Getting 10psi Boost on a NA engine...

[LETZRIDE]

Re: Getting 10psi Boost on a NA engine...

Lets see if I can help any further...

it goes on to say...

"The intake and exhaust sytems of a running engine constitute a highly complex system of high and low pressure waves resonating and bouncing around inside the plumbing."

The waves are caused by the valves which open and close. When the intake valve suddenly closes, that column of air that was rushing down the runner still has velocity and inertia. It therefore produces a "shock wave as the air smashes into the valve, sending a pressure pulse backwards into the intake manifold at the speed of sound."

At certain frequencies the opening and closing events will begin to resound or exho the air column in a "coordinated way otherwise known as resonance, which can cause energy from reflected pressure waves to combine with the force of static air pressure to push more air into the cylinder than would happen from air pressure alone."

[Mighty Thor]

Re: Getting 10psi Boost on a NA engine...

Yeah, the engine is like a huge pump. It sucks its own air. Unless you add force induction to it.

I've seen some n/a stangs do crazy things with induction by doing front cut out and sticking a huge tube to it. I guess this a good concept of forcing air on an n/a engine. Of course the faster you go the more gets push in there. You do have to remove the air filter when you are racing to make it more effective.

[LETZRIDE]

Re: Getting 10psi Boost on a NA engine...

Yeah, the engine is like a huge pump. It sucks its own air. Unless you add force induction to it.

I've seen some n/a stangs do crazy things with induction by doing front cut out and sticking a huge tube to it. I guess this a good concept of forcing air on an n/a engine. Of course the faster you go the more gets push in there. You do have to remove the air filter when you are racing to make it more effective.

I'm not sure you would have to remove the air filter to do this...since this is just basically resonation tuning. I'll post up some of the calculations for runner lengths and such when I get home later...I think I actually want to invest some time into doing this....but it won't be done for ATLEAST a year probably....I have access to some buddies who do tool and die, so making this shouldn't be too hard....just time consuming, and tedious as far as the calculations and testing will go....

[LETZRIDE]

Re: Getting 10psi Boost on a NA engine...

btw, for what its worth, the book talks about www.grapeaperacing.com as a site that has some useful info regarding computing intake runner length using wave motion theory...I haven't been on it more then 30 seconds, but it looks like it could have some decent stuff...I'll look into it further after work...just another thing for you guys to read into if you are interested though...

[jimmysprinkle]

Re: Getting 10psi Boost on a NA engine...

Technically, this would work wonders if air acted like a non-turbulent fluid. If you could make everything constant in the engine ( frictionless intake runners, uniform air temp, uniform air intake metal temp, no turbulence in airflow), you could use pulse modulation to achieve some kind of "boost", if you'd like to call it that.

Think of it like a punching bag. You hit it, and it starts to swing away, then towards you. Hitting the bag while it's coming towards you only makes it harder to punch. Hitting it while the bag is moving away from you makes it easier to hit, and if you time every punch, the bag will really start to swing. Does this make sense?

The problem is it's fundementally impossible to achieve this effect in an engine. It's not just intake runner length. Technically speaking, you'd need a uniform intake runner (perfect cross-section area, perpendicular to the valve), and the air would have to be non-turbulent, which is impossible sense the air coming through the throttle body is redirected into the runners.

I'm sure in highly specialized applications, you might be able to emulate these effectsfor a short term (as you mentioned, there's a limited powerband), where the airflow comes close to being non-turbulent. But there's no way you'd come close to implementing it in any production engine.

Also, remember that boost is a measurement of resistance, not airflow. You could get up to 10psi of boost, but that would be like punching the bag as it's swinging towards you-- it's just hard and unproductive. In essence, this theroy actually makes it easier for the engine to breath.

I'm in a lot of physics classes for aerospace engineering in college, that's where I'm basing my info from.

[LETZRIDE]

Re: Getting 10psi Boost on a NA engine...

I don't see how this wouldn't be feasable...how much of a difference can air intake temperature make as far as how fast the air travels, and how it resonates? You are also redesigning the intake manifold, so you are making it as frictionsless and as smooth as possible...since its not going to become more resistant at any point, it is not a variable.

To help the velocity you would taper the intake port...you would want a 1.7-2.5% decrease in the intake runner area per inch of the runner. So basically its a 1-1.5 degree taper...

You would need to make sure that each runner is the same size I believe as all the other runners...and this stuff is mod specfic..there are several calculations that take into acount your cam duration and overlap and such...I just don't want to start throwing in calculations right now and confuse people ...

The thing is, even if there is a bit of variation caused by some variables (i.e changing weather, humitiy, ect...) you only need that rush of air to go into the valve at some point when it is open...it can be when it first opens, when its halfway closed, or just before it closes...the air is travelling at the speed of light, I'm sure if it is tuned properly you will be able to achieve this.

Infact, I have heard that some aftermarket intake manifold companies actually do this intake and pressure wave tuning to a degree...just they don't tell you...

