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exhaust size?
http://www.woodsbuggy.com/phpBB3/viewtopic.php?f=3&t=5850		 Page 1 of 1
Author:  earlytimz [ Fri Feb 20, 2009 9:00 pm ]
Post subject:  exhaust size?
At what point do you really NEED a 1 5/8 header?
There has to be some science behind the sizes. I'm sure it's easy to say bigger is better, but that's not always true. Will a smaller engine run better or make more power and/or torque with the 1 1/2? In other words, can you do more harm than good with a "bigger than needed" exhaust? I assume there are several things you must consider ie: cc's, heads, compression, aspiration, back preasure, etc. So how do you figure it?
Not interested in "just get the big one so you can upgrade later" answers. I'm looking for real answers.
Thanks!
Author:  Odyknuck [ Fri Feb 20, 2009 10:18 pm ]
Post subject:  Re: exhaust size?
Asmaller engine will run better with a smaller exhaust system. The smaller exhaust will scavenge better and give you better lower end torque that is prefered for what we do.. Larger exhausts are better if your running WOT all the time.
Author:  rockrockets1 [ Fri Feb 20, 2009 10:21 pm ]
Post subject:  Re: exhaust size?
OR A BIG ENOUGH MILL

LET HER BREATH
Author:  earlytimz [ Fri Feb 20, 2009 10:24 pm ]
Post subject:  Re: exhaust size?
That's what I was thinking... But how do you figure it? Or what's a good rule of thumb?
Author:  rockrockets1 [ Fri Feb 20, 2009 10:30 pm ]
Post subject:  Re: exhaust size?
don't realy know .When I ran a 1835 or 1914 I always ran 1.5 to have some bottom end .But after running a 2332 I liked the way the 15/8 made it turn up .But with the big bore it still had plenty of low end.So in saying that I don't know my buddy Jeff Busby runs a 1.5 header on what ever motor he belives in a small header .He likes the crisp low end snappyness
Author:  Strong [ Fri Feb 20, 2009 10:43 pm ]
Post subject:  Re: exhaust size?
Early, Go to www.ssheaders.com. Then click on "headers 101". A great one page header sizing. Hope this helps.
Author:  earlytimz [ Fri Feb 20, 2009 11:12 pm ]
Post subject:  Re: exhaust size?
Hey man, that was some good reading on header basics. I wish it included a calculator or something, but I guess they aren't in the business to give away their secrets.
I'm running a small stroker (2054) so I was thinking I should probly go with the 1.5" header. After reading that, and with rock's suggestion, it kinda validates my thinking.
I appreciate yall's help. Anyone else?
Author:  jesse [ Sat Feb 21, 2009 2:38 am ]
Post subject:  Re: exhaust size?
i run a 2180 with the 1 5/8 and its great
Author:  Strong [ Sat Feb 21, 2009 9:25 am ]
Post subject:  Re: exhaust size?
Early, Also the other end is as important to go along with this tourque header. If you are running dual carbs. The Venturi (interchangeable throat inside webers or delortos) size should be about 2mm smaller than the intake valve. Example 44mm intake valve would use 40 mm venturis. Remember this is not the size stamped on the outside of the carbuerator.
Author:  Firebug [ Sat Feb 21, 2009 9:35 am ]
Post subject:  Re: exhaust size?
One thing I learned about headers is that on 4 cylinders they should all run into one. Help me out Strong,,,and BTW good to see you back on Woodsbuggy.com,,hope to see you in the woods soon,,better yet come to Corinth.. Good luck ET.
Author:  Strong [ Sat Feb 21, 2009 2:18 pm ]
Post subject:  Re: exhaust size?
Yes firebug you are correct. The 4 into 1 header scavenges the cylinders the best. Therefore it produces the best low end torque. I think i might be coming to Corinth (march 13-14) with a very large SUPRISE. See you then.
Author:  wildwillie [ Wed Feb 25, 2009 9:18 pm ]
Post subject:  Re: exhaust size?
dam good to see you back around.. strong and im a 1.5 fan my self
Author:  earlytimz [ Wed Feb 25, 2009 10:48 pm ]
Post subject:  Re: exhaust size?
Strong wrote:
Early, Also the other end is as important to go along with this tourque header. If you are running dual carbs. The Venturi (interchangeable throat inside webers or delortos) size should be about 2mm smaller than the intake valve. Example 44mm intake valve would use 40 mm venturis. Remember this is not the size stamped on the outside of the carbuerator.


