Re: 1.8 head on 2L performance/tuning question

[Brett Van Sprewenburg <brett@netacc.net>]

>WHACK!  (J/K)
>
>I would have to reason that the 2.0l would make more power at the high end
>and that the 1.8l would have more torque.

I assume what you're saying is that the 2L head would make more HP at
the top, while the 1.8L would have more torque?  This probably is not
the case, as it is a pretty well known behavior that the 1.8L head on
the 2L block does seem to make more HP (at the high end) then the 2L head
on the 2L block.  (it's just like my previous statement from my other
email, it doesn't seem to be as huge as some people make it out to be).

>You said it yourself, the 1.8 flows intake
>the best and the 2.0l gets rid of the most exhaust...  Doesn't the 
>high-end go up when you reduce back pressure?

It's not just back pressure we're dealing with here, especially in the case
of Cathy's engine.  She has substituted the 2L head for the 1.8 head with
a Euro cam and wanted to know what was up with the performance envelope.
Now as far as having a better high end when back pressure is reduced,
I'd have to say yes and no.  Consider a short tube tri-y header, dyno
proven to help low range and mid range torque more then the high end.
Swap out that header, keep the rest of the exhaust the same as possible,
and put in a long tube 4 into 1 header and the high end really perks up
more so then the low / mid range.  Both arguably reduce back pressure.
This just goes to prove that an engine is a more complicated equation
then it might seem.

>Or do you need other parts to acomplish
>what I'm talking about.  I've read and been told that the 2.0L head on a 1.8L
>block is a losing combo but the 1.8L head on the 2.0L block should 
>be a winner.

Jim J. has a 2L head on a bored 1.8L block, seems to work very well for
him.  If you look at the intake ports between the two heads, the
2L's look definitely physically smaller.  Making the passages smaller
will cause greater air velocity at lower rpms, which will create more
low rpm torque.  Just look at the famous 40mm vs 50mm intake manifolds.
Without changing the port size (obviously) of the cylinder heads, swapping
out the 40mm manifold for the 50mm does indeed soften the low end while
helping the high end.  Admittedly, this is with the same exhaust port
size, but the exact same exhaust.  Like I said, it's complicated.

>because you have the extra 200cc displacement and the better intake flowing
>head plus back pressure for torque.   I don't have any figures for the gains
>but maybe someone does...

It appears that the 1.8L outflows the 2L head roughly an average of 11cfm
starting around .2 inches of valve lift.  At the exhaust side, the 2L
head outflows the 1.8L by 13cfm at about .3 inches of lift.  This
translates into different behaviors at different rpms naturally.

>
>Geordy Rostad
>(refinancing my home to by a new fuel  pump)

Just thought I'd throw more ideas around.

==Brett

 \/  '84 Scirocco (ITB racer 2B) | "Hot VW's, take two home. They're small"
\/\/ '88 Scirocco 16v (Show), '92 Passat 16v (Winter+) | - brett@netacc.net

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