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327 Posts
Discussion Starter · #1 ·
Ram air effect on horsepower. Say the Dyno say's your doing 160 hp and 93 ft lbs of torque, What the dyno can't measure is Ram Air effect. With more air comming down snorkle more fuel is being delivered automaticaly by ECU.

More Air+Fuel = More Horspower

If in fact you gain 14 hp with pipe and PC3 how much more is that than stock when you bring ram air into arena? and how in the hell can you tune a PC3 proper without just running it rich on top side of RPM's to adjust for RAM AIR?

If you gain 14 HP on Dyno. In truth with more air forced down it's throat. Could really be 25 hp?

If you add NOS and get 213 on dyno what is the true Horspower with RAM AIR?

Where's that Phyisic's guy when ya need him. Has to be a forumla for this?

If Jessie Jame's had a ZX12R I'd ride with him.


Seems like I have heard 7 hp more at a particular speed, Hmmmmmmm now ya got me pondering this again.<img src=http://www.ezboard.com/intl/aenglish/images/emoticons/laugh.gif ALT=":lol">
I know folks that tried the leaf blower treatment with no success. You would have to hook up some serious fanage...I would think to get an accurate dyno readout.

Not just a BAM traitor
but a BAM good one.....</p>

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1,077 Posts
I dont know much about combustion engines, A few things I do know that in motoGP sometimes a team will jave one bike that runs with ram air and another bike that does not. (Generally a rider specific thing) This is because it sets up the enigine to run differently making horsepower differently at different rpms.
If there was a way to set up the amount of fuel entering as a ratio of the rpm and gear then I believe significant improvements in top hp could be made.

If anyone is interested I can do the calculations to the utmost of my low abilities (Still only at junior level physics courses and my teachers still complain about my math) but the calculations will on be for the amount of (I believe this would be the right term) boost (air pressure over normal)
I can think of only two ways so far
1 Use Velocity of vehicle plus bernoulis eqn to determine boost
Somebody who undestand engines would then have to take the boost numbers and figure out the additional fuel required and how much hp that would result in.
2 Somebody would have to have a base dyno run with no pressure on the ram air opening then run the bike at a certain speed (for best results high speed) pegged out. Then based on the bikes coefficient of drag we should be able to determine the force the engine was applying to reach the equilibriom of zero acceleration. And via that the HP. (Although this is probably most exact I think there are to many variables invovled that may throw it off i.e. direction of wind)

Somebody once posted some numbers on how much hp it increased but I dont remember the numbers or how they got them.


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1,077 Posts
Sorry missed your post mono
I agree I couldn't remember the numbers posted but seven was what was in my head, that makes two who remember that number just not for what speed I think it said 90mph maybe that rings a bell for you? If not oh well.


yah....I remember someone saying that after 90 or 100, ram air would kick in., I am no math whiz but I doubt it just hits. I am sure it builds preasure slowly as the speed increases. Therefore, fuel would have to slowly increase with MPH and added cylinder head preasure.....or something like that.

Not just a BAM traitor
but a BAM good one.....</p>

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327 Posts
Discussion Starter · #6 ·
Now here's another ?

With 30% more air flow on B1 model what difference in HP would 30% more air flow deliver?

This ram air issue, There has to be a hard set of number's for this somewhere? I'm gonna do some research. And find out what I can.

Also temp change's with ram air has a major role in gain's. The other morning it was in the 40's here and WOW my bike came to life. It was fun<img src=http://www.ezboard.com/intl/aenglish/images/emoticons/smile.gif ALT=":)">

If Jessie Jame's had a ZX12R I'd ride with him.


