First, I received two complementary and representative questions regarding the noise levels emitted from Screamin’ Eagle II mufflers on touring bikes. Rich owns a TC88 Road King and Jerry an ’06 Softail Classic. Both consider the SE II mufflers too loud. Both want improved performance but want a quieter version. Both ride behind windshields.
To answer Rich and Jerry, first let me point out the conflict between mufflers and windshields. Screamin’ Eagle II mufflers are about as quiet as any, but windshields reflect sound.
Wonderful things, windshields. They add another hundred or so comfortable miles to a day’s ride, keep the rain off and the bugs away. You can hear the tires sing, the wind swirl, and the joints in the roadway. On the downside, windshields also echo any sound coming from the engine room, good, bad or loud. Long-distance riders favor quiet exhausts and stock air cleaners for the same reason they favor windshields—comfort.
An aftermarket air cleaner and a set of loud Harley pipes add 5 peak horsepower to a stock engine; 2 will be from the mufflers and 3 from the air cleaner. This is the gain and the proportions I measured when I first threw an iron Sportster on Jerry Branch’s dyno in 1982 and when I last tested an ’09 TC96 over at Barnett’s. At mid-rpm, where we mostly ride, the gain may be 3—that is about all. In return for that amazing 2 or 3 horsepower, you get to listen to your additions honk and roar all day and into the night.
Note that while Screamin’ Eagle parts may add 3 horsepower, a downshift can deliver 10. A downshift stays tucked away until you need it and it hardly makes any noise at all.
Both the bikes, Rich’s and Jerry’s, come from the factory with poor mid-rpm performance. It is a matter of tuning. They are too lean, the timing is likely retarded, and the cams are optimized for emission regulations. The easiest performance improvements come from adjusting the air/fuel mixtures; a black box for the EFI and a richer jet needle or Mikuni HSR for the carbureted engine.
Getting some cubic inches
My testing has shown, time and again, that the most effective way to substantially increase power in the mid-rpm range of any engine is to make it bigger. Porting, cams, and exhausts may add a little, but nothing comes close to cubic inches for midrange power. Harley has been applying this principle for more than 25 years. Between 1985 and 2006 they went from 80 cubic inches and 57 horsepower to 96 cubic inches and 70 horsepower. The power gains have been roughly proportional to increased displacement. Bigger is indeed better.
Rich’s TC88 Road King can quietly gain 25 percent in midrange performance by fitting Harley-Davidson’s 95-inch pistons, with no other change. No loud mufflers and no honking air cleaners. However, it might cost a thousand bucks to do so.
Jerry’s TC96 can be bored to 110 cubic inches and perhaps more for a similar result. It’ll cost even more, though.
Just be sure that you use cams with 30-degree intake-valve closing angles. More good engine builds have been ruined by fitting big cams than any other mistake.
Second, in another question regarding muffler noise levels, Jim Willan asks: “Joe Minton wrote in the June ’09 issue about wrapping Kerker baffles with fiberglass cloth. He said it then has the best power, torque, and sound level. He didn’t say if that sound was louder or quieter than before the modification, and that is my question.
My Kerkers are too loud for me—too much pop. Will his modification quiet them some?”
To answer, first, Jim’s mufflers no longer have enough packing to matter. That is why they are loud and pop on the overrun. Repacked with fiberglass cloth they will be much quieter and they will stay that way. They’ll produce more power, too. I designed that Kerker muffler Jim has in 1987, and the original was packed with 10-ounce fiberglass cloth. Ten years and tens of thousands of miles later, it was still packed with the same cloth and was no louder.
Like most aftermarket mufflers with fiberglass packing, the Kerkers Jim refers to come with loose fiberglass wool (or matting). It is cheap to buy and short lived. Within a couple of thousand miles, at best, the wool gets blown out and the mufflers are essentially empty—and very loud.
I was once smacked in the face by some of this stuff. I happened to be standing behind a bike during its first dyno run with a new fiberglass-packed muffler. From that I learned to ignore shards of glass emanating from the back of new mufflers and also learned to stand to the side. That first time, though, we thought the motor had blown.
I have known about this problem for just over 30 years; I have written about it any number of times. I would not run a new muffler before I checked to see how it was packed and then, almost certainly, re-wrapped its core with glass cloth. I believe most of us would pay another $20 or so to get glass cloth packing in our new $600 exhaust systems. Shame on them.
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