[s-cars] New 5 cylinder vs. AAN

[Jared Robinson]

yeah, what he said
a square block has equal length stroke to equal diameter bore or 1:1
motorcycles are generally short stroke, big cylinder, huge valve over square
monsters.
Take, for example, the new BMW S1000RR.
80mm bore... 49.7mm stroke! 192bhp at 13,250rpms (redline at 14,200)
that's a 1.6 ratio bore/stroke ratio
where as a Harley 88 has a 3.75" bore and a 4" stroke and they don't really
rev that well, but they've got a lot of low end grunt and torque

and the most extreme example of this is Formula 1
currently 2.4L V8s with a maximum bore of 98mm... which means that MOST
constructors take advantage of those huge pistons and go with the ultra
short 39mm stroke... for a ratio of
*drumroll*
2.5!!!!

they were also LIMITED to 19,000rpms (18,000 after 2007)
I think Renault or BMW tested their motors to over 22,000rpms.




On Thu, Oct 14, 2010 at 7:19 PM, JC <jc at j2c3.com> wrote:

> "squareness" = ratio of bore or piston diameter to stroke
>
> Quick answer: For any given displacement, short fat pistons are happier
> about spinning faster vs. long skinny ones.
>
> Bigger bore allows for bigger valves as well.
>
>
> > Sorry, I'm not as edumacated as yourself in the engineering
> > department.  ;-) Can you explain the advantages of having a
> > .94 under-square block over a .89 measurement?
> >
> > And thanks for the CEPA designation; I was looking for that
> > and haven't seen it in any docs yet.
> >
> > Cheers
> > Robin
> >
> >
>
>
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-- 
Jared Robinson