Found this, its probadly old news.

Does this applied theory of 2 pipes inside of one another, and thus making the smaller diameter piping flow air faster, apply to pipes of a larger size, say 3 1/2" to 4"?

http://www.mimousa.com/weapon-r-secret-weapon.htm

any ideas.. it even has flow bench tests results.!

 

I see the idea behind this working for larger pipes of course. The air velocity going through the inner pipe as it reaches the throttle body helps "pull" the air flowing through the larger outer pipe. The thing is, if you want to build an intake system that takes full advantage of the engine you have to find the piping size that best suits the amount of air the engine demands. Too big of a pipe and your intake air velocity slows down, too small of a pipe you start to restrict the intake air flow, but this is a whole other topic.

Same theory can be applied to turbo exhaust systems. Which is why you see a lot of the real high performance exhausts gradually increase in size as they reach the end of the car from the turbo. You basically want a small size at the turbo to have the exhaust gas velocity flow quickly, thus help spool the turbo up faster. Then towards the middle and end of the exhaust you want a bigger and bigger pipe to help relieve all the pressure built up at the turbine due to the smaller diameter. So you will essentially for example if you want a 3.5" exhaust, start at 2.5 then gradually work your way up to 3.5". But then also note, you don't want a too small pipe at the turbo that it becomes a restriction itself!

N/A exhausts run purely off of exhaust gas velocity to help aid in scavenging the air from the other exhaust ports. So in theory you would want to have just one optimal size throughout the whole exhaust that gives you the best gas velocity. Though I will have to double check on this since it might be possible to run a system where you slightly increase the size towards the end to get better performance on n/a's.

I haven't seen this theory applied much to FC exhaust systems, but maybe I haven't been looking in the right places.

 

So then the question is.

How do you get a pipe inside, another pipe with a air gap?

I have gained 1/2 second on my quarter mile time, by modifing a RB racing header with 3" of straight piping from the block before any turns, which is allowing for increased exhaust gas velocity & scavenging.

I can't imagine making an entire exhaust system with pipes running inside of one another.

wonder how this could be done?

 

Get both pipes, slide smaller one in. At the edges or ends of the pipes weld in 3 or four small support "columns" that hold the smaller pipe up inside the larger pipe. You can place them in a triangle pattern or square. You might want to make the inner pipe towards the opening of the TB a bit shorter than the larger one to help scavenge the air off the larger one.

I suppose if you want to make an entire exhaust using this setup you would have to make sure both pipes have the same shape so they fit within each other. I don't see a FC exhaust being too difficult as it is for the most part straight. I would think the bends would have to be sectioned off possibly to get the pipes to fit in each other.

 

The only problem is we aren't using stationairy engines, so the amount of air the engine demands, changes with every change in RPM. It will never be ideal. You could ofcoarse run a variable intake, but that doesn't change diameter, only length. Works great for N/A...

Riz.

Riz.

 

The gains in such a setup would be so minimal if not non-existent.

 

Can you prove anything you just said?

I know I went from 14.7 to 14.2 with no other modification other than lengthen the primary header tubes..

so..., data proving what you say would be nice, unless its just your uneducated guess.

 

Calm down chief, I am not disputing your claim. Yeah, improving exhaust gas velocity by moving the header bends farther from the opening of the exhaust port WILL have a noticeable gain.

I am talking about putting a pipe within a pipe to try and increase velocity.

 

I am very calm. I get tired of people posting things, they have no proof of what they say. Thats all.

I was talking about the same thing you are.

The gains from a pipe in pipe system. Since piping is super cheap, and doing the work myself. The cost would be low.

I personally think being the exhaust pressure waves from the rotary engine travel much faster than a standard piston engine. The rotary gases are hotter on average also, so knowing this data. You would only produce more capability to flow air through the entire engine.

 

I would have to agree?


If we are talking a boosted engine...well..all things are "equal" under pressure. Boost pressure is a function of resistance to flow, the flow resistance comes from the inlets and ports.

if there is boost pressure present in the manifold the air is already there under pressure..increasing air velocity would mean nothing...because when the intake ports open..air is going to move as a function of higher pressure moving to lower pressure regardless and when the ports close it restricts flow returning pressure ..and thus the velocity of your "intake pipe" is meaningless.

 

True, with a turbocharged system it is the pressure differences that you want to use to help you gain better efficiency. Thus why you would idealy you would want to run a big exhaust on that type of setup, taking into note as I stated before, you do want a smaller opening at the turbo and then step this up as you exit the exhaust so you can have your pressure difference.

The OP is talking about N/A intake and exhaust, because if he had a turbo car, anything can be compensated with an increase in boost and wouldn't have a need to research too much into detail about how to design a better intake/exhaust system. I say he gives it a try and let us know how he feels the system works whether its through the intake or exhaust.

