Transcribed from a source i will not divulge, here is an interesting article i took the time to transpose onto my computer for your viewing pleasure. There is a second part to it, and when i get some time, i will transcribe that as well. Enjoy.


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It all begins at the piston. After expelling spent combustion gasses through the open exhaust valve during the exhaust stroke, the piston reaches TDC. At approx. the time the piston begins its journey back down the cylinder during the intake stroke, the intake valve opens and suction draws in a fresh air/fuel charge through the intake tract. By the time the piston reaches BDC, the intake valve is closing, and it is here we can begin our examination of the occurrences along the length of the intake tract. For these few milliseconds we aren’t concerned about what is happening inside the combustion chamber or cylinder. Our attention is focused on the column of air that exists between the back of the closed intake valve and the opening of the ram tube, or on a carbuerated engine, the entrance to the plenum directly below the carb.

The instant the intake valve closes, it initiates a chain of events within that column of air. A set of four of these events will always occur in a particular order. These four events constitute a harmonic cycle. Each event involves a change in the pressure and velocity of the air/fuel mixture in the tube. These changes always begin at one end of the tube (either the closed valve or the open end) and progress to the other end. This progression, or tranversal occurs at the speed of sound; a harmonic cycle consist of four tranversals.

The first tranversal is a result of the fuel mixture adjacent to the valve coming to a sudden stop. As it does, it builds up a pressure which is equal to the product of the air density, the air velocity and the sonic velocity. As the incoming molecules of air hit this pocket of air that is already stopped, they also stop, and the volume of stalled air grows in size, creating a division between the two zones. This “front” is like a weather front on the evening news. The front separates reigons that are at different pressures. This front moves away from the valve and toward the open end of the tube at sonic velocity. It is the front between to two reigons that tranverses the tube at the speed of sound, NOT a portion of the air/fuel mixture itself. Each wave actually moves through the air without being of it. When the front reaches the open end of the tube, the molecules of air nearest the open end begin to flow away from the opening end of the tube. This volume of zero pressure air flowing away from the engine that extends towards the closed valve at the speed of sound, constituting the second tranversal, where the air in the tube is at zero pressure and negative flow. Then the air the closed valve experiences a negative pressure equal in magnitude to the positive pressure initially developed when the valve first closed, thus initiating the third tranversal which also travels away from the engine. Once the front reaches the end of the tube, the air inside is entirely stagnant, and at the negative pressure, air once again begins to flow into the open end of the tube. This represents the beginning of the fourth tranversal, where all the air in the tube is at zero pressure and has a positive velocity traveling toward the engine.

With this fourth tranversal, one harmonic cycle is completed, although its difficult to imagine all of this taking place in the short timespan between the valve closure and the valve opening. The beginning of the first cycle of the next harmonic begins when this flow reigon reaches the closed valve, and, again the pressure rise is equal to the density of the charge, the velocity of the charge, and the speed of sound, which, at 60 degrees F, is equal to 13,240 inches per second! Tests have concluded that the most effective time to open the valve was after the third harmonic-the intake is opened just as the pressure rise begins to occur at the valve head after the 12th tranversal. Experiments have also showed that when tuning for the 4th harmonic, the intake runner had to be too short and couldn’t fully contain enough air/fuel mixture to completely charge the cylinder. And efforts to tune for the second harmonic resulted in extremely long runners the acceleration of an excessive air/fuel mass, so the third harmonic is the most advantageous.

Testing resulted in a formula to calculate where the ram effect will come into play. To wit: N x L = 84,000, where N represents the desired engine RPM to tune for and L is the length in inches from the opening of the ram tube to the valve head. Lets say your running at Bonneville with an engine that develops peak horsepower at 8400 rpm want to tune for maximum ram effect at that level. The N should equal 10 inches, as in 8400 x 10 inches = 84,000. To achieve ram tuning at 5500 rpm, simply divide the constant, 84000, by 5500 rpm. The result of 84000 divided by 5500 is 15.27, the ideal distance for the intake tract as measured from the opening of the ram tube to the valve head.

The effects of ram tuning reveal themselves as blips in the horsepower and torque curves which can either be tailored (by manipulating runner length) to coincide with, and enhance, the power peak or to bolster some other area of the power curve. In other words, just because a given engine may make maximum power at 7000rpm, doesn’t mean you have to utilize the benefit of ram tuning at that speed. In fact, in most cases, you wouldn’t. A drag race engine, for example, would have its intake system tuned for a speed a bit above the midpoint of the engine speed range. Is ram tuning responsible for where peak torque and horsepower are made? Well, it can shift the peaks a few rpm, but the more dominant contributors are found elsewhere (camshaft, compression ratio and so on). But there is no doubt that ram tuning can be a useful tool for enhancing a given power curve.

 

interesting info, cant wait to read part 2

 

That is good info, but port velocitys, and cam timing events change the numbers.Opening and closing events will change when the harmonics start and end. The 3rd sign wave is a good place to start though.

