Back-pressure and Rich/Lean?

(2011-09-25 14:20:17)

1. Reconor Says: I have a 1996 EFI Semi-Stock 460 big block in my F-250. There are pipes that come down to a Y and go into a gutted CC. Then just straight out the cat with no other pipes. I need to know if this will hurt my engine due to lack of back pressure, and how to tell if the engine is burning too rich or too lean. I have an upstream O2 sensor before the CC so my check engine light remains off. Also i already have inspection and emissions covered for life so i dont need to be told how illegal this is and blah blah blah...just if little/no back-pressure will hurt this specific engine, and how to tell if its burning too rich or lean, so please dont answer unless your a mechanic and/or actually know what your talking about. Thanks!

2. Michael Says: One of the big issues of back pressure is how it affects the EGR valve (although you may already have removed that if you have destroyed the cat). Check out pages 20-23 of the first source for an in-depth discussion of how back pressure affects the various types of EGR valves. You may not care about emissions but too much EGR flow will really mess up the engine operation, like breathing into a paper bag.

Burning rich or lean most of the time is easy to check - the color of the spark plug noses tells that story as well as it did when Jan and Dean were singing about Dead Man's curve. Dark is rich, white is lean, tan is just right. For dynamic testing, if you can get a digital voltmeter connected to the upstream O2 sensor it will tell the story very well. Rapid switching is right on, high voltage (like 0.8V) is too rich, low voltage (like 0.1V) is too lean.

3. Pete M Says: The back pressure lost by gutting a catalytic converter probably won't affect your engine at all.

Odds are good that if anything, it will give you a little more power.

As far as your concern regarding rich/lean, I wouldn't worry about that either, your engine computer will take care of that for you.

Sounds like you're good to go since you've already got your emissions covered.

4. woof Says: i have ran cars with exhaust and without exhaust. carbed, efi, turbo, natural, it doesn't matter as far as harming anything and the only difference i ever noticed is fuel mileage being worse without exhaust due to lack of scavenging unburnt fuel.