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327 Posts
Discussion Starter · #7 ·
Marketers just can't resist it. Ram air! The words themselves summon up images of rushing wild beasts, or of secret military aircraft operating on futuristic principles.
Unfortunately, on snowmobiles, ram-air is as functional as tail fins were on cars of the ’60s.
What is it? Ram air just means using a forward-facing air intake to gain some extra intake pressure. We have all, as children, felt the pressure of moving air on our hands when we held them out the window of the family car. When moving air is brought smoothly to rest, the energy of its motion is converted into pressure. Motorcycles went through a "ram-air" period in the early 1990s, during which street bikes were equipped with the forward-facing "rocket-launcher" engine air intakes seen on many road-racing machines.
While it's appealing to imagine the forward velocity of a snowmobile being converted into free supercharge, the actual air pressure gain is extremely small at snowmobile speeds. For example, at 150 mph, the pressure gain when air is efficiently brought to rest is 2.75 percent. Because this is a dynamic effect, it is proportional to the square of the air velocity. At a more realizable snowmobile speed of 75 mph, the effect (again with 100 percent efficient conversion of velocity into pressure) will be only one-quarter as great — that is, just under seven-tenths of one percent.
In fact, velocity energy is not converted into pressure at 100 percent efficiency. A figure of 75 percent efficiency is usual, which reduces our notional ram-air gain at 75 mph to one-half of one percent.
Therefore, at normal snowmobile speeds, ram air is a myth. However, something much more interesting lies behind it, ignored by the advertiser's busy pen. That something is airbox resonance.
In order to implement ram air, the carburetors or throttle-bodies of our engine must seal to an airbox whose volume is large enough that the intake cycle of one cylinder cannot pull its internal pressure down significantly. Box volume is typically 10-20 times the engine's displacement. Then the forward-facing air intake is connected to the box. When this assembly is tested on the dyno — even without an external fan to simulate the high-speed rush of air past the intake — it is discovered that the engine's torque curve is greatly altered, with new peaks and hollows.
Why? The answer is airbox resonance. If you hold the mouth of an empty bottle near your open mouth as you loudly hum scales, you find that at certain “hum frequencies” the bottle reinforces your humming, which becomes louder. What is happening is that the springy compressibility of the air in the bottle is bouncing the slug of air in the bottle's neck back and forth at a particular frequency — higher if the bottle is small, lower if it is larger. Your humming is driving a rapid plus-and-minus variation of the air pressure inside the bottle.
The same thing happens inside a resonant airbox. The volume of air in the box is the “spring” in this kind of oscillator. The mass of air in the box's intake pipe is what oscillates. The “humming” that drives the oscillation is the rapid succession of suction pulses at the carb or throttle-body intakes. If the volume of the airbox and the dimensions of the intake pipe(s) are correctly chosen, the airbox can be made to resonate very strongly, in step with the engine's suction pulses. The result, when this is done correctly, is that the engine takes air from the box only during the high-pressure part of its cycle, while the box refills from atmosphere through its intake between engine suction pulses. This produces a useful gain in torque.
Using this idea, motorcycle engines have been able to realize torque increases, in particular speed ranges, of 10-15 percent. In race engines, it is usual to tune the airbox to resonate at peak-power rpm to increase top speed. For production engines, it is often more useful to tune the box resonance to fill in what would otherwise be a flat-spot in the torque curve, resulting in smoother power and improved acceleration.
Early resonant airbox systems used long intake pipes that terminated in forward-facing intakes. More recent designs do not connect the ram-air pipe to the box at all, but terminate it near the airbox entry. The actual entry pipe is a short piece of tubing with bellmouths on both ends. This is done because (a) the potential gain from actual ram air is too small to worry about, and (b) it's easier to tune the airbox with a short tube.
Where vehicle speeds are very high, gains from ram air are significant. This was discovered by Rolls-Royce in the late 1920s as the company developed its R Schneider Trophy air racing engine. At speeds above 300 mph, it was noticed that the R’s fuel mixture leaned out enough to cause backfiring. When the mixture was corrected for ram-air pressure gain, the engineers realized they had a "free" source of power. At 350 mph the gain from ram air is almost 15 percent. Similar mixture correction is necessary when ram air is used on drag-race and Bonneville cars and bikes.
Intuition suggests that a forward-facing intake made in the form of a funnel, large end foremost, should somehow multiply the pressure of the air, resulting in a much larger pressure gain at the small end. Sadly, intuition is wrong. In order to convert velocity energy into pressure, the air has to be slowed down, and this requires a duct that widens rather than narrows. Next time you fly on a commercial airliner, note that its engine intakes widen as the airflow approaches the compressor face. Such widening passages are called diffusers, and they are universally used in the conversion of velocity into pressure.
Language often plays tricks on us — especially when language is used by product advertisers. "Ram air" sounds much more appealing than "resonant airbox." Nevertheless, it is airbox resonance that actually generates a significant power gain. At snowmobile speeds, ram air is just words


Found info above on snowmobile site

If Jessie Jame's had a ZX12R I'd ride with him.

