Exhaust Slip-Ons Poll, What Is Current On Your F6B.

[53driver]

...It may not seem like much, but this pressurization and re-direction sucks about 10 hp out of the system.

Okay, I'm late to the party, and certainly not an engineering exhaust scientist.
But if an exhaust can "suck about 10hp out of a system" couldn't a differently engineered (read as aftermarket) exhaust restore that?

[shooter]

George I did a little research last night. Cycleworld put a set of monster ovals , so same design on a stock HD. 103 motor. Before and after dyno pulls yielded a 5% increase in HP and a 9% increase in Torque. Granted its not a B but it is an internal combustion engine.

[srt8-in-largo]

Okay, I'm late to the party, and certainly not an engineering exhaust scientist.
But if an exhaust can "suck about 10hp out of a system" couldn't a differently engineered (read as aftermarket) exhaust restore that?

That's exactly how I know about the 10 hp; replacing that exhaust with a free flowing one yields about that much power.

[srt8-in-largo]

George I did a little research last night. Cycleworld put a set of monster ovals , so same design on a stock HD. 103 motor. Before and after dyno pulls yielded a 5% increase in HP and a 9% increase in Torque. Granted its not a B but it is an internal combustion engine.

Can I first say that I'm not trying to be obstinate or hard-headed. Really, I'm not!

Skeptical yes; but not arguing for the sake of arguing.

Dyno's can be made to give you whatever information you want. When magazines and retailers dyno, or otherwise test, product that they're receiving advertising money for, there's an incentive to show the product in a favorable light. I won't accuse Cycleworld of skewing results but I will point out this conflict of interest which makes their results non-definitive to me. In the professional world of scientific and engineering testing, such conflicts send the results automatically to the round file.

I'd be much happier to see results like this from a Joe Schmoe user like you or me where no money is exchanging hands.

Let me ask this, how many exhaust design articles can we find where they say it's beneficial to send gases into pressurized chambers?

How many designs like this do we see on race vehicles?

This is an exhaust for sound man, not performance.

[53driver]

That's exactly how I know about the 10 hp; replacing that exhaust with a free flowing one yields about that much power.

Okay...so if the stock exhaust on a bike is similar to the one in your "non-performance vehicle example", then by merely replacing the exhaust, with a V&H or Thunderheader, we can then see possibly a horsepower increase?

I concur that pipes don't actually "make" horsepower...the engine "makes" horsepower, but I'm concluding from George's examples that a freer flowing exhaust allows the engine to achieve more of it's potential if it's not already peaked.

And I'm not trying to be obstinate or argumentative. I'm trying to learn....

[srt8-in-largo]

Okay...so if the stock exhaust on a bike is similar to the one in your "non-performance vehicle example", then by merely replacing the exhaust, with a V&H or Thunderheader, we can then see possibly a horsepower increase?

I concur that pipes don't actually "make" horsepower...the engine "makes" horsepower, but I'm concluding from George's examples that a freer flowing exhaust allows the engine to achieve more of it's potential if it's not already peaked.

And I'm not trying to be obstinate or argumentative. I'm trying to learn....

It depends on the OEM muffler, 53. If the OEM muffler is particularly restrictive, installing a freer flowing exhaust should show some gains. But if the OEM muffler is already free flowing, putting an aftermarket free flowing exhaust won't do much of anything.

And, for the little bit I know, putting a restrictive exhaust on can never be good in terms of power.

Engine builders speak of something called "pumping losses"; among other things, pumping losses are power losses due to the engine moving air. Assuming for the moment that we're talking about a naturally aspirated motor like we have, airflow into and out of the motor is accomplished solely by the pistons; they "suck" air in on the intake stroke and "push" air out on the exhaust stroke.

Air movement is not a "freebie"; it takes engine power to breath. The potential gains from a K&N air filter or from an aftermarket exhaust are based on creating a freer flowing air path... which reduces pumping losses... which makes more of the existing power available at the rear wheel.

[srt8-in-largo]

Just for grins here's a GL1800 dyno from a guy called Nedro on the other forum. From what I gather, his bike is stock and the AFR readings were done with a tail pipe sniffer. AFR of 13 at the tail pipe should be about 12.5 or so pre-cat; which is pretty much exactly where we want to be. With the AFR dialed in so nicely, the only other thing a guy like Don Guhl can play with to make more power is timing... and breathing mods or a hotter cam.

From other comments in that thread, it looks like most agree that this is a typical result... 95 to 100 hp at the wheels on a stock platform.

[shooter]

And George I'm not trying to ram anything down your throat. I really enjoy a stimulating conversation. Listen you have to understand that this exhaust is not a race exhaust. Any good street exhaust has to balance HP and Torque. There has to be a compromise of flow and back pressure. Its a complicated design. No body would go to the trouble of building an exhaust this complicated unless there were benefits. These guys don't phone it in. I apppreciate your views George.

[srt8-in-largo]

Thanks Shooter, I appreciate and share that sentiment.

Nothing would make me happier than to see someone put ANY exhaust on this bike and show 105 or 110 hp. Then we'll debate dyno calibration, operator technique, and environmental conditions

[F6Bobber]

Attachment 13043

All in all I'm pretty happy with the way they turned out. Stripped and recoated for < $100, still pissed it had to be done in the first place!