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moparman
Dodge Dakota
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9/25/2004
08:07:00
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 Subject: catalytic converters
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Will the removal of the converter effect my gas millage and or preformance???? I had it off for some time now with no problems. I know,the O2 sensor has to reach a certain temp. before it funcations. Being that close to the converter will it reach proper operating temp. now that the converter is gone??????
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TERRY
Dodge Dakota
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9/25/2004
09:37:14
|  RE: catalytic converters
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Gas mileage my go up a little as well as power.
I doubt you will notice either, regardless of some of the claims made here.
Your check engine light will come on if your truck is 96 or newer, due to the downstream o2 sensor.
I tried everything to trick it with no sucess, I didn't want to spend the money for a cat-box that may not work.
I case anyone makes claims of backpressure being lower causing power loss due to no cat., just ignore those comments, they are wrong. Back-pressure is the enemy of any 4 cycle engine.
Without getting into the science of it, just look at any performance engine, they all have open exhaust when legally allowed.
Changing from 1.5" headers to 2" headers would make a small loss in tourque and a small gain in HP, but after that freeflowing exhaust will only help.
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Bob Lincoln
Dodge Dakota
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9/25/2004
10:38:09
| RE: catalytic converters
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Illegal, $2,500 fine.
There are plenty of high-flow cats out there.
Back-pressure is necessary to any 4-cycle engine. I'm not surprised you don't get into the science of it.
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TERRY
Dodge Dakota
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9/25/2004
13:34:36
| RE: catalytic converters
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I agree with Bob, just get a new converter, I got a catco for $60, you'll be legal, enviro. friendly, and no check engine light.
And Bob, no you don't want back pressure in the exhaust. A vacuum would be optimal for exhaust evacuation and cylinder refilling.
Hot combustion gasses need to be removed as quickly and easily as possible.
Power is actually lost when the piston has to push the exhaust from the cylinder, and when combustion heat remains, it hinders the density of the incoming A/F mixture.
Now I don't mean running open heads, that would be the same as restrictive exhaust, it would be like the exhaust hitting a wall.
Headers can be used to actually suck combustion gasses out of the cylinder. Using the inertia of previous exhaust pulses flowing through a pipe creats a low pressure area allowing the gasses to easily evacuate the cylinder and help get incoming A/F mixture moving.
By the time the exhaust pulses have gone the as far as the cat. any scavenging effects are weak at best and just need to get out of the system.
So back pressure is only an unwanted effect of the movement of gasses from one place to another.
Header pipes, collectors, and collector extenders are only used to inhance the flow of gasses not to create back pressure.
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TERRY
Dodge Dakota
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9/25/2004
13:52:17
| RE: catalytic converters
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P.S. Bob Lincoln, disdain is not a good personal trait.
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Bob Lincoln
Dodge Dakota
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9/25/2004
18:53:16
| RE: catalytic converters
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Then don't display it. I do not. I merely point out that he makes a statement and doesn't back it up. I didn't say that backpressure is good, but that it is necessary (a minimum amount) to maintain exhaust velocity.
Here is a good article on backpressure:
http://www.proficientperformance.com/tech_back_pressure.htm
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TERRY
Dodge Dakota
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9/25/2004
20:18:24
| RE: catalytic converters
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" I'm not surprised you don't get into the science of it." that is your uncalled for, disdainful remark. This statement implies that I don't know what I'm talking about.
Here is a quote from your article that reinforces what I had already said.
"The exhaust system should have minimal restriction to the exhaust flow that is being released in order to create the most amount of power from the engine. With restriction present, backpressure is developed, making the engine work much harder to release the exhaust out of the engine cylinders.
The standard for exhaust diameter is to not run too large of exhaust, for the engine needs a certain amount of backpressure. This is correct in the sense of one should not run too large of diameter exhaust tubing, but the statement of the engine needing backpressure is not. You need to have the least amount of backpressure possible to produce maximum power."
The quote below is not a comment on back pressure it only speaks of gas velocity, which is not caused by back pressure.
"Too large of diameter exhaust will cause a power loss and loss of low end torque because a larger pipe has less exhaust stream velocity than a smaller pipe. If the exhaust pipe is too large, then the exhaust flow will be slowed with less velocity."
Your handy article proves me right, thank you.
Next time please know what your talking about before you attack my intellect.
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