Psi clarification + HP stuff


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butterbeer2fd

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Aug 8, 2007
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Okay, so I'm still in the process of learning about cars, and I'm starting to get it more and more, but what exactly do people mean when they say like 463 whp @ 18.9 psi? Are they talking about the pressure being put upon the piston when the fuel ignites? Also, for boost they say like 8 psi boost. Where is the pressure going to? How much is considered a lot?

Also, I have another question to ask about horsepower/torque. On the dyno, they say the horsepower continues to rise because the RPM's are rising. Well if the RPM is rising, doesn't that mean that the torque is rising as well, meaning that the torque curve should go up to? Why exactly does the torque curve/horsepower curve go down when the engine is working harder???

Sorry for all the questions, hahaha I'm just trying to get clarifications cause I'm totally confused about this stuff.
 
ok, first know that horsepower is a function of torque, dyno's dont actually read horsepower, they read torque.

horsepower = torque multiplied by rpm devided by 5252.

so if i have 180lbs of tq at 6000rpm then i know i will have 206hp at 6000rpm.

now to address your first question, im not sure if your aware of this but it has to do with turbocharged cars, turbochargers push extra air into the intake manifold and eventually into the combustion chamber which is measured in PSI or BAR or kpa. in regards to your questions "what is alot" there is no answer, its really peronal and depends on the car, for an evo 20psi is low, for a honda 20psi is high.
 
OHHH okay I kinda get the horsepower / torque thing. Okay, so why exactly do torque curves drop down and go up? Shouldn't they be increasing since the engine is working harder??

and for the psi part, the psi part is the measure of the pressure of air being forced in from the turbocharger?? why exactly (in terms of the above example) would it be less effective on the evo rather than a honda? is it because of the cylinder size or somehitng?


thanks!!! i've been confused about this stuff for ahilwe haha:thanks:
 
butterbeer2fd said:
OHHH okay I kinda get the horsepower / torque thing. Okay, so why exactly do torque curves drop down and go up? Shouldn't they be increasing since the engine is working harder??
Click to expand...

its mathematics, per the equation above, it is impossible for peak tq to exceed peak hp.

butterbeer2fd said:
and for the psi part, the psi part is the measure of the pressure of air being forced in from the turbocharger?? why exactly (in terms of the above example) would it be less effective on the evo rather than a honda? is it because of the cylinder size or somehitng?
Click to expand...

i never mentioned anything in regards to effectivness
 
butterbeer2fd said:
and for the psi part, the psi part is the measure of the pressure of air being forced in from the turbocharger?? why exactly (in terms of the above example) would it be less effective on the evo rather than a honda? is it because of the cylinder size or somehitng?
Click to expand...


It doesn't mean that its less effective, Evo's are turbocharged cars which has the means to be heavy turbocharged way from the standard of its stock engine, and usually, the psi on a heavily turbocharged Evo are more than 20psi, which is why 20psi is low for evo, meanwhile honda's are NA kings, they don't usually get turbocharged, since their parts are all suitable for NA not turbos, so if you put in a turbo in a engine that is suitable for NA, surely 20psi is very much for the engine.

Put it this way, a person that takes drug and a person that don't take drugs, for that person that takes drug 20gram of marijuana is definitely not enuf; but for a person that don't take drugs 20gram of marijuana and they could possible die, got it?
 
So that's why I saw somewhrere that B16B makes 184.3 bhp!
(118 * 8200) / 5252 = 184.23 bhp :bow:
 
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