Can supercharger and turbocharger boost pressures be compared?

[Jay 535i]

I'm just wonderin'...

If a certain supercharger setup claims 7psi and another turbocharger setup claims 7psi, is it safe to assume that the power outputs of the two kits will be roughly the same, or is it more complicated than that?

Naturally the power delivery will differ, but I'm wondering about peak output.

Assume for the moment that all other things remain equal (e.g. injectors, manifolds, etc.).

[winfred]

very roughly, due to the differences in the boost curves of superchargers and turbos they effect the engines natural power curve in different ways

[GoldenEagleFan]

All things being equal (practically not possible, but for conversation ok) 7 psi boost is 7 psi boost.

However, there is a big difference between superchargers and turbos in that a turbo is using heat energy from the exhaust that would otherwise be wasted and is much more efficient at producing the 7 psi boost.

A supercharger is a mechanically driven device and as such sucks power directly off of the crankshaft, effectively robbing the hp out of the engine. It is not uncommon for a supercharger for a 2.5-3.0L engine to rob 50hp from the output at 6,000-7,000 rpm.

Another caveat, depending where you want your power, a supercharger can be a great choice for the reason that since they are mechanically linked, you get gains at essentially all rpms, where a turbo for an automotive application isn't as effective until approx. 3,000 rpm.


So 7 psi is 7 psi, but the output from your engine will be quite different with the same boost.

[winfred]

yea what i said :D


So 7 psi is 7 psi, but the output from your engine will be quite different with the same boost.

[rob101]

boost is boost, but power comes from boost and flow. so you have to look at flow as well. The super or turbo may be so small that it chokes the flow, therefore to get the same amount of flow you would need to up the boost.

But as mentioned a super does take more power from the belt drive than a turbo does from the exhaust. so if you had 2 identical compressors then the turbo would make more power as it is more effecient in how it obtains power from the engine needed to compress the charge (ie from the turbine, or belt drive)

I assume you are talking about a centrifugal vs. a turbo. it is easier to compare them as the compressor stages are identical.

[F4Phantom]

FIY, BMW has just developed a steam powered turbo from the exhaust heat.
http://www.gizmag.co.uk/go/4936/

[Jay 535i]

Thanks guys. You've answered my question.