Mandrel Bent Tubing

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From: cosworth0078_REMOVE_457238_THIS_@yahoo.com

I want a 2-1/2" ID MANDREL Bent tubing exhaust sytstem! I have to
have it NOW. Why? Because I read that this is THE hot setup for a
Cosworth. And, I remember reading in a mid-70's "Car and Driver"
magazine issue on the car: "what good is it to have a trick engine if
the exhaust lab corks up the exhaust?". Or, something to that
effect....I am going by memory, here.
I have raced my Cosworth with open exhaust, years ago, and it is
a VERY DIFFERENT car with no exhaust system! But, that is not an
option, for me, now. I live in a much better neighborhood than I did
when I was in my 20's. (The neighbors frown on loud cars.)
I am not an exhaust expert. I am going with what I understand,
here. So, I am told that a REAL mandrel bent exhaust system is not
really available to Cosworth owners. There are mandrel bent
systems that have been worked up for certain applications, Like for
one writer's Camaro, but not for our Cosworths. What my local shop
owner told me was that to make a complete mandrel bent system, for
the Cosworth, would require many small off-the-shelf mandrel bent
pieces welded together. No regular shop is going to have a mandrel
bender. They are very expensive machines. What all shops have is
what he called a crimp bender. It leaves crimps in the inside of
every bend and a concave linear spot on the outside of that bend. A
true mandrel bent tube will have none of this, being perfectly
smooth, inside and out. Now, if you are still with me, welding a lot
of mandrel bent pieces (to replicate, exactly, the stock Cosworth's
exhaust system) would defeat the purpose of having the mandrel bends,
because you would have a whole lot of seams caused by the many welds
at every spot a bent tube was welded onto the whole. The muffler
shop guy went on to explain that with all the bits and pieces (using
the off the shelf mandrel bent "U's" and "elbows", etc. would be cost
prohibitive and not be better than a very clean crimp bent system.
What say you, one and all?
-Clark




[This is message #9553 by user cosworth0078 on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]

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From: rondeau3_REMOVE_513711_THIS_@yahoo.com

Clark, you got it, the only option to have the same flow as a true
mendrel bend 2 1/2" would be to go with a 2 3/4" done on a normal
crimp pipe bending machine, that way where ever you have a flat spot
in one of the bend you still keep at least 2 1/2" in thos area.
Going with 2 1/2" like I did you lose at least 1/4" every time you do
a bend.

Al




[This is message #9558 by user rondeau3 on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]

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From: doctorduke_REMOVE_474538_THIS_@yahoo.com

According to both actual dyno testing on my car and numerous
engine simulations I have run using two different simulation programs
the OEM exhaust consumes 40-50 HP in pumping loss at
high revs, and a free flowing system is the most cost effective
modification you can do. A 2.5" mandrel bend pipe from the converter
outlet and a Walker Dynomax muffler would recover most
of this power and send it to the rear wheels.

I've designed such a system for a '76 model using the OEM
routing and LH muffler hanger. A new RH hanger would have
to be fabbed from a clamp and piece of rod. If we could
find a vendor who can mandral bend the exhaust pipe, we
might be able to do a club or co-op program.

Adapting my design to a '75 would be problematic because
they use a different LH muffler hanger and the dual pipe
outlet.

Duke




[This is message #9559 by user doctorduke on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]

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From: cstwcam_REMOVE_954760_THIS_@yahoo.com

The muffler
> shop guy went on to explain that with all the bits and pieces
(using
> the off the shelf mandrel bent "U's" and "elbows", etc. would be
cost
> prohibitive and not be better than a very clean crimp bent system.
> What say you, one and all?
> -Clark

Apparently that is what I have from the sound of the concave outside
radius of the bends. The insides are smooth though not like the parts
in the auto supply stores or even the 2 inch vega system I installed
a few years back. Yes, the aftermarket system was 2 inch. The new
system is a BIG improvement believe me. Looks like you maybe right Al


Art




[This is message #9569 by user cstwcam on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]

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From: rondeau3_REMOVE_813993_THIS_@yahoo.com

<a href="http://www.magnaflow.com/03cat-back/hotrodkit/03hotrod.htm">http://www.magnaflow.com/03cat-back/hotrodkit/03hotrod.htm</a>

Art, there is a lot of supplier out there, if you look at this link,
they offer U-bends, 45 deg., 90 deg., the choice is off limit.

It seems that your exhaust was bent on a different machine though, I
don't see the same flat spot inside your pipes like I have on mine.

I'll make a picture comparison between a 2.5 non mandrel and a true
mendrel bend side by side and will post it in 0539's album, I'll let
you know once I have it on.

Al




[This is message #9570 by user rondeau3 on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]

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From: kconnair_REMOVE_291535_THIS_@yahoo.com

Eric, Eric, Eric,

Don't you know... never ever give up even the slightest chance to
involve your wife in the hobby in a useful way or not. The dent was
wifedom's way of punishing you for keeping your toys & hobby too
much to yourself. ;)

I agree with your assessment of the exhaust system. If you go big
enough, mandrel bent becomes far less of an issue.

Enjoy your new sounding Cosworth...

Kevin.







[This is message #9590 by user kconnair on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]

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From: ericc_seattle_REMOVE_517145_THIS_@yahoo.com

I just had a complete new 2 1/2-inch, crimp-bent exhaust system
installed on my '75 CV #1881. Complete meaning from the header all
the way out over the axle in the stock location. He used a Flow
Master muffler. He even fixed me up with a stainless steel, two-
outlet tip off some Cadillac SST application. Not stock, but looks
like those tips the Honda guys use. Traditionalists may cringe at
that, but I like the look, and he threw it in gratis. Total cost for
the system was $550. The car is stock except for the Hutton duel
Weber set-up.

I was totally blown away by both the sound, and the performance gain
over the old stock system. The car used to peak at around 6000 rpm
in power. Now, I get pull up to the tach limit, and maybe a little
more. And the sound. I know I raved about the sound when I put on
the Webers, but this is the real deal. It's pretty mellow when
driven with a light foot. But what fun is that? With things wide
open, EVERYBODY looks. Just like 20 years ago on my '83 GS750ES with
the Kerker K2S and no baffle, except now I can afford the ticket.

I'm no engineer. I leave the tech stuff for others to hash out. But
as for the mandrel bending, I guess my point is: I don't see the
point. On a stock motor, could you actually notice the difference
over a crimp-bend? The take-home message is that you go bigger on
the exhaust from the header out, not that every bend is perfect. In
a racing application it might be important. But I question whether
you could get mandrel done for what I paid, and if you would know the
difference if you paid for it. Tech guys?

The only unintended effect of my new exhaust system is that it forced
me to have the big dent in the roof fixed, the one I put there by
dropping a headlight bucket on it THE DAY I BROUGHT THE CAR HOME!
This after my wife had offered to help me stow parts, and I told her
to bugger off and let me enjoy my new toys in peace. Stuffing parts
in your rafters over your new car with no help after four beers
should probably not be part of the Tech Tips. Anyway, I couldn't
have a car that sounded so cool showing that huge dent.

Vrooom, vrooom.

Eric




[This is message #9587 by user ericc_seattle on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]