SuzukiSavage.com - exhaust pipe size

scubachef Full Member Offline SuzukiSavage.com Rocks! Posts: 140	exhaust pipe size 10/26/11 at 17:04:44 I noticed our pipe is 1 3/4 outside but is hiding a 1.25 id pipe....has anyone run only a 1.25 id pipe? What is the reason for the jacketed pipe? From my search it is thought to be heat right, maybe looks, but not performance related correct? Thanks in advance.
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Gyrobob

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Re: exhaust pipe size
Reply #1 - 10/26/11 at 17:36:05

scubachef wrote on 10/26/11 at 17:04:44:

I noticed our pipe is 1 3/4 outside but is hiding a 1.25 id pipe....has anyone run only a 1.25 id pipe? What is the reason for the jacketed pipe? From my search it is thought to be heat right, maybe looks, but not performance related correct? Thanks in advance.

The fat outer pipe is supposed to suffer less heat-bluing, and the Suzuki stylists think fat pipes look bitchin.

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Gyrobob

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Re: exhaust pipe size
Reply #2 - 10/28/11 at 06:31:13

Also, a 1.75" pipe is too large for this motor in stock form. The powerband for which it is tuned needs a smaller pipe. I don't know exactly what the size should be, but it needs to be small enough to hold adequate exhaust velocity to suit the rpm range for max torque, which is a fairly low rpm range for an LS650.

At one extreme, say, a 1/2" pipe, the bike would idle fine, but would make about 5 hp because it would be strangled when it tried to put out more power.

At the other extreme, say, a 3" pipe, it might look audacious, but at that diameter it would be approximating an open exhaust port, destroying torque at any rpm.

The sweet spot is where the pipe is small enough to keep exhaust pulse speed high enough, yet large enough to not cause too much restriction. It's always a trade off, and, BTW, has to be matched to the breathing ability of the motor. Put a big piston, big valves, hot cam, larger carb, and high compression on it, and you'll need a larger pipe.

Even that pipe will have to be fine tuned,... if you build a high rpm high horsepower motor you'll need a larger pipe. On the other hand, with all those mods you might want to build a torque motor that would pull like a locomotive at 2,500 rpm,.. that'll need a smaller pipe.

Ain't this fun?

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« Last Edit: 10/29/11 at 05:52:58 by Gyrobob »

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teabowl13 Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 535	Re: exhaust pipe size Reply #3 - 10/28/11 at 06:50:23 Looks like GyroBob is on his second cup of coffee already... I've got some catching up to do!!
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Gyrobob Serious Thumper Offline Posers ain't motorcyclists Posts: 2571 Newnan, GA Gender:	Re: exhaust pipe size Reply #4 - 10/28/11 at 07:01:14 teabowl13 wrote on 10/28/11 at 06:50:23: Looks like GyroBob is on his second cup of coffee already... I've got some catching up to do!! Second cup of tea, actually.
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LANCER

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Re: exhaust pipe size
Reply #5 - 10/29/11 at 05:35:02

The stock header is only 1.3" ID which is minimally adequate for a totally stock engine.
Replacing the stock muffler with one that flows better, even just a HD unit, will require a little rejet and tune, but will improve efficiency and add a little power.
Going the next step by replacing the stock cam with a Stage 1 Performance cam improves air flow such that replacing the stock header with one that has 1.5" ID will dramatically improve air flow and engine efficiency throughout the entire rpm range, with the most improvement in the midrange.
Thiis would of course require a reject/tune of the stock carb, or if you want an even better boost in overall efficiency/power then replacing the stock carb with one designed for performance will add even more efficiency & power.
The next step up, if you want to go there, is a larger piston. Sad

They come in 95, 96 & 97 mm with an increase in compression ratio. Even here there is a choice of near stock CR or jump to a 10.5:1 CR. Do that and a 1.65 ID pipe (1.75" OD) will Jack performance even more.
I do recommend that when boring the cylinder for a larger piston the cylinder should have the silicone carbide treatment be done. It will reduce friction; reduce heat as a result and make a bit more power available; reduce possible seizure if you run low on oil; and increase cylinder life dramatically.
If I had just one mod to do to an engine it would be the silicone carbide treatment for the cylinder?
The 1.65" ID pipe is the most needed for this engine when used on a street bike. If you build a racing engine, though unlikely for the LS650, then perhaps something larger might be considered but that is way above in our normal daily functioning bikes.

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Built2Last Serious Thumper Offline Tempt Fate Posts: 1447 FTF Gender:	Re: exhaust pipe size Reply #6 - 10/29/11 at 05:42:34 I, like the Suzuki stylist team, think they're bitchin' as well.
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scubachef Full Member Offline SuzukiSavage.com Rocks! Posts: 140	Re: exhaust pipe size Reply #7 - 10/29/11 at 12:04:29 thanks for the responses everyone!!!!
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Mavigogun

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Re: exhaust pipe size
Reply #8 - 10/15/19 at 13:36:35

LANCER wrote on 10/29/11 at 05:35:02:

Going the next step by replacing the stock cam with a Stage 1 Performance cam improves air flow such that replacing the stock header with one that has 1.5" ID will dramatically improve air flow and engine efficiency throughout the entire rpm range, with the most improvement in the midrange.

