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  #16 (permalink)  
Old 12-06-2004, 05:03 PM
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It shouldn't matter what kind of muffler you use with flamethrowers because the whole system should take place after the mufflers anyways. You definitely dont want flames going through your mufflers lol.

Any type of muffler should do simply because it shouldn't be even near the flames.

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Old 12-06-2004, 05:23 PM
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This has been discussed before and all the info is in the Knowledge Base along with the flame throwers sites.

The concept that maximum power is obtained by zero pressure in the exhaust is only partially true. There should be absolutely no back-pressure from the collector rearward, but the diameter of the system beginning with the exhaust valve is a compromise.
The highest efficiency for the system requires a minimum speed for good exhaust gas velocity to insure that gas does not "back up" into the chamber during overlap at low engine speeds,
and that the "suction" (negative pressure pulse) effect of a resonant (tuned length) and/or collector (overlapping exhaust pulses) system is optimized.
To predict what primary size will be best for a specific motor, you must know where you want the engine to develop peak torque.
If the existing torque peak is at bit lower RPM than you prefer (typical in under-cammed or stock motors), it can be "bumped" a bit by increasing the primary diameter. If the torque peak is too high (motor is "peaky", with no range and poor recovery from gear changes), the peak can be adjusted down by using a smaller pipe. A change of 1/8" in the primary diameter will raise or lower the peak torque RPM by 500 or so.
This factor slightly overlaps the effect of primary pipe length, but the pipe length generally will not change the peak torque or the RPM at which it occurs.
A length change has the effect of improving the torque on only 1 side of the peak by "borrowing" it from the other side. A shorter pipe improves the torque after the peak (reduces it at lower RPM), preventing the curve from flattening out so quickly as speed increases. A longer pipe extends the torque curve backwards to improve the engine's flexibility, at the expense of after-peak torque.
Another instance where a slightly larger pipe may help is where the departure angle of the pipe from the flange is very sharp (typically downward). The added cross-sectional area immediately after the flange apparently helps reduce the restrictive effect of a small radius after the port.
This partially explains why some header models or brands work better than others with similar dimensions.
If the primary pipe inside diameter is more than 1/8" larger than the actual port opening in the head, the header flange bolt pattern can be slotted slightly to raise the centerline of the primary pipe above the center of the port, until the bottom of the pipe just matches. This puts the pipe's effective center closer to the most active area of gas flow, and the mis-alignment at the roof allows the highest-pressure gas an easier path away from the port; also adds some degree of anti reversion.
If controlling reversion is more important than maximum port flow (e.g. primary diameter is very large), the mis-match should be at the bottom of the port where gas flow is slowest, and therefore most likely to reverse-flow at low engine speed.
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Old 12-06-2004, 08:31 PM
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"the p51 also used water injection did it not to supress detonation and increase milage?"

To supress detonation, yes..to increase range, no. The water injection system was of limited quantity, for very limited use. The Merlin engine used in the P51 (this engine was also used in the Spitfire, and an early version in the Hurricane) was rated to sustain 67 inches boost for up to 5 minutes, using water injection. At this power setting, the engine delivered about 2000 horsepower@22,000'. Of course many pilots talk of using this boost level for 10 minutes or more, but I think half of it may be just that...talk. Most pilots wouldn't deliberatly take such a chance, especially deep in enemy airspace. I'm sure it happened, just not routinely.

Anyway, to answer your question, yes, and no

By the way, the P51 had a wonderful range from the time it was built. It had a large fuel capacity to start with, and the Merlin engine, when leaned out and set for cruise flight, was very economical. Unfortunately, it wasn't in squadron strength until very late in the war. Until then, it was up to the Spitfires and P47's (both with a positively dismal range, though the Jug got much longer legs later on) to escort bombers. Until the P38 began operations in the European theatre, the escort fighters were forced to turn back shortly after landfall on the continent. When the P38 showed up, it was the only fighter in Europe (or the world, for that matter) capable of escorting bombers from where the other fighters turned back, to the target, or nearly so, giving German fighters quite a surprise initially. For a short period in Europe, before the P51B went into operations, and the P47 was equipped with drop tanks and larger internal fuel cells and got a better range (Spitfires never got legs worth mentioning), the P38 was the only saviour of many Allied bomber pilots. Before that, German fighters simply loitered just out of range of Allied escort fighters and beat the **** out of the bombers at will. Do a search for "Black Thursday" and you'll see what can happen to bombers without fighter escort.

You can probably guess I'm quite a fan of the P38, and Lockheed, the company who built her
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