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Muffler inlet/outlet pipe diameters [?]

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twas_brillig

Jedi Knight
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Our BJ7 is running a stainless steel exhaust system. The stock Healey inlet pipes are about 1 13/16" OD; our outlet pipes are 1 3/8" OD (nearly 1/2" smaller in diameter than the inlets).
Are our outlet diameters the same as on stock/mild steel systems? Thoughts as to why (and the impact) of having a significant difference between the muffler inlet and exhaust diameters?
Thanks,
Doug
 
might be that tube and pipe have different wall thicknesses, and that some back pressure may be beneficial
 
Don't have a 'stock' system to measure, but the setup was similar in the Ansa system I had--since modified--on my BJ8; i.e. the last section of pipe out of the rear resonators was a smaller diameter than the rest of the tubing. When the Ansa mufflers and resonator gave up the ghost I grafted in some generic glasspacks and replaced the last section with larger diameter tubing. Our BN2's SS system also has a smaller tube exiting the muffler (the single downpipe is very large by comparison--close to 2" OD, maybe more).

This is pure speculation, but I think a lot of the aftermarket mufflers are glasspacks. The smaller tubing--like zblu mentioned--may be to increase back pressure to 'force' more of the sound into the glass packing or, possibly, to better approximate the back pressure of the original mufflers, which were probably the baffled type. However, I doubt the aftermarket people spend much effort calibrating their systems to original--maybe they're just saving some money using smaller diameter tubing.
 
Just measured pipe diameters on a side curtain BJ7 (ours is roll-ups), and the inlet pipe is about 1 11/16" and the outlet 1 3/8". This is a slightly different inlet diameter than ours, but that's probably due to the tool and the chap (me) wielding the vernier.
Doug
 
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