Date: Fri, 4 Apr 2008 20:58:23 -0400
Reply-To: Gary Stearns <gstearns@OPTONLINE.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Gary Stearns <gstearns@OPTONLINE.NET>
Subject: Fw: Neils' Downpipe/"Y" pics + exhaust flex bushing and pipe
reducer questions
Content-type: text/plain; format=flowed; charset=iso-8859-1; reply-type=original
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
----- Original Message -----
From: "neil N" <musomuso@GMAIL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Friday, April 04, 2008 11:30 AM
Subject: Re: Neils' Downpipe/"Y" pics + exhaust flex bushing and pipe
reducer questions
> <G>
>
> Yup it's a Frankenstein!
>
> Not fired up yet. Still lots to do.
>
> Neil.
>
> On Thu, Apr 3, 2008 at 11:18 PM, Jake de Villiers
> <crescentbeachguitar@gmail.com> wrote:
>> Geez Neil, that's truly FUGLY, but I bet its going to work just fine.
>> :)
>>
>> I think the flex is a great way to isolate the mass of the muffler. Have
>> you fired it up yet>!
>>
>>
>>
>> On Thu, Apr 3, 2008 at 8:25 PM, neil N <musomuso@gmail.com> wrote:
>> > Hi David.
>> >
>> > Yes. Thanks. For sure.
>> >
>> > I'll be bracing exhaust system from muffler to Driver and Pass. side
>> > of engine. Lot's of threaded holes on Driver side of block, not so
>> > sure where to mount from pass side. Maybe I'll do it from from bottom
>> > of accessory bracket. (No PS pump there.)
>> >
>> > Is using a flex joint in exhaust system a bad idea?
>> >
>> > I'm kind of modeling mine after this design (Tiico I think):
>> >
>> >
>> http://tubaneil.googlepages.com/Vanagonjettaexhaust.jpg/Vanagonjettaexhaust-full;init:.jpg
>> >
>> > Thanks,
>> >
>> > Neil.
>> >
>> >
>> >
>> >
>> >
>> > On Thu, Apr 3, 2008 at 7:28 PM, David Marshall
>> > <mailinglist@fastforward.ca> wrote:
>> > > Neil,
>> > > Are you going to add any bracing for that exhaust system? You really
>> want
>> > > to design that so there is NO flex in the system and the exhaust
>> > > moves
>> with
>> > > the engine. Envision a ruler off the edge of a table - vibrates
>> > > quite
>> well
>> > > - if you put it between two tables it is rock solid. If there is any
>> > > vibration in the exhaust you will hear it, feel it and eventually
>> > > break
>> it.
>> > >
>> > > David Marshall
>> > >
>> > > http://www.hasenwerk.ca
>> > > Box 4153, Quesnel BC, Canada V2J 3J2
>> > >
>> > > Engine Conversion FAQ - http://www.hasenwerk.ca/faq
>> > >
>> > >
>> > >
>> > > On Thu, April 3, 2008 18:36, neil N wrote:
>> > > > Hi all.
>> > > >
>> > > > Thought some might get a kick out of seeing the massively ugly
>> > > > concoction I came up with. Yes those are some truly horrible welds,
>> > > > and yes it's over welded, but it's a long story. Believe it or not,
>> > > > I
>> > > > spent many hours on that thing! And no, I'm not making a new one!
>> > > > (for
>> > > > now anyway --- :^)
>> > > >
>> > > > Questions:
>> > > >
>> > > > The flex bushing shown on same page, looks like a butt weld type. I
>> > > > bought it knowing it would be, but looking at it in hand, it just
>> > > > seems like a slip fit would be stronger. Is there such a thing?
>> > > >
>> > > > When looking at Dynomax.com catalogue of pipes, the terminology of
>> > > > ID/ID or ID/OD reducers has me confused. I want to reduce the
>> > > > 2-1/4"
>> > > > OD pipe to stock Vanagon pipe (1-3/4" ? OD) as I'm using a stock
>> > > > Vanagon muffler.
>> > > >
>> > > > Partial exhaust and flex bushing pics:
>> > > >
>> > > > http://tubaneil.googlepages.com/exhaustdownpipey
>> > > >
>> > > > Enjoy your laugh! --- :^)
>> > > >
>> > > > Thanks,
>> > > >
>> > > > Neil.
>> > > >
>> > > >
>> > > >
>> > > > --
>> > > > Neil Nicholson. 1981 Air Cooled Westfalia - "Jaco"
>> > > >
>> > > > http://web.mac.com/tubaneil
>> > > > http://tubaneil.googlepages.com/
>> > > >
>> >
>> >
>> >
>> > --
>> > Neil Nicholson. 1981 Air Cooled Westfalia - "Jaco"
>> >
>> > http://web.mac.com/tubaneil
>> > http://tubaneil.googlepages.com/
>> >
>>
>>
>>
>> --
>> Jake
>> 1984 Vanagon GL
>> 1986 Westy Weekender "Dixie"
>> Crescent Beach, BC
>> www.crescentbeachguitar.com
>> http://subyjake.googlepages.com/mydixiedarlin%27
>
>
>
> --
> Neil Nicholson. 1981 Air Cooled Westfalia - "Jaco"
>
> http://web.mac.com/tubaneil
> http://tubaneil.googlepages.com/
| 
