A/F Ratio and HP?

[Doug Axelrod]

Can anyone point me to a graph of horsepower as a function of Air/Fuel ratio? And, for extra credit, can anyone show me one with a detonation risk overlay?

Strangely, this is for development of a business metaphor. Go figure...
thanks

[Hotfingrs]

Doug, I don't think such an animal exsists. One pull on a dyno will show rpm, horsepower, and air/fuel as well as torque. You would have to make a jet change in the carb and then do another pull and check air/fuel vs hp...and that's with all other variables remaining constant. There is a very thin line between making max hp and meltdown, that's why most run rich for the street and not max hp. For detonation you also have heads, compression ratio and timing variables. Other than comparing different dyno pulls, knowing what changes you made, I don't think you will find what you're looking for....

[Excaliber]

Ideally A/F ratio would remain the same, or nearly so, throughout the rpm band.

In other words, static, like the worker bees in your business model.

Ernie

[Hotfingrs]

Ernie, The key word is "ideally" but without a tunable EFI it's not gonna happen

[rdorman]

I would think you would be able to calculate a theoretical curve but I have not seen one. The math should not be that hard to come up with. As for detonation, to calculate its effects I would think would be next to impossible. Where did it start, when did it start, chamber design and flame front path, yadda, yadda, yadda. Of course if you had some poor sole who actually completed a dyno pull with detonating engine and then pulled again with no other changes except perhaps fuel of sufficient octane then you might have it.

Good Luck!

Rick

[Doug Axelrod]

Guys, this is not a cobra question, it's a metaphor question.
What I'm trying to show is indeed a graph of hp as a function of the A/F ratio. The metaphor is how an organization responds to "efficiency" efforts and how function increases to a point where detonation occurs. Savvy? I'm happy for the moderator to banish me to All Cobras if needed. I have to believe that someone has constructed such a curve, even if it is made of multiple individual runs or using some engine system with tunable A/F.
Thanks

[rdorman]

I got the metaphor idea from the start! But....................

Just about anyone who has posted their dyno pull here will have changed the air fuel and may have posted both. So there you have it! As for detonation, I know it makes a great word for a business metaphor but I don't think a/f plays a major part in it so you may not see the results you are looking for. Perhaps using 'miss' instead of 'detonating'?

Perhaps you might persue the VE course as the metaphor? Just a thought! What ever you end up with, it would be interesting to see.
Rick

[Anthony]

My take (understanding) on hp is that is a function of how much chemical energy is released, and percent converted to mechanical energy. The limiting factor is the amount of oxygen that can be consumed, such that the maximum hp is obtained when running a little rich, ensuring all of the oxygen is consumed, although not all of the gas is consumed. Economy is maximized when just the opposite, all of the gas is consumed with a little oxygen left over. Since I believe the perfect A:F ratio is 14.7:1, then I would think (really guessing) to get max hp somewhere between 14-14.5:1, and highest economy at or slightly above 14.7:1 .


Hp potential is determined upon the effeciency of the engine to "pump" air, the more air, the more O2, the more hp. You can also increase hp by reducing internal engine friction, increasing piston sealing, reduce internal windage, engine accesories, cooler intake temperature (more O2), etc.

I 've seen graphs on maximum hp potential vs. A:F ratio, showing best economy and where max hp is obtainable, and that may be what your looking for.


I'm sure the engine builders can elaborate much more, and/or correct me.

[Doug Axelrod]

I 've seen graphs on maximum hp potential vs. A:F ratio, showing best economy and where max hp is obtainable, and that may be what your looking for.

That would be of great interest. Trying to get the curve from dyno sheets would take a significant number of pulls with everything constant but A/F....

[Anthony]

Here is what you're looking for.

http://www.carcraft.com/techarticles/116_0402_tune/

[HighPlainsDrifter]

Hi,
even with the wide band oxygen sensor it is going to read richer and richer as the duration of your cam increases. If you then try to lean out a motor with a big cam , it really won't work,you're going the wrong way. You actually have to read the plugs or measure the changes on a dyno or dragstrip, the meter isn't going to help with dirty cams.
Perry.

[Anthony]

Here are some graphs, regarding I think a triumph.

http://www.buckeyetriumphs.org/techn.../AFMonitor.htm

[RICK LAKE]

doug axelrod Doug as far as the A/F ratio thats covered. What you want is a Knock sensor readout. If you look at a LS1 chevy motor you will see they have 2 sensors 1 front and 1 rear under the intake they produce an AC voltage went the motor is knocking and the computor retards the timing until it gets to a certain value and then starts adding again timing. It also reads when the EGR valve is working and how much flow is involved. You can get a Knock sensor kit from Jeg's or Summit. I don't think they have a output for a print out. I am not sure. Hope this helps. I will find the article on this, this in an tech series in Hot Rod done years ago. My basic answer is right but the rest may be a little off. Rick Lake

[Doug Axelrod]

Anthony,
Yes, that's the idea. Now I need some way of overlaying "risk" to the engine on top. Anyone have a quantitative measure of knock/preignition/whatever as a function of A/F ratio?

[NeedAntiVenom]

Doug,

Here is another site with similar info.

http://www.mr2supercharger.com/AFRSRF.html

Any detonation is potentially destructive, but much better tolerated by the engine under light load as the fuel charge, pressures and temperatures are lower.

[Doug Axelrod]

Jim,
Extremely useful, particularly pointing out the change in slope either side of the stoiciometric optimum.
Now, anything graphic I could use on preiginition/detonation risk as a function of A/F ratio, given constant load, etc?

[NeedAntiVenom]

Doug,

Take a few Advil then...

http://www.remtechnology.com/applications/airfuel6a.pdf

What you want depends on so many variables that there is no concrete ratio.