THe human brain doesn't use 10% of its horsepower. BUT what it does do is use 90% of its horsepower to maintain behind the scene functions. Like the heart and the kidneys and muscles and blood and Homoestasis. In most cases the human brain does use 10% of its horsepower for cognitive thought but its still running 100% at all time.
Luffy could in theory use gomu gomu giant fusen to fill up his lungs with a ton of air. Then use gear 2 to pump that air. Squeeze all that Oxygen in his lungs into his blood stream and then like a valve twist his body up so all that blood is forced to his brain with the last "twist' being his neck so his brain is shut off from his body that giving him 100% of his brain power for his thoughts and not 10% (with 90% dealing wiht his body) plus ontop of that the blood being super oxygenated blood makes his brain run faster giving him more power under the hood
So the idea in short would be luffy trading in control over his body temporarily for hieghtened brain power to stragize or think clearer.
Luffy could in theory use gomu gomu giant fusen to fill up his lungs with a ton of air. Then use gear 2 to pump that air. Squeeze all that Oxygen in his lungs into his blood stream and then like a valve twist his body up so all that blood is forced to his brain with the last "twist' being his neck so his brain is shut off from his body that giving him 100% of his brain power for his thoughts and not 10% (with 90% dealing wiht his body) plus ontop of that the blood being super oxygenated blood makes his brain run faster giving him more power under the hood
So the idea in short would be luffy trading in control over his body temporarily for hieghtened brain power to stragize or think clearer.