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1.8L head on 2.0L block
But who in the world has a stock 1.8L head on a stock 2.0L block and a stock
2.0L head on a stock 2.0L block?? Anyone??
Dave
----- Original Message -----
From: "Dan Bubb" <jdbubb@ix.netcom.com>
To: <scirocco-l@scirocco.org>
Sent: Saturday, June 28, 2003 6:44 AM
Subject: Re: 1.8L head on 2.0L block
> I've been thinking about this alittle more. We all know what that means!
> I was thinking about the conditions in the cylinder during the intake and
> exhaust and how that is related to flow.
> The power an engine produces is largely related to how much air it burns.
> >From that is subtracted the various inefficiencies. Pumping losses,
> inefficient combustion, heat losses.....
> If your intake is restrictive then you get less air and proportionally
less
> power. So, 7% less air pretty much starts you at 7% less power. The
probable
> most important secondary effect on the intake side is intake velocity. The
> same amount of air at a lower velocity will generally produce less
> turbulence in the combustion chamber, slower burn and less power.
> Flow thru the exhaust is not a power producer. It's a power loss. The
> exhaust valve starts to open well before the piston reaches BDC on the
power
> stroke while the cylinder pressure is still very high. So, alot of the
> exhaust gets a huge boost out the port due to the really high pressures
> (compared to intake pressures or the average pressure level in the exhaust
> system).
> Once this slug of exhaust is out the piston still has to do work to force
> the rest of the exhaust into the pipe, but the general exhaust system
> pressure isn't that high (on the order of a couple psi even for an
> inefficient system) so the power lost pushing the remaining exhaust out is
> not huge. Now, obviously, the lower the exhaust port flow the more power
is
> lost pushing the exhaust out and you also will get more charge dilution
with
> high exhaust back pressures that will have an effect on the amount of
power
> produced by the incoming charge.
> The main point is; power is directly related to intake flow, it is
> secondarily related to exhaust flow. i.e. the cylinder pressures producing
> power (in the area of 1000 psi) are directly related to intake flow and
the
> cylinder pressures loosing power (<10psi) are directly related to exhaust
> flow.
> Having said all that it seems like intake flow is the most important (and
as
> Dave points out, it's not just the port. it's the entire intake tract) and
> exhaust flow of secondary, although not insignificant, importance.
> On the topic of intake velocity; I'm not sure the 2.0 head necessarily has
> better velocity despite the lower flow. I haven't seen an actual 2.0 head,
> only pictures, so I could be wrong, but it seems the primary restriction
to
> flow is the center divider between ports is a big chunky lump on the 2.0
and
> is more streamlined on the 1.8. So, it could be lower flow without the
> benefit of higher velocity.
> Anyway, having now shot my mouth off again in favor of the 1.8 head, I
still
> would like to see dynos comparing the two heads.
> Dan
>
> ----- Original Message -----
> From: L F <rocco16v@netzero.net>
> To: Dave Ewing <MK1Scirocco16v@attbi.com>; <scirocco-l@scirocco.org>
> Sent: Saturday, June 28, 2003 7:34 AM
> Subject: Re: 1.8L head on 2.0L block
>
>
> Dave,
> You are right; the exhaust is positively expelled, whereas the intake
only
> relies on vacuum to fill the cylinder (NA engines).
> However, the intake isn't more "restrictive" per se, it just doesn't have
> the irresistable force in action that the exhaust has. This is why the
> intake valve(s) is almost always larger than the exhaust valve(s)....the
> intake needs all the help it can get.
> You stopped short on one sentence; the exhaust has to exit the tailpipe
> into the atmosphere....not just into a pipe. (that's why low restriction
> mufflers/cats, mandrel-bent large diameter tubing, etc. are important)
> It's one reason to try to put the end of the tailpipe in a low-pressure
area
> of the vehicle rather than a high-pressure area; helps scavenging.
> Good disscussion.