[jimmysprinkle]

Re: Getting 10psi Boost on a NA engine...

It wouldn't be feasible because you would have to redesign and create an entire intake manifold, which would be extremely cost prohibitive.

You'll need to understand thermodynamics (haha, I'm not trying to sound like a nerd) to understand how little disturbances and variances in humidity, temperature, air density in the incoming air will affect the entire system.

You're only considering intake velocity and pulse modulation (timing the valve events to create a pulse of air that helps the engine work more efficiently). Thus, you're assuming that the air is entering uniformily, as in the air only flows in one constant path with no disturbance in flow. In this case, everything would work great. The problem is that's not how air flows in a NA application. The air swirls around, creates pressure differences around intake runner turns (just like how long tube headers can create a vacuum -pressure difference- after each exaust pulse, which scavenges the next exaust pulse) , and this is why pulses wouldnt work. Air wouldn't hit the valve uniformily, thus air wouldn't uniformily pulse back to the valve evenly. The result is that the pressure (boost) thatwould've been gained through the air pulse is lost back up the intake.

This is probably really confusing, and trust me, I'm not trying to knock your idea, but it just wouldn't work.

Now velocity tuning is very real and has a great effect on intake design. But as for naturally aspirated "boost", it's just not feasibly possible.

[T-Mill]

Re: Getting 10psi Boost on a NA engine...

The resonance or "waves" the book is referring to isn't actually talking about the movement of air... its referring to the movement of air pressure. Change in air pressure across a distance is less finicky as change in air direction and velocity. Whether or not this is something that someone with only mechanical equipment could accomplish is doubtful, but I'm with letzride that it does seem feasible...

Think of the air in the runners like a slinky... the rings can compress toward one end, but the spring itself doesn't actually move. This is what happens to air since air is relatively easily compressed, and since there is very little time between the closing and opening of the intake valve, I can see how the air could remain compressed in the runner while the intake valve is closed, long enough for it to still be compressed when the valve re-opens. If 10psi "boost" were to be produced, the actual compression of the air would have to be quite a bit higher, though, because it is going to already be releasing into the vacuum created above the runner, as well as through the intake valve once it opens... you would not only have to take into account the runner shape and volume, but the shape and volume of the chambers before and after the runner...

There'd be some heavy engineering involved with getting something like this to ever be effective, but if done right (and by right, I mean perfectly) I could see it...

[T-Mill]

Re: Getting 10psi Boost on a NA engine...

In order for this to work...

The volume of air in the intake runner would have to be greater than the volume of air inside the cylinder immediately after the intake valve closes, when at the same psi... so if the volume of air inside the cylinder immediately after the intake valve closes is 500cc's @ 1psi, then the volume of air in the runner would have to be greater 500cc's @ 1psi... now in this situation the air in the runner will be compressed, so it's actual volume will be less as it's psi will be higher...

Don't know if ^that^ makes sense, but what I'm trying to explain is that if you think of how much greater the cylinder volume is than the volume of the runner, you'll see how much the actual compression in the runner would have to be in order to effectively gain as high as 10psi boost... if the volume of the air in the runner at a given psi is any less than the volume of the cylinder at the same psi, then the cylinder will just suck in the available compressed air, more easily until the pressure levels out, but the actual volume of air that enters the cylinder won't necessarily increase... you might still achieve boost but it'll be exponentially lower as you decrease the volume in the runner below the volume in the cylinder...

[Cobalt camaro]

Re: Getting 10psi Boost on a NA engine...

I have heard of this from an engine masters builder and his explanation was that if the overlap of the engine was tuned enough, as the exhaust gasses are exiting through the exhaust port the intake valve opens the air will rush into the low pressure area of the cylinder which also happens to help expel exhaust gasses. This phenomenon of intake air helping to push out the exhaust gasses along with the downward stroke of the piston helps to create a pressure in the cylinder that is greater that atmospheric pressure 14.78 psi. So I would say yes you could see a higher pressure if the overlap of the cam was such that it helps to push out air, but like it was said before this is only done on high reving engines, and this type of overlap on low rpm engines causes horrible engine performance and bad gas mileage.

[techsan23]

Re: Getting 10psi Boost on a NA engine...

I have heard of this from an engine masters builder and his explanation was that if the overlap of the engine was tuned enough, as the exhaust gasses are exiting through the exhaust port the intake valve opens the air will rush into the low pressure area of the cylinder which also happens to help expel exhaust gasses. This phenomenon of intake air helping to push out the exhaust gasses along with the downward stroke of the piston helps to create a pressure in the cylinder that is greater that atmospheric pressure 14.78 psi. So I would say yes you could see a higher pressure if the overlap of the cam was such that it helps to push out air, but like it was said before this is only done on high reving engines, and this type of overlap on low rpm engines causes horrible engine performance and bad gas mileage.

You are talking about scavenging, which is fairly common in the cam world.

[LETZRIDE]

Re: Getting 10psi Boost on a NA engine...

