SAE vs. ICAO Baselines…

[stevesrt8]

Originally Posted by EricG

Oh no - I'm boasting right there with you brother - I didn't intend that to be taken as a bad thing. My run came at an estimated DA of about 0 or sea level...pretty good conditions for the Ohio Valley.
I don't know much about boost applications, but what you are saying sounds right to me.
Eric

No harm, no foul. I did not take it bad at all. Just proud of my car. I'm sure we all are! I could not BELIEVE that a 4200 pound sled could move like that, and that's why it is remarkable to me. Still is. And trust me on this one, it's MUCH faster now!

Regardless of what you know about boosted motors, almost anyone would agree that when you pressurize the intake, the HP goes crazy. And I used to drive a turbo car, it behaved very differently in the mountains of Kentucky than my N/A hot rod did!

So all I'm trying to get across is that if you're going to correct the time there should be some sort of "correction" for nitrous or boosted cars since they make their own "air".

Any thoughts?

[Midnightsun300c]

Eric:

I was hoping that you would step forward and show your metal. Thanks for the response and I think that your summary of my goal is accurate. I want to establish a standard that all forum members can use. Should we use the SAE baseline or ICAO baseline while making our atmospheric correction?

The underline incentive for me to pursue this goal is so that everyone is just that much more accurate when comparing their engines performance from different parts of the world.

You bring up a different point as well, and that is just how accurate the correction is. And I think you have already touched on the answer which is that it is only as accurate as the measurements. The formula, the math is absolute. Whether the SAE calculator gives us a good or bad number depends on whether or not we enter good or bad data.

Weather stations are very inexpensive and I would hope that most tracts have one to establish their published data, but I do not know. They make and I own a portable weather station that is quite handy and you can hang out the window on your return trip back to the starting line that will give a true track reading. The particular one I have measures both dry and wet bulb, humidity, and absolute barometric pressure. It is quite handy. I have found this the key to performing well in bracket racing. As the day progress and weather systems pass through, or temperatures rise you can make those .01" adjustments to your ET that keeps you in the hunt. Even without the track weather station quite often there is a FAA weather station nearby that will give reliable data for your track. Undoubtedly there will be tracks that have better data than others and some that have no usable data at all.

You touched on another benefit of using corrected data while discussing engine performance and that is the effort made to only race on a cold clear days. Think of how much more fun we would have if we didn't limit our track time to only days that will give us the best times without correction. Members could be openly comparing notes throughout the summer without the cloud of slower ET times.

I am glad that you are OK with the SAE standard. I will mark you down as a yeah for purposes of conduction this Ad Hoc survey. This brings the count to 4 nil in favor of SAE, unless I misinterpreted your post. Here is the online calculator that I use. I think that you will find the discussion on this website interesting and informative in regards to atmospheric correction. Engine Tuning Calculator - dew point

[Midnightsun300c]

Originally Posted by stevesrt8

I also would like you engineering types to express your views on the various forms of supercharging, turbo, mechanical, and nitrous/chemical. Please advise us how we factor these into said corrections.
Nitrous is especially interesting with its unique combination of cooling and pressurization of the manifold with no parasitic losses. I'd like to see that quantified!? The main interest I have in this thread is comparing the D/A adjustments between N/A cars and boosted cars. I maintain that boost or nitrous "create their own" air and thus are not entitled to the same correction factor that an N/A engine is. What do you think?

Steve, this turned out to be a lot simpler that I had imagined. It was more of a concept solution than any nuts and bolts, so to speak.

Atmospheric corrections for chemical and mechanical forced induction...

Turbochargers and Supercharger:
Let’s agree that superchargers and turbochargers mechanically maintain an artificially elevated level of air pressure in the intake manifold. This elevated intake manifold pressure is maintained regardless of the ambient air pressure. It follows that a 6 psi supercharger at sea level is going to provide 6 psi at 5,000 feet. It also follows that there would be no correction for altitude for a supercharged or turbocharged engine as the available air for the engines combustion cycle would be the same regardless of the altitude.

This is not to say that there is no correction necessary for varying weather conditions. Humidity affects the percentage of oxygen in air and temperature affects the mass of the air as always. It would then follow that to normalize separate mechanical forced induction engine tests one would still use the SAE formula but run both calculations with an elevation of 0.

Nitrous Oxide:
I think we can agree that the injection of N20 in liquid form at approximately 1000 psi into or immediately before the manifold does several things. It drops to manifold pressure of approximate 15 psi and evaporates causing the surrounding air to cool significantly. It also increases the oxygen concentration of the intake manifold because it is of a higher oxygen concentration than the air. As a result your intake manifold charge has a higher percentage of oxygen content because of the nitrous oxide and an increased mass because of the cooler temperature. This benefit is regardless of altitude, temperature or humidity. If it cools 70 degree air 30 degrees then it will cool 40 degree air 30 degrees as well.

Now here is where it becomes interesting. A N20 injection system commonly doses out its charge in units of horsepower and to achieve that 75 shot or 100 shot it injects a given amount of nitrous per unit of time. Therefore a 100 shot will add 100 horsepower at sea level or 5,000 feet over and above whatever horsepower the engine is making without it at the time. In other words, the amount of available oxygen in the intake manifold will be whatever the ambient amount is plus the additional effects of the N20 injection.

It now follows that to apply atmospheric correction to a nitrous injected engine one must figure the correction factor the same as a naturally aspirated engine but subtract the added horsepower from the nitrous before applying the correction factor to the horsepower.

In summary, it is my opinion following the above thought process that to apply atmospheric corrections to supercharged and turbocharged engines one must use the SAE formula with 0 elevation. To apply atmospheric corrections to nitrous engines one must use the naturally aspirated horsepower of the engine.