I don't disagree with what you wrote Carl, but that wasn't my point. The item being changed is the heads (flow). I understand that you can run less boost with the higher flowing heads, I just don't understand why that matters.
I tried to answer that in my second sentence: "Having to run more boost to make a given amount of hp means you are running higher cylinder pressures (and have more pumping losses because the exhaust manifold pressure is higher) and thus need more octane, relative to a better flowing motor that can make the same hp at lower boost." I guess that was just too terse, but I had to get back to work
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A lot of people seem to think that there is some big advantage to running lower boost and making the same power. I don't get that. Boost is just the pressure in the intake. It is cylinder pressure that creates horsepower, aids detonation, and stresses the bottom end.
The same mass of air at the same afr and everything else releases the same amount of energy in the cylinder, true. However, how much of that energy can be extracted as cranshaft hp is where all those efficiencies come in and let a better flowing motor make the same power at lower boost. Higher boost in the intake means higher pressure in the exhaust manifold, and that means more power wasted on the exhaust stroke, for example, fighting those pumping losses to get the burnt gas out of the cylinder and into the manifold. In the turbo, the turbine and compressors are generally more efficient at lower pressure ratios (until you go too low but I'm assuming we aren't there yet since a turbo that big would be basically unspoolable). That means that less hp is wasted driving the turbine, and less goes into heat in the compressor, so again, you get more hp out of the crankshaft.
I also understand that due to the efficiencies, the ultimate potential is higher with higher flow and lower boost. But sans detonation, the same mass of air and appropriate amount of fuel will create the same results, whether they be copious amounts of power or catastrophic failure. With detonation, I could see high boost being an advantage since there will likely be less air mass and fuel in the cylinder because it is less efficient and likely to detonate at a lower power level.
Even at the same hp level without detonation, the efficiencies matter because they mean less waste heat goes into the heads/pistons/oil/exhaust valves/cooling system, and less stress is placed on the headgaskets, ring lands, and everything else, because you can make that same hp with lower cylinder pressures. A better flowing lower boost motor will last longer and be less prone to detonation if the tune is off a little than will a poorer flowing motor at the same hp level but higher boost.
I tried to answer that in my second sentence: "Having to run more boost to make a given amount of hp means you are running higher cylinder pressures (and have more pumping losses because the exhaust manifold pressure is higher) and thus need more octane, relative to a better flowing motor that can make the same hp at lower boost." I guess that was just too terse, but I had to get back to work
.A lot of people seem to think that there is some big advantage to running lower boost and making the same power. I don't get that. Boost is just the pressure in the intake. It is cylinder pressure that creates horsepower, aids detonation, and stresses the bottom end.
The same mass of air at the same afr and everything else releases the same amount of energy in the cylinder, true. However, how much of that energy can be extracted as cranshaft hp is where all those efficiencies come in and let a better flowing motor make the same power at lower boost. Higher boost in the intake means higher pressure in the exhaust manifold, and that means more power wasted on the exhaust stroke, for example, fighting those pumping losses to get the burnt gas out of the cylinder and into the manifold. In the turbo, the turbine and compressors are generally more efficient at lower pressure ratios (until you go too low but I'm assuming we aren't there yet since a turbo that big would be basically unspoolable
). That means that less hp is wasted driving the turbine, and less goes into heat in the compressor, so again, you get more hp out of the crankshaft.I also understand that due to the efficiencies, the ultimate potential is higher with higher flow and lower boost. But sans detonation, the same mass of air and appropriate amount of fuel will create the same results, whether they be copious amounts of power or catastrophic failure. With detonation, I could see high boost being an advantage since there will likely be less air mass and fuel in the cylinder because it is less efficient and likely to detonate at a lower power level.
Even at the same hp level without detonation, the efficiencies matter because they mean less waste heat goes into the heads/pistons/oil/exhaust valves/cooling system, and less stress is placed on the headgaskets, ring lands, and everything else, because you can make that same hp with lower cylinder pressures. A better flowing lower boost motor will last longer and be less prone to detonation if the tune is off a little than will a poorer flowing motor at the same hp level but higher boost.
