So...I've been working on some math lately, and figured since I had it all broken down into nice little spreadsheets I would share.
Why would you need / want to use these?
- Calculating your engine CFM.
- Calculating the flow capacity (volume or velocity) of different size pipes tailored to
your engine (exhaust or intake).
- Calculating potential max HP achievable with each pipe size.
As an example, I have a much abbreviated version below. These numbers were calculated using a 3.5L engine, working at 90% volumetric efficiency, with a max boost of 15.5psi, and a redline at 6Krpm, using 16ga. T409 Stainless Steel; based on 686CFM:
DIA. | Inside Area/sq ft | Velocity/fps | Max cfm | Intake HP | Exh. HP
2.00 0.0191650391 597 517 345 235
2.25 0.0246164280 464 665 443 302
2.50 0.0307392405 372 830 553 377
2.75 0.0375634766 304 1014 676 461
3.00 0.0450591363 254 1217 811 552
3.50 0.0620947266 184 1677 1118 762
4.00 0.0818560113 140 2210 1473 1004
What do these numbers tell you?
That the inside area of a 2.5" SS pipe is 0.03...sq ft which has a max cfm of 830. Also that an engine flowing 686cfm flows air at a velocity of 372fps, has a maximum obtainable horsepower of 553hp if equipped with a 2.5" intake, and 754hp if equipped with a dual 2.5" exhaust.
(Don't forget, for dual pipes, double the numbers.)
Now, these numbers have not taken into account the friction loss caused by bends or restrictions by mufflers. Nor do they account for the skim loss caused by laminar air flow against the surface of the pipe. This is purely an example of air flow in, or out of your engine, and the parameters caused by the restriction of different diameter openings ie. pipe size.
If you would like to see customized results to your own CFM, follow these simple instructions:1. Visit
THIS website and enter
your cars parameters into the data boxes.
2.
CLICK the SUBMIT button.
In the bottom R hand corner of the graph produced, you will find your car's CFM.
3. Download or edit as a Google Doc
THIS spreadsheet I've created, from Google Drive and enter your car's CFM into the
Volume / CFM column colored in
RED.
4. Fill your cars CFM value into any/all cells within the
Volume / CFM column, that you want data for. I wrote it for 1" - 4". The results auto calculate based on your CFM input.
I wrote it in a step by step fashion to show my work. It should be pretty easy to follow.
- Downloading the spreadsheet and adding your CFM will tell you the volume and velocity of
your engine's airflow with each pipe size.
-The inside area and radius of each pipe, Max HP for intake and exhaust, and Max CFM, are NOT dependent on your engine's cfm...these are static numbers for each pipe size.
**NOTE: When air velocity reaches 450fps the sheer speed inhibits air flow and acts as a restriction. Velocity above 450fps is to be avoided.
As always, with any questions, comments, or concerns, please don't hesitate to hit me up with them. I love being here and hope this stuff can be useful to someone else.
I hope that wasn't too confusing.
