pressure=hp

[urq]

... actually, smooth, polished surfaces in the intake tract can be as bad as
smooth surfaces on a golf ball.  If you have laminar flow, the velocity
adjacent to the surface of the tract is zero too.  It actually can help to
have rough spots along the edge to break up the flow at the boundary.
Turbulent flow can actually be a good thing.

When you are talking about a static situation pressure is pressure ...but
this isn't the case in the dynamic case ... what you have is something like
an electrical circuit with "voltages" and "resistances" ... and pressure is
analogous to voltage, and any restriction to flow provides a resistance.
This means that just because you see 15 PSI above atmospheric at the
backside of the throttle body that there is 15 PSI at the outside of the
intake valves ... and given the restriction there definitely not 15 PSI in
the cylinder when the valve closes.  The boost pressure is just working to
force more flow ...

One more thing about 15 PSI of boost ... 15 PSI of cool air will put more
oxygen atoms into a cylinder than 15 PSI of hot air.  I read in one of the
Audi docs that the addition of the intercooler to the turbocharged engine
provided more of an increase in horsepower than the simple addition of a
turbocharger sans IC.  Some people actually make things worse by trying to
ask too much from their turbo by pushing up the boost level ... as the turbo
gets less efficient it will heat the intake charge even more.  Spend a few
minutes trying to find out what benefits can be gained by improving the IC
on your car ... interestingly enough you might actually end up reducing the
max boost pressure, but the density will be higher and you'll actually get
more work out of the engine!  Hot air also means you have be wary of
preignition and you can't push the timing as much.  Notice that the ECU
actually receives parametric information about *two* characteristics of the
intake charge ... pressure and temperature.

You also need to be careful at times to fully understand the intentions of
the manufacturer ... it so happens that Audi does spend some effort trying
to tweak the performance of its motors.  Something that looks like a
indiscriminant port mismatch between the head and the exhaust manifold might
just be there to prevent reflection of pressure waves back toward the
exhaust valve.

I don't claim to be an expert on this sort of thing myself ... just passing
on a few things I've picked up over the years ...

HTH!
Steve Buchholz
San Jose, CA (USA)
>
> >Tell me, am I wrong in assuming that if the intake manifold
> >experiences 15psi in one MC engine that uses stock EM and Turbo, and
> >another more modified MC engine also sees the same pressure at the
> >intake ports, it's still 15 pounds going into the combustion
> >chamber? After all, if the engines still have the same set up at
> >that point, (combustion chamber) 15lbs is 15lbs. Am I right? I
> >realize that a better turbo and larger more efficient manifolds and
> >runners will net you more flow and thus more potential, but will one
> >engine make more power than the other without internal mods? I need
> >help understanding this if I am wrong. Thanks for the help.
>
> Okay, here's hoping I get this all right(crossing fingers):
>
> Basically, no matter what the pressure, pipes will always restrict
> flow, particularly if they're goofy shaped or have a really rough
> surface.  Smooth is usually good in pipes for flow(not for golf
> balls; they're dimpled for a reason!)  The problem with a really nice
> smooth intake manifold is you have less turbulence, so fuel mixing
> might not be as spiffy.  Maybe moving the injectors back further
> would correct this, but I suspect there's probably a good reason they
> are right where they are(someone else can probably tell you exactly
> why, I have no idea.)
>
> You're right, gains are not as large in a turbo engine since you're
> pushing air into the engine, not relying on the engine itself to suck
> air through the whole intake system etc.  Pressure losses up to the
> intake manifold(where boost is measured by the ECU) will only hurt
> efficiency because you make the turbo work harder to get the same
> pressure at the intake manifold; it'll be making extra pressure at
> its outlet, and the more you compress air, the hotter it gets, etc.)
> If you can find an IC that performs in other regards to the same
> capacity or better than the stock unit, then that's one sure way to
> go to make the turbo work less(thus charge air temp will be lower
> going into the IC!  Woohoo!); this is basically the case with the
> 200q20v single-pass IC.  Just a WHOLE lot more plumbing to make it
> all work  on the 20vt :-)
>
> The caveat is that a turbo car isn't always force fed, and it takes
> exhaust to make those turbos spin...when you snap open the throttle,
> it's initially an NA engine, and it could probably be argued that the
> better the engine does in those conditions, the faster it'll
> transition to a forced induction motor.  More exhaust flow spins that
> turbo up faster...and if you just so happen to be running a larger
> turbo(so you can run higher boost more efficiently), then anything
> that helps get it going faster is a Good Thing.  I guess what I'm
> saying is that as long as you don't hurt the engine while it's under
> boost, if you help it while it's -not-, that's also a Good Thing.
>
> Is it worth ripping the thing apart?  From what I remember reading a
> few weeks ago when this thread came up with Javad etc, the advice
> seemed to be "hey, if you've got everything off already anyway,
> certainly, get the DIY kit and match the gasket surfaces etc on the
> intake side, remove casting burrs and other obvious imperfections
> etc."  I think Javad had a disclaimer about how matching the gasket
> surfaces to the ports on the exhaust side was rumored to be less of a
> Great Idea.
>
> Note that installing a custom IC is both expensive and a royal PITA
> for most Average Joes...and it's difficult to pick "the right one."
>
> Brandon, I'd try some searches on the archives, see if you can find
> an old thread that goes over this subject...like I said, it was just
> covered a few weeks ago in a nice big long thread.
>
> Brett
> --
> ----
> "They that give up essential liberty to obtain temporary
> safety deserve neither liberty nor safety." - Ben Franklin
> http://www.users.cloud9.net/~brett/
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>