Re: It's Sooooooo Quiet


"dizzy" <dizzy@xxxxxxxxxxxxxx> wrote in message
news:69v844l02hu925h27337jhvlefl5tcubl1@xxxxxxxxxx
dual45s wrote:

The Vance and Hines Ovals are very free flow mufflers. They have next to
no
restriction in the lower RPM range but really flow some exhaust as the
RPM
goes up.

Should not that "but" be an "and"?

Could be - your choice.

The Touring Mufflers have more restriction to flow at low RPMs but
don't flow quite as well as you get into the upper third to quarter of the
rev range.

Should not that "but" be an "and"?

No, that should be as is.

The result is you have moved your power band down the RPM range
with the swap.

How does a more-restrictive exhaust "move the power band down the RPM
range"? (Obviously, it's understandable how it could curtail high-RPM
performance.)

There are a lot of reasons why this happens but happen it does. Among the
reasons is when using an "open" exhaust system the reversion of the
sound/exhaust wave has nothing to block it and you end up getting some
amount (depending on cam timing) exhaust flowing back into the combustion
chamber (I'm assuming you have more than a casual knowledge of how to make
bikes faster). This is not an issue when you are running at high RPM as the
exhaust will exit the exhaust system before it has a chance to start back up
the pipe. Some times you can actually see the reversion taking place (on
carb equipped bikes) if you remove the air cleaner(s) as there will be a
very fine mist of fuel spitting back out of the carbs on straight pipe
equipped bikes.

Straight or Drag pipes are a good example. Time a bike's acceleration in the
0 to 50 range with fully open pipes (even if the are exactly the optimum
length). Then insert those 6 inch tubes that are little more than perforated
pieces of tubing and rerun the acceleration test. You Will be faster.
Straight pipes and by extension all super free flowing exhaust system work
best at the top end and screw up your bottom end. Loud does not equal fast
in this particular case even though a whole lot of folks think they are
faster because the bike "sounds faster".

There are a lot better explanations than the above in the various tuning
books for motorcycles. However, it is very well documented in most (if not
all) the tuning books dealing with Harley motors. Specifically, I'd read
Branch Flowmetrics written by Jerry Branch if you really want to delve into
what happens as you vary the major components like exhaust, head design,
carburetion, etc.. He did all the tuning on the Harley Flat Track motors for
the factory race team (he may still be at it) and is a recognized expert in
the Harley world. There is also a book devoted to tuning Sportsters (sorry,
I can't remember the name of the author - Buzz something or other) that also
covers this very thoroughly. I have also seen this covered in a book (you
can call foul here as I can't remember the title) on tuning Japanese multi
cylinder bikes.

I have no idea if you can move a power band say from the upper range to the
middle through just exhaust changes and not effect the lower range. I'd
guess it is possible but would take some very fancy exhaust tuning.

Now a couple of asides. (1) Loud pipes don't save lives. They just make you
slow. (2) A motor cycle motor is a motor cycle motor. It doesn't matter if
it is a Harley or a Ducati. The tuning factors are pretty much the same even
though how you do it may vary to a great degree. (3) Save the grading of my
writing and punctuation as I'm not interested. Challenge what I say to your
hearts delight but save the other stuff for someone that might be impressed.
--

Wayne
AH52
The road goes on forever



.

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