Ok , I know all engines are different but what have most
of ya seen best HP with on a naturally asperated engine?
I always thought like 12.8 but more I talk to manufacturers they say closer to 13.5.. any thoughts?

Ohh yeah,I have a Wideband.

 

Peak torque is typically where your engine will run the richest since that is the engine's peak volumetric efficiency point, around 11.8-12.3 is fairly common. Past peak torque less fuel is reuired and peak hp is typically found in the 12.8-13.5 range as you indicated.

 

Thank you Monte.

 

some engines like to run leaner (hotter) and make more power doing it. as long as detonation is controlled in these situations, the engine will typically make more power. running rich is just a safety factor and an insurance factor, it doesnt actually add power if you run rich. and the only reason running lean can make more power, is simply because of the extra heat produced. in situations where alchohol and nitro is used a motor can make a gob more power running slightly lean.

 

Peak torque, VE and A/F ratio don’t really have a relationship like that, what most people see as a relationship is just an area where the currently common design compromises overlap.

Yes, peak torque and VE do happen at the same point, but that is because the torque curve and VE curve are the same curve. If your engine ran at 100% VE all the time your torque curve would be a flat line with the same value (ex, roughly 399lb-ft for a 350).

And yes… maximum torque numbers usually happen at lower A/F ratios then max HP. That’s simply because most engines use extra fuel to cool the chambers and slow combustion to control detonation and an engine will be more prone to detonation at lower rpms, where it builds maximum cylinder pressure (usually at max VE)… so running richer will usually suppress detonation longer and allow you to run a more aggressive tune, making more torque. Of course, that tune is to rich for maximum cylinder pressure production so at higher rpms where cylinder pressure isn’t as high because VE is dropping off and the piston is moving relatively faster then the flame front you can start leaning out the A/F ratio to make maximum power.

With most current production designs, the maximum hp and torque is usually made at the a/f ratio that allows you to run the closest to optimum timing without detonation. Usually at about 12.5:1 or higher for HP and just under 12 for torque. Newer, fastburn chamber designs (LT1, LS1, Vortec, Fastburn...) tend to be more efficient and have better detonation control moving those ratios up into the 13.5:1 range.

If detonation was taken out of the picture then max torque and HP would happen at stoichometric (14.7:1) or even higher. There are port/chamber designs that work well at ratios as high as 23:1, and some Winston cup style engines make max power in the 18:1 range (remember, if they can make the HP using less fuel then that means more laps, and they all run at BSFC’s in the low .3x range). If you can do a good job at controling timing and heat, you can use a lean mixture to control burn speed and peak pressure delay just like most people use a rich mixture.