"Mike Smith" > wrote in message
...
> But one would think that head design would have more to do with an
> engine's power and efficiency than the block does, no? So why does the
> 2.5L I5 make only 150 hp?

I'm not an expert on the subject but the head itself is most likely one of
only several components that goven HP. Slapping one of two Lambo heads on
an inline block of the same size doesn't necessarily mean that the engine
itself is 1/2 of the Lambo's HP (so 250) because of other factors that could
be going on.

A few googles turned up that the Lambo and Jetta are about the same bore and
stroke. However look at the compression ratio...Lambo 11:1, Jetta 9.5:1.
That's gotta have something to do with it (and the Jetta not needing premium
fuel).

The Jetta also could have conservative ECU settings as well. It doesn't
require premium fuel so the timing settings are tuned for that and not for
power. It's been rumored that this engine is not currently tuned to it's
full potential and there's quite a bit of room to grow there.

So what I'm getting at is that all things equal the Jetta probably would be
250HP. But there's enough going on that it makes the Jetta 150hp instead.
Now whether a loss of 100hp compared to 1/2 of the Lambo's engine is too
much given those other differences, I couldn't really say, but they
definitely come into play.

Also note that VW has never been in a HP race with the competition. All out
HP is not what VW is about with their passenger cars. VW has usually tuned
its cars (we're talking the non-high-performance ones like Jettas and Golfs
and not cars like the R32) for an overall balance suited to daily driving
and not balls-to-the-wall racing. HP isn't everything when it comes to
everyday driving.