>
> Larry
> sandiego16v
>
> ----- Original Message -----
> From: Dave Ewing
> To: scirocco-l@scirocco.org
> Sent: Saturday, June 28, 2003 1:10 AM
> Subject: Re: 1.8L head on 2.0L block
>
>
> Along with Chris's statement, wouldn't you think that the pressure that
> the
> piston creates when forcing the exhaust out of the cylinder is greater
> than
> the vacuum that is created via the throttle body? As far as exhaust is
> concerned (atleast the type of exhaust that most of us are running,
fairly
> free flowing) I would have to say that the intake is more restrictive
than
> exhaust. I realize you can increase intake flow by adding a cam or
bigger
> TB or whatever but it is limited to some extent or another, the exhaust
on
> the other hand only has to exit the head into a pipe. It doesn't have
to
> pass through the air filter, intake boot, TB, intake, etc. I don't know
> if
> this is relevant but something that makes sense to me.
>
> One other point to consider is that I would rather have the exhaust flow
a
> little better than the intake (whether the intake ports are hogged out
or
> not, either way) so that the heat is leaving the motor more efficiently.
> 16v motors run hotter due to their increased compression and the higher
> rpms
> needed to make useable torque.
>
> I understand the importance of velocity, speed, etc. but when you
consider
> that you could make a smaller port flow better than a larger port then
> this
> would be an argument against the 1.8 head considering that the 2.0 heads
> are
> newer and more technology has gone into the port design. I don't know
the
> specifics but wouldn't you agree that VW wants to consistantly improve
> their
> motors especially with tighter emmissions standards?
>
> Actually, all of this is rather irrelevant as most power hungry listers
> have
> already ported and polished their 1.8 or 2.0 heads so stock standards
> don't
> really apply but I, again, would much rather have a newer head on my car
> that hasn't seen as many miles or as many kids beating it to death.
Since
> the 1.8 heads came on the scirocco/jetta/golf and the 2.0 heads only
came
> on
> the jetta/golf/passat, I'd think that the 1.8 heads on the sciroccos
have
> taken the most beating.
>
> Dave
> ----- Original Message -----
> From: "Chris DeLong" <green536@hotmail.com>
> To: <amalventano@sc.rr.com>; <jdbubb@ix.netcom.com>;
> <scirocco-l@scirocco.org>
> Sent: Friday, June 27, 2003 3:52 PM
> Subject: Re: 1.8L head on 2.0L block
>
>
> > Ok so then you are saying that increased air velocity due to port size
> and
> > shape DOES NOT flow more air? Hmm, I would think that INCREASED air
> velocity
> > would yeild more flow due to the forced induction characteristics that
> you
> > mentioned below.
> >
> >
> >
> > Chris DeLong
> > Fine Tuning
> > 206.367.5503
> > www.finetuningperformance.com
> > Seattle, WA USA
> >
> >
> >
> >
> >
> > >From: "Allyn" <amalventano@sc.rr.com>
> > >To: "Chris DeLong" <green536@hotmail.com>,
> > ><jdbubb@ix.netcom.com>,<scirocco-l@scirocco.org>
> > >Subject: Re: 1.8L head on 2.0L block
> > >Date: Fri, 27 Jun 2003 14:05:54 -0400
> > >
> > > > More airflow=better efficiency=more power.
> > >
> > >umm
> > >depends on runner diameter/taper / rpm
> > >rpm change = different intake air pulse size/speed, therefore some
> > >configurations make more power at low rpm, where some others make
more
> > >power
> > >at higher rpm.
> > >just boring the crap out of intake doesnt give you more airflow in
all
> > >situations. narrower intake passages cause faster air velocity while
> > >filling
> > >the cylinder, and that very momentum can actually cause a forced
> induction
> > >effect, as it squeezes that much more air in the cylinder just before
> the
> > >intake valve closes. this is how some engines can have a volumetric
> > >efficiency approaching (and possibly exceeding) a value of 1. the
> narrower
> > >intake is not perfect though, as it begins to restrict airflow at
> higher
> > >rpm.
> > >
> > >so... from an intake perspective, a stock 1.8 head is meant to flow
> most
> > >efficiently at a higher rpm than a stock 2.0 head is meant to.
> > >Al
> > >
> > >
> > >
> > >_______________________________________________
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> >
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