Engine Ops with No exhaust system. facts wanted.
Join Date: Jan 2008
Location: lancs.UK
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There seems to be some confusion over pipe-length......Remember, we're dealing with SOUND...Take a guitar, pluck the string, it will vibrate with maximum amplitude at the centre (skipping-rope)
Now lightly touch the centre of thestring and pluck in the normal place, the string will now have a s-shape...2 opposite-phase vibrations at twice the "free" frequency.......repeat at the quarter-node and again,the string will vibrate, snake-like an 4 sections.
The same principles apply to brass instruments didgeridoos and aircraft exhausts!....the shorter pipe has a much tighter-defined frequency-range from "into" and "out of" resonance, than a longer pipe.....all to do with Fundamental Frequency and Harmonics.
Also ties in with vibration, resonance and stuff vibrating itself to bits!
Regarding the "burnt-valve" issue.....draw a circle and plot yopur cam timings on it.....you'll see a large number of degrees where both inlet and exhaust are open simultaneously.....Why doesn't the "new"charge get ignited by the previous one, and why doesn't it all go straight downthe flue-pipe?- Indeed, why doesn't the flame-front go back up the open inlet valve and set fire to the whole inlet-manifold and carburettor?
lots of questions, a complex answer of interacting physics.
Now lightly touch the centre of thestring and pluck in the normal place, the string will now have a s-shape...2 opposite-phase vibrations at twice the "free" frequency.......repeat at the quarter-node and again,the string will vibrate, snake-like an 4 sections.
The same principles apply to brass instruments didgeridoos and aircraft exhausts!....the shorter pipe has a much tighter-defined frequency-range from "into" and "out of" resonance, than a longer pipe.....all to do with Fundamental Frequency and Harmonics.
Also ties in with vibration, resonance and stuff vibrating itself to bits!
Regarding the "burnt-valve" issue.....draw a circle and plot yopur cam timings on it.....you'll see a large number of degrees where both inlet and exhaust are open simultaneously.....Why doesn't the "new"charge get ignited by the previous one, and why doesn't it all go straight downthe flue-pipe?- Indeed, why doesn't the flame-front go back up the open inlet valve and set fire to the whole inlet-manifold and carburettor?
lots of questions, a complex answer of interacting physics.
Join Date: Jun 2007
Location: deepest darkest recess of your mind
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In essence tho, there isn't a huge difference between the nitro funny car engine and the larger aircraft engines, large capacity, superchargers etc, but more importantly limited rpm range. Funny car engines are actually rather limited with their rpm range, the clutch does all the work of loading the engine actually. Which is one reason why the exhaust systems are rather similar - open pipes. As far as burning valves, that happens because of the uncorrected leanness of mixture that will generally occur when you take the exhaust system off. A properly tuned engine won't burn valves just because it has no exhaust to speak of. But if it was designed and tuned for one, and you remove it, that's another story.
Join Date: Apr 2007
Location: australia
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I think you missed the point. Any supercharge engine is not reliant on the exhaust system. N/A engines are that's the point fuel engines are the extreme example that's all as they are in your face and you can see the result when it all goes wrong.
Cheers
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