Calculating CFM used from Dyno sheet ?

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hoffman900
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Re: Calculating CFM used from Dyno sheet ?

Post by hoffman900 » Sun May 20, 2018 7:11 pm

swampbuggy wrote:
Sun May 20, 2018 6:58 pm
VERY VERY interesting Bob, would appreciate anything you can add, Mark H. =D>
Well, this is pretty typical of what is (was?) used in Australian V8 Supercars:
Image

Here is similar to what NASCAR uses:
Image


One of the EMC teams used this one year:
Image

a tunnel ram is essentially that, except with the carburetors sitting over the runners and the bellmouths flush to the floor. Plenum volume on this manifolds are too big for circuit racing. I don't know what the insides look like, but I believe they're a bit like this:
Image
Basically a tunnel ram with lid.


In regards to Acoustic Wave Action vs Mass Inertia, This is one of the all time great threads here:
http://speedtalk.com/forum/viewtopic.php?f=15&t=28901
Vannik, Schmidtmotorworks, and Nitro2 are the posters to pay attention to (not that others don't add anything, they certainly do!).
-Bob

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Re: Calculating CFM used from Dyno sheet ?

Post by Scotthatch » Sun May 20, 2018 11:32 pm

15267463087920.jpg

So am I to assume that the people that posted fully agree with this page on acoustical wave and how it works to make power?
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Re: Calculating CFM used from Dyno sheet ?

Post by SchmidtMotorWorks » Sun May 20, 2018 11:48 pm

This CFD might be helpful to visualize.
The all receive the exact same signal.
Only one pulse is used and allowed to decay.

Image
http://www.schmidtmotorworks.com Aerospace Machine Work: Prototypes, Tooling, Molds.

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Re: Calculating CFM used from Dyno sheet ?

Post by SchmidtMotorWorks » Sun May 20, 2018 11:55 pm

Here is how it plays out in a tunnel ram

Image
http://www.schmidtmotorworks.com Aerospace Machine Work: Prototypes, Tooling, Molds.

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Re: Calculating CFM used from Dyno sheet ?

Post by Scotthatch » Mon May 21, 2018 1:16 am

SchmidtMotorWorks wrote:
Sun May 20, 2018 11:48 pm
This CFD might be helpful to visualize.
The all receive the exact same signal.
Only one pulse is used and allowed to decay.

Image
So you agree with how that page works???

It says right on it that even the 2nd harmonic is only good for 10%

So ram is doing the other 90%

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Re: Calculating CFM used from Dyno sheet ?

Post by gruntguru » Mon May 21, 2018 1:54 am

I think the 10% is the pressure peak above average pressure. So in a "perfect" intake tract you could get 10% supercharge or 110% VE.

"Inertia" and "Wave" tuning are the same thing. Imagine hanging a broom handle vertically from your hand and oscillating your hand up and down - that's inertia. Now imagine the same experiment hanging a long "slinky" spring. At certain frequencies your hand will feel lots of "inertia" and at other frequencies very little "inertia".

Wave tuning harnesses the inertia of the air column. The air column is compressible/springy - not rigid.

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Re: Calculating CFM used from Dyno sheet ?

Post by hoffman900 » Mon May 21, 2018 5:47 am

Scotthatch wrote:
Mon May 21, 2018 1:16 am
SchmidtMotorWorks wrote:
Sun May 20, 2018 11:48 pm
This CFD might be helpful to visualize.
The all receive the exact same signal.
Only one pulse is used and allowed to decay.

Image
So you agree with how that page works???

It says right on it that even the 2nd harmonic is only good for 10%

So ram is doing the other 90%
Read the thread I linked to. Clint’s first post in the second page:
nitro2 wrote:
Tue Nov 15, 2011 1:35 pm
Inertia = 0% Waves = 100%

Lets say we ignore the pulsing effects in the intake at IVO, for simplicity lets say they aren't there. Then at IVO, the inertia when the intake valve starts to open is 0. The inertia in the intake is going to stay at 0 indefinitely, unless acted upon. The action, piston motion (and also residual intake waves but we got rid of them above, and exhaust suction or reversion), causes wave action which in turn causes the intake motion and of course intake inertia increases. Same idea when its all slowing down, wave action happens then the intake motion decreases. Absolutely nothing happens in the intake without wave action, it just sits there stopped. The A/F mixture half way up the runner (or anywhere else) knows absolutely nothing about speeding up from dead stopped until a wave from the cylinder travels up the runner to tell it to get going, and it doesn't know to stop either until a wave tells it to stop. Actually its a series of waves not a simple sinusoidal wave (see further below).

