Intake Manifold Design

whittlebeast · Post by **whittlebeast** » Mon Jul 31, 2006 12:52 pm

http://www.team-integra.net/sections/ar ... icleID=466

Interesting reading

AW

S.Bretz · Post by **S.Bretz** » Mon Jul 31, 2006 6:57 pm

Well... the ITB do ont benift from the resonace tuning, but DO benifit from tunnel raming.

When the inlet valve opens, a low pressure wave travels up the runner toward the plenum (or atmosphere). When the low pressure wave hits the plenum or atomsphere, the high plenum pressure shots down the runner toward the valve...it timed correctly, the high pressure wave will make it into the comubustion chamber just as the valve is closing... trapping the highger then 100% VE in the cylinder.

a really easy way to calculate the desired length it
90/ (RPM/1000)= desired length

EI....I want torque peak around 7,000 rpm.

90/7=12.86 in.

You want to put the peak tq right in the middle of you gears...if you shift at 7k and the rpms drop to 5k, then tunnel ram peak at 6k.

I used that theory when I built my intake manny...it seems to be working pretty well to. At about 6200-6300, i can hear the faint sound of what sounds like ITB's...

ITB work just like a closed intake manifold...just that he atmosphere acts as a huge plunem...

Also, the slower moving air in a system is usually the part of the system with the highest pressue...so bigger plenums mean more pressure.

Bow · Post by **Bow** » Tue Aug 01, 2006 9:17 am

That is very interesting figures you posted up.
If that the length of the runner itself or the length from the open end of the runner to the valve?

I have been using a formula out of the book Desktop Dynos by Larry Atherton.

He talks about tuning the intake length for the different pulses that occur as the wave bounces back and forth in the runner:

Second Pulse Length: =108000/RPM
Third Pulse Length: =97000/RPM
Forth Pulse Length: =74000/RPM
Fifth Pulse Length: =54000/RPM

So by this formula, with a peak at 5800 RPMs, the lengths (in Inches) are:

Second Pulse Length: 18.62
Third Pulse Length: 16.72
Forth Pulse Length: 12.76
Fifth Pulse Length: 9.31

I am running Engine Analyzer Pro software and the differences are interesting.

I am aiming for a peak HP around 5800 RPMs on a 2400cc inline 4.

With S.Bretz formula, I get:
Tq: 190 ft/lb @ 5000
HP: 212 @ 6950

With the Desktop Dyno Formulas, I get:
Second Pulse Length:
Tq: 190 ft/lb @ 5280
HP: 211 @ 6450

Third Pulse Length:
Tq: 192 ft/lb @ 4460
HP: 213 @ 6800

Forth Pulse Length:
Tq: 196 ft/lb @ 5240
HP: 218 @ 6540

Fifth Pulse Length:
Tq: 194 ft/lb @ 5000
HP: 217 @ 6150

Interesting.

These simulations were run with the only thing changing was the runner length. The runner is 44.4mm (1.732 In) diameter.

Bow

S.Bretz · Post by **S.Bretz** » Tue Aug 01, 2006 3:56 pm

Oh....sorry, I forgot to mention that. I ment to but I quess I got side tracked.

That length is from the centor of the valve stem to the opening in the plunem of the atomosphere.

This formula isn't the most precis...it just gets yo close to where you need to be.

Umm, that 3rd 4th 5 th pulse stuff you have there...are those numbers off by a factor of 10?

Bow · Post by **Bow** » Wed Aug 02, 2006 7:25 am

S.Bretz wrote:Oh....sorry, I forgot to mention that. I ment to but I quess I got side tracked.

That length is from the centor of the valve stem to the opening in the plunem of the atomosphere.

This formula isn't the most precis...it just gets yo close to where you need to be.

OK, cool! Thanks for the update.

Umm, that 3rd 4th 5 th pulse stuff you have there...are those numbers off by a factor of 10?

Nope.

The Fifth Pulse, for Example: 54000/5800 RPM gets you a 9.31 In runner, from the center of the valve stem.

S.Bretz · Post by **S.Bretz** » Wed Aug 02, 2006 2:24 pm

Ohhh. I see. its a constant divided by the angular velocity..that makes more sense now.

!!!ALEXANDER · Post by **!!!ALEXANDER** » Wed Aug 02, 2006 3:03 pm

Does anyone here know where I can find decent supplies for fabricating an intake manifold?

I'm making (dreaming?) a dual plenum one to fit a small V8.

I know where I can get the flanges either water jet or plasma cut, but the individual runners are a problem.

The math tells me a 1" round cross section is just right for my size valves and engine CID.

I could go with 1" round but when they run next to each other up the middle, my dual plenum length becomes way too long, and intertwining to shorten things up makes too many bends.

I would prefer to use 1" X 1.75" and nobody makes it anyhwere!

Bow · Post by **Bow** » Thu Aug 03, 2006 7:47 am

http://www.rossmachineracing.com/index.htm

That is one place that sells parts.

What exactly are you trying to do? ITBs on a V8?

S.Bretz · Post by **S.Bretz** » Thu Aug 03, 2006 11:28 am

www.velocity-of-sound.com has some nice velocity stacks.

edit: forgot the 3w's.

