[Diy_efi] Smog pump and emissions testing question...

[Brian Renegar]

I've got emissions testing coming up for my 91 Mustang.  Here in Maryland, 
they do the "road dyno" testing now.  I'm trying to prepare and have 
everything tuned properly so it will pass.  The engine is fully built with 
twin turbos.  The thing I'm worried about the most is the cam, which is a 
Motorsport F303.  This particular cam is not "emissions legal", however 
that doesn't mean it won't pass.  I've passed with another Motorpsort cam 
(E303), which has more overlap than the F cam does.  The F cam, however, 
has more lift (.512 versus .498) and more duration (I forget those specs), 
and I don't know how that affects emissions.

So anyways, the other issue is that I have removed the smog pump and all of 
it's associated tubing and vacuum solenoids.  I was planning on just 
installing the pump and running the hose directly to the exhaust, since 
that's what the computer's strategy would be during warm 
operation.  However, I just had an interesting conversation with a 
friend.  He suggested instead of running the tube down to the exhaust 
H-pipe, to run it to the back of the cylinder heads (which is the other 
location the factory setup runs the smog pump to).  He said that the longer 
the exhaust gasses are in contact with the fresh air being pumped in, the 
more residual combustion (I guess you could say) will occur, and the lower 
the emissions.

It sounds like a good idea to me.  But I'd love to hear what others have to 
say about this too.  BTW, I have a programmable chip with data logging 
capability, so I will be able to decrease the timing, and set all fuel 
trims to 14.7:1.  It still worries me some though, that I have forced 
induction.  If the dyno operator decides to give it too much gas, I will 
HAVE to add some fuel, or risk blowing the motor up.  And from what I've 
seen, and heard by others, the dyno operators here know absolutely nothing 
about how to properly run an engine on the dyno.  Things like shifting too 
soon, and then having to floor the gas in order to keep the rpm where it's 
supposed to be during the test!

Brian


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