chitwnsazn

iTrader: (3)

exactly, SP wouldn't just do something to make my numbers look higher than they should so maybe I just got a good engine lol. I did use sea foam to clean the engine and stuff. I don't know think that justifies my high numbers though. hmmm I guess I'll have to take my car to the track and see how fast it runs

SPORTcoupe

iTrader: (2)

Sorry to dig up an older thread but I don't understand how these #s are possible.
Here are my calculations:
Stock = 180 rwhp @ 14.7 psi (atmospheric pressure)
180rwhp/14.7psi = 12.25 rwhp/psi
Now the engine is crammed with 16 psi over stock for a grand total of 30.7psi (with the fuel to match of course)
12.25rwhp/psi * 30.7psi = 376 rwhp
Where does the extra 100 HP come from?

The reason I bring this up is because these calculation allowed me to predict my rwhp @ 5 psi perfectly.

Anyone?

~Alan

qtb33

It can come from many things including compressor and turbine eff.

CP_Ree

iTrader: (1)

Yea, as stated above, turbo size and efficiency do affect hp gains per psi of boost. My SC did 188whp/185tq bone stock on our dynojet. I can see the difference between dynos and cars making as much as a 12 whp difference though it is known that Mustang dyno's do read lower sometimes.

Kaiser

iTrader: (1)

What weight did they factor in on the Mustang dyno? Did they enter the correct elevation? Those are 2 things that would throw it way off.

Alan-
You cannot predict hp by psi. Suppose I hooked up an air compressor to my motor that put out 100psi at 38cfm. Would I put down 1225 hp? It depends on how many cfm it flows at what psi. I'm glad that you are happy with the number you put down but basing all cars on your equation with different turbos and efficiency ranges won't work.

Verge

200 whp on a stock 300...



nope, definitely something fishy there

SPORTcoupe

iTrader: (2)

I get your analogy there but it doesn't quite work that way either.
Pressure is created when the turbo out-flows the head.
Without any head-work done, the amount of flow the head can support remains constant so more flow from the turbo is what creates pressure.

I might be totally off on this, but that is how I understood the creation of positive pressure.

Assuming the above is true, as long as the turbo is able to keep up the same pressure, the turbo can be considered efficient.

To me, it's easier to break it down to a single detonation in the combustion chamber:
At WOT the pressure inside the cylinder relative to atmosphere is close to 0 psi which is 14.7psi relative to the stuff you find in outer space (vacuum). At WOT there is also 1 part fuel per 12.0 parts air in the chamber.
Add 5 psi of boost and .42 parts fuel (to keep a 12:1) ratio and you have created the same system you had before but with more air and fuel.

Somebody tell me why I'm wrong.

~Alan

NAZTY97

for one, the laws of thermo are not linear, especially when Volume, Pressure, and Temperature of gasses are involved. Any changing of any of those factors can greatly vary any equation that yields output.

think about it... on colder days, denser air, turbo feels reallly good,... hotter days, thinner air, turbo feels very weak... same components, same car, same gas, same everything, but atmosphere is different... output changed....

SPORTcoupe

iTrader: (2)

You've noted the fact that my math does not include every factor imaginable, but still doen't tell me why the concept is wrong.
BTW, when doing my calculations, I was assuming ceteris paribus.

~Alan

chitwnsazn

iTrader: (3)

Got any ideas on what is going on? cuz the dyno result are right there...I'd be a happy man if I knew what it was?

NAZTY97

The short of it... if you put more fuel, more air in same size cylinder,... wouldn't Pressure and Temperature change???

verylost

Sportcoupe,

Nasty97 is correct in saying that the laws of thermodynamics applying to this situation is not linear. You can't easily say that 1 psi will make a set amount of hp.

For example, 1 psi may make 1 hp. 2 psi will make 4 hp and 3 psi will make 16 hp. These numbers are in no way representative, but I am trying to show you the relationship.

Another flaw in your logic is 14.7 psi or atmospheric pressure. If the pressure of intake air were atmospheric pressure, there would be no air flowing into the engine.

I am a little tired but I think I'll take a crack at remember my old thermo and fluid dynamics days.
Let's assume a fixed amount of fuel during ignition and fixed volume in the cylinder and fixed stroke by the piston. In this instance, to make more power, we need a greater stroke velocity.
We also need to assume that at normal conditions, the cyllnder doesn't fill 100%. Otherwise, we're already at maximum potential.

In order to fill cylinder with more air, we need to increase intake pressure (FI). What this does is fill the cylinder faster. However, we are referring to volume. Volume in relation to length is to the 3rd power. This is one of the mistakes in thinking that pressure is related to power in a linear fashion.

There is definitely more to this proof, but it would take me forever to come up with a final power equation for a 1 cylinder engine with respect to intake pressure.

SPORTcoupe

iTrader: (2)

I highly disagree.
What do you think the pressure of intake air is considering no forced induction and WOT?

On the intake stroke, the piston is moving down while the intake valve is open.
The theory of diffusion says "particles move from a region of higher to one of lower concentration"
When the piston is moving down, it's creating a lower concentration of particles and therefore the intake air flows in to fill the space.

We (humans ) use this concept to breathe.
We don't suck in the air, we just create a lower concentration of air particles in our lungs using a muscle and air flows in to fill the space.

~Alan

P.S. To a certain extent I agree with everything else you guys are saying, which is why I mentioned in the beginning that my canculations are rough.

NAZTY97

Ok... did you think about that last statement of diffusion theory???

Fewer particles = lower pressure... the filling or occupation as a result of that is pressure equalization... and that applies to whether the differnce is minimal or large,.. which in human's case, our breathing is near and always generally around atmospheric since we do not require high psi oxygen to breathe.... and that action is caused by the volumetric change in your lung, expansion and contraction of a semi-permeable membrane,... just as a piston changes volume in a cylinder....

Pressure by definition is the amount of force applied to a surface by the fluid in contact with it, so fewer particles are going to apply less force and more particles of the same fluid in the same space will apply more pressure... hence boost or charging,... and when added in conjunction with all the laws of thermo and properties of gases, you will find that minor changes can yield significant differences in output, to which none are linear. For those who are ME's or took both levels of Thermo,.. we had to do thermo cycle optimization, to which we had to play with all factors (P,V,T )at each stage of the cycle and those results are very interesting, and show how conditions varying can greatly affect the effeciency and output.

SPORTcoupe

iTrader: (2)

Lots of awesome words in there, but nothing that disagrees with what I said above.
And I did specify NO forced induction and WOT didn't I?

~Alan