It's important to understand that "wave tuning" as most people think of it is a very specific thing that is primarily related to what happens during overlap rather than during the rest of the cylinder filling period. Only during IVC to IVO do the events in the intake behave like a sinusoidal (or similar) wave and what this wave is doing just before overlap determines to a large degree what happens during overlap. The exhaust wave at overlap plays the other part. So how much effect so called "wave tuning" will have on power really depends largely on how much gain can be made by having a good overlap flush event vs. a not so good overlap flush event.

Wave tuning during the rest of the intake process (i.e. the main cylinder filling process) is a whole different story. The waves are simply an infinite series of tiny wave events all summed up. How they sum up determines what you get for cylinder filling. This is not a sinusoidal event at all. It is also the part of wave tuning that most people don't know too much about.
-Bob

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Re: Calculating CFM used from Dyno sheet ?

Post by user-23911 » Mon May 21, 2018 7:46 am

Scotthatch wrote:
Sun May 20, 2018 11:32 pm
15267463087920.jpg


So am I to assume that the people that posted fully agree with this page on acoustical wave and how it works to make power?
No.

user-23911

Re: Calculating CFM used from Dyno sheet ?

Post by user-23911 » Mon May 21, 2018 7:52 am

SchmidtMotorWorks wrote:
Sun May 20, 2018 11:48 pm
This CFD might be helpful to visualize.
The all receive the exact same signal.
Only one pulse is used and allowed to decay.

Image
That's not quite right either.

It's an acoustic transmission line.
When there's a change in acoustic impedance, there's a reflection.
When the wave gets to an opening (plenum) the wave (pulse) is inverted and reflected.
When the wave hits a solid object (closed valve) the wave is not inverted but still reflected.

Whet the above sim does NOT show is whether the valve is open or closed.


The principle is exactly the same as used in telecommunications for finding cable faults using a pulse echo tester.
That's how you know both the distance to the fault AND you know whether the fault is an open circuit or a short.

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Re: Calculating CFM used from Dyno sheet ?

Post by swampbuggy » Mon May 21, 2018 9:02 am

Wow--- i am loving all this, sure glad my simple thread (??????) turned into ALL of this extra data, thanks guy's Mark H :D

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Re: Calculating CFM used from Dyno sheet ?

Post by Scotthatch » Mon May 21, 2018 10:22 am

My problem with that page is this

If I take a gen 1 sbc the head has a runner length of 5.5 in and a single plane standard race intake is 6.5 in long

So using that I can figure rpm for the harmonic

2nd = 11000 rpm good for 10%
3rd = 8083 rpm good for 7%
4th = 6166 rpm good for 4%
5th = 4500 rpm good for 1%

So we should see increase in power at those points in the rpm band and if it a sinusoidal wave then at the half way point between them we should see a drop of the same amount from a baseline ..... in essence we should see the wave in the power output of the engine as it helps or hurts the power output yet we don't
15269124405140.jpg
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Re: Calculating CFM used from Dyno sheet ?

Post by DrillDawg » Mon May 21, 2018 11:03 am

1100 x 141 x .705 \ 6900 = 15.84

If your heads flowed 450 you would peak around 7500rpm, so....

1100 x 141 x .705 \ 7500 = 14.5"

that's why you see extended runners in some single plane intakes

That's using swampbuggy's 516 and 282 duration at .50
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Re: Calculating CFM used from Dyno sheet ?

Post by Scotthatch » Mon May 21, 2018 11:15 am

DrillDawg wrote:
Mon May 21, 2018 11:03 am
1100 x 141 x .705 \ 6900 = 15.84

If your heads flowed 450 you would peak around 7500rpm, so....

1100 x 141 x .705 \ 7500 = 14.5"

that's why you see extended runners in some single plane intakes

That's using swampbuggy's 516 and 282 duration at .50
Not sure I understand what you are saying.......

What formula are you using and do you have more information about the engine

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Re: Calculating CFM used from Dyno sheet ?

Post by DrillDawg » Mon May 21, 2018 11:19 am

I posted the formulas on page 9 and its the OP engine.
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Re: Calculating CFM used from Dyno sheet ?

Post by Scotthatch » Mon May 21, 2018 11:33 am

DrillDawg wrote:
Fri May 18, 2018 3:09 pm
Intake tract length tuning

2nd pulse

((1100x 1\2intake can duration )x .96)\rpm

3rd pulse, same but use .705 instead of .96

4th pulse, Same but use .538 instead

OK ... not a formula I have seen before so where is it from and what is it based on ?

OP engine?? Code for something?

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