Well if you had a big budget of course you can design such an intake system. Take the 787b for example. Though this is what you would want to do ideally (run variable intake runners), the common thing to do is just to pick a "power band" so to say, where you would want your engine to take advantage of your intake system. This is where you will notice your new peak power. Of course this is why you always see those aftermarket intake systems advertised as "ram air" (the shorter ones) which will allow you to increase power on the higher RPM due to the shorter intake, then you have the longer ones which help increase power on the lower rpm range. It is all about compromising. This is why you see RB headers increase power at a certain RPM range, they are not tuned of course for the whole power band (variable exhaust).

Designing an N/A intake and exhaust system is alot of work to get the optimal performance out of the engine. You also have to take account to the rarefraction pulse from the exhaust, towards the intake. This can be adjusted through primary header tube length, shorter=resonate at higher engine speed, longer=resonate at lower engine speed. If you can get the rarefraction wave timed just right as the intake/exhaust overlap, this will aide in pulling your new fresh air into the combustion chamber (scavenging). This is the process they use when they make headers when you see them marketed as resonance tuned

I suppose in an ideal world if you really wanted to, you can run a variable intake, and variable exhaust to give you the best engine power/torque curve at any given rpm using these principals.

I believe Ferrari designs their intake and exhaust systems using these principals.

 

On top of that, you have to understand how the weapon R intake works. The reason I said the gains would be minimal, is because the OP stated that putting a smaller pipe into a larger one would create a higher velocity intake stream.

The weapon R has two intakes. The small pipe in the center draws air through the hole in the front of the filter. The larger pipe draws air from conical section of the filter. My point is, you cant get higher velocity by putting a small pipe into a larger one and cramming a K@N on the front of it. The intake portions of the pipes have to be seperate. The weapon R achieves the greatist space efficiency and least drag by having them in one filter unit. Without doing what the weapon R intake does, you'd have to have the small pipe within the larger one, and the intakes of each be remote with each other. If you didn't make the intakes of each remote from one another, you'd have mad turbulence at the intake portion of the pipe, thus canceling out any effect the setup has.

Also remember the RX-7 has an AFM in the way. Not only would this system not work, but it would be worse off than the stock intake hose. Unless you have a standalone that deletes the AFM, it makes no sense.

 

Yes, it is based on a concept that I know goes back at least to 1937. If you look in some mid-70s carburetors, you may see a similar internal tube which does pretty much the same thing. Also, the intake looks like a slightly modified version of the AEM Dual Chamber Air Intake. However, based on precedent from BDC, you can ignore all historical records and post your own home-made findings on internet forums and everybody will think that you are an engineering pioneer.

Yes, the general concept is based on a 3:2 diameter ratio, but as with everything in the world, I would imagine that it could be tweaked one way or another for a particular application. With a few exceptions, aerodynamic theory is pretty much based on ratios as opposed to scales.

"The velocity stank inside the air filter is a TRUE VELOCITY STACK."

Most advertising with flow bench results is bullshit. Not that flow benches are bad, but they have a specific scientific purpose which is almost always perverted by the advertising weenies. All that really test tells you is that the intake system works great for generating a low indicated pressure at one given point in the system when hooked up to a vacuum cleaner. On that same test set I can show you that a junk yard carb has a "better" vacuum flow reading than your EFI manifold, but somehow I don't think you will trade me.

Bend both pipes separately, cut open the large pipe, mount the small pipe inside with tabs or pins of some sort, then weld the large pipe back together?

Another problem will be tuning the custom exhaust system. I am pretty sure that tuning the length and volume would affect performance more than the fancy concentric pipe trick. Normally, you would start with a long exhaust and cut off small amounts, recording dyno information for each cut. Not only would that involve a lot of expensive dyno time, but you would probably have difficulty making a clean cut and maintaining the structural integrity of the small pipe's mounting system. Also, since there is a lot of surface area in such an exhaust system, so you may end up with an exhaust that increases low-end torque at the cost of high-end horsepower... but that is just speculation on my part.

The 787B's variable intake traded about 30 peak bhp for a better torque curve, which is why it was specifically designed for short track use.

 

I'm definitely not an engineer. I just do experiments and post what I find. Take it or leave it, Mr Aviator.

B

 

Good point, I really did ignore all that AFM and stock intake tract. I was mostly focusing this on intake design in general, but its a good thing you did note this. This is why ideally for the best n/a performance you would run individual throttle bodies to each port.....

 

To expand on that further, it would be better if you ran individual throttle bodies for each rotor. Keep the primary and secondaries on each rotor, but split them with each thier own plenum and throttle body. Yeah, you'd lose VDI, but you would make up for it in the long haul.