Cascade Crew

[blue89]

I'm reading through my How To Build Horsepower Vol 2 by David Vizard and I had some questions. Does anyone know this or can verify how to do the math? I'll summarize what I've learned from the Helmholtz plenum. Open pipes (independant TB) seem to follow a little different design than below mentioned.

The tuned runner theory seems to have 2 aspects; length and cross area. The length is based on 1st or 3rd order harmonics of the runner length and required tuning rpm. Since lower RPM's need longer tubes than higher RPM's and 1st are longer than 3rd, designs are usually done for upper RPM limits on the 3rd order scale to save room and for practicality.

Vizards example:

10,000RPM needs 7 inches. Subtract 1.7" for every 1000RPM lower.

Simple enough. The cross area is based on the valve, since the highest restriction is the valve. For his example he used a typical 2.05" SBC intake valve. 2.05" DIA gives 3.3 sq.in. If the runner is well ported, the valve has an equivalence area of 82% which yields 2.705sq.in.

This 2.705sq.in. should be the smallest the runner should be at any point. From the back of the valve, the runner should gain 1% sq.in. per inch of travel up the runner away from the valve. So an 11" long runner should be 3.21sq.in. when it hits the upper plenum.

Has anyone seen this big of a taper in any production/performance TBI/TPI setup? He mentioned that if low speed power production is needed, then the port should be smaller. I assume this is to enhance low RPM chamber filling similar to the effect given by hydrolic lifters.

If this 1% taper is needed for producting power, then I have yet to see it used in a production vehicle. But I've never owned any performance intakes or vehicles.

[blue89]

A good example is my 2.8L. The valve is 1.72" so 2.32sq.in. At 82% thats 1.905sq.in. The upper runner area is around 1.39sq.in. And I've wondered why the V6 doesn make power....

At 15" the runner should be 2.39sq.in.

[Xophertony]

you should make a new intake for your v6. make me one too

[Dewey316]

Blue.

Great tech subject!

There is a little more to it, really if you are going to tune this stuff, you need your cam specs. You need make sure the 3rd wave actualy hits when the valve is open.

the equation should be:

Length = (ValveClosedDuration x 0.25 x 1300 x 3TargetHarmonicWaveNumber) / (RPM x 3) - 1/2runnerdiam.

The equation you ahve is backwards. You need a longer runner for the lower the RPM, using Vizards info, you need to ADD 1.7" for every 1000rpms. I also think for some reason, I want to think that that Vizards equation is for the 2nd wave. I would have to run the numbers for sure to figure it out.

I have also seen it said the 1.5%-2.0% tapper on the runner is ideal, I have no idea how the taper will effect the helmholtz tuning, it may not change it all, but it may also mean you need a slightly longer runner (by mm's) to nail your target valve event.

[Dewey316]

I'll add!!!

If you are building a V6 intake, and are putting all this work into it, you could get even more complex. If you build 2 plenums, you can also tune the pulses in the plenum as they hit the throttle body, it is an even more complex tuning peice, and it is more effective, the lower the number of Cyls feeding off the plenum is.

[blue89]

I made a mistake. Every 1000rpms lower you ADD 1.7". My bad.

Vizard did mention that dual plenums would work great for a 6 cylinder engine. The lower cylinder/plenum works better and is easier to tune with stronger resonances.

I like your equation better than vizards. But I think that it should be noted that vizard designs the runners differently for an open runner intake setup and a Helmholtz Resonator intake.

For an open runner intake he gives ((720 - ECD) x .125V x 60 x 12)/360 x RPM

Where ECD = effective cam duration, V = speed of sound in hot air, and RPM is RPM.

His final equation looks more like yours, where it takes in account the effective length of the pipe.

But if a Helmholtz intake is required, the runner design follows the 10,000RPM - 1.7"/RPM stuff. But then you have to design the TB runner length and plenum volume.

I'm not trying to build an intake (yet) but I think that its important to know everything you can about something before you start stabbing idea's together. So in this respect, I believe that my intent of converting to a TBI short runner as like a LT1 setup is misguided.

I'm not trying to design the plenum yet, I'm just trying get the runners down. I think that the existing V6 intake can be made better, but how better if unknown. After reading and knowing what I know, its hard to see people spend 400 bucks for the Truelo intake.

[QwkTrip]

I have nothing to contribute about the runner design because I'm totally clueless what you're talking about. But I'm wondering what is your target engine speed range? I'm just guessing but I suspect that the end goal is to maximize the area under the torque curve in the rpm band that your engine spends the most time during hard acceleration.

[blue89]

I guess you really want to just make produce the most amount of torque (under the curve) at the highest RPM possible. So if you start at the maximum spin of the rotating assembly (crank, connecting rods) and then the size of the valves and work your way up you'll get there you'll maximize that. Dewey, insert comments below. lol.

[Dewey316]

Blue,

You may even know more about this than I do, I have looked at all the stuff, and read about it. That is as far as my knowledge goes.

I the equation you posted is about the same, it is basicly the degree of the intake closing to intake open, then figuring the amount of time you need for the pulse wave to hit the end of the runner, and revert back towards the intake, and calculating the length of the runner so that wave returns when the intake is open.

