Michael Maskalans <dml@tepidcola.com> wrote:
> Hey Jon-
> I think I remember that you keep a bunch of mandrel bent 3" tubing
> 90ūs that you use for Stieger Performance intakes. Is that stuff
> stainless or aluminum, and what's your source?
Its aluminized steel; the cheapest place I've found it so far is
JC Whitney, of all places. :-) Used to be under $20 each but its
kept creeping up, I think they are a bit over $20 now. Kinda pricey,
depending on how many you need. (I usually wait until I need to order
enough to qualify for one of their free shipping deals which helps a
little at least.) If anybody knows of a cheaper source for mandrel
bends, I'm always interested in new sources. One of these days, I'd
like to try my hand at fabricating a set of headers. (I get the
feeling I'm going to want to build a set of turbo headers one of these
days.) :-) I could probably use my bender, but it seems like
tighter mandrel bends welded together are likely to be the better way
to go for that. I keep wondering if it would work to build a mandrel
for my compression bender; fabricating a makeshift mandrel probably
wouldn't be *too* bad, the trick would be getting the stupid thing
back out of the pipe after its been bent around it. I think true
mandrel benders have a hydraulic ram that they use to pull it out,
which is why you often see gouges on the inside of a mandrel bent
tube. Getting back to sources, Bassani has some 180 degree U bends in
3" for around $12-13 each, though it is 18ga instead of 16ga, and
appears to be plain, non-aluminized steel. (Then again, if you're
welding up aluminized, its gonna rust too, just at the joints instead
of all over.) (They have stainless too, as does JC Whitney, that's
more money obviously.)
Does the Jetta need a full 3"? I tried to find some compression
vs mandrel bend flow or horsepower data, but didn't have a lot of
luck. It would be really interesting to bend up the same exhaust,
except with mandrel bends in the one and compression in the other and
run them on the same motor on the same dyno. About the best I could
do was http://www.bobsmuffler.com/dyno.htm (along with the
corresponding "mandrel myths" page), but its less than convincing,
IMHO. (Particularly the first graph on that page which shows an
increase of 0.1 horsepower. The max torque went up an impressive 13
lb-ft, but if you look at the graph, you can see that's only because
of that first part of the graph where its dropping down into the
regular "curve". (And that's another weird thing, I've never seen the
torque and HP "drop" into the curve, how does that happen? Its almost
like the tranny shifted there or something, I dunno.) Anyway, they
have a little part of the graph you can zoom into where they say "you
can see how the mandrel bending pulls ahead in the mid to upper rpm
range", but the increase is so small that they felt it was necessary
to zoom into that area, and furthermore, it definitely does NOT show
the mandrel bending pulling ahead in the "mid to upper RPM range".
When I look at that run, I see two systems making nearly identical
power with the exception of an increase in the range of 2-5hp and
ft-lbs over a tiny 150rpm window! (And this is the first graph they
put on their site to convince folks of the benefit of mandrel
bending?) I dunno, seems like there has got to be better data out
there than this. (They actually link to one of their competitors on
their "mandrel myths" page, the competitor claimed an increase of
power with a compression bent system over mandrel.) I don't know that
I'd be inclined to believe that, but who knows how controlled *any* of
these tests were?
Anyway, I seem to be rambling a bit. :-) I guess what I'm
wondering, out loud, in a quasi-coherent manner is, what real world
difference will the mandrel bends have, and is it worth the price? A
3" OD mandrel bend which is something like 1.5 feet long is in the $20
range, whereas a straight 3" pipe would be something like $3 per foot,
so the cost is definitely on the side of compression bending, but at
what power expense, if any? Seems like if you used 3" pipe, even with
compression bends, it should flow at least as well as a mandrel bent
2.5" system? I think? :-)
(I do actually have 3" dies for my exhaust bender, but I haven't
tried out any 3" pipe yet, mostly because I haven't had a need to yet.
So I'm not sure how much it would tweak the pipe.
--
-Jon-
.- Jon Steiger -- jon@dakota-truck.net or jon@jonsteiger.com -.
| '96 Kolb Firefly, '96 Suzuki Intruder, Miscellaneous Mopars |
`-------------------------------- http://www.jonsteiger.com --'
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