Hey Strong, you seem pretty slick on this stuff...
What's the downside if this ratio isn't correct? Like venturis to small as well as to big compared to valve size?
Author:  Strong [ Thu Feb 26, 2009 12:27 am ]
Post subject:  Re: exhaust size?
Early, If you had say 36 mm venturis with 44mm intake on a healthy stroker motor it would be real tourqey at low rpm and flatten out severely at 4000-6000 rpms. If you had 44mm venturis with a 44mm intake on the same strocker motor it would bog at low rpm (you would have to clutch it and hope you didn't break the transaxle) and probably turn 8000- 10000 rpms. My 2643cc runs 48 trijet delortos with 40mm venturi and 44mm titanium intake valve. It with spin up without clutching it and bump off the 10,000 rpm rev limiter easily. Thats with 39.5 cut boggers, 4.56 six rib and 3.75 first gear. Hope this helps.
Author:  earlytimz [ Thu Feb 26, 2009 12:50 am ]
Post subject:  Re: exhaust size?
:shock: Dang Dawg
I appreciate the school'n, makes sense, thanks!
Where do you ride? I wanna see that buggy in action sometime.
Author:  Strong [ Thu Feb 26, 2009 1:22 am ]
Post subject:  Re: exhaust size?
Going with firebug and some of my friends to Corinth,March 13-14. That buggy is in the shop getting repaired.It was either the 3rd,4th or maybe the 5th flip that ripped the front end off. No problem though, i have a backup buggy i'm bringing. Please come and bring family or friends or both.
Author:  jim [ Thu Feb 26, 2009 6:36 am ]
Post subject:  Re: exhaust size?
I would imagine that someone has crafted a formula or algorithm for determining exhaust system mechanics, but the number of variables is mind-blowing. A dyno test is always how HotVW magazine proves out hypothesis or theory.
Some of the variables are:
-type of fuel
-air or water cooled
-rpm range
-driving habits
-atmospheric pressure
-cam/ valve timing curve
-restrictions (i.e. muffler)
-exhaust coating or wrapping (exhaust tubing temperature)
-exhaust bend geometry
-exhaust internal flow characteristics (turbulence)
All of this assumes that you never have a leak at the head, which may require thicker flanges than "normal". Any flanges thinner than say 1/4" may warp and lose their sealing properties. Hold a straight edge across the flanges of a used buggy exhaust system and you will see what I mean.
Author:  earlytimz [ Thu Feb 26, 2009 10:30 am ]
Post subject:  Re: exhaust size?
Hey Jim,
That's what I was getting at in my first post or two. I know there has to be a formula somewhere. Even without taking into consideration all the variables, seems like there would still be a "good rule of thumb".
You can also do a "redneck tune" on your exhaust. Alot of guys do it on old school metric bikes that they've put straight pipes on. It involves drilling a hole in the pipe and putting a washer welded to a bolt (kinda like an eye bolt) in the pipe and turning it to increase or decrease exhaust flow restriction. Sounds cheezy I know, but the numbers don't lie.

Strong,
I made it to the Greenville buggy event. Got to meet Firebug and Kybc... Still ain't sure about them fellers!
Corinth falls on the weekend of my boy's birthday so gonna have to miss that one. I would like to come down and ride with you Bama guys sometime though. I usually go down to Greenville, Al and deer hunt every year. I have friends that belong to a big hunt club there. All those guys are super cool and I always feel welcome in Al.
Author:  kybuggy1 [ Thu Feb 26, 2009 11:12 am ]
Post subject:  Re: exhaust size?
There is a good rule of thumb.... 1 1/2' on a woodsbuggy, 1641 to a 2500 :D
smaller motors would be better off with even smaller primaries, but I dont know if they make 'em.
Throttle crispness n quick acceleration is where its at for woods riding/tight hillclimbing.
Might loose a few ponies, but worth it when you need to pedal the hell out of it.

Larry
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