ECU for 14k rpm V8

[Chris Conlon]

At 08:33 AM 9/27/01 -0400, Eric Fahlgren wrote:
>
>   http://members.home.net/pfahlgren/cars/turbo/87_bmw_f1.jpg
>
>I found it interesting that the throttle body is _before_ the
>turbo inlet.  I would think that causing a vacuum in the whole
>intake tract would cause poorer throttle response (anathema
>of a road racing engine), but that's only a guess.  Anyone
>got a good explanation for this?  Lower stress on turbine shaft?

There's a fair chance it would improve throttle response. A
draw through setup causes the turbo to run at a higher PR during
lower power operation, and that keeps it at a higher RPM. (With
the compressor side in relative vaccum, compared to a blow-through
setup, the turbo can reach a higher rpm from the same exhaust
energy.) Since the speedlines are relatively flat near the peak
efficiency island, you can get a lot of boost (not necessarily
the max) pretty quickly when you get back on the throttle.

One thing that's usually considered a drawback, especially on
draw-through blower apps w/o a bypass, is that charge temps are
higher under light power than they would otherwise be. (The
higher PR you're running, the more the charge is heated; with
the throttle more closed than normal, PR must be higher to give
the same MAP.) This might possibly have been an advantage if
they used some kind of witches' brew fuel that was hard to
vaporize. I seem to recall the Honda engine from the same era
had a fuel like that.

These points are probably more true of a street car, though.
The single-TB pre-turbo setup would have needed special oil seals on
the turbo, to deal with the oil sucking problem Bruce mentioned.
These seals supposedly produce a little more friction than the
normal kind, and I doubt anyone wants that. They used to be
available despite this, but seem to be less common nowadays. It's
entirely possible that the car in question did have dual throttles,
a setup like that is even shown in MacInnes. This lets you get some
of the advantages of draw-through without the big oil sucking
drawback.


   Chris C.

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