RE: Throttle Body & Intake Manifold Polishing

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

There actually are reasons not to have a polished smooth surface on the
inside of "dry" intake manifolds as well.  As the air flows down the runner
if it is smooth the effective velocity of the air right next to the surface
is -0- as the air "sticks" to the walls of the duct.  One can actually get
better flow through the runner by deliberately creating turbulence at the
point of surface contact.  I had done a patent search to try to get more
info on this, but so far to no avail.  I know that there is a BMW engine
builder called the Metric Mechanic that uses this technique on their
engines.  It would seem to me that once the majority of the porting was
completed you'd make small grooves in the surface perpendicular to the
direction of flow, spaced at some distance from each other.  I'd like to be
able to find out more about this before I start to rebuild the engine on my
QTC ...

On a similar note, I've heard several times that some of the rear cylinders
(4 &/or 5) tend to run lean.  I guess the first question is is the problem
due to less efficiency in clearing the cylinder during exhaust or a problem
with the manifold?  If this is the case, perhaps the 2-piece EM I'll install
will help.  On the intake side it appears that the cylinders at the other
end of the "log" will naturally get more flow due to the more direct flow
path.  Has anyone tried mods to the IM to try to balance the flow in the
runners?  Any thoughts?

Steve Buchholz
San Jose, CA (USA)

> -----Original Message-----
> From: DeWitt Harrison [mailto:de@aztek-eng.com]
> Sent: Monday, August 30, 1999 7:50 PM
> To: River6822@aol.com
> Cc: quattro@audifans.com
> Subject: Re: Throttle Body & Intake Manifold Polishing
> 
> 
> On Mon, 30 Aug 1999 16:32:16 EDT, Scott Calabrese wrote:
> >[ ... ]
> >1) What should I use to polish the throttle body and the 
> intake manifold ?
> >
> >2) Is there a point where the throttle body and intake 
> manifold can be too 
> >smooth ?
> >I can have the whole thing electropolished, but will it be 
> too smooth ?
> >A friend voiced a concern that with carborated motors, you 
> could get things 
> >too smooth and the fuel would not mix correctly.
> >[ ... ]
> 
> Just one remark concerning the "too smooth" concern: the IM is
> dry. That is to say the fuel is injected at the intake port and does
> not traverse the manifold so the fuel mixing issue as stated is moot.
> 
> Matching the IM to intake ports is at least as important as smooth
> flow through the TB and IM. This is a manual operation that simple
> polishing or honing cannot accomplish.
> 
> DeWitt Harrison
> Boulder, CO
> 88 5kcstq
>