header damage dyno test

[chimp koose]

I picked up a copy of I think engine masters the other day as there was an article in there dyno testing an engine with progressively larger damage to the headers in each stage of the test . Results made me wonder why I ever studied header design to the extent that I have . Evidently , and supported by dyno testing you can feel free to clearance with the BFH  and feel little to no noticeable difference in performance . They beat those headers down WAY more than anyone here would ever feel the need to with nowhere near the effect on performance that I would have expected . I suggest you read it so you can set your mind at ease when you next have to clearance a pipe . The effects are mostly cosmetic . interesting read .

[enjenjo]

I have read the same thing.

[jaybee]

That makes sense to me. Four stroke engines use tuned exhaust, but two stroke engines really exploit everything in the exhaust stream because a port window in the cylinder wall doesn't have the ability to fine tune everything the way you can with a camshaft. The expansion chamber of a two stroke has constantly changing cross section through most of its length and every bit of it is for a purpose...right down to the exact length from port to the end of the stinger. Almost all of it is either sending positive or negative pressure waves back up the pipe to the exhaust port. This is a pretty decent page on the subject.  http://www.motorcycle.com/how-to/how-twostroke-expansion-chambers-work-and-why-you-should-care-3423.html

Seems to me as long as the dimple doesn't excessively restrict the cross section or occur so suddenly it causes turbulence the result makes sense...though it's not so obvious I would have been sure of the answer without knowing it had been tested.

[idrivejunk]

I've always cringed more from the weakening or thinning the tube, flange warpage from beating or creating a hot spot aspect but its good to know that even the more significant "dimpling" doesn't hurt power. As with everything, I reckon location is everything. I'd imagine exh valve temps are not affected much unless you hurt the cross section.

[Harry]

Along the same line....has anyone heard of dimpling straight exhaust to make them quieter. No mufflers.

[chimp koose]

Dimpling the pipe would work , but only so much . I did a bit of experimenting on my sons cobra exhaust on his bike this summer. The muffler was a straight thru perforated pipe with the exhaust going from the outer tube thru the holes into the center pipe and out .When I drilled out the capped end of the perforated pipe at the start of the muffler it was LOUD . When I wrapped the outside of that same pipe with roxul insulation it was quieter than stock . I once saw an insert I forget who makes it , that looks like the spiral fluting of an auger that slides into a sidepipe to quiet it down by causing the exhaust to lose its energy by swirling it . Not sure if it works or not but was an interesting idea

[Crosley.In.AZ]

Along the same line....has anyone heard of dimpling straight exhaust to make them quieter. No mufflers.

Chambered exhaust on gen 1 Camaro was this design , as I recall