Amazing air inlet speed.

[Matra et Alpine]

Didn't think it was supersonic 90
Thinkign about it though, the long strokers of the day woulf certainly pull air fast through narrower and less well understood inlet valves and head design.
You got any reference for it ?

[90ft]

I'll try to dig it up.
I remember an article writen about the ZX12R and velicity stacks.
It was a long time ago. I'll dig.

[Matra et Alpine]

I'll try to dig it up.
I remember an article writen about the ZX12R and velicity stacks.
It was a long time ago. I'll dig.

Cheers, I'll go dig too.
I DO remember the ZX12 having major problems and ending up having to put a "snout" to pull air from IN FRONT of the bike fairing -- sadly it made the bike ugly up close

[PerfAdv]

http://www.hondaracingf1.com/php/aud...e=video&size=1

If the pistons are moving up and down 300 times a second, wouldn't they be breaking the speed of sound barrier? Not that inlet speed approaching the speed of sound isn't impressive, it's more a question of it causing a sonic boom. If not, then what causes supersonic planes to create sonic booms?

[Dino Scuderia]

The problem has surely been encountered before in other racing arena's but not F1. It would seem the high revving motorcycle engines would face approximatley the same issues.

[Matra et Alpine]

Bike engines are smaller capacity.
So each intake charge is much smaller volume ( and modern bieks are 4s ... you need to go back LONG time to the 8s and 6s ( and they were of even SMALLER capacity )
Piston speed in an F1 at MOST reached 38m/s IIRC ( read it somwhere a while back ). ( Speed of sound is 340m/s ) So we're a long way away.
But as air/fuel is drawn through a restricted inlet valve then the reduction in cross section area leads to increases in speed.

[PerfAdv]

The new ‘ten-cylinder’ has broken the 8,000rpm barrier and reaches a maximum of 8,250rpm. At 8,000rpm each piston covers 20 metres a second. At 18,000rpm the pistons of the F1 engine move at 25 metres a second. The difference is that the M engine must last for a ‘lifetime’ while the F1 engine only has to travel 500 miles or so.

Even at half the crankspeed the M6's pistons are moving almost as quick as the F1's. The short stroke of the super high-revving F1 engine which limits piston speed. Still, 25 m/s is way off the 340m/s speed of sound. The 300 times a second stat is what initially made me think they're supersonic...

[Cyco]

PerfAdv: That quote from BMW is slighly misleading - the M5/6 pistons hit a max speed of 20m/s, a F1 piston averages 25m/s, with a max about 40m/s

[SLoppYJeeP]

The problem here might be that the air needs to be moving too fast to fill the cylinders properly. With air whipping around the intakes at the speed of sound, it might create vacuums and areas of variing preasure that would lead to poor fuel mixing or cylinders that arent filled with air. I really dont know, but it might be something like propellers on air planes.....apparently they dont work as the aircraft approaches supersonic speeds.

[PerfAdv]

PerfAdv: That quote from BMW is slighly misleading - the M5/6 pistons hit a max speed of 20m/s, a F1 piston averages 25m/s, with a max about 40m/s

This is the article that I got the quote for the M6 and BMW F1 engines.
http://www.carpages.co.uk/bmw/bmw-m6...2-05-11-05.asp

This page explains the relationship between an engine's stroke, max RPM and piston speed. ( nice short explanation )
http://www.mustangsandmore.com/ubb/S...stonspeed.html

The piston speed of F1 engines don't necessarily have to relate directly with revs when compared to engines meant to rev much lower, as piston speed is more an indication of stroke. Eventhough F1 engines rev to almost 20k, atleast part of what helps them stay together is a short stroke.

Assuming a 5.0 litre V10 has B&S measurements approximately twice that of a 2.4 litre V8. At a given RPM, say 6,000, the engine with twice the stroke will have twice the piston speed.

[2ndclasscitizen]

Thats why a Top Fueller engine that only revs to about 9000rpm has pretty much the same piston speed as an F1 engine due to the huge stroke

[90ft]

At 2.4 Litres the V8 is very similar to a bike engine.
A bike engine being 1.2 and having 4 cylinders. They rev to 12,000 which is nowhere near as high but it's as close as you'll get ina production vehicle.
I found the thead which was writen about the velocity stacks in a ZX12R.
It was a conversation between engineers. And completely annuls my previous reply with the image.
It goes on a bit and refers to the current F1 engines (but this was in hte 5.0 V10 era) but I have the most relevant parts below. Makes interesting reading.


