| Author | Message | ||
     Alex |
Hi to all of You, it will take me some time to write this post, so please donīt mind if I write things that someone else wrote before. I will try to share some of the things Iīve learned. I used to be a teacher for aerodynamics in army helicopter pilot training while beeing a pilot myself for over ten years. Nowadays i run a little speed shop for Harleys and Buells especially head porting service. Thatīs why I did the R&D work for the FAST system. I simply like to write down thougts that come to my mind so please donīt expect a technical essay. "Air" from an aerodynamic point of view: air is ideally seen as an incompressible fluid in subsonic aerodynamics. This does not mean that air can not be compressed, it just states that air does not change its density during acceleration or deceleration in free flow as long as we talk about a speed range well below the speed of sound. I donīt remember exact numbers but shooting air even with a higher subsonic speed against a wall results in only a small amount of density change within the target point that is neglectible for most practical issues. So air is ideally seen as incompressible (just like water) in subsonic fluid dynamics like free air flow along an airfoil or through a port with varying cross sectional areas. This assumption is important for some fundamental laws of subsonic aerodynamics as it states that the volume of air does not change during flow. So if You flow 5 cubic feet into a hose there will be 5 cubic feet coming out at the other end. Now if we add "time" we can state that if we flow 5 cubic feet within 1 minute into a hose there will be 5 cubic feet within 1 minute coming out at the other end. This is called "flow volume" typically measured in cubic feet per minute or CFM. Thatīs what all the flow bench guys are talking about. Now letīs see what is happening in a hose with variing cross sectional areas when air is flowing through it with subsonic speed: I will call the hose a port from now on. Imagine a port that starts with a huge diameter keeping this diameter for a while (Section 1) then tapering down to a much smaller diameter, again keeping the small diameter for a while (Section 2) to afterwards opening up again to its original diameter (Section 3). Whatīs going to happen when we flow 5 CFM of air through this port? When using a flow meter it will tell that at every cross section of the port thereīs a constant flow volume of 5 CFM. Within the smaller diameter middle section as well as within the bigger start and end sections. The difference between the sections is the air speed which is much higher in the middle section. Mathematically flow volume can be expressed as the product of Cross sectional area and speed: Flow volume = Cross sectional area * Speed As flow volume does not chance within the port (ideally incompressible fluid) one can easily state: Flow volume FV Section 1 = FV Section 2 = FV Section 3 This is identical to: Cross Sectional Area CSA 1 * Speed S 1 = CSA 2 * S2 = CSA 3 * S3 As Cross Sectional Area 2 is much smaller than 1 and 3, Speed 2 must be much higher than Speed 1 or 3. So flow speeds up when entering section 2 (without changing its density) and slows down again when entering section 3 (again no density change). This is the aerodynamic viewpoint of what everybody simply knows as the function of a jet or a diffuser. Furthermore You can see that any increase in flow volume without changing the cross sectional area will increase air speed: More Flow Volume = Same CSA * More Speed With those simple physics in mind there are some interesting things to look at: The velocity stack: as a velocity stack tapers down in diameter it looks somehow like a jet proposing to speed up the air. It actually does speed up the air when comparing air speed at the stack entrance with air speed at the stack exit. Unfortunately most people think that it will add additional speed when compared to other inlet systems. Yet thatīs not always true. Let me explain. Assume we have a cylinder head with a port capable of flowing 130cfm at max. If You add a restrictive flow filter flow will drop to letīs say 110 CFM. This will cause the air speed to drop as well as less volume is flowing trough the same sized port. Now if You remove the air filter and add a non restrictive velocity stack flow will be up to 130 CFM with air speed rising. Now You could state that the stack added velocity or speed. On the other hand if You add a high performance air filter that allows the same 130 CFM to enter it will result in the same air speed. So exchanging the high flow filter with a velocity stack will simply do nothing for air speed. What Iīm saying is that a velocity stack often increases speed because it replaces a more restrictive system. If it replaces a system that allows the same amount of flow it simply adds nothing to velocity. I wanted to write about head porting goals and differences between injection and carburator systems when seen from an air speed point of view, but at the moment my time is running out. Furthermore I believe that people like Blake have written the same things like me in the meantime. So I will stop now. Hopefully no one has been bored too much reading this text  Best regards Alex M-TeK Engineering | ||