FIntruder · Post by **FIntruder** » Sun Aug 06, 2006 6:23 am

So is the shape of the reflective surface, the part of the plenum that the pulse reflects off of, important? Most plenums look to be curved in that section. Would a flat area reflect better? Then a square or rectangular plenum would work.
My project is a low revvin' motorcycle engine without much room for runner length. The lower the rpm, the longer the runner needs to be for peak. I guess it comes down to what it always does, you go with what fits. I'll have to do some math but is there only one length at which the pulses are timed right? With a shorter runner the pulse with move back and forth more quickly and thusly may have two peaks.
It seems to me a shorter runner will have many more waves hitting the valve at the right time. My runner through the TB and into the plenum may be about 8". Also two cylinders are sharing one TB and plenum so there are two sets of waves in there. That could be either really good or they may cancel each other out and my motor will not even start. I guess I'll be the first to know.

mattho9 · Post by **mattho9** » Wed Aug 16, 2006 3:08 pm

FIntruder wrote:So is the shape of the reflective surface, the part of the plenum that the pulse reflects off of, important? Most plenums look to be curved in that section. Would a flat area reflect better? Then a square or rectangular plenum would work. .

No, The shape is one of the least important aspects. The pulse is reflected when it meets a change in gas composition, area, or temperature.

FIntruder wrote:My project is a low revvin' motorcycle engine without much room for runner length. The lower the rpm, the longer the runner needs to be for peak. I guess it comes down to what it always does, you go with what fits. I'll have to do some math but is there only one length at which the pulses are timed right? With a shorter runner the pulse with move back and forth more quickly and thusly may have two peaks.
It seems to me a shorter runner will have many more waves hitting the valve at the right time. My runner through the TB and into the plenum may be about 8". Also two cylinders are sharing one TB and plenum so there are two sets of waves in there. That could be either really good or they may cancel each other out and my motor will not even start. I guess I'll be the first to know.

This is much more complex than that. A short runner manifold at low rpm will definitely have many reflection cycles. They will reflect first emitting from the open intake valve and reflect back at the plenum towards the valve. Waves can undergo superposition when two waves meet. This totally alters the speed at which the wave travels. Plus the amplitude changes thus altering the tuning benefits. Very complicated subject.....

Matt

Bow · Post by **Bow** » Thu Aug 17, 2006 6:34 am

FIntruder wrote: My project is a low revvin' motorcycle engine without much room for runner length. The lower the rpm, the longer the runner needs to be for peak.

What is your max power RPM going to be?

What size Engine?

FIntruder · Post by **FIntruder** » Thu Aug 17, 2006 6:14 pm

1360cc Suzuki Intruder engine. 680cc per cylinder, makes 62 peak HP at 4500rpm and has a broad torque curve that peaks at 84 ft lbs with the small 36mm CV carbulators. It kept revvin' past 4500 but the power went away. I hope it will perform better with the 45mm throttle body I'm plannin' on using.

Bow · Post by **Bow** » Fri Aug 18, 2006 1:08 pm

Tuned Intake Runners

Peak Power Target @: 4500 RPM

Tuned Manifold Runner
Second Pulse Length: 24.00 In. 609.6 mm
Third Pulse Length: 21.56 In. 547.5 mm
Forth Pulse Length: 16.44 In. 417.7 mm
Fifth Pulse Length: 12.00 In. 304.8 mm

Minimum Port Cross-sectional Area Required

Peak Power @: 4500 RPM
Cylinder Bore: 3.701 In. 94 mm
Cylinder Stroke: 3.858 In. 98 mm

Minimium Area: 1.252 Sq. In. 8.074839607 Sq. cm
807.4839607 Sq. mm

Engine Air Capacity CFM

Bore: 3.701 In. 94 mm
Stroke: 3.858 In. 98 mm
Number of Cylinders: 2

Engine Displacement 83.00 ci 1360 cc
Volumetric Efficiency: 0.86

Total Air Capacity: 92.95 CFM
Single Cylinder Air Capacity: 26.098

That is what I get with your numbers.

FIntruder · Post by **FIntruder** » Fri Aug 18, 2006 5:11 pm

Thanks for the numbers. Did you get all of that just from what I gave you or do you have a data base that had the bore and stroke? Is it important to try to tune on an earlier pulse? A 1.5" diameter intake runner would be large enough from the info you gave, is going with a larger size, say 1.75" gonna have any drawbacks?
I'm not looking to get more RPM out of this motor, more interested in drive-ability, single throttle body and being able to tune each cylinder independently if necessary. The front carb is jetted differently than the rear but I am not sure if it is because the front has different needs due to heat or if it is because the front is a downdraft Mikuni and the rear a sidedraft Mikuni.

Bow · Post by **Bow** » Mon Aug 21, 2006 8:14 am

FIntruder wrote:Thanks for the numbers. Did you get all of that just from what I gave you or do you have a data base that had the bore and stroke?

I looked up the bore and stroke of your engine on the internet.

Is it important to try to tune on an earlier pulse? A 1.5" diameter intake runner would be large enough from the info you gave, is going with a larger size, say 1.75" gonna have any drawbacks?

The pulses you tune for are basicly for ease of installation. The higher pulse gives you a shorter runner. Running a larger intake runner than your intake port on the head will degrade your performance due to the decreased velocity of the air flow.

I'm not looking to get more RPM out of this motor, more interested in drive-ability, single throttle body and being able to tune each cylinder independently if necessary.

You sound like my kind of guy.

The front carb is jetted differently than the rear but I am not sure if it is because the front has different needs due to heat or if it is because the front is a downdraft Mikuni and the rear a sidedraft Mikuni.

I am not sure about the carb jetting, but if I was doing a project like this, I would match the throttle bodies to a size close to my carbs and attempt to reuse as many of the stock parts as I can. The factory did the design work, why try to reinvent the wheel?

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