Maximum advance

Axel Rietschin axel_rietschin at compuserve.com
Wed Jul 25 12:45:47 GMT 2001


>
> Axel Rietschin wrote:
> > Turbo engines are mostly constrained by the knock limit, i.e. they run
with
> > less than optimal advance past a certain boost pressure. Actually, the
> > engine responded very well to increasing ignition advance but I had to
stop
> > and back off when knock started, however, there was more in there :-) I
>
> Axel,
>
> Did you play with reduced boost/more advance to see where the
> optimum lay?  Probably different for every fuel...

Actually, I did to some extent but I found out I had not reached the point
of diminishing returns, i.e. more boost still equalled more power. Also the
engine has a relatively low CR of 8.8 to 1 so you have to charge a lot to
make it efficient. Last, the turbo has a flow limit and this constrained the
max boost I could use; the pressure goes down as rpm goes up but the
ignition point stays surprisignly approximately the same over a large
portion of the upper rev range so it is clear that less boost allows for
more advance but torque goes down in the process. With a highly
knock-resistant fuel all you want to do is charge more (provided your air
temp stays reasonable) and use more advance, I guess ;-)

--Axel







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