Since you are going for a short runner, really the 3rd wave is going to have to be your target, if you figure it trying to hit the 2nd wave at a reasonable RPM, you get some pretty long runners, to the tune of 24"-25". You would have to have some VERY large ports to pull that off.

I will also point out, that IIRC you should be tuning the RPM for the torque peak, not the HP peak. That way you maximize your under the curve area.

Remeber, this same stuff works for any tube in the intake or exaust. You can even tune the intake tube, based on the distance from the plenum opening, to the air filter opening. You will get a pressure wave there also, and can calculate it out, and try to pick a length that hits the 1st or 2nd wave at the same RPM that you intake is tuned for.

[blue89]

THANKS!

I don't know that much, I just like to read. Call it post college learning depression

I'm with you on the 3rd wave tuning. I'm curious though if I could possibly get the correct taper down the runners to make it all worth while. The upper intake on the V6 is easy to fabricate, but the system won't work if the runners aren't tapered right. I'm going to go to the garage now and measure some intake stuff. Brb.

[Dewey316]

Here is sort of the idea of what you want with the runner taper.



You can see, the design is really just an individual velocity stack for each runner, that all draw from a common plenum.

I found a nice little calculator for port size...

http://www.rbracing-rsr.com/runnertorquecalc.html

----------------

I also looked up the helmholtz formula.

642 x c x sqrt(A / LV) x sqrt( (C-1) / (C +1) )

L = runner length
A = runner area (cm2)
V = displacment per cyl
C = compression ration
c = speed of sound (340 m/s)

This equation will give you the RPM for the resonance of the intake. If we plug in some numbers to this, we can compare it to vizards numbers. I'll base this calculation on a 3.1L V6, with a 1.72" valve and 11:1 compression, going for a torque peak of lets say 5000 rpm. Using vizards formula, we should use a 15.5" runner, I'll plug that into this equation.

642*340*(sqrt(12.3cm2 / 516cc*39.4cm))*(sqrt(10/12)

218280*(0.02)*(0.91)

3972rpm

That seems a little off of what vizards formula is. You can check my math, but I am sure vizards system overly simplified, and does take all the variables into effect.

[Dewey316]

Hmm, ran all 3 equations.

The first equation I gave, came out to a 30.55" runner

The one you gave, ended up with a 5.5" runner.

The helmholtz formula gives us on in the 14" range.

There seems to be some diffrences, I will need to do some more reading and more calculations, and try to figure some of this, now I just done got myself more confused. I also probably need to go thru and make sure that all of my units work out right. Maybe I am getting the wrong unit on some of this, and causing the calculation to come out wrong.

[TecherB]

I don’t know if this will help much no math here just what I have noticed looking at different intake set ups.

One that comes to mind in your discussion is the duel tunnel ram set up. The 2 carbs are mounted on top of large tubes that taper down in to the size of the head. Going from memory this is a high Torque high Rpm setup.

another that comes to mind is the early fuel injection when each cylinder had an individual pipe leading from the head strait up (no plenum.)

Have you seen the inside of the new V8 Intakes like the ls1 and Chrysler.
They have that big open chamber that appears to have these big runners that sweep from top to bottom on them. this is just the out side appearance, when in fact they are just big open chambers the top has some fins to get the air swirling but the closed area of the runner is only a couple inches long and the opening size is about the size of the port in the head.

I that made any since to you congratulations I'm looking for some cut away photos to help show what I'm saying.

last of all one thing I remember from my schooling is don’t make the intake surface too smooth you want the air to be disrupted when it goes in to the combustion chamber it combines better with the fuel better burn. a super smooth intake will not allow for the best combustion of the fuel and air and you will have more un-burnt fuel than you want and less power.

[Dewey316]

Here is a cut-away from the LS7, you can see the taper on the runner a bit here.



Porsche also uses a velocity stack style intake on their motors.

This is a big engine cut-away, so I'll just post the link.

http://www.seriouswheels.com/pics-2006/2006-Porsche-Carrera-GT-Cutaway-Engine-1280x960.jpg

[blue89]

Nice pic dewey! That shows it pretty good.

I think that the main difference between the independant throttle body velocity stacks and the tuned helmholtz plenum is that when the plenum is not flowing air into the cylinder, its volume will act as part of the plenum itself.

The only thing that seems to be common between the two is the taper. 1% to 2%.

[blue89]

I've looked at both the heads and the intake of the 2.8L system. Terrible design. The head port measures 1-3/4" x 1". The upper intake manifold port measured 1-11/16" x 1" ! ! ! ! ! Slightly smaller, PLUS it has a rounded corner. WTF? Who thought that was a good idea?

That pic of the LS7 intake is just perfect looking. I don't think that it could be duplicated in a stock cast piece. Not the 2.8 at least.



It does not appear that there is enough room in the UIM to make it even a 0.5% taper. BUT, it does seem like they may have the length somewhat correct.

[QwkTrip]

[blue89]

I guess I forgot about that part. Its intention was never to be a performance anything. Sad.

So how did the sbc or bbc in the early days of racing produce power to 10,000RPM? It seems like they would have to have huge valves, massive runners, and enourmous carbs. The rotating assembly must have been beafy. Why have people stopped producing engines of this magnitude?

[QwkTrip]

[QwkTrip]