MicroSquirt.com read only forum (Jan.15,2018)

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

Interesting reading

AW

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.

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

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?

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.

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

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!

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

That is one place that sells parts.

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

http://www.velocity-of-sound.com has some nice velocity stacks.





edit: forgot the 3w's.

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.