People speak in WHP because that is what can be practically measured in most cases by the typical owner, vs pulling the motor and having it dyno'd out of the car.

 

Yes of course everybody puts the car on a Dyno which measures the whp. Bust most of the dynos then calculate/estimate the bhp value also, right?
In France, this is most of the time this bhp value (extrapolated from the whp measure) that we talk about.

For example, stock s2000 most of the time get values around 225-235 bhp on a Dyno.
And the s2000 with the TTS c30 kit I bought made 376bhp (extrapolated) on a Dyno. But I didn't know the measured who value.

I would be surprised if I get 380whp on my car, even with a better tune...

 

You may not in France. As mentioned, I was just providing the average whp here in the states. We don't further extrapolate bhp here. Just rough estimate if its important to you. WHP is what hits the street and what matters really. Considering the stock S2k is rated 240 engine hp, and you are calculating 225/235bhp, tells me right there your numbers are already down from the get go, which may explain some of your lowered expectations. It does seem everywhere else but the states delivers lower dyno numbers. Throw in the variables of the handful of different dynos we use here, some being hub, and several being roller and it can get further convoluted. I think we all mostly agree on the Dynojet as the Median/standard which falls about in the middle and is what my 380whp quote was based on. They are the most popular Dyno here it seems. On that dyno the stock F20 generally do 195-200whp and ap2 205-215whp.

 

PSI is nothing compared to cfm. You can have 10psi out of a water hose and 10 psi out of a fire hydrant, and the fire hydrant will flow more water. Same with impellers flowing air. 10# through a 2” charge pipe is less air(oxygen) than 3” charge pipes.

 

True however we i assume are all talking about s2000's with a fixed size intake manifold and cylinder displacement, so if you get a impellar that flows more cfm your going to naturally get more pressure when everything elze is fixed as mentioned. There is no garden hose vs fire hydrant in our application. This is especially true on a supercharged set up where even the header is fixed size/design. When you get into turbo now you are talking about changing the flow dynamics and much more variance because of the manifold design and turbo size and efficiency. Important to keep things relative to the comon application or things spiral out of relevance.

 

Larger pipe will move more fluid but 10psi thru a fixed diameter pipe is 10psi no matter how it's produced and moves the same amount of air. This is what this discussion is all about. Only difference in engine output power is the power needed to produce that boost and there are significant differences in supercharger designs and vs turbo-chargers. The Mighty Car Mods lads ran a couple of leaf blowers for forced induction once. No parasitic power loss from them.



-- Chuck

 

This shouldn't really be that difficult to understand.

Its true its all about cfm, not psi. But if talking about a given platform, with given parameters (same engine, same IM, same exhaust, etc), psi becomes a handy, measureable surrogate. We know if we increase psi, without changing anything else, we've increased cfm.

Likewise, if you change one of the parameters, like you add a larger header and free flowing exhaust, you can increase cfm even as psi goes down. You therefore increase hp even though psi has gone down. The relationship between psi and cfm has changed. You now have a new reference point for psi as a surrogate for cfm.

Psi as a surrogate for cfm only works if everything else is the same. If you compare one S2000 to another, looking at psi vs hp, you need to be sure EVERYTHING is the same. Otherwise its two different size pipes, and psi as surrogate for cfm no longer works.

If everything really is the same, like you switch to a different supercharger on the same car, without changing anything else, at the same psi, AT THE SAME RPM, the differences in hp (on the same dyno, same atmospheric conditions) are down to differences in losses between the two systems, their efficiencies.

Psi can't magically produce more cfm in the same size pipe just because of where/how/what generated the psi.

It think too many times the pipe is a different size in ways people don't realize. They then note a difference in psi vs cfm reference points (by noting one psi produced more hp than another), and make an inaccurate conclusion that somehow the psi in one system was somehow superior psi.

 

Yep, well articulated