Re: Catalytic Converter question

["James J." <m1garand@speakeasy.net>]

All,
   Yes, air-pumps really do cause the un-burnt fuel to combust, but 
they do it right after the exhaust valve, where the exhaust gasses are 
still essentially burning (depending on operating conditions) so there 
is no additional "flame" beyond what is already there.  In other words, 
if you were to run your engine w/out any exhaust manifold, you would 
already see flames coming out of the heads.  The un-burnt gasoline is 
already above combustion temperature, and it just needs a little air to 
support combustion.  Unburnt hydrocarbons are just as bad as some of the 
combustion byproducts, which is why carburated cars had the evaporative 
adsorption canisters.  A back-fire would require a big plug of gasoline 
to go off, not the dilute quantities that an air-pump supports.
   As far as why I would want to add a Cat to my MGB, the one car I'll 
(possibly) be adding it to would be a daily driver and I don't feel like 
contributing to the acid rain problem after I've just spent all this 
money on paint.  Seriously, w/out preaching, we all have a 
responsibility to help keep the planet clean, and hi-flow aftermarket 
Cats don't take out a huge chunk of power.  I can always bypass them at 
the track if I need to.  On the roadster, I wouldn't bother, but the 
plan is for the GT to see daily DC beltway traffic (read: gridlock), and 
after being stationed in California and seeing what the LA smog is like 
I'm willing to trade 5 to 10 HP for some healthful air.
   Anyone who knows me knows I'm not a tree-hugger, but I don't dump my 
old oil in the yard or in the gutter (I take it to a Jiffy Lube-type 
place) either.  Some of the old emission-control stuff did more harm 
than good, and some of it really works.  According to one study I read, 
late-70's and early 80's 4-cylinder cars are the worst offenders out 
there, even though they had a full compliment of emissions gear.  I 
think it has something to do with them being carburated ( and typically 
not tuned well) and the drivers using Wide Open Throttle all the time to 
overcome the effects of the power-sapping gear.

Telewest (PH) wrote:

> Dunno why you would want to add a cat by choice, they sap power.  I doubt
> unburnt fuel damages cats (leaded does), it is a common problem in colder
> climes and the cat is not effective for several miles.  Many years ago I saw
> a modified cat fitted with a spark plug to ignite the unburnt fuel and so
> get it up to working temp much more rapidly, don't know whether this was
> ever adopted by manufacturers.  Unless emissions regs required it I wouldn't
> fit any of the pollution control stuff.
>
> PaulH.
>
> ----- Original Message -----
> From: "James J." <m1garand@speakeasy.net>
> To: <mgb-v8@autox.team.net>
> Sent: Saturday, September 06, 2003 1:31 AM
> Subject: Catalytic Converter question
>
>
>  
> > All,
> >    I've been toying with adding catalytic converters to an MGB-GT that
> > I'm planning on making a daily-driver after a V-8 conversion (w/
> > closed-loop fuel injection) and restoration.  From what I understand,
> > though, unburnt fuel can damage catalytic converters.  I know that
> > air-pumps are added to cars starting in the late 60's to inject air into
> > the hot exhaust to allow any un-burnt fuel to combust before entering
> > the atmosphere, long before Cats became mandatory.
> >    So my question is:  Does a car  w/ Cats require an air-pump, and
> > heads designed for an air-injection rail?  Even if the car is running
> > closed-loop?  What is the little air-tube on Cats for, and is it
> > required for proper use?
> >    Thanks, and please.. no feline jokes....
> > James J.
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