Re: engine decision's... I have made up my mind.

["Brian Wagner" <scirocco_88_16v@hotmail.com>]

Top End - Pistons and up

 A "burned valve" is a valve that has overheated and lost its ability to
hold a leak-free seal. Valve burning is usually limited to exhaust valves
because they run much hotter than intake valves.

The diagnosis of a burned valve is usually the result of a compression test.
If a cylinder shows little or no compression, it frequently means the
exhaust valve is not sealing. The valve may or may not be actually burnt
(melted), but have other physical damage such as cracks or areas where
pieces of metal are missing or eroded away from the valve face.

The cure for this condition is to remove the cylinder head, replace the bad
valve and reface (or replace) the valve seat. As a rule, the head is usually
given a complete valve job at the same time because the rest of the valves
and guides probably need attention, too. If one exhaust valve has failed,
the rest are probably on the verge of failure if they haven't already
started to leak.

WHY VALVES BURN

There are several reasons why valves burn. One is normal wear. As an engine
accumulates miles, the constant pounding and thermal erosion wears away the
metal on the face of the valve and seat. The exhaust valve sheds most of its
heat through the seat, so when the face and seat become worn and the area of
contact is reduced, the valve starts to run hot. Eventually the buildup of
heat weakens the metal and pieces of it start to break or flake away. Once
this happens, it forms a hot spot that accelerates the process all the more.
The valve begins to leak and compression drops. The result is a weak or dead
cylinder and a noticeable drop in engine power, smoothness and performance.

A bad exhaust valve will also increase exhaust emissions significantly
because it allows unburned fuel to leak into the exhaust. High hydrocarbon
(HC) emissions, therefore, may also be an indicator of a burned valve.

An exhaust valve can also burn if the valve lash closes up for some reason
(improper lash adjustment, cam or lifter wear, a bent push rod, worn rocker
arm or cam follower, etc.). The lack of lash (clearance) in the valvetrain
prevents the valve from closing fully, which causes it to leak compression
and overheat.

Valve burning can also be caused by any condition that makes the engine run
hot or elevates combustion temperatures. This includes cooling problems,
abnormal combustion like detonation or preignition, loss of exhaust gas
recirculation (EGR), retarded ignition timing or lean fuel mixtures.

VALVE RECESSION

A condition known as "valve recession" can allow the valves to recede or
sink into the head because of excessive seat wear. This causes the valve
lash to be lost which allows the valves to leak and burn. It occurs
primarily in older engines (mostly those built prior to 1975) that were not
designed to run on unleaded gasoline. When leaded gasoline was still around,
lead acted like a lubricant to reduce valve seat wear. But when lead was
eliminated, it meant engines had to be made with harder seats. These older
engines didn't have hard seats, so many began to experience valve wear
problems when switched to unleaded fuel. If you're driving an antique or
classic car, therefore, you should either use some type of lead substitute
fuel additive to protect the valves or have the seats replaced with hard
seats when the engine is overhauled.

Brian
88 16v
87 16v
86 8v (sold)

----- Original Message -----
From: "Neal Tovsen" <sixteen.volt@verizon.net>
To: "Brian Wagner" <scirocco_88_16v@hotmail.com>; <sfwilliams@home.com>;
<Josh.Hignight@phoenix.edu>
Cc: <scirocco-l@scirocco.org>
Sent: Monday, August 06, 2001 4:14 PM
Subject: RE: engine decision's... I have made up my mind.


