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(ASCEND) Re: [all] Glowing headers

Felix,

Apologies Felix for mis interpreting your comments.
I get to do 2nd year reading class next year!!  Writing comes later1

I don't think we're arguing here! I hope not any road.

There is nearly always some unburnt O2 in the exhaust as it leaves the
port (aka O2 sensors).  As I am sure you are well aware the air pump
causes the residual fuel to burn immediately and hopefully in the
'thermal reactor'.  

Without an air pump the fuel may continue to burn 'slowly' (too little
O2 but high heat), but it does react 'further down the tract' when it
hits higher levels of O2, which suprisingly appears not to be at the
tail pipe.
Particularly on overrun the fuel explodes; according to the damage to
packing in my racers tail box, about 12 inches from the tail pipe.
Unless the ingnition is refecting off the air/exhaust 'boundary' layer
at the end of the pipe and going back up the pipe....Sounds like
advanced sonics (pun intended!).


IanC




Felix Miata wrote:
> 
> Ian Cowley wrote:
> 
> > Felix Miata wrote:
> 
> > > Mooogmn wrote:
> 
> > > > If anyone out there has any insight into why an exhaust header would glow, I'd
> > > > appreciate hearing any ideas.  The car is timed to factory specs.  It is using
> > > > the Leading and  Trailing plugs that the 86+ motors use.  However, the car
> > > > runs the 12A distributor and ignition.....The car is an '85 GSL with an '88
> > > > 13B motor, carbureated.
> 
> > > Glowing is NORMAL, if you're driving with any significant load. If
> > > you've been pushing it hard, park, and look, they'll likely still be
> > > red. Carbureted cars have less precise fuel control, so extra high EGT
> > > is a little more common. In any event, NA rotary EGT generally runs
> > > around 400F higher than boingers, typically in the 1200-1700 range. If
> > > they never glow, something's wrong. Have your friend drive your car with
> > > you as a passenger, before starting out, pull the carpet away from the
> > > firewall. Also, pull the A/C drain line out of the firewall. You should
> > > see red through the hole most of the time. Also you can hold engine
> > > speed above 6000 in neutral a couple minutes to brighten them up.
> 
> > My racer (12A) headers run at about 500degC (932degF) (6" from port)
> > under 5000rpm and about 925-950degC (1700-1740degF) under full load.  My
> > car is right hand drive, so if I rest my left foot against the
> > tranmission tunnel its very hot, even through the racing boot!  My mild
> > steel headers are steel blue when cool.
> 
> > Even my 140hp 12A road car used to warm up the headers a bit!
> 
> > The reason is simple.  A 4-stroke engine only washes the exhaust port
> > with hot gases for just over one half cycle of the crack in every two
> > cycles.  I.e. for 3/4 of the time its cooling.
> 
> > A rotary almost continually pours 1900deg F gases out the exhaust.
> 
> > Felix's comments on fuel control (running rich) tends to cool the
> > combustion not raise it IMHO, but seriously heats up the exhaust further
> > down the tract, where hot unburnt gases meet cool oxygen.
> 
> Read it again. Nowhere did I write either the word rich or the word
> lean. Poorer fuel control from a carb means errors in both directions,
> rich and lean.
> 
> Downstream of the exhaust port in an engine with tube headers there is
> no cool oxygen to meet the hot exhaust until it leaves the tailpipe,
> long after the section of exhaust that glows red, unless the tailpipe
> exits near the right front tire or the engine is installed in the rear
> of the car. Engines with headers don't have air pumps to add air
> (oxygen) to the exhaust.
> --
> "   Moral habits . . . cannot safely be trusted on any other foundation
> than religious principle, nor any government be secure which is not
> supported by moral habits. . . . Whatever makes men good Christians,
> makes them good citizens."        Daniel Webster
> 
> Team OS/2        ***        Rotary ONLY since 1973
> 
> Felix Miata        ***        http://www.gate.net/~mrmazda

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| Ian Cowley    Network Design Consultant                          |
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