On Sep 8, 2007, at 2:33, jon@dakota-truck.net wrote:
>
> 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.
pretty pricey indeed. that probably approaches the cost of just
having an exhaust shop bend it up, although the turbo downpipe
probably requires the tighter bends of a welded mandrel setup, and
that's where the cross section would be most important.
> (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.
my thought as well - the closer to the motor, the more important
maintaining diameter would likely be. I have nothing to back this
other than intuition of course.
> 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.)
I think for a daily driven car that I don't wash nearly enough
stainless is worth it if you're building something that you're happy
with. if you aim to replace it in 3-5 years anyway or not keep the
vehicle then whatever but I stick with stainless for my exhausts.
Bassani gets $56 for a single 3" 16ga 6" radius stainless mandrel U.
$50ea if you buy 11+, $43 for 100+, $36 for 500+.
$71 for 5' of 16ga stainless tubing. ($60ea for 4-6, $48 for 7-9, $45
for 10+)
<http://www.bassani.com/universal/tubing/>
I only see aluminized steel from Heartthrob Exhaust at JC.
There are a number of sources that I found through Google but I have
not had a chance to look through them yet.
<http://tinyurl.com/yrqusu>
> Does the Jetta need a full 3"?
no, but it wants it. :-) It doesn't need anything at all, and
probably won't for 10-15 years.... but a freer intake and exhaust
help the stock turbo flow more CFM at the same boost level, and are
great supporting mods for bigger compressors. A lot of people put on
bigger turbos with stock piping and say it's great but there are
others who have demonstrated faster spooling and less smoke out of
the same turbo with just freer flow, and I'm definitely a believer in
that camp.
> 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)
My thought is that when you're dealing with a restrictive exhaust it
would probably make a difference - a 2.5" on a 318 that has a few
tighter bends in it I expect you could see a difference in the single
digits on a dyno, but on a 3"+ exhaust I'd bet that as the page you
linked to above points out the difference is minimal.
> 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? :-)
probably as well as 2.75 pipe. I'd need to measure the cross section
of the middle of the bend to be more than guessing of course....
The nice thing about fabricating with mandrel bends that you can't
really ignore is that with a mandrel, if you cut the tubing in the
middle of the bend it's still round, and can be welded to a straight
section or a bend on another axis right there. You can't do that
with a compression bend.....
>
> (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.
Well I was thinking that the biggest reason to go mandrel was the
cost of dies and my lack of a bender. I should put a tailpipe back on
the Dakota at some point (removed for shock clearance). If you
happen to have a tubing expander that'll go to 3" as well (it needs a
slip at the muffler), maybe we could bend up something for the Dakota
at Daktoberfest and see how it works. and how the cross sections
compare. I could ever go aluminized on that since it'll not need any
welding if I con get at leash 5' of 3".
-- +-- Mike Maskalans ---------------- Rochester, NY ----------+ | '98 Dakota CC, SAS on 40s '84 RamCharger 4x4, plow truck | | '02 Jetta TDI 5sp, daily '97 Intrepid, not on the road | +-------------------- <http://mike.tepidcola.com/trucks/> --+
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