Standard air has a density is about .076 pounds per cubic foot. Now, let’s ram a 200 mph ZX-12 into it. 076 X 200 squared = 3040, divided by 4311= .7051 psi. That is .7 psi OVER atmospheric pressure of 14.7 psi, no? Add the .7 to the 14.7 and you get 15.4 psi in the airbox at 200 mph. That is a 5% increase in the density of the air going to the engine, which (since an engine is just a machine that supplies oxygen molecules to be mixed with fuel in a more or less standard ratio and burned to produce power) results in about a 5% increase in power. By now some of you are hollering, ?yeah but what about the air the engine is using OUT of the air box that needs to be made up?? Well true, but that depends on the FLOW not the pressure. Remember that pressure at the entrance to the engine STANDING STILL, NOT RUNNING is 14.7 psi. (standard day). You are only adding to that number. If the opening in the inlet is large enough allow the necessary amount of air to pass through it at wide open throttle-max RPM (stationary) the ram recovery will only increase the density. How much air IS that anyway?
Well, on an 1197cc engine at 11,000 rpm it’s 232 cubic feet per minute (assuming 100% volumetric efficiency). That’s not very much, comparatively speaking. Take a look at the intake on current F-1 car; it needs to handle more than 3 times that much. So what I’m saying is that the air inlet on our bikes is plenty big and probably quite good at ram recovery.
Velocity stacks are there to smooth the already pressurized air from the airbox on it’s way into the injector body, and they are there to harness and capture the extra energy in the moving column of air caused by the sonic waves traveling up and down through this column. These waves, which really do travel at the speed of sound, are caused by the sudden starting and stopping of the moving air and the rapid opening and closing of the valves. When the valves open, one pulse starts back upstream, towards the entrance to the tube (stack). When that pulse reaches the open end, another pulse is generated that starts back down towards the cylinder. These pulses are of course, moving much faster than the moving air which is only going about 180 mph. The principle of and reason for varying the length of the stacks is to get these waves in sync so that they get to the valves just before they slam shut, thereby increasing the local velocity (and amount) of air molecules that make it into the cylinder. It is easy to understand, then, why different length stacks work better at different rpms. One length will help up high, possibly at the cost of low end, and vice versa. One particular length is the best compromise for total area under the curve?. It is therefore very important to have the correct inlet shape AND length (this is of course also the theory of exhaust tuning). If you narrow the cross section in a tube flowing a compressible fluid, the local pressure will drop because the speed goes up (think venturi effect) and then if and when the cross section gets larger again the speed drops and the pressure returns to what it was going in. The volume remains the same. This phenomenon is one of the ways we get volumetric efficiencies greater than 100%.
The shape of the inlet of the stack maximizes the flow FROM the airbox or atmosphere into the tube as described above. The radius on the entrance of the stack is very important, but only up to the point that there is no loss. It can’t add but it can certainly subtract it. Regarding having different lengths on groups of cylinders, what you get is some cylinders working better at one point and others at another. The peaks are softened, it spreads power a bit.
Historical note: Those of you that have cited the different length stacks on the older Chevy Big Block engines, the lengths are different not for that reason, but because there are two different length inlet ports in the original heads. Short ones and long ones. The different length stacks just make them all the same from the stack entrance to the inlet valve.

One of the main advantages of FI is the fact that the "Sonic Wave" that comes "Out" of the engine (When long valve timing / duration is used) is that as the piston comes up at lower speeds, the velocity of the intake air is overcome by the upperward piston movement and pushes air through the Carburetor the wrong way and leans the engine out, which is not as bad with FI because the amount of fuel it delivers is not dependent on the "Signal" generated by the airflow over the Needle Jet.
My point was that the new length decreased the damage created by the Sonic wave and the Bell mouth shape allowed more air to be captured "Directly" and sent into the engine, vs, the shorter stacks with a smaller Bellmouth!

[90ft]

I had previously mention the stacks were to short...... the bell too small the stack actually too straight all of which may not be a disadvantage to drag racing .
My reference coming from a road racing background is the firing order across the stacks (looking foward) that causes a vortex.....uneven distribution of air available for each stack many successful euro/WSB teams 600cc & 750cc used uneven stacks.

Although your "vortex" theory is interesting, I think (just my opinion) the length variance is really more focused towards torque spread. Consider this, F-1 and F-3 engines currently utilize computer controlled, servo operated variable length inlet stacks. This has been used in WSB (at least in R&D to my knowlege) to increase power at various RPMs rather than depend on a fixed peak point and thus a compromise.

