This was an extremely simple hypothesis to test for. Does a loose muffler create a performance advantage?
The engine chosen to test was a purple plate AKRA clone. There are 3 images attached. They are all screenshots of back to back dyno tests of the same engine. To adequately control this experiment, the only variable that was changed was the little pipe's muffler (RLV 4117), all dyno tests were started with a crankcase oil temp of ~150F and a head temp of ~100F. All tests were run within a 12 minute window. The pipe chosen was a RAPP Fab thick flange weenie pipe. I clamped the muffler to the header as is the design intent of this system. I thought about trying the dyno test with the muffler completely loose and not clamped but I did not for the following reasons: a) I did not want to damage good parts i.e. bugger up the threads. b) I thought that the odds of the muffler staying on the header for an entire heat/feature was unlikely if it was 3 turns loose and not clamped. c) that was the reason I decided to perform a test where there was no muffler at all.
The first image 4315 is with the muffler hand tight, a stainless worm type hose clamp was used to secure the muffler to the header (the header's little steel tang).
The second image 4316 was the same engine, literally minutes later, allowing my fans to cool the engine back to the starting point. The muffler was loosened 3 full turns and again clamped to the tang on the header.
The third test, image 4318 was the RAPP fab little pipe with no muffler at all.
The conclusion I come to based on the data attached is there is no performance gain to be had with a loose muffler. In fact, the data suggests that at high rpm, a tightened muffler performs better. The data also shows that removing the muffler altogether does in fact give you a performance gain, especially at higher rpms. Also it should be noted that without a muffler, even with earmuffs on, the engine was loud AF and anyone within earshot of the track would be able to tell something was amiss.
We seem to live in an age where folks can just
create a theory without any data to support it. This is simply speculation. What really bugs me, is folks will
argue about that.
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Here's what 3 full turns loose looks like:
