Mower with car exhaust?

[DriverOne]

I read somewhere that your average riding lawn mower puts out 10x more emissions per hour than a car. This, I know, is due to the cat-con. My question for the gurus is, if I have a standard ride-on lawnmower with say a 5hp forward-mounted engine, would it be feasible (or safe) to remove the OE muffler, install a downpipe, run a cat-con and say a MK1 Golf muffler to the rear, and possibly have a more environmentally friendly (and quieter) lawnmower?


Hypothetically.

[deathegg]

Propane conversion.

[gauge_half_inch]

The only concern I would have is adding to much back pressure, causing it to run poorly. Other than that keep the cat away from anything important. They get HOT.

[Movin]

Doubt you would build enough heat to light off the cat. Also it would not have enough
extra oxygen.

A small engine should operate a pulse air check valve very well and provide the oxygen.

you would also need to richen the mix a tiny bit to make sure cat has enough HC to
keep working.

you could harvest a broken up honeycomb cat and put the cat stuff in a gutted out briggs muffler with any muffler desired plumbed cat back.

Your mileage and power will suffer slightly because of the extra fuel required to
operate a cat. If you could add a o2 and computer this could be mitigated slightly,
by spiking rich, back to leaner for power and right back to rich cars provide just enough
rich to keep the cats going.

Cost for fed mandated or cal mandated emissions is not pretty.

This still leaves dangerous levels of NOx. You will have to lower the effective
compression to cool the combustion temp, or recirculate some inert exhaust to
clean up NOx at the cost of using more fuel and losing more power.

No wonder the guv taxes fuel by the gallons and mandates how much fuel economy
can improve.

[htchbck]

^^ What Movin said! Also, never seen a riding mower with a 5 horse... even the old snappers I've worked on with a rear engine (under seat) have been at least 7. My mother-in-laws John Deere has an 18 horse V-twin liquid cooled with a radiator over half the size of a festiva one!

[fujioko]

The air /fuel ratio must be kept at 14.65:1 for the cat to work. Air cooled engines tend to run rich to help stabilize engine temperature.

[Movin]

The air /fuel ratio must be kept at 14.65:1 for the cat to work. Air cooled engines tend to run rich to help stabilize engine temperature.

Close enough, depending on your text book. Now out into the real world.
We have the technology to keep the engine exactly at that AF or any other
we may need. I mean unwavering dead on.

Take any of your lab scopes. Set the width for 5 - 10 MS. Set the height
to 2 volts. Hook your input lead to the o2 sensor wire, piggy back it so
that the cars computer works normally. With the engine running the
voltage will be displayed as a trace across the screen.

What you will see is the required sine wave of way too rich to leaner and back
fast enough that the engine will run with out missing but each combustion
chamber has enough dirt to feed the cat. The cat requires an incredible
amount of energy to work. On one 6 cylinder engine taking it from best tune
to the mandated sine wave and adding the air pump to make it clean enough
the mileage at 55mph went from 29mpg to 22 mpg.
Interestingly at best tune the HC CO were cleaner than with the sine wave
and the cat temp was equal to the rest of the exhaust, it was not working!

Back when this technology was being developed we could not build 100k
miles cars that could keep best tune or anything close to it. So we had
cats and bigger engines with cheap fuel to make clean air, and we still
have that monkey on our back.

Don't let the monkey or the cat go hungry!!