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| Should I lose a cat? | |
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| Tweet Topic Started: Sep 4 2014, 02:50 PM (605 Views) | |
| crispycritter | Sep 4 2014, 02:50 PM Post #1 |
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My '97 3/5 Hatch is only giving about mid to upper 30's (mpg's) in a mix of 2 lane and freeway driving. The car has larger then stock tires (185/60-15) but stock 4.38 final drive. I drive 65-70 most times on the freeway and 55-60 on 2-lane roads. My last Metro was a '98 3/5 Hatch and it got 42-48 mpg's in the summer. The only major difference between the two cars that I'm aware of is the exhaust, the '97 has a catalytic converter built into the exhaust manifold and another cat in the "normal" location. The '98 only had the one "normal" cat. I have another nearly new headpipe with the single cat and a "normal" exhaust manifold. Should I swap the exhaust out or will this cause check-engine light problems etc. Just looking for better mpg's like everyone else. THANKS! |
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| David95237 | Sep 4 2014, 02:59 PM Post #2 |
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![]() this is what my cat had in it, you can see how it restricted the exhaust. You can pull your o2 sensor out and put a pressure gauge in the exhaust to check for back pressure. |
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| Justahoby | Sep 5 2014, 12:27 PM Post #3 |
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Unqualified informant
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Honestly, even though I do not like cats, I can tell you the area calculated in the comb often exceed the pipe diameter(EDIT: AREA)..There are different ways in calculating flow in a pipe, and flow for air people use often, but changes in exhaust when hot vs cold ect. Now turbulence is an issue, however if you have a given pipe after the Cat of a specific size for the power you are running that velocity is King. Now I dont run a Cat, but if you must do so legally ( actually we all required to on these cars by federal law) , Just remember that of whole actual cross sectional are and pipe diameter for flow and velocity. I sold my 383 stroker to a friend who wanted cats for cleaner exhaust ( he is picky clean) , and they were small cats, i estimated the area of all squares and it was a hair more than the 2 1/2" dual exhaust.. Just as much power as before when in my truck... Its not my favorite to use, but cutting off does no always net a difference. Just an unbiased view( really I would love to shove it down the politicians throat who mandated to get his breath clean) EDIT: DIAMETER , I meant Area Edited by Justahoby, Sep 5 2014, 12:37 PM.
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| myredvert | Sep 5 2014, 07:14 PM Post #4 |
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myredvert
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Trying to compare apples to apples by looking at "paper or plastic" and not taking a good look inside the bag to make sure there are the same type of apples in both bags is often a fruitless exercise. Are the two engines you're trying to compare even in the same state of health to make a reasonable comparison, i.e., >Do you know the compression and condition of the internal components of the engine that was giving you better mileage? >And this one? >Have you done a proper compression check? >Vacuum tested or take it to an exhaust shop to check to see if the cat is plugged? >Has anything changed in your typical driving conditions/style from then to now? >Any codes? >Are there any notable differences in oil consumption between the two cars? I would suggest not chasing visible differences and first try to objectively verify the internal condition of your engine, exhaust, chassis, driving style, etc., and find which of those things (or combination of them) may be affecting your fuel economy. Good luck!
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| crispycritter | Sep 5 2014, 10:33 PM Post #5 |
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Thanks all! As far as compression, it seems to be over 200 with enough cranking(approximately 8-10 compression strokes) also no check engine light so I assume no codes(?) Oil consumption on both cars were similar at about 2000 miles per quart. I'm probably leaving stuff out but not on purpose. Now I have a serious problem(see my new post in Engine Tech and Diagnostics) as car is suddenly not running. Any help in getting it going again would be GREATLY appreciated! |
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