> What's wrong with a top end? (What IS a top end?) Why will I get burnt
> valves?
>
> I'm getting the feeling here that we're all either too lazy to explain, or
> none of us actually knows the answer to the backpressure question...
>
> Neal
>
> > -----Original Message-----
> > From: owner-scirocco-l@scirocco.org
> > [mailto:owner-scirocco-l@scirocco.org]On Behalf Of Brian Wagner
> > Sent: Monday, August 06, 2001 4:44 PM
> > To: sfwilliams@home.com; Josh.Hignight@phoenix.edu
> > Cc: scirocco-l@scirocco.org
> > Subject: RE: engine decision's... I have made up my mind.
> >
> >
> > BP is essential to the life of the engine, without it you will get burnt
> > valves and a top end.
> >
> > Brian
> >
> > 88 16v
> > 87 16v
> > 86 8v (sold to neighbor)
> >
> >
> >
> > >From: "Scott F. Williams" <sfwilliams@home.com>
> > >To: "Josh Hignight" <Josh.Hignight@phoenix.edu>
> > >CC: "scirocco List" <scirocco-l@scirocco.org>
> > >Subject: RE: engine decision's... I have made up my mind.
> > >Date: Mon, 6 Aug 2001 16:27:15 -0400
> > >
> > >Okay, you got me there. Let's say that no *4-stroke* motor needs
> > >backpressure. :^)
> > >______________________________
> > >Scott F. Williams
> > >Account Manager
> > >GENUiTY - Eastern Region
> > >100 Wall Street, 10th Floor
> > >New York, NY 10005
> > >Voice: 212.416.1745
> > >Cell: 917.648.2256
> > >Fax: 212.618.5160
> > >scott.williams@genuity.com
> > >
> > > > -----Original Message-----
> > > > From: owner-scirocco-l@scirocco.org
> > > > [mailto:owner-scirocco-l@scirocco.org]On Behalf Of Josh Hignight
> > > > Sent: Monday, August 06, 2001 4:15 PM
> > > > Cc: scirocco List
> > > > Subject: RE: engine decision's... I have made up my mind.
> > > >
> > > >
> > > > Umm, 2-strokes benefit from backpressure. Since most 2-stroke
> > > > engines don't
> > > > have mechanical valves, the back pressure helps to eliminate
blow-by,
> > >thus
> > > > increasing power because it maintains that there is a mixture to
> > > > burn in the
> > > > chamber (Hence the reason my r/c car barely runs when the pipe
> > > > falls off).
> > > >
> > > > But that's beside the point when it comes to dubs. Just thought
> > > > I'd mention
> > > > it.
> > > >
> > > > Joshua Hignight
> > > > Student Services/Technical Services
> > > > New Mexico Campus
> > > > (505) 821-4800
> > > >
> > > >  -----Original Message-----
> > > > From: Scott F. Williams [mailto:sfwilliams@home.com]
> > > > Sent: Monday, August 06, 2001 1:11 PM
> > > > To: jdbubb@ix.netcom.com; Neal Tovsen
> > > > Cc: scirocco List
> > > > Subject: RE: engine decision's... I have made up my mind.
> > > >
> > > > Let's kill the myth that backpressure helps an engine. NO ENGINE
> > >BENEFITS
> > > > FROM RESTRICTION IN THE EXHAUST SYSTEM! The reason normally
aspirated
> > > > engines may gain more torqe with a smaller diameter exhast,
> > is because
> > >the
> > > > higher velocity in the system creates a greater scavenging
> > effect that
> > >in
> > > > turn allows for cleaner combustion chambers, wich means more
air-fuel
> > > > mixture per stroke, which means more power.
> > > >
> > > > Zero backpressure is always the ideal. Complete scavenging and
> > > > high exhaust
> > > > velocity are always the goal.
> > > > ______________________________
> > > > Scott F. Williams
> > > > Account Manager
> > > > GENUiTY - Eastern Region
> > > > 100 Wall Street, 10th Floor
> > > > New York, NY 10005
> > > > Voice: 212.416.1745
> > > > Cell: 917.648.2256
> > > > Fax: 212.618.5160
> > > > scott.williams@genuity.com
> > > >
> > > > > -----Original Message-----
> > > > > From: owner-scirocco-l@scirocco.org
> > > > > [mailto:owner-scirocco-l@scirocco.org]On Behalf Of Dan Bubb
> > > > > Sent: Monday, August 06, 2001 2:55 PM
> > > > > To: Neal Tovsen
> > > > > Cc: Patrick Bureau; scirocco List
> > > > > Subject: Re: engine decision's... I have made up my mind.
> > > > >
> > > > >
> > > > > somebody, please somebody explain this BS about lower backpressure
> > > > > causing loss of power!
> > > > >
> > > > > Neal Tovsen wrote:
> > > > > >
> > > > > > > 2.5" Pipping finishined with stainless Remus or Borla
> > Muffler.(to
> > >be
> > > > > > > decided)
> > > > > >
> > > > > > Did you mean 2.25"? 2.5" is pretty damn HUGE for a N/A 2.0L
> > > > engine. With
> > > > > > such a loss of backpressure, you might actually lose power.
> > > > Since you're
> > > > > > ordering the manifold/downpipe from TT, you could go with their
> > >2.25"
> > > > > > exhaust system with a Borla for a sweet full setup.
> > > > > >
> > > > > > Looks like a screamin' setup otherwise. Go for it!
> > > > > >
> > > > > > Neal
> > > > > >
> > > > > > --
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