| Firebolt020283 |
wow ok that makes alot more cents then the rest of this stuff alex (i didnt think it was boring) thanks | ||
| Court |
Thank you Alex. Sounds a little like the development that resulted in the evolution of the jet engine to the fanjet. I was, with the water thing, mostly just pointing out that the use of "never" or "always" in these dicsussions is like running a 100 meter dash with your rigth foot nailed to the ground. Court (who used to revel in proving that 1 + 1 = 3 - mathematics is beautiful) | ||
| Trenchtractor |
Ok, so bubba was saying the ram air effect is important... Cool. Some points about RAM AIR. We are talking about road bikes, yes?? So what are normal speeds for road bikes? When I had my R6 I wanted to know where ram air effect started to work. So a mate of mine and I did some speed runs, in the Northern Territory where there are open speed limits. The test was obvious. Do full throttle accelleration testing in high gears and see if I could plot a common point of benifit. In 4th 5th and 6th gears, additional acceleration was available from between 180 and 200 KPH. I would say that 180KPH is very high speed for a streeter. I acknowledge that different manufacturers tune air boxes to different speeds. Second point, the R6 air box is a sealed unit in it's entirety, from the mouth of the intake through to the throats of the throttle bodies. The XB, however, has the forward scoop for the intake as the cooling duct for the heads. The back of the duct is open, so there isn't all the pressure there that you'd like. Granted, there is pressure, but where is the box tuned?? I have tried to replicate the testing I did with the R6 on the XB12. I can find no noticable gain in the high speed area. I have, however, opened up the airbox and can honestly say there is more to be had through better breathing. I'm still using the stock stack, but simply opening the air box has given the bike a freer reving nature and more mumbe up top. Next point, I was led to believe that if you left the interactive valve open you would suffer no penalty. It was my stop gap meassure in the interum to getting a better exhaust. I thought it sounded better open. I have just proven the bike slower if you dissable the valve and lock it open. I was wrong there. NOW, I HAVE TO APPOLOGISE... For my little outburst earlier... I do my own R&D for me. I feel though that sometimes you give an inch and someone ALWAYS wants to take a mile. So I was a little fired up. My bad. I share my ideas freely 'cos it'd be a shame for everyone to have to figure out the same 5h1t from scratch. I can get some cheap dyno time, but I want to have all the parts made and road tested prior to embarking on that mission. That and having to feed a family as well as my hobby. But I am one of the lucky guys, I get to have both. | ||
| Glitch |
Hopefully no one has been bored too much reading this text Not gonna happen. Thank you very much! You and Jens have added much insight and clarity to this discussion. Man, ya'll are good! So can this be applied to exhaust, maybe in the opposite direction, to help scavenging during overlap, the way this helps with cylinder fill? Am I learning? This is good stuff! | ||
| Lightisright |
RRW, when they tested an XB12S, dynoed it with a faulty, stuck open exhaust valve. It had a big hole in the middle. They concluded that it does work and is better to have it working. | ||
| Mookie |
ok, this thread has gotten to large for me to have the time to read but i am still going to ask the question of if I will have improvements by using the 12 airbox on my 9/ race kit/ecm and one of these systems | ||
| Firebolt020283 |
well mookie if u use the fast system u dont use a airbox | ||
| Blake |
Mookie, The 12 airbox lid will improve performance by itself. Add the K&N filter and remove the snorkel and you will further enhance the performance. Not sure if any of the tested systems other than the FAST system will do any additional good. That is the big question we are waiting to resolve. | ||
| Trenchtractor |
After a lot or research, I am going to do the following... 1. use the factory race air cleaner. 2. use the factory air box lower. 3. cut the air cleaner cap out of the factory 12 air box top (just the bit that seals against the top of the air cleaner). 4. make a aluminium retainer for the top cap so the filter remains sealed. 5. insulate the base of the air box. This method will have the following benifits: 1. cost very little, 2. allows me to use the factory race air cleaner I already own, 3. retain the factory placement of the breathers and temp sensor, 4. remove the bottle neck that is the air box, 5. retain the focal top to the air cleaner that points into the velocity stack, 6. reduce intake air temp, 7. provide that glorious intake ROAR. | ||