Thiis would of course require a reject/tune of the stock carb, or if you want an even better boost in overall efficiency/power then replacing the stock carb with one designed for performance will add even more efficiency & power.

Any reports from folks that have actually done this? Aside from more power, is cooling sufficient for sustained operation into the presumably increased speed range?

Tangential to the original post, how can we measure engine output to calculate exhaust demands? How does exhaust length factor in to exhaust pressure?

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2007 LS650 s40, presently being rebuilt

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DragBikeMike

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Re: exhaust pipe size
Reply #9 - 10/15/19 at 14:02:12

There are plenty of formulas and tables available on the internet. If you use them, you will find that the calculated/recommended exhaust pipe size for a 40 cubic inch cylinder is 1.5" to 1.62" inside diameter. They are based on the assumption that exhaust gas velocity of 300 feet per second is optimum. This also would be based on typical anticipated engine operating speed, which for the Savage would be around 4000 to 5500 rpm.

I am running a large header pipe (2" OD x 1.79" ID). I would prefer a 1.62" ID pipe but that would require a custom fabricated header. Not easily come by in my neck of the woods. I think I'm making good power and the bike runs great, but my max torque would probably be a couple of ft-lbs higher if I had a properly sized header.

If you stick with the stock header pipe, you might be able to pick up a little extra juice with this special exhaust insert. I don't think anyone has tried it yet. You could be a tailblazer. Cool

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1554878768

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Armen Serious Thumper Offline Half-Witted Wrench-Jockey from Jersey Posts: 1431	Re: exhaust pipe size Reply #10 - 10/16/19 at 06:49:40 DBM, Do you think the 1.75 Mac header would work on a 695cc motor with the usual heavy breathing tricks (cam, carb, etc)?
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Fast 650

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Re: exhaust pipe size
Reply #11 - 10/16/19 at 10:41:06

Armen, I crunched the numbers on that some time back. The available cams have little to no overlap so pipe length has almost no effect on tuning. Diameter is all that matters on these engines. For a 695 build the sweet spot with a 1.625" ID pipe is 5300 rpm, and 6200 rpm with a 1.75" ID pipe. So with a stock cam the 1.625" ID is nearly a perfect match and the 1.75" ID pipe would work nicely with the performance cams.

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DragBikeMike

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Re: exhaust pipe size
Reply #12 - 10/16/19 at 10:45:47

Armen, that MAC header is working good on my 652cc engine so I suspect it would work better on a 695cc. I know this may sound like I'm splitting hairs, but the header is actually 1.79" ID, not 1.75". That additional .040" makes a significant difference in cross-section since its a squared function.

I may have a unique setup due to my stock muffler. I didn't just punch a hole straight through the thing. It still utilizes a torturous path to scrub off the acoustic energy. So its not like a tuned system, just low restriction. If that large ID header was combined with a straight through muffler (like the glass pack that comes with the MAC system), it might kill all the low end. I'm not sure and I never tried it. I did start it up with the MAC muffler but it was so obnoxious I never even rolled it out of the garage. It was a non-starter. I just took off that MAC muffler and replaced it with a Dyna unit with catalyst. That also never made it out of the garage due to it being way too loud for me. I want good power with low noise. So I worked some more on the stock muffler and was able to make good progress without increasing the noise level. I actually think it sounds pretty good, certainly not anemic.

As I recall, it was you who turned me on to the MAC system. I'm glad you did. I was looking for a commercially available over-the-counter system that utilized a larger head pipe. You mentioned the MAC. I am always snooping around and the MAC is the only system I have run across that uses a bigger head pipe. We need a vendor who is willing to fabricate good quality 1.62" ID header pipes, complete with flange.

Is your engine poked out to 97mm? Roll Eyes

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Armen Serious Thumper Offline Half-Witted Wrench-Jockey from Jersey Posts: 1431	Re: exhaust pipe size Reply #13 - 10/16/19 at 10:49:59 To be clear, I never used the MAC. I have a stock head pipe and a Ryca muffler (the quietest one). Right now the motor is 650, but I have all the goodies for the 695 tart-up.
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Mavigogun Serious Thumper Offline We roll farther together Posts: 775 Progressive Texas	Re: exhaust pipe size Reply #14 - 10/26/19 at 20:47:28 Armen wrote on 10/16/19 at 10:49:59: Right now the motor is 650, but I have all the goodies for the 695 tart-up. Could you point me toward documentation for such a build? Or would yours be a first?
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