</p>Edited by: <A HREF=http://pub56.ezboard.com/bkawasakizx12r.showLocalUserPublicProfile?login=wardawg>WarDawg</A> at: 9/14/02 11:11:59 pm

the rush of air available going into an egine like the 12 is approx 100mph......hench the 100 mph threshold

next....... everyone forgets te mass air sensors that
if designed properly have enuff latitude to compensate
for the real world..... rubber hits the road hp
as opposed to just static/dyno hp
(not applicable to turbos or blown engines)

therefore unless an anamoly exists
not necessary to allow/compensate with the pc3
the std kaw EFI should be sufficent up to about 250hp
maybe a little more

there is not a direct correlation with air
a rough rule of thumb is at 50mph
air quadruples at 100..... quads again at 150...
quads again at 200
so at the top for the 12 more than ample air is available
with resulting pressure

hope this helps


forgot to mention in regards to the resonance
on the intake side with or w/o airbox

that same tuning capablity happens on the exhaust side

ideally it would be tuned on both
the total scope is exacerbated with the addition of
extractor exhaust....... which can be tune for
torque..... or max hp
sometimes they are tuned to a resonance......
creating a hit..... at a certain rpm

most aftermaket pipes are not matched to the std factory setup
this is a major contributor to most of the headaches involved with replacing the std exhaust......

some of the pipes resonate..... a lot
with BIG holes in the torque curve
drag racing.... no big deal ...... shift points well between
3-4rpms....road racing a little broader, some of the slower
corners or hairpins

riding on the street with a peaky engine...... no fun
the 2stroke with the expansion chambers, being a good
same principle.....diff animal


· Registered
9,975 Posts
Good point WD...I'd start with a boost gauge attached
to the air box an make a high speed run...I haven't
done this so I don't know how many pounds (or bars)
the scoop makes at top speed. But if you knew, you
could setup a big air box on the front of the bike with
a pop off valve set to open at the boost amount you
get at top speed, and then pressurize the box. That way
when running on the dyno, you could simulate boost
at high speed on the dyno.

Alternatively, you could put a plate over the intake to
deflect pressurized air to take away "boost" at high speed
to see how much your top speed drops without ram air.

I'd really like to know too, and I'd like to play with
adding more mouth to the ram air...but of course, ram
air is like a turbo, it adds boost which raises the


Jere, West Palm Beach, FL ,

You must be fast, 'cause I was hauling ass when I passed you!</p>

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1,336 Posts
Here is what someone needs to do to get the answer. First, do a normal dyno run to get a baseline reading. Then, get a leaf blower that will blow 180 MPH. I saw one at Home Depot yesterday that advertises 180 MPH. Now, take the end of the leaf blower and duct tape it to the ram air opening to the point where it is completely airtight at the connection and there is no blow by. This should pressurize the airbox with the effect you arte looking for. The reason leaf blowers just pointed at the intake don't do much good is the blow by around the intake. In the real world, 180 mph air is force fed through the ram air intake but when you just point a blower at the intake, it has little effect unless it is completely sealed around the opening.

When doing this though, I would start the blower out at somewhat less than full power until the bike starts to climb up the RPM range. Then as the RPMs rise, increase the speed of the blower. This way, the air/fuel won't be so screwey at low RPMs. But I think this would give a true reading of just how much the ram air adds at speed.

Hey 238,

Have you seen the Hayabusa Formula One racer? Its made by Suzuki, weighs 950 lbs, has 175 hp, costs $25,000. Its not as fast as that monster you built but was pretty interesting.


Just for the hell of it...how much air can a super charger produce? Is it more than a Ram air, and if so, why didn't the motorcycle industries utilize chargers? BMW had a factory bike with a super charger, and if my memory serves me corectly, the bike did quite well and made some good hp.
I realize in the auto motive world, a super charger robs some power because it is a power take off type thing which is operated off a pulley and belt.
Anyone with some coments....

Not just a BAM traitor
but a BAM good one.....</p>

check out articles from port rider mag
airbox pressure measured
all to same standard
horsepower & torque recorded with & w/o the ram air
so one can see the obvious difference
average hp gain......single digits
as someone noted earlier more gains midrange....

most stack bikes are design intake..& exhaust for optimum
not to say is some1 had very deep pockets
you could redesign a bike intake & exhaust to
operate in the very narrow ranges of racing
& see better or bigger results

oct & dec 1999
tested in dec issue
unfortunately no zx12-r zx-9r or zx-7r......????
khi keeps there bikes on a tite leash
bikes are least available for tests

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