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Message started by Michael L on 08/05/14 at 15:08:27

Title: backpressure
Post by Michael L on 08/05/14 at 15:08:27

Hey guys

A quick question about the thing with backpressure.. I've always thought that the savage was best suited with some kind of restriction baffle in the exhaust, in order to create backpressure. I've been runing with a trumpet style pipe with only a perforated tube inside, thinking that soon I would have to come up with some idea to put in a baffle of some kind.. Then I read this in the tuning guide:

"in general, small mufflers with large straight-through, perforated tube baffles, make the most power and the most noise".

Does this mean that this type of muffler pipe actually do have some backpressure in it?

Title: Re: backpressure
Post by Dave on 08/05/14 at 15:27:50

Open exhaust and straight through pipes do make the most power at full throttle and higher rpm's (and they do make the most noise) - but that comes at a cost. The engine can become hard to tune, and often does not run smoothly at all rpm's, and may lose some usable torque at lower rpms.

Exhaust systems with baffles help to cancel exhaust pulses that can result in flat spots in the power delivery.

https://www.youtube.com/watch?v=KjKUKhHQLHg

If you are drag racing and operate at full throttle most of the time, then you can live with a cranky powerband. If you are riding around on the street and in traffic, you are most likely better off with a baffle in your muffler.

Dave

Title: Re: backpressure
Post by Serowbot on 08/05/14 at 15:31:22

Virtually none... and while it is possible that it can make more peak HP,... but it will be in a very limited rpm range and all at very high rpm...
So,.. the bike will feel weak... because it needs more throttle to do anything...

Most people that think they want more HP,.. really want more torque...
They want the bike to feel like it doesn't need full throttle, because it pulls really good without needing to go full throttle...
That's torque...

Dang'it... Dave beat me to the post... ;D....

Title: Re: backpressure
Post by Kris01 on 08/05/14 at 21:02:19

You do not need any backpressure at all...ever. Backpressure is a restriction like putting a banana in your tail pipe. You don't want it. Most people confuse backpressure with wave tuning. They are two separate animals.

Title: Re: backpressure
Post by Serowbot on 08/05/14 at 21:37:20

Wave tuning, and backpressure are two separate things...
... but,.. you do need back pressure if you want a wide powerband...

Title: Re: backpressure
Post by Michael L on 08/05/14 at 22:35:22

Aah I see.. Then I do need to put something in it.. Thanks for clarifying!

I have this other tapered style universal pipe, looks similar to a dyna type,
It has a kind of crooked Wall in the middle, where the gasses Can slip past the sides. It's looks like it's made by cutting a "tongue" in the inside tube, and Then bending it Down. Does this Sound right? Whats your opinion on that type of baffle?

Maybe I should save up and buy a dyno... :o

Title: Re: backpressure
Post by Dave on 08/06/14 at 04:18:48

6A5348521110210 wrote:

Well.....the idea is not to create a lot of restriction....but to cancel out the pressure pulses and waves that can hurt performance. I suppose if you built a really big muffler you could do that without making too much restriction. I know the airplanes in WWII seemed to get along just fine without anything but a short piece of exhaust pipe - but they operated pretty much at one speed for hours at a time while in flight.

For me the muffler does 2 things. It allows the engine to operate smoothly, and it allows me to get along with my neighbors and ride in peace. I hate motorcycles that are really LOUD.

Dave

Title: Re: backpressure
Post by Michael L on 08/06/14 at 12:50:58

Great video there Dave.. Just Wish I had watched it sooner, before I went out and bought some exhaust wool for the baffle in my trumpet pipe..... :P
Im surprised perforated tube baffles performed so poorly..

Those dyna type mufflers, are they the best choice there is to get maximum low-mid torque? What type of baffle do they typically have?

Title: Re: backpressure
Post by Dave on 08/06/14 at 13:24:03

The DYNA has a 1-1/4 inch diameter pipe that would go straight through that fancy chrome housing - except the put a plug right in the middle to block the flow. Then they drilled a hole bunch of holes in the pipe on both sides of the plug. The exhaust entering that 1-1/4" tube has to exit the pipe and go into that chrome housing....and then it bounces around a bit and goes back into the pipe on the backside of the center plug....and flow out the back of the muffler. The exhaust squeezing through all those little holes dampens the pulses, as well as going into the large outer shell.

Dave

Title: Re: backpressure
Post by Michael L on 08/07/14 at 06:58:34

Looks like it's quite similar to the one i've got.. Think I'll try that one again.. It does feel like my bike won't pull unless it gets more throttle than it used too need..

thanks

Title: Re: backpressure
Post by WD on 08/07/14 at 07:42:13

Running a Dyna style on my 98 netted me 25+ mph gains on the top speed. Sounded terrible though.

Having driven behind 3 Savages and a VN1500J with modified exhausts... the sound of an open piped, Dyna or similar muffler equipped, or universal small 4 stroke dirt bike muffler gets old fast. Spending 3 hours behind them round trip, was close to agony.

The stock muffler on the other hand looks terrible, weighs too much (robbing top speed potential, every 10 pounds extra is a 1hp net loss), is too quiet, is in the way of taking your kids-grandkids-nieces-nephews for a ride (never take your wife, unless you hate her).

Title: Re: backpressure
Post by Greg on 08/07/14 at 10:46:13

0211550 wrote:

The stock muffler on the other hand looks terrible, weighs too much (robbing top speed potential, every 10 pounds extra is a 1hp net loss), is too quiet, is in the way of taking your kids-grandkids-nieces-nephews for a ride (never take your wife, unless you hate her).

I wish I would have known this before my divorce. :)

Title: Re: backpressure
Post by Michael L on 08/09/14 at 17:02:13

I was lookin for a k&n filter in the kedo.com magazine, when I came across a "torque valve" for the yamaha sr. Basically just a small cone you put in between the head exhaust port and the header. Curious to know how it works I found some interesting Info.

"The correct term is Anti Reversion. Jim Feuling invented it, AFAIK. Does it work, yes. Variations of anti reversion were practiced in engine tuning / building in the past where an exhaust manifold worked better when it was a larger diameter than the port exit. Kenny Roberts had a pipe for the TT back in the 70's or 80's when Feuling first introduced the devises he invented. I remember asking a friend who had a lump on his TT500 pipe and he said proudly' "It's a Robert's Pipe!" A mistery then, I know how it works now. Is it needed? That's the question. It's not for high rpm power but to kill any flat spots from reversion in the low to mid range."

Title: Re: backpressure
Post by Bubba on 08/12/14 at 13:13:49

this is the inside of my pipe...
http://i823.photobucket.com/albums/zz155/onelunger/IMG00224.jpg
I love it...not too loud...ok, well pretty loud...the big tab in there is followed up with a bunch of can opener type cuts in the pipe. Seems to give me plenty of torque and backpressure...