Michael Maskalans <dml@tepidcola.com> wrote:
> On Sep 8, 2007, at 2:33, jon@dakota-truck.net wrote:
>> Michael Maskalans <dml@tepidcola.com> wrote:
>> 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.
Yep, that would be my intuition as well. (That is, as the exhaust
diameter gets smaller in relation to the size of the engine, the cross
section becomes more important.) So like you said, you might see a
few HP on a 318 by switching from a 2.5" compression to a 2.5" mandrel
system, but put that same system on a stock 4 cylinder and there might
be no difference.
> 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.....
That's true, and if I ever put together a set of headers, that fact
alone is probably enough reason to use mandrel bends for that
application.
>> (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".
Yep, I think my largest expander will go up to just under 4". I
use it for 3.25" all the time, so 3" definitely isn't a problem. As
far as the pipe goes, I don't know how they compare for cost, but I am
pretty sure Napa sells 3" in 10' sticks. Ironically, the last time I
bought exhaust tubing from Napa, the aluminized was actually cheaper
than plain steel. I haven't figured that one out yet, but whatever,
I'll take it! :-) You'd probably need to order it in advance though,
I don't know if most stores would stock the 3".
--
-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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