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

To: "Brian McGarvey" <brianm@zbt62.eastnet.gatech.edu>, "Scott F. Williams" <sfwilliams@home.com>
Subject: RE: engine decision's... I have made up my mind.
From: "Neal Tovsen" <sixteen.volt@verizon.net>
Date: Mon, 6 Aug 2001 17:25:30 -0400
Cc: "Brian Wagner" <scirocco_88_16v@hotmail.com>, <scirocco-l@scirocco.org>
Importance: Normal
In-Reply-To: <Pine.LNX.4.33L2.0108061708100.28303-100000@zbt62.eastnet.gatech.edu>
Sender: owner-scirocco-l@scirocco.org

Very interesting. If I interpret this correctly, and combine it with Scott's
most recent explanation, backpressure isn't actually involved in the burnt
valve problem except that it is one way of solving the issue. By this logic,
a long exhaust pipe (with volume greater than some threshold...probably at
least the volume of one cylinder and something less than the volume of the
whole engine) with no backpressure would also take care of the issue.
Obviously, this is impractical on a motorcycle, hence the use of
backpressure.

Does this make sense, or am I talking outta my arse?

Neal

> -----Original Message-----
> From: owner-scirocco-l@scirocco.org
> [mailto:owner-scirocco-l@scirocco.org]On Behalf Of Brian McGarvey
> Sent: Monday, August 06, 2001 5:12 PM
> To: Scott F. Williams
> Cc: Brian Wagner; scirocco-l@scirocco.org
> Subject: RE: engine decision's... I have made up my mind.
>
>
> Ok.
> From the wonderful world of Motorcycles and Really fast really tiny four
> cyln. The problem with zero back pressure is a simple one of temperature.
> Very similar to pouring cold water into an over heated engine. If you have
> zero back pressure possible with only a very staight short pipe as the
> motor is heated up and the exhaust is forced out the short pipe in bursts
> the cool air rushes back in and the temp shock of the "cold" air vs hot
> metal and that would be how you get bent/broken/shattered parts. IFRC.
> brian
>
>
>  On Mon, 6 Aug 2001, Scott F. Williams wrote:
>
> > It isn't the back pressure that makes more torque. It is the proper port
> > velocity and properly tuned acoustics in the exhaust system. A
> shock wave
> > blasts out of the combustion chambers with each exhaust pulse.
> Once it hits
> > an obstruction, a bend, or other pulse, the wave then reflects
> backwards and
> > pushes any unburned fuel and air mixture back into the
> combustion chamber.
> > This also promotes greater chamber fill and thusly more low-end torque.
> >
> > Someone educate me about the burnt valves thing, though. I
> forget why that
> > happens. Is it because you've got oxygen hitting red-hot metal?
> > ______________________________
> > 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 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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Follow-Ups:
- RE: engine decision's... I have made up my mind.
  - From: "Scott F. Williams" <sfwilliams@home.com>
- RE: engine decision's... I have made up my mind.
  - From: Brian McGarvey <brianm@zbt62.eastnet.gatech.edu>

References:
- RE: engine decision's... I have made up my mind.
  - From: Brian McGarvey <brianm@zbt62.eastnet.gatech.edu>

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