Date: Fri, 4 Apr 2008 18:27:51 -0700
Reply-To: neil N <musomuso@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: neil N <musomuso@GMAIL.COM>
Subject: Re: Fw: Neils' Downpipe/"Y" pics + exhaust flex bushing and pipe
reducer questions
In-Reply-To: <003d01c896b8$267e4f20$6401a8c0@downstairs>
Content-Type: text/plain; charset=ISO-8859-1
Wow. Thanks Gary. Great reading.
I am finding the flex pipe aspect of this quite interesting.
As for the muffler, I'm using a Walker Quiet Flow stock Vanagon
muffler. I want this exhaust o be as quiet as possible. I am running
2" ID pipe from "Y" to the cat though. And for sure, the primaries are
too short. Partially a space constraint issue, and partially my lack
of skill sets.
I've never done this kind of thing before. Big learning curves.
The engine carrier, and exhaust are the first times i've done any MIG
welding. So thanks, I guess my welds aren't too bad, though if you
were able to see them close up.... well that ain't gonna happen! ---
;^)
If I had used 1-3/4" OD mandrel bent tube, with a larger radius, for
the primaries, I could have allowed more space between the pipes and
ended up with much easier access to finish running welds between the
pipes. As it was there just wasn't room (especially for a welding
newb) between the pipes. Like a 3/8" or less. I tried, but ended up
"chasing" the weld up between the pipes from my home made "Y"
collector to a point where I could finish (seal) the weld.
I will likely make a new down pipe at some point soon. Maybe I could
run the primaries rear ward, then forward under the carrier to a
collector, then run a "U" back to the rear. Would be tight though.
Maybe better would be to keep the same routing, but run longer
primaries down and around the bottom of carrier to "Y", then a shorter
2-1/4" OD pipe to cat. Either way, I was afraid of getting the exhaust
too close to the DS shock. Something I was more concerned about than
primary pipe length. There is ample clearance though as it stands and
I can live with torque and HP loss. Anything is better than what was
there. --- :^)
Thanks for the information on the flex pipe. It was interesting to
read about the vibrations etc.
Neil.
On Fri, Apr 4, 2008 at 5:58 PM, Gary Stearns <gstearns@optonline.net> wrote:
> I just caught this thread and have some info that might be useful. The
> (neatly done) downpipe is a Tiico for sure. As for the...ahem... less
> neatly done downpipe, if you're a novice welder, the welds in your pictures
> are beautiful. If you have 10 years of experience, maybe it's time to
> consider another hobby;-).
>
> I've had a Tiico in my '88 for @100k and struggled with a lot of exhaust
> problems early on. I also have some experience with road racing and vintage
> racing which required me to dive into header design and function more than
> most listees might. Too bad you didn't hear this sooner, but the secondary
> pipes (the two that are parallel to each other) are too short, and will
> actually kill power and torque (for VW's with this 4-2-1 setup, the
> primaries are cast into the manifold). I can see from your pictures that
> you may not have the room to lengthen the secondaries similar to the Tiico
> setup, but consider it if possible. For the sake of discussion, the
> typical I-4 conversion with HP and torque peaking at @ 4,800 rpm, wants
> secondaries that are close to 36" long. This causes the low pressure area
> between the reflected pressure waves to reach the cylinder just as the
> exhaust valve is opening again. This is what creates a header's "extractor"
> effect making more power and making an open exhaust scream at high rpm. The
> Tiico secondaries are pretty close to the optimum 36" (one is 36" the other
> is about 34.5").
>
> The placement of the flex-pipe is a continuing debate in the Tiico Yahoo
> Group. The spot where Tiico installs the flex-pipe is useless in my
> experience. I cut this one out and added a longer more flexible one before
> the inlet of the converter on the transverse run across the rear. Doing
> this did cause the whole run to move 4-5" to the right, requiring some
> re-positioning of the mounts for the converter and muffler. The the overall
> length changed very little since the Magnaflow straight thru muffler I used
> has a shorter body than the stock muffler. Prior to moving the flex-pipe
> to be in-line with that transverse run, I had constant exhaust system
> cracking (I even cracked the tubes inside a stainless muffler). Since the
> change of flex-pipe location, no cracks at all. My MIG welder is looking
> pretty lonely.
>
> If you consider the unusual configuration of the exhaust on a Vanagon it
> shouldn't be hard to see that the flex pipe installed as Tiico did can't
> solve vibration caused damage to the exhaust. Any engine installed in a
> Vanagon has the crankshaft running in a fore / aft orientation, with the
> transverse section at the rear running perpendicular to the crankshaft. The
> primary vibrations from power pulses run sort of concentric to the
> crankshaft center, ie: the cylinder block rotates back and forth around the
> crankshaft in very small amounts. This rotational vibration is what's so
> destructive to Vanagon exhausts. With a solid connection to the engine
> block, the transverse run across the back vibrates so that the left side
> goes up while the right goes down; basically trying to pivot around a
> centerpoint related to the center of the crankshaft. The vibration is only
> a very small amount of motion, but it can cause damage since it abrubtly
> reverses direction thousands of times per minute and has the leverage effect
> of 3 feet of system hanging from the motion source. At @3,800 rpm the
> vibration of that transverse exhaust section apparently hits it's own
> harmonic frequency causing the vibration to be magnified many times. The
> weight and position of the exhaust components and supports will cause the
> rpm of this harmonic vary between engines, even to the point where it
> disappears in the normal rpm range of a particular engine. I'm sure this is
> why some conversion owners have never had an issue with exhaust system
> failures.
>
> To eliminate vibration on this side-to-side run, the run has to be
> "de-coupled" from the engine and it rotational vibration. Imagine that run
> without the cat and muffler supports and with the ability to pivot from the
> left side so that the tailpipe end on the right can be freely raised and
> lowered; no resistance caused by it's connection to the engine. The run
> would be de-coupled in this example. Positioned where Tiico put it, the
> flex pipe would have to be able to rotate to permit the tailpipe to be
> de-coupled. Since these accordian type flex pipes can't rotate, the
> side-to-side run remains firmly coupled to the engine's rotational
> vibrations. With a flex-pipe installed in-line with that transverse run,
> it can flex as it was designed to. You've "de-coupled" the exhaust from the
> vibration source while significantly changing it's harmonic frequency. As I
> said, vibration cracks are history for me.
>
> BTW, to be sure that you get all of the available power from any I-4
> conversion engine, consider using something other than a stock Vanagon
> muffler. At the very least, the inlet and tailpipe are both too narrow to
> permit the flow that these engines need (1.875" I think). I'd say don't go
> below 2"; 2.25" will flow pretty well; 2.5" and you're ready for that wild
> cam and bumped compression ratio.
>
> For some excellent info on the design and construction of exhaust headers
> and high perf. systems try Burns Stainless.
> http://www.burnsstainless.com/index.htm. These people are some of the best
> in the USA at fabricating and supplying materials for the ultra expensive
> headers used by Formula One and similar racing. Don't miss the Technical
> link on the left side of their home page. If "art" to you is top notch
> industrial design, be sure to spend some time surfing the Burns site. Their
> fabrication is some of the best industrial design "art" I've seen anywhere.
>
> Gary
>
>
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