Calculating CFM used from Dyno sheet ?

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Re: Calculating CFM used from Dyno sheet ?

Post by Warp Speed »

Scotthatch wrote: Fri May 18, 2018 4:42 pm
DrillDawg wrote: Fri May 18, 2018 4:28 pm As the intake valve closes, a pulse is sent up through the intake tract and as the pulse hits the opening of the intake tract the pulse is bounced back toward the intake valve, time it correctly and you help increase your ve, that's why motorcycles are using variable length velocity stacks now days. Works on the exhaust, works on the intake.
I understand the idea .... just not seen data to support it and as I keep checking dyno numbers with inertia ram and it hits the peak number right I have trouble believing that is what is going on... I have looked for dyno sheets that have a power bump before peak power that might show a pulse showing up a little early from peak power as in not tuned to peak and I am still looking
Combustion data with intake, cylinder and exhaust pressures show this in detail. Air has mass, but very little force compared to the pressure wave.
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Re: Calculating CFM used from Dyno sheet ?

Post by Scotthatch »

15251040053770.jpg

You mean something like this one that he posted before where all the pressure events cross the 0 line at the closing point of the intake? I have trouble believing that would happen in a real motor...
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Re: Calculating CFM used from Dyno sheet ?

Post by Warp Speed »

It happens, and looks just like that!
You start studying that stuff, and things begin to make sense in a different direction........then it starts to get complicated again! Lol
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Re: Calculating CFM used from Dyno sheet ?

Post by Stan Weiss »

Looking at the posted picture, I have a couple of questions.

Is 630 crank degrees rotation? If so isn't that 10 BBDC?

At RPM in the power curve do I want to see this happen?

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Re: Calculating CFM used from Dyno sheet ?

Post by Warp Speed »

It's really hard to tell exactly what that little snip is showing, especially with no legend. I was just referring to the sign waves of pressure that are constantly moving through the system. Capturing these to your advantage are the keys, and what dictate the event placement.
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Re: Calculating CFM used from Dyno sheet ?

Post by digger »

tdc is 360

the 630 is not the IVC its the dashed grid line marker, each dash line is spaced 30* apart by default so IVC is ~624 (i.e 84* ABDC)

optimize the IVC to trap the most mixture, but the amount it traps is dependent on other events and the prior history of the what went on earlier in the cycle. the amount you trap then changes the other events (i,e, how much you need to exhaust) so you go round and round in circular logic understanding how each event influences another to converge on the optimal. then you compromise for rpm you want.
Last edited by digger on Fri May 18, 2018 7:32 pm, edited 1 time in total.
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Re: Calculating CFM used from Dyno sheet ?

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15266863213430.jpg
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Re: Calculating CFM used from Dyno sheet ?

Post by Stan Weiss »

Thanks for the full picture. It is what I believed. 0 to 720 / 2 full crank rev / one complete cylinder cycle. So 640 would be BDC. 630 = 10 BDDC 624 = 16 BBDC

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Re: Calculating CFM used from Dyno sheet ?

Post by hoffman900 »

Stan Weiss wrote: Fri May 18, 2018 7:48 pm Thanks for the full picture. It is what I believed. 0 to 720 / 2 full crank rev / one complete cylinder cycle. So 640 would be BDC. 630 = 10 BDDC 624 = 16 BBDC

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Stan,

That's my graph. Let me know what you want to see I can I pull up some. Numbers, wave directions, etc.

Also, It doesn't always cross zero at the same point.
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Re: Calculating CFM used from Dyno sheet ?

Post by pastry_chef »

Scotthatch wrote: Fri May 18, 2018 1:09 pm The formula as it is in the superflow manual

15266624958120.jpg
Thanks Scott.
Does anyone know the first origin of that Z-factor formula?
Perhaps one of those engine development books like Taylor, Philip Smith or Heywood?
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Re: Calculating CFM used from Dyno sheet ?

Post by Scotthatch »

pastry_chef wrote: Fri May 18, 2018 9:53 pm
Scotthatch wrote: Fri May 18, 2018 1:09 pm The formula as it is in the superflow manual

15266624958120.jpg
Thanks Scott.
Does anyone know the first origin of that Z-factor formula?
Perhaps one of those engine development books like Taylor, Philip Smith or Heywood?
I tried to find out years ago ... it's in several manuals just like the superflow manual ...only reference I ran across was that it was done by some well known Japanese engineer
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Re: Calculating CFM used from Dyno sheet ?

Post by digger »

Stan Weiss wrote: Fri May 18, 2018 7:48 pm Thanks for the full picture. It is what I believed. 0 to 720 / 2 full crank rev / one complete cylinder cycle. So 640 would be BDC. 630 = 10 BDDC 624 = 16 BBDC

Stan
thats wrong BDC is 540 (360+180=540)
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Re: Calculating CFM used from Dyno sheet ?

Post by randy331 »

Scotthatch wrote: Fri May 18, 2018 3:16 pm I think the pulse thing may be a joke
Pulses are a Joke ??

I had one that had a dip at 7000 rpm. A few cams, a couple intakes with work on them more than once, 3 sets of heads on it, 2-3 collectors on the headers,..lots of dyno pulls over 8-10 dyno sessions, a few carb spacers, 3-4 different carbs. That stubborn power dip stayed there.

Then switched out my headers for a set the dyno shop had hangin on the wall,.... and power dip gone.
Same primary pipe diameter.

What did away with the dip if it wasn't waves ?

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Re: Calculating CFM used from Dyno sheet ?

Post by Stan Weiss »

hoffman900 wrote: Fri May 18, 2018 7:55 pm
Stan Weiss wrote: Fri May 18, 2018 7:48 pm Thanks for the full picture. It is what I believed. 0 to 720 / 2 full crank rev / one complete cylinder cycle. So 640 would be BDC. 630 = 10 BDDC 624 = 16 BBDC

Stan
Stan,

That's my graph. Let me know what you want to see I can I pull up some. Numbers, wave directions, etc.

Also, It doesn't always cross zero at the same point.
Bob,
At what RPM is that and what RPM is Peak HP?

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Re: Calculating CFM used from Dyno sheet ?

Post by Stan Weiss »

digger wrote: Fri May 18, 2018 10:21 pm
Stan Weiss wrote: Fri May 18, 2018 7:48 pm Thanks for the full picture. It is what I believed. 0 to 720 / 2 full crank rev / one complete cylinder cycle. So 640 would be BDC. 630 = 10 BDDC 624 = 16 BBDC

Stan
thats wrong BDC is 540 (360+180=540)
Sorry, my bad. :oops:

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