Re: Turbo engine "theory"

[Alex Jenner <alexj@domain.elided>]

C M Smith wrote...
> Not a theory.  SAAB, Volvo, and now VW are proving that turbo is the
> way to easy high performance engines every day with high torque, well
> built turbo engines that last easily as long as aspro engines.

Just to clarify it wasn't my intention to knock VW or Saab, and I don't doubt 
that a turbo engine can be convinced to give the most power for a given 
capacity, for whatever tricks I suggest you throw at an 'atmo' engine, you can 
always say "now lets add a couple of pounds of boost". What I was saying was it 
doesn't always make a lighter solution.

Take the VW (180bhp for 1.8L) and Saab 900 (205bhp for a 2L) giving 100-105bhp 
per litre. Now road cars with more than 105bhp/litre exist, and I don't see how 
these engines must be any heavier (the pound for pound question) than the turbo 
ones. 

Now if a 200bhp/litre race engine was the target, the 'atmo' engine designer 
might give up trying to deal with the problems of running a 2 litre, 4 cylinder 
engine at super high revs and use a greater number of smaller pistons, in which 
case (all else being equal) it might be a little heavier than the 4 cylinder 
turbo.

> As for torque and horsepower, well they is related you know. In fact hp
> and torque are directly related and proportional to rpm. Torque is the 
> only thing that counts for acceleration rates. Power only matters at 
> high speeds (if you doubt this try beating a Magnum V10 pick up across
> an intersection sometime)

Well I'm not into running red lights ;-) but having never met a Magnum V10, I'm 
guessing that what you mean is that torque is real handy for 1st gear 
acceleration - True, you don't have the option of changing down a gear if 
you're already in 1st. But as you say, torque and horsepower are related and 
it's torque at the driven axle, not the flywheel, that matters. Power matters 
most for acceleration precisely because it is directly related to torque and 
rpm.

I think we had this discussion in the digest before. You will get the best 
acceleration for a given gear at the engine *torque* peak, but by selecting a 
lower gear (increasing the axle torque), you will get the best acceleration for 
a given road speed, at the engines *power* peak. Hence my tongue in cheek 
comment about torque being for people how don't know how to (or want to) change 
gears. Of course if your power band is too narrow, and your gearbox is slow 
with wide spaced ratios, then more low down torque is handy, but far from being 
the "only thing that counts for acceleration".

> Now, not to say I don't prefer a highly strung very high output rev like
> a maniac aspro engine to my stump pulling SAAB engines. But the point
> responded to was more along the lines of "which one works better.....

In the end it all comes down to which gives the biggest smile..... having one 
of each is probably the way to go.

All the best....
Lex Jenner

Alfasud Ti (no torque worth talking about)
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