It is very easy to see the vortice thing.
Just place a lipstick camera or a hi speed cam corder in back of an air box while on dyno
(old airbx...... hole in airbx..... sealant around hole) rev engine up.... fog lightly to see air
by the firing order rushing into the stacks you will see on an uneven air distribution among cylinders [much as the work done on "strobing" engines.... regarding valvetrains]

Does not effect hondas & ducatis as much a direct result of the V(vee) angle & the resultant firing order as a result of the firing order on a 4stroke + v angle.... do the math
hondas use very short stacks on their racing interceptors never was a complaint of tractability

rushing air always twists....... very much like you twist a towel to wring it out...... in some cases pulling air AWAY from the next cylinder across the bank worse it oscillates across the box even in steady. The 12's stacks almost even with the floor of the airbx
not a good thing.

most 600cc engines have huge "still air boxes" some approaching 10 litres...... many larger than the 12's box (of note they are enlarged in WSB europe) the volume actually helps against this anamoly not at all what people actually are referencing when they say "ram air" even nascar with their fast speedway machines take their supply from a LOW pressure area..... that acts as a still airbox if anyone could RamAir..... they could
by the way they recognized the uneven distribution was a problem when they went to the 366 engines........ & started turning them faster(10k rpm)........ they were seeing huge drops between some cylinders of intake air distribution...... as a result of firing order
in the intake plenum some cylinders were dangerously lean on an individual basis
they were burning pistons crazy where the overall AirFuel ratio should have been right .

I am familiar with the variable length stacks I also see the 2 short stacks on the 1 & 4 cylinders & the slightly longer stacks on the 2 middle cylindes very prevalent

this year Yamaha did just the opposite.......strange altho I think I know why more of an associatted problem with the exhaust (4 into 1..... 4 into 2 into 1 etc....another aside)
no less when chopping throttle.... when entering a corner the air stops & reverts.......
you progress thru the turn then open the throttle back up the 4's for years were prone to lite switch like reaction where ducati & honda(rc51) had little or no problem in roadracing the lament was 750 vs 1000cc the reality the 4's had soften the hit .

Tell me, are you familiar with the term "stand-off", the visual fuel reversion from an inlet throat?

I am familiar with the term....."stand off" very much the same as the term " recarburetion"
that fog present in front of the bell inlet

have seen it dealt with in different ways from muslin...... to nylon stockings over the bell inlet to a carb to the Lectron carbs..... which ere very flat very very close to the actual inlet track usually without stacks or inlet past the carb

If you look at it in relation to firing order the way it oscilattes .....twists across the box
its easy to see even distribution is unlikely as i mention b4 the increasing size of the "still air" part of the air box

with an inline 4 that anamoly is exacerbated by matching the exhaust in several configurations which also pulses the inlet & exhaust tracts effecting cylinder filling
on & off throttle use such as circuit racing really brings it to fore

has been noted in many publications the difficulty of getting the EFI bikes the circulate say 4 instance the infield Daytona where they showed plenty on the straights & banking
this year with Yamaha going & a hybrid/quasi carb/injector setup in the 600's will prove very interesting (diff height stacks again) Ducati never had a problem Aprilia very little when Honda switched from their v4 to the RC51 found the twin easier to tune on EFI very hard to ignore the obvious.

[Cyco]

Assuming a 5.0 litre V10 has B&S measurements approximately twice that of a 2.4 litre V8. At a given RPM, say 6,000, the engine with twice the stroke will have twice the piston speed.

I understand that, but the F1 engine at 21k rpm is running nearly 3 times as fast as the 8250rpm red line in a M5.

The reason I brought this up was at the time BMW released those numbers Racecar Engineering had the figures from the F1 engine and if I get a chance I'll find them and put them up.

[culver]

A couple of notes about supersonic flow.
1. You won't hear a boom. The boom is caused when something else moves through the air. F3000 and LMP cars already use supersonic air intakes as a way to restrict airflow to the motor.
2. No mater what you do on the sucking/engine side of a supersonic orifice, you CAN NOT get more air to flow through it. One of the properties of supersonic flow is so long as the flow is supersonic, nothing downstream of the supersonic orifice will affect the gas upstream of the orifice. No shockwaves, sounds, temp changes, reduction in pressure etc. Nothing gets through. So if for what ever reason the flow goes supersonic, that's all the air they can get. Now they can try to get more air by making changes that keep the intake flows subsonic (larger throat diameters for example).