Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties exhaust systems

exhaust systems

Post Thu Nov 19, 2009 7:05 pm

Posts: 109
evening folks, i've been watching this board for years and have some questions about UL exhaust systems. i'm building a bobber, mild stroker, late style fxst springer, wishbone frame, and disc brakes.....have a 1958 style brake pedal and master cylinder, okay you're starting to see where this is going...............pipe routing....thru the frame or out and under. if i run the style without going thru the frame what will ground clearance be like?.....keeping in mind the late style springer, maybe 3 to 4 or so over a stock 36-48 springer. next question would be in a general way, what style exhaust would be best to start with, .....2 into 1, duals, mufflers and what kind, i'm not going racing but don't want to throw away usable torque at common road speeds and rpms. i have looked at all the easy to find pipe suppliers, are there any other options out there? coming up on the 3rd year on this project and now doing preassembly to ensure all components are happy together.....mark

Post Thu Nov 19, 2009 8:13 pm

Posts: 2688
Location: Los Angeles, CA
Paughco makes some UL pipes.

Post Tue May 18, 2010 8:49 am

Posts: 74
Location: Wichita, KS
A. if you're running a 3 or 4 over springer you should have no clearance issues unless you go play in the dirt or hop curbs . (personally i've always liked the look the "s" pipe gives , but on a raised frame an outside pipe might give better visual balance . )
B. conventional wisdom is that you get more midrange torque with a longer 2 into 1 . I've heard 40" to 48" is optimal but would love to hear from some of you motorheads on real world vs dyno experience .

Post Tue May 18, 2010 10:17 pm

Posts: 1654
as a general comment I would go with the longer 2 into 1 for overall road use. If you build it to more-or-less stock length you will find the pipes are near enough 40" from rear cylinder and 59" on the front, ie 1.5 times the rear pipe which is reasonably correct relationship. 2 into 1 will improve mid-range at the expense of top end.

Personally, I don't like short rear pipes, especially on flatheads, because they tend to make the rear cylinder mixture a touch weak and flatheads have enough cooling issues already.
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Wed May 19, 2010 11:34 am

Posts: 2688
Location: Los Angeles, CA

Post Sun Jul 11, 2010 5:50 am

Posts: 4
Location: Exit 91, Brick, NJ
I don't think your FX springer is 3 to 4 inches over an old springer but not 100% sure (I know that's not what your asking, just a side note). I am working on a siomilar project with an FX springer and it seems the new springer is about 2",s longer then stock and with a large diameter rear tire they don't sit that high in the front end. I can take the measurements from my springer (center of axle to the bottom tree) if someone has an older springer to measure and compare. This would give us both an idea how the chassis will sit and might be helpfull in making your decision (an mine) on exhaust.

Another source for flathead exhuast is Kick Start but they don't have a web site.

(Jersey) Mutt

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