 

Whatever Don. Where did you hear that? If you didnt find it in the last issue of Import Tuner, theres no way it will hold water with me.

 

Hold water how ever you want. Facts are facts. What SAE paper was this quoted from? Honda, Cosworth, Yamaha, etc.? Cam timing and duration will change the IN and EX wave lengths. Been common knwledge, and printed for years. A closing angle of 70 degrees chances the sign wave and RPM range VS 80 degrees. A 4 valve head increases the " behind the valve" pressure than a 2 valve head that flows the same number" because of velocity, or stack-up rate you are talking about. If not there is no reason to go to a 4 valve head VS a 2 valve.


Modified by DonF at 10:27 PM 4/23/2006

 

You should go to MIT for this ****.

 

I was refused at MIT, needed a scholarship. Good party town though. RPI was also good.

 

So where did you go to school? What was your major?

 

I may have missed the sarcasm, needed to read it in Super Chevy or Mustangs - R - us to know it was true. Got a degree from Barney's Chevron in 68.

 

Bump to keep current...How does the cams ramp angle change the sine wave? Is it due to a slower/faster opening of the valve? I could see how it would change it, so would changing the ram tube length to compensate for the sine waves change be beneficial. I hope I didn't miss the point completely...

 

TTT cause I want to know as well.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DonF &raquo;</TD></TR><TR><TD CLASS="quote">I may have missed the sarcasm, needed to read it in Super Chevy or Mustangs - R - us to know it was true. Got a degree from Barney's Chevron in 68. </TD></TR></TABLE>

You did miss the sarcasm, DonF. I didnt think i needed to put the but next time i will. You really think i get **** from Import Tuner?

 

Off hand, does anyone know the distance from the valve head and the mouth of the intake port on a B16 head?

 

Nice read! I just have a question, does ram tube length mean runner length in an IM? And how does diameter come into play? The reason for asking is a lot of guys I know who have had put bigger IM's removed them due to loss of whp. How much material is taken off the IM if I just had my IM ported? Thanks again for the read!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DonF &raquo;</TD></TR><TR><TD CLASS="quote">I may have missed the sarcasm, needed to read it in Super Chevy or Mustangs - R - us to know it was true. Got a degree from Barney's Chevron in 68. </TD></TR></TABLE>
LMAO Don I went to a branch of your school. It was called Monroe's Shell.And I was in and out of that school for 21 years .Mostly out.

But I learned there that to get the same answer as above all you have to do is divide the RPM into 132,000. Say your turning 9500 .9500 into 132,000 is 13.8"
That's from the valve seat to the very end of the runner.If its ITBs then to the end of the stack.
That's straight out of the SUPER FLOW book. You know the one that comes with the flow bench. Now tell me how wrong it is.

 

Shut up Randy. What do you know anyway? All your work is on the wrong side of the motor

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Combustion Contraption &raquo;</TD></TR><TR><TD CLASS="quote">Shut up Randy. What do you know anyway? All your work is on the wrong side of the motor </TD></TR></TABLE>
Sarcasm right? LOL

 

Ya, thats what the was for. Randy, have you ever read "The Scientific Design of Intake & Exhaust Systems?"

 

dude how stuff works has an article on this and it doesnt use as many big words and is easier to udnerstand. and this phenomenon is why we have variable geometry intake manifolds, to change the lenthg of the runner at different rpms.

like GSRs, oh yeah and that one company lamborghini.

 

I really do learn something new everyday

 

A little additional info for anyone wondering.

PR3 Castings are about 3 inches from the intake port entry to the valve. "ABOUT". Close enough to dial in your calculation.

 

Thanks, now I have a headache

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by b19coupe &raquo;</TD></TR><TR><TD CLASS="quote">Thanks, now I have a headache </TD></TR></TABLE>

nothing im sure a quick drive with the 2 liter wouldnt cure!

 

I read the first two paragraphs drunk and it made sense...

tomorrow I'll read the rest. good night

 

I typed that out years ago......... "Ramming the Rat" July 1999 Hot Rod

The second part of the article......


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The Engine

In upcoming issues, we'll feature our 1963 Nova "The Wilshire Shaker," a street-legal replica of a mid-'60s altered-wheelbase match-race Funny Car. And what better powerplant to totally capture the "run what ya' brung" vibe than this Hilborn-injected Rat? But unlike the Hilborn-injection setups of yore, modern units are completely adaptable to EFI. By incorporating an Electromotive Total Engine Control (TEC) ignition and fuel-management system, our Nova will have street manners that match its power output.

