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How much, if any, difference would a half inch hole in the centre part of an exhaust make to economy? It created a bit of a flat spot, that much I know, but does it directly affect how much fuel is used?
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apart from dieing from the fumes you mean?
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A new exhaust, (if they still make them), will double its value. :-)
Last edited by: Old Navy on Fri 27 Aug 10 at 18:19
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(if they still make them)
They do, theres no parts issue with them, its a myth - same day delivery for my exhaust, it was on the shelf. It just occurred to me to ask whether the hole was to the detriment of economy.
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>> (if they still make them)
>>
>> They do, theres no parts issue with them, its a myth - same day delivery
>> for my exhaust, it was on the shelf. It just occurred to me to ask
>> whether the hole was to the detriment of economy.
Very likely, the exhaust will be designed to work with a certain amount of back pressure to aid combustion at the cylinder head - a hole in the exhaust, especially the nearer you get to the engine, will affect performance and fuel economy.
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About 5 mpg on my old Mini... every two years...
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Ah good, I was hoping I might get an improvement over my mpg figures :-)
My first tank was 32mpg but my second, once id adapted to how it drives was 38 mpg - hopefully some more to come - I think its life in the city hasnt helped but now its getting good hot runs its feeling more lively everyday.
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A dose of injector cleaner often helps give a city use car a clear out.
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I always understood the best thing to do with exhaust gasses was to get rid of them, look at piston-engined aircraft.
I thought back-pressure as an aid was a myth (except as an economy measure on 2-strokes).
I understand the concept of venting exhaust gasses at the rear of a car is to the detriment of efficiency. The further the gasses have to travel, the cooler they become. The cooler they become, the denser they become. The denser they become, the greater the 'pumping' effort required to get rid of them.
I expect NC will now blow me out of the water. ;>)
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But the denser they become, the less volume they occupy, so the easier it becomes to push them down a pipe of the same bore?
I thought I read somewhere that actually it's not so much back-pressure as a pressure wave, the result of combining pressure pulses from a number of cylinders. The lengths of the individual sections are tuned so that the negative phases from one cylinder help absorb a positive phase from another. So the integrity of the entire system is vital to economy and performance?
Or is that all gobbledegook? Come on NC, help me out ! :)
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>>I thought I read somewhere that actually it's not so much back-pressure as a pressure wave, the result of combining pressure pulses from a number of cylinders. The lengths of the individual sections are tuned so that the negative phases from one cylinder help absorb a positive phase from another
I agree with that to a degree. I'm not sure it's a negative pressure so much as a reduced positive pressure. In an open system, where each cylinder is vented straight out, would it matter?
C'mon NC, where are you? D'yer think he's just seeing how deep we can dig ourselves?
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i messed with straight through systems in my youtht
i found some kind of baffle that caused a back pressure gave a better top speed
no idea why
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My understanding is similar. The exhaust is tuned so that the pulses of exhaust gas moving down the pipe help draw the exhaust gas from subsequent firing cylinders down the exhaust pipe, and improve efficiency. Or something. I'm out of my depth too here :-)
Every car I have ever owned which has developed a blowing exhaust has seemed down on power and thirstier as a result, but I can't say this is a scientific measurement. Just feel.
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yes, the blowers always feel a little "flat"
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The answer my friends, is blowing in the wind....
Well.... actually its scavenging!
tinyurl.com/2wvpalt
'' The extreme would be to remove the exhaust system altogether but, for those of you who have experienced it, if the exhaust breaks near the manifold, all power is lost. For a normaly aspirated (non-turbo) engine in particular it is important to retain a certain amount of back pressure. It can also be important where the first exhaust box is situated. The reasons for this are all to do with exhaust scavenging which is to do with negative pressure pulses reflected back up the exhaust manifold to remove the last of the exhaust waste from the engine. ''
Hope that helps, (and NC agrees with me!)
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Get a Gun Gum bandage Stu:)
Pat
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>>Get a Gun Gum bandage Stu:)<<
No chance - it was the failure of one of two of these 'repairs' that gave need to replace the pipe in the first place. Its all fixed now anyway.
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Sorry, I'm on holiday - in leafy North Yorkshire!, where else?
Yes, back pressure is always bad, and always minimised by serious designers.
The exhaust length does affect the wave tuning - where a refelected wave of reduced pressure coincides with the time just before the exhaust valve closes, thus helping evacuate the last of the exhaust, and to suck in a bit of inlet air during the cam's overlap. So, yes a flat spot at certain revs can be expected if that process is interrupted.
Of course, leaks ahead of the lambda sensor can cause all sorts of fuelling mayhem.
To the coast tomorrow if it's fine - to the railway museum if not!
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both places will be very busy tomorrow NC
I suggest you let the crowds have em
i do on bank holidays
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Blowing exhaust/economy - Bellboy
