GY6 Exhaust System Design Opinions

[WildMan]

OK Reb's,
I'm looking for opinions from you Reb's, for my Custom Built GY6 Stainless Steel exhaust system I'm designing for my Ice Bear Trike...

HEAD PIPE: I'm going w/ 1 1/4" x 16 ga #304 Stainless Steel Tubing for the Head Pipe...

MUFFLER: Muffler 4" dia. x 12" L... I'm going w/ 4" x 16 ga #304 Stainless Steel Tubing for the Muffler Body, & 1 5/8" dia x 16 ga #304 Stainless Steel Tubing for the Baffle Core... Baffle Core will be drilled for a 1 1/4" exhaust port surface area (32 holes 7/32" diameter)... Muffler Body will be insulated w/ 1/4" thick baffle packing held in place w/ perforated 22 ga #304 stainless steel...

QUESTION
Now I'm trying to decide if I want a 3" long turn down tail pipe or a 12" long turn down tail pipe... Then of coarse the next question is what diameter should I make the tail pipe??? Should I make the tail pipe 1 5/8" dia same the baffle core diameter??? Or should I reduce the diameter to 1 1/2", 1 3/8", or 1 1/4" diameter???

Please weigh in w/ your opinions...

David Sr.

[xs650]

Once the exhaust has gone through the core, smoothed and cooled off some the 1.25 inch is plenty big enough. The 1.25 will prolly be a bit quieter than the bigger ones.

[kliff]

Dec 28, 2010 0:10:04 GMT -5 WildMan said:

OK Reb's,
I'm looking for opinions from you Reb's, for my Custom Built GY6 Stainless Steel exhaust system I'm designing for my Ice Bear Trike...

HEAD PIPE: I'm going w/ 1 1/4" x 16 ga #304 Stainless Steel Tubing for the Head Pipe...

MUFFLER: Muffler 4" dia. x 12" L... I'm going w/ 4" x 16 ga #304 Stainless Steel Tubing for the Muffler Body, & 1 5/8" dia x 16 ga #304 Stainless Steel Tubing for the Baffle Core... Baffle Core will be drilled for a 1 1/4" exhaust port surface area (32 holes 7/32" diameter)... Muffler Body will be insulated w/ 1/4" thick baffle packing held in place w/ perforated 22 ga #304 stainless steel...

QUESTION
Now I'm trying to decide if I want a 3" long turn down tail pipe or a 12" long turn down tail pipe... Then of coarse the next question is what diameter should I make the tail pipe??? Should I make the tail pipe 1 5/8" dia same the baffle core diameter??? Or should I reduce the diameter to 1 1/2", 1 3/8", or 1 1/4" diameter???

Please weigh in w/ your opinions...

David Sr.

IMHO, and after a bit of testing, 1.25" is too large for a head pipe on any engine under 180cc.
What I have found that works, keeps exhaust velocity high, and makes for an easy to jet system, starts with 1" I.D. (10"'s long) slip fit into a piece of 1.125" I.D. (8"'s long) which is then slip fit into a 1.25" I.D. pipe, 6"'s long to your muffler. Muffler core should be 1.375" I.d. 12"'s long, with a 3-5" tail pipe 1.50" I.D.

Your method of baffling, holes, dia., and such, sounds good, but I'd incorporate it to my spec for the pipe, and I think you'll have an excellent performing exhaust, stock, and one that will grow with the engine, with no further changes up to 180cc.

Just my HO, from past experience.

[Rebel]

What Kliff says makes a lot of since. If you go directly into a 1.25 inch pipe you can get some back turbulence that will increase pressure. Stepping up makes a more laminar flow.

[jmkjr72]

ahh the simple joys of a 4 stroke exhasut

like kliff said you dont want to go to large too fast the step up process helps things flow faster

[WildMan]

A thanks for the feed back...

Kliff your spec is pretty close to what I originally was thinking... But thought I should clarify the tubing for the head pipe is 1 1/4" OD x 1 1/8" ID, NOT 1 1/4" ID... I was going to come out of the flange w/ 1 1/8" OD x 1" ID short stainless nipple then to the 1 1/4" OD x 1 1/8" ID... 1 1/8" OD x 1" ID is what I would've preferred but it wasn't available to me.. What was available to was 1" OD x 7/8" ID & 1 1/4" OD x 1 1/8" ID...

xs650 suggested 1 1/4" for a tail pipe, I'm not sure if he's talking ID or OD... Also any thought as to length of tail pipe... Longer would likely be quieter as well... My options are 12" or 4" long, but I not sure what affect the longer pipe would have... Quiet exhaust would be great for me, but I don't want it to be a disadvantage ether... Kliff do you have any thoughts on the tail???

David Sr.

[kliff]

Sorry it took so long to get back to you david, still got hundreds of loose ends to tie up, and my head ain't quite screwed on tight yet either...

Pipe, this is where I get all my stuff...
www.mandrel-bends.com/catalog/

They sell SS but I find the size selections in mild steel better.

As for tail pipe, I like 'em short, but as on a Trike, where longer is needed, I think I'd up the size to a 2.5 > 3" OD. The "work" has been done in the stepped header and muffler. We are truly left with slow flowing waste gas that merely needs a dump to atmospere, or a low pressure area. Had we used a more common, single sized(small) head pipe, I would agree with XS650, as you are still controlling a high speed exhaust flow, but my design has the exhaust spent, by the time it leaves the muffler.

[WildMan]

Thanks Kliff
There's diffidently a bit art work & mind bending involved in exhaust designing... It makes a person understand why a good after market exhaust systems can be so expensive... I built 5 exhaust systems (shooting in the dark designing) in the past, & it tends to get a bit pricey... Quality of exhaust design doesn't make much of a difference in the cost ether, you can build an expensive poor design or an expensive good performing design...

Ya, I've been buying my tubing from the same company... I'd like to invest in some low tech bending equipment & tools, but at the moment I don't have any extra free floor space to anchor a bender or even to anchor a bench for a bench bender... I've out grown my shop, need a bigger building for a shop...

David Sr.

[jmkjr72]

sparky the blue tip wrench is my friend for bending
that and some old scraps of wood and break drums and what not to bend around

the down side is you eithre need a long enough peice or you need extensions to sleave insode our outside of what you are bending