Calculator for intake tubes

[Clay Pitkin]

I am looking for something that may be able to tell me or to figure for me to figure how much tube or air inlet to my carbs.

In a nut shell, I am running 3 40MM's Mikunis into a 1000 CC engine. Currently I have an aluminum block that encompasses all 3 carbs, then adapts to a chrome tube, which then adapts to a intercooler. What I am looking for is do I have to many twists and turns etc? Am I loosing my air pressure by the time the air reaches the carbs?

TIA
Clay

[sanger351]

Clay,
You may want to take a look at this article.  http://www.hotrod.com/techarticles/marlan_davis_technical_advise/cold_air_inlet_sizing.html

It may or may not have what you are looking for.  I am sure that you know that generaly the less bends and adapters the better, but packaging constraints do not always allow optimal set ups.  A pic of your system may help you get more information. 

For what it is worth I read somewhere on the ingersol-rand website that oval tubing flows better than round.  I would love to hear what Blue and others think about that.
Good luck
Sean

[roadtrip]

Clay

You might also look at www.purplesagetradingpost.com
                               scroll down to Sumners home page
                               scroll down to lots of Bonneville racing info here - next to pic of AckAttack
                               scroll down about 2/3 page to usefull info #3 - figuring air inlet scoop size
                                                                         info from John Burk & Tom Burkland

DonS         

[Sumner]

Clay

You might also look at www.purplesagetradingpost.com
                               scroll down to Sumners home page
                               scroll down to lots of Bonneville racing info here - next to pic of AckAttack
                               scroll down about 2/3 page to usefull info #3 - figuring air inlet scoop size
                                                                         info from John Burk & Tom Burkland

DonS  

http://purplesagetradingpost.com/sumner/bvillecar/bville-scoop%20info-1.html

and a spread sheet here...........

http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html

Sum

[Milwaukee Midget]

You might also want to check out David Vizard's book, "Tuning the "A" Series Engine".  While it's Brit-car specific, he's a nut for flow testing, and I suspect a lot of what he's done would be applicable to your racer.  He goes into great detail on ramcharging effects, port shapes, port matching and ram pipes, and has dozens of dyno charts to back up his research.

I'd loan you mine, but it's been my bedtime reading for the last 6 months.

[panic]

That Davis article is a puzzle.
He spends all that time calculating engine size, VE, 3456, converts MPH into f/s, blah (which, IMHO, if the reader did not know what these were this is not a project within his competence).
And then no explanation of the effect of increased MPH (pressure), or the target air speed in the duct?
His formula incorporates the square root of MPH as a size variable:
200 MPH duct is 1 ÷ (2^.5) vs. a 100 MPH duct, or 70.71% duct area, while the density due to pressure only increases from 14.88 to 15.4 (assuming 14.7 psi base) or 96.6% area.

Am I tripping over something important?

[Dean Los Angeles]

Am I tripping over something important?

Oh, yes. The "blah" part was the key.  Your head says that the faster I go the more pressure I can get into the engine. Sadly, this doesn't work any where near the way you think. The difference in pressure between zero and 200 mph is about 3/4 psi. That's it. Air is nearly incompressible at the low speeds LSR vehicles run (less than Mach 1) On a 500 hp engine that might equate to 10 hp. Any increase is free horsepower and is important, just not the amount you would figure.

The calculation for the inlet size is important so that you don't undersize it and cost lost horsepower, or oversize it and cost wasted drag.

All of this is in front of the intake system. What you are asking is how much of this am I losing through plumbing losses before it gets to the cylinder. All surfaces in the intake cause drag which reduces the conductance of the tubing. The only way to determine if your system will allow enough flow to support the engine is to put it on a flow bench.

I know, that's not what you had in mind at all. (I remember the "blah" part.) Very tough to do any other way.

[panic]

I don't think you grasped my point.

"Your head says that the faster I go the more pressure I can get into the engine. Sadly, this doesn't work any where near the way you think. The difference in pressure between zero and 200 mph is about 3/4 psi" is, in fact exactly what I said.

The Davis formula shows a change in inlet size vastly greater than this.
Why?