

If I blocked the drain hole at the lowest point of the intake tube and put a garden hose in the front intake (on your bike, not mine thanks) the air filter would provide enough resistance that the duct would fill and the water would spill out those 6 holes. Some water might seep through the air cleaner under the weight of water but most of the water would surely just bleed out the top. Right or wrong?
 
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