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Ok, allow me to start with a few polite requests. I have a history of getting dragged into a certain type of discussion, and I'd REALLY like this one to stick to some things.

This will be a pretty detailed examination of the physics of what occurs in the intake, specifically the runners, during on intake phase. I want this to please be a purely scientific debate on the subject. If you "don't like" something, or feel "it's not the way things are done," I beg of you to refrain from throwing suck rocks into the debate. If you think it's "cheap" or "ugly," I ask the same. I want to look at what works, and hopefully share some of the very cool things I have been learning lately.

Now the intro. I have my hands on a engine simulation program, Engine Analyzer Pro V3.3 I'll refer to it as EAP. This is so amazing I can't even begin to describe. It fully simulates EVERYTHING, actually having a virtual piston, valves, intake stream, everything. Outputs just about anything that occurs in the engine. I can look at the pulses in the intake over the whole course of a 4-stroke cycle. I can look at the pulses at any RPM, or boost.

Now for some education in intake pulses. Air in the intake runners does not move in a steady flow. Quite the opposite. When the valve opens, air in the runner has to accelerate, start flowing into the valve, then slows down rapidly and stops as the valve closes. This causes pulses of pressure to move up and down the runner, inverting (from high to low), and bouncing back from the plenum.

The common school of thought is to have the runners at such a length, that you get a high pressure pulse arriving at the intake valve about when it starts to open. Certain lengths of runners boost certain RPMs, as the time between intake events changes with RPM, but the time for a pulse to bounce up and back is pretty much constant (speed of sound). Pressure/temperature do make a difference, but it is pretty small.

From my testing, I have found it is indeed quite true that pulse tuning can create high pressure, higher than what is in the plenum, and boost power.

There is, however, a secondary consideration. When the valve opens, pressure drops. There is a suction going on, and it draws a vacuum until the air in the runner can "catch up" by coming up to speed, and the pressure at the top of the valve starts to come back up. It's important to realize that while pulse tuning can add power, the suction after the valve opens can lower it. Let me call this after opening pressure drop (AOPD).

What I discovered, is VERY interesting. As boost rises, so does the density of the charge in the runner, as with it, it's MASS. It gets heavier. Simple physics tell us it takes more work to get a heavier object to move. I realized that all the common write ups on intake tuning are written for NA cars, and ignore this important fact of increased mass in the runner. It changes things DRASTICALLY. As the boost goes up, the AOPD which is sucking power away, becomes a important part of the equation. It starts robbing power very quickly. The air in the runner has a harder and harder time keeping up. Higher RPMs, also make AOPD increase, as the timeframe is shortened for the air charge to accelerate.

So, what's the solution? Simple, REAL short runners. Like 2" by initial calculations. We lose lots of the pressure tuning, as now we are catching like the 10th bounce of the pulse rather than the 4th. But the pressure tuning, never really helped that much. Not nearly as much as the AOPD was killing things. With the short runners, the air mass in the runner is a fraction of before. It gets up to speed quickly, and the pressure at the top of the valves don't drop nearly as much, and recover much faster.

The results through EAP, are simply amazing. 30% more peak HP compared to the stock intake. 15% more peak HP than the average "short" runner intake. This is at 29psi. At 15psi, the effect is only a 1/4 as pronounced.

So this may be the new way to go for high-boost cars.
 
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Discussion Starter #2
Here's a illustration for you. This is at 7000RPM. The y-axis is PSI in absolute scale (14.7 being atmospheric pressure). The plenum boost is 29psi. The x-axis is the crank position.

Notice the differences? The most vital spot is just about right in the middle between TDC and BDC, that's when the valves are fully open, and the piston is moving it's fastest down the bore. That's essential time. Notice how much more pressure there is with the short runners? The long runners "starve" the intake valve, and don't recover until the valve is practially closed. The short runners snap back from the initial vacuum quickly and have much more pressure through the whole intake cycle. Lots more air mass gets into the cylinder.
 

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Does that EAP give you a whole powerband? What effect do the ultra short runners have on the power and torque curves overall?
 

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Very interesting info. Can you compare how the short runner design will affect spool in terms of changing the torque curves between 3-4.5k? In other words, traditional thinking about short runners suggest that it hurts air velocity at lower rpms, so would going with short runners hurt spool because less air would be entering the combustion chamber at lower rpms? Hope that's not confusing.

One thought I've had was to take several stock manifolds and then chop them to shorter and shorter lengths and then tig a "log-style" surge tank on to try and measure the change that shorter intake runner lengths have on the overall behavior of the engine. The benifit of this testing is that if you are using the same style log (say a 4" aluminum pipe) you can remove the variable of having different surge tank designs, which will allow you to focus on runner length.
 
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Discussion Starter #5
I turned the turbo off, so I can see the HP without having to wait for spool up, which obviously drastically changes the shape of the HP curve. Note this is at 0psi, and the advantages of the short over the long gets greater in relation to boost. So this is as bad as it gets.

Spool up will be a little slower, can't get something for nothing. This is going to be a serious setup for maximum power, not a daily driver. Having a "spool up" nitrous kit would do wonders for the car. Since lots of the big single turbos are doing this now, this approach just takes it a step further.

Once you get to the power, 5000-8000RPM and full boost, this manifold should kick the crap out of everything.
 