The object of port fuel injection is to eliminate flow restrictions caused by the nozzles and venturis present in a carburetor and to optimize mixture distribution between the cylinders - fuel sprays into the individual ports, enabling equal flow. But the hassle associated with a constant-flow mechanical-fuel-injection setup on the street centers on fuel metering. Typically, the fuel pump is driven at a direct ratio to engine speed. The fuel pressure rises with speed and feeds more fuel to supply the greater demand of the engine as rpm ascends. Despite the use of metering valves and bypass circuits, it is virtually impossible to obtain optimum performance over a wide range of engine speeds. If you adjust for best power at the top end, the mixture will be lean at the bottom end and vice versa.

The Electromotive TEC-II system adapts easily to the Hilborn 396-C-8LEL EFI-specific intake manifold (2 7/16-inch-diameter throttle bores) to provide accurate fuel metering for any driving condition. A complement of sensors (TPS, MAP, [0.sub.2], CTS, IAT); eight 55lb/hr injectors (specified for this particular application); and a powerful computer which utilizes a direct-fire, distributorless, crank-triggered ignition system and phase-sequential injector firing. No, the Southern match-race stocker boys never tuned their motors with a laptop PC, but they never dreamed of running on the street either. We're nuts, though. The work is based around a GM Performance Parts 502 (PN 12371171) which was checked for proper bearing clearances before commencing a grueling 30-pull dyne party.

The Test

Dyno runs were first made with runner lengths of 19 1/2 inches - the distance from the intake-valve head to the bellmouth of the ram tube, which we achieved with the standard 12-inch stacks and the Hilborn throttle-body casting. Shope soon discovered that the calculated engine speed for the appearance of the blip on the torque curve didn't match the dyne-pull results. A comment by test-assistant Steve Abruzzese as to the possible effect of intake duration, caused Shope to remember that Chrysler's testing was done with comparatively mild camshaft events, while the cam in the 502 is a hotter 224 degrees duration at 0.050-inch lift and is a fast-acting roller to boot. For this engine, Shope calculated that a better formula would be NxL = 80,300.

After a 30-minute break-in, Baechtel let 'er rip. The best of three pulls yielded 518.1 hp at 5,000 rpm and 602.3 lb-ft of torque at 3,500 rpm. Compare that to a stock carbureted ZZ502 (502 hp at 5,200 rpm and 567 lb-ft at 4,200 rpm), and it is clear that the Hilborn/Electromotive EFI unleashed a wall of bottom-end torque and a respectable dollop of horsepower as well. And just as Shope had predicted, there's a blip in the torque curve which reflects the increased cylinder filling brought on by the harmonic tuning (see "Proof of the Pudding"). Shope also calculated that the ram effect was good for a whopping 3psi boost in intake-charge pressure at 4,800 rpm. That's close to the output of some small blowers - and it's free!

We made more pulls to test the efficiency of different runner lengths and achieved this by shortening the Hilborn tubes in 2-inch increments. With 17 1/2-inch runners, we gained 5 hp and 10 lb-ft, producing 528.3 hp at 5,400 rpm and 607.2 lb-ft at 3,700 rpm. Trimming more inches from the tubes reduced total runner length to 15 1/2 inches; horsepower and torque fell off slightly to 525.1 hp at 5,500 rpm/604.3 lb-ft at 4,000 rpm. We also tested the naked throttle-body casting (no tubes), resulting in a runner length of only 9 inches. This placed the third harmonic tuning speed at 8,900 rpm, well above our redline. Output diminished to 508.8 hp at 5,500 rpm and 547.1 lb-ft at 4,200 rpm, indicating the effect of turbulence which will form just inside the throttle body when the bell-mouth entry is absent. This turbulence reduces pressure, the flow area, and power.

As the sample tune-speed graph indicates (see "Proof of the Pudding"), agreement between calculated speeds and observed blips is quite good. Still, this procedure is not an exact science. No two dyno runs are exactly the same, and the general slope of the torque curve can cause the peak of the blip to occur at a different engine speed than that calculated by the equation. Regardless, ram tuning is very real. If you have any doubts, check out the intake manifold of practically any engine designed during the last 15 years. From the Ford 5.0 to the Chevy TPI to the Dodge Magnum, you'll see tuned runners - a sure sign that Detroit is quite hip to the lure of free horsepower and torque.

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Also might wanna read into some NACA/MIT papers from Jun 1944

tn-935

more info

Someone, I think a brilliant engineer by the name of Bob Graham, deduced that if we tuned our intake runner to the point where the resonance was greatest, it would give the maximum push to the air and fuel when the intake valve opened at any given speed. The theory proved correct in the tests on the single cylinder and the results were reduced to a formula that was used from that day forward for ram manifolds on Chrysler engines. The runner as measured from the valve seat to the plenum (the open area where they normally meet under the carburetor,) can be determined by dividing 84,000 by the length of the runner = the speed the runner will work the best. An example is:

84000 (constant) = 5250 rpm
16 (runner length)

Billy Shope comment about everything over on Speedtalk.

Modified by Mista Bone at 2:35 AM 7/27/2006


Modified by Mista Bone at 2:38 AM 7/27/2006