I have heard of this from an engine masters builder and his explanation was that if the overlap of the engine was tuned enough, as the exhaust gasses are exiting through the exhaust port the intake valve opens the air will rush into the low pressure area of the cylinder which also happens to help expel exhaust gasses. This phenomenon of intake air helping to push out the exhaust gasses along with the downward stroke of the piston helps to create a pressure in the cylinder that is greater that atmospheric pressure 14.78 psi. So I would say yes you could see a higher pressure if the overlap of the cam was such that it helps to push out air, but like it was said before this is only done on high reving engines, and this type of overlap on low rpm engines causes horrible engine performance and bad gas mileage.

it says that you can get it in cars that turn 5000rpms...and yes this is what I am talking about...

Now it says that you may loose performance in other areas of the power band...but for my application...with the stall when I'm WOT, I don't drop below 4900-5000 rpm ever...so I may loose a little performance part throttle, but I think WOT performance would be perfect...


I wonder how this would impact your valves though? Would this added stress take its toll on your engine, or would you still be ok?

[LETZRIDE]

Re: Getting 10psi Boost on a NA engine...

heres some more info for those that are interested...http://auto.howstuffworks.com/question517.htm

The intake system on a four-stroke car engine has one main goal, to get as much air-fuel mixture into the cylinder as possible. One way to help the intake is by tuning the lengths of the pipes.

When the intake valve is open on the engine, air is being sucked into the engine, so the air in the intake runner is moving rapidly toward the cylinder. When the intake valve closes suddenly, this air slams to a stop and stacks up on itself, forming an area of high pressure. This high-pressure wave makes its way up the intake runner away from the cylinder. When it reaches the end of the intake runner, where the runner connects to the intake manifold, the pressure wave bounces back down the intake runner.

If the intake runner is just the right length, that pressure wave will arrive back at the intake valve just as it opens for the next cycle. This extra pressure helps cram more air-fuel mix into the cylinder -- effectively acting like a turbocharger.

The problem with this technique is that it only provides a benefit in a fairly narrow speed range. The pressure wave travels at the speed of sound (which depends on the density of the air) down the intake runner. The speed will vary a little bit depending on the temperature of the air and the speed it is moving, but a good guess for the speed of sound would be 1,300 feet per second (fps). Let's try to get an idea how long the intake runner would have to be to take advantage of this effect.

Let's say the engine is running at 5,000 rpm. The intake valve opens once every two revolutions (720 degrees), but let's say they stay open for 250 degrees. That means that there are 470 degrees between when the intake valve closes and when it opens again. At 5,000 rpm it will take the engine 0.012 seconds to turn one revolution, and 470 degrees is about 1.31 revolutions, so it takes 0.0156 seconds between when the valve closes and when it opens again. At 1,300 fps multiplied by 0.0156 seconds, the pressure wave would travel about 20 feet. But, since must go up the intake runner and then come back, the intake runner would only have to be half this length or about 10 feet.

Two things become apparent after doing this calculation:

The tuning of the intake runner will only have an effect in a fairly narrow RPM range. If we redo the calculation at 3,000 rpm, the length calculated would be completely different.
Ten feet is too long. You can't fit pipes that long under the hood of a car very easily.
There is not too much that can be done about the first problem. A tuned intake has its main benefit in a very narrow speed range. But there is a way to shorten the intake runners and still get some benefit from the pressure wave. If we shorten the intake runner length by a factor of four, making it 2.5 feet, the pressure wave will travel up and down the pipe four times before the intake valve opens again. But it still arrives at the valve at the right time.

There are a lot of intricacies and tricks to intake systems. For instance, it is beneficial to have the intake air moving as fast as possible into the cylinders. This increases the turbulence and mixes the fuel with the air better. One way to increase the air velocity is to use a smaller diameter intake runner. Since roughly the same volume of air enters the cylinder each cycle, if you pump that air through a smaller diameter pipe it will have to go faster.

The downside to using smaller diameter intake runners is that at high engine speeds when lots of air is going through the pipes, the restriction from the smaller diameter may inhibit airflow. So for the large airflows at higher speeds it is better to have large diameter pipes. Some carmakers attempt to get the best of both worlds by using dual intake runners for each cylinder -- one with a small diameter and one with a large diameter. They use a butterfly valve to close off the large diameter runner at lower engine speeds where the narrow runner can help performance. Then the valve opens up at higher engine speeds to reduce the intake restriction, increasing the top end power output.

[3.4grapeofwrath]

Re: Getting 10psi Boost on a NA engine...

This I would have to see to believe. The way I see this logic is hard to understand. If at any point the exhaust and intake valve are opened at the same time it would seem to me the exhaust gases would also force there way back into the intake track. I don't see how they would only flow in one direction.

[ssms5411]

Re: Getting 10psi Boost on a NA engine...

this i would have to see to believe. The way i see this logic is hard to understand. If at any point the exhaust and intake valve are opened at the same time it would seem to me the exhaust gases would also force there way back into the intake track. I don't see how they would only flow in one direction.

x2....