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Maybe building a little on the direction FattyCBR is going.
Is there anything that could be done to an intake manifold that would increase spool and low rpm (2.5-3.5K) torque if you were at say 20-24 psi by the end of this rpm range?
 
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Discussion Starter #8 (Edited)
so can you take other factors into account with this software. what i am thinking about are things like runner diameter, if the runner tapers down as it approaches the head, the radius of the entrance from the plenum to the runners. also can you take into account the different textures of the runners, as in having the rough texture of a stock casting or the smooth as glass texture of a runner that has been extrude honed or polished? what about the effects of different plenum volumes? where did you get this EAP program from? what cam did you use in you simulation? could you run the sims with different cam specs
 
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Discussion Starter #10
Hmmm.....I may go all the way on this one. Dual stage manifold. Three plenums, two sets of runners. Flapper valve or set of butterfly valves open at 5000RPM. Below is a VE comparison of the 2" single plenum vs duel plenums, long runners, and tuned intake pipes.

You can see a HUGE difference. By having the blue in effect until 5000RPM, then switching, it will REALLY kick ass. Spool would be VERY fast, notice it peaks right in the spool up RPM range, and the top end would absolutely wail.
 

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This is a pretty damn interesting thread, and in all honesty i thought these pressure waves would not exist in a forced induction engine, but obviously i thought wrong.

Would these shorter runners have any negative affect on fuel atomisation ?
 

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I'm not sure if you've read about some work being done on motor bike heads. Some results indicate that port polishing and enlarging the diameter of the runners is the wrong way to go due to some of the effects you've mentioned. The alternative, reducing runner diameter, has shown some impressive gains. If you have the time it would be great to see the effect of reducing the diameter at the choke point to about 65% of its original value. This should increase the velocity of the incoming charge and get around some of the issues you mentioned.

http://mototuneusa.com/think_fast_intake_porting.htm

^additional info
 
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Discussion Starter #13 (Edited)
I'll try it, but making the runner smaller causes more of a restriction. For all my calculations, I used runners with the same area as the openings at the head. But I'll see what it does.

But, how can we make the ports smaller anyway? Does us no good to make the runners smaller than the ports. Logic would suggest it just kills power, and the tests confirm this.

Also to keep in mind, the ports are 25% smaller than what convential thinking suggests they should be, which is 85% of the valve area. So it may be they are already optimized as suggested by that site.

I don't think I'll be able to match the performance of a dual stage with a single stage, no matter what I do.
 

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Awesome research Anarkey.. that is what I have been waiting on.. I have been working on dual path or triple path intake manifold for some time now.

I have some drawings of dual path intakes. I will redesign them with the curent data and post them on here.

Very good engine analizer. I wil have to get it ;)
 
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Discussion Starter #15
It's still a tough decision. Just a single plenum, 2" runners, and use some nitrous to give it a quick "kick in the butt," or go with a full dual stage intake? The advantages of the long tubes and split plenum start going away very fast as boost builds. Once the air starts getting denser, the tubes just start becoming a restriction pretty fast.

If I did make a dual stage plenum, where it actually has a electrc-servo to switch stages, would anyone buy it? It'd be probably $1500 for such a thing I'd guess.

Also, what would be the best way to shut off the short runners under 5000RPM? 6 butterfly valves, one in each runner, tied together? Any better ideas?
 

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AnArKey said:
It's still a tough decision. Just a single plenum, 2" runners, and use some nitrous to give it a quick "kick in the butt," or go with a full dual stage intake? The advantages of the long tubes and split plenum start going away very fast as boost builds. Once the air starts getting denser, the tubes just start becoming a restriction pretty fast.

If I did make a dual stage plenum, where it actually has a electrc-servo to switch stages, would anyone buy it? It'd be probably $1500 for such a thing I'd guess.

Also, what would be the best way to shut off the short runners under 5000RPM? 6 butterfly valves, one in each runner, tied together? Any better ideas?

Derek, very interesting thread here. As you probably know, my car will hopefully be the test bed for the intakes, and I would love to test yours out, if you get it done in time.

I work at a Ford dealership, and the 3.0L DOHC Taurus has an electronic dual path intake, as well as the newer 3.8L motors in the windstar. Maybe you could look in to the actuators that they use, and wire it up to the AEM. I just don't know if the butterflys that they use would be big enough for our intakes. But you could still use their actuator to control them, and make the butterflys yourself.
Hope this helps.

Tim
 
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Discussion Starter #17
I'm really leaning toward keeping it simple, and just running a single plenum with 2" straight runners (not a cut set of stock runners). The short runners, make more power with BOOST, in addition to RPM. Which means, that they are have a big power hole from 3000-5000RPM at like at 0psi, but by 15psi, it's even, and more boost/RPM from there, keep getting stronger and stronger vs a normal manifold. Having a little 50 shot of nitrous and hitting it at 3000RPM, I should spool up almost instantly, and be going like a bat out of hell all the way to redline. The HP curves look awesome, just keeps going up and up to redline.

Since the nitrous is just a spool up tool, it will be on for 1-2 seconds per usage and that's about it. A 10lb bottle should last 100 pulls.

I sincerely hope this setup will be the new ass kicker for serious HP. Not the best daily driver setup.
 
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Discussion Starter #19
2JZ engine, stock head, stock cams. Also tried varios cams, they just add a extra 5-8% power up top.
 

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Derek interesting research. I would definatlely pay 1500 for a setup like that. Do you think you will go forward with this and make one.
 
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