| Darthane |
TT - you're describing exactly what I had in mind also. I already have a very similar setup, minus the 12 airbox nipple and the heat blanket. Made the top plate for the air filter out of plexiglass...LOL | ||
| Alex |
@ Glitch Yes besides making an engine flowing more air You can additionally make use of intake tract length as well as exhaust length tuning. Unfortunately this only works in a small rpm range with fixed length systems. It is often used by dragracers as they run the engine in a much smaller powerband than street engines are run in. It would need different techniques like systems that can vary their length to make use of it through the complete rpm range. Best regards | ||
| Glitch |
Thanks again Alex! | ||
| Brucelee |
So is anyone going to manufacture those heat blankets for our 9s and 12s??? | ||
| Firebolt020283 |
bruce they come with the f.a.s.t. system | ||
| Mookie |
thats what i thought. I allready have the 12 airbox on my bike and like what it does but I didnt know if any of these systems were going to add performance to this or if i switched, what changes i would see. | ||
| Alex |
Mookie, if You want to get an idea of what the FAST system does, do the following: remove the tank cover; completely remove the upper air box cover; remove the air filter; reinstall the tank cover; ride it but donīt use dirty roads or go off road as You have no air filter! This is the core technical idea behind the FAST system. Additionally the FAST system provides an air cleaner and the thermal blanket but the main target is to get rid of the restrictive air box. Let me know what You find out. Best regards Alex M-TeK Engineering | ||
| M1combat |
Uhh, yeah... DON'T do that Mookie. | ||
| M1combat |
"Let me know what You find out." Don't mean to be a prick, but go find out for yourself. | ||
| Firebolt020283 |
yea i wouldnt advise that eather | ||
| Phillyblast |
It's not as terrible an idea as it sounds (just don't do it on a dusty road). All you need to do is check some of the dyno charts that show a decent bump in HP when the run is done sans aircleaner to get what Alex is talking about. I'm guessing the idea is to get an aircleaner assembly that has enough flow to mimic running without one? | ||
| M1combat |
It can get terrible really quick. One piece of sand clamped between a valve and a seat... Maybe lodged in between the piston and cyl. wall... Yeah, brilliant advice. Destroy your own equipment. Don't recommend it to others. | ||
| Blake |
I'd calculate the odds of that happening on a "clean" road to be about, ohhh, one in a billion. | ||
| Ortegakid |
yea,ran no filter for a year on tracks,open stacks on my 1100,never a prob. | ||
| M1combat |
One in a billion? Just the other day I was riding along, minding my own business (on a clean road mind you) when all of a sudden a truck comes barreling out of a dirt road right in front of me of course dragging a big plume of dust right along with him. A few days before that I was following a truck out the spars (my favorite twisty road) when he dropped a wheel in the dirt on the inside of a corner. I would have run a whole lot more dirt through my engine than I wanted to. Suit yourself though I suppose... | ||
| Darthane |
Mookie - if you want to try the 'open intake' test while still keeping your air filter in place, drop by my place sometime after I get back. I have a lower airbox lid that already has the proper hardware in place, as well as the plate to seal the top of the filter (or we can cut up the XB12 box and fit it on there instead). | ||
| Blake |
When ever I run into a dust cloud, I pull in the clutch and shut the throttle till I'm through it. The odds of "a piece of sand} getting stuck on the valve seat, yeah, one in a billion. Dirt/dust entering the combustion chamber, very likely. See the difference? Just trying to keep it honest here. | ||
| M1combat |
I suppose I see your point, but why would you even want to allow dirt/dust in the combustion chamber? Are the power gains really that much? It just seems like a very bad idea to me. In any case, I suppose I flew a little far off the handle in my wording but I still think it's a bad idea. I'd be that one guy that roasts his engine in fourteen seconds flat. | ||
| Henrik |
Alex, thanks for the excellent explanation and for sharing your insight. Running with just velocity stacks is a very common mod on SV (and other) race bikes. I wouldn't do it for a long time on my long distance, daily rider. But for a quick test, I wouldn't worry about it. Henrik | ||
| Hogs |
For what its worth..Been running my 5 inch stroker Big Twin on the street with 4 inch open Velocity Stack no filter what so ever for the past 5 years NO plms., cute try your experiment NO worries..... |
