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March 24, 2024
Final Exhaust System
It's been two and a half years since I installed the bulk of the exhaust system, and I made some decisions back then that I'm having to follow through with now.
I tucked the silencers (mufflers) up under the boot floor to be more out
of sight, and cut passages through the rear valance for the exhaust
tips. I was unsure back then on exactly what to do to finish the
job, so I just put it off.
Well, it's now time to do something, even if it's wrong.
I determined back then that the original tips wouldn't work as supplied
because they came out at the wrong angle. Even after cutting them
from the silencers, they were still much too long.
So here is the starting point.
I bought some 2-1/2 inch exhaust tubing to experiment with (same size as
the original tips). I like "sausage" cuts on exhaust tips, and
started with a cut angle that sort of followed the contour of the lower
valance.
This looked good to me, but I really wanted them to be polished
stainless and have a little more finished look, so I searched online for
some tips that were close to this. After failing at that, I
started to consider using the original tips after all, just modifying
them to match my design.
The original tips are polished stainless, and a double wall. The 1-3/4"
inner tube is the actual exhaust pipe, while the outer 2-1/2" polished
pipe is more cosmetic. The stainless was tough to cut. I
used a composition blade on a chop saw.
I had to expand the silencer's stub pipe a little to get the tip to slide in.
Trial fit. I think this will work.
Welded the tips to the silencers with stainless MIG.
Well, no mod like this ever goes without a fly or two in the
ointment. In this case, the fly was the fuel tank outlet. It
was just above the left front corner of the left silencer, and it
didn't appear that there was enough room for the fuel pipe to come out
and make a graceful turn.
I needed a way to make a more compact right angle fitting. After
mulling a few complex and wonderful solutions to this, I finally decided
to look at using a standard banjo fitting. The female thread for
the original compression fitting is 1/2-20. This is not a common
thread for banjo bolts, but I did manage to find one.
I believe the normal use for this banjo fitting may be in brake systems,
which is a high pressure, low volume application. Thus the pretty
small passages.
I thought they were too small for a fuel system, so I drilled them out to a more respectable size.
Also, considering the exposed place where these parts will live, I
fretted about the zinc plating they came with. I know from
personal testing that the zinc on typical hardware items is pretty much
just cosmetic, and doesn't last long in the wild. So they got
stripped of their token zinc, and replated, followed by a nice chromate
passivation to protect the zinc. The banjo had a 1/8" NPT outlet,
so a 5/16" compression adapter was screwed in to accept the fuel line.
I bent up a piece of welding wire to the shape of the fuel pipe that has
to route to meet the pipe that comes from the front of the car.
They meet on the outside of the left frame rail just in front of the
rear suspension. Then bent some copper nickel tubing to match.
The other issue with this new fuel pipe arrangement is that the lower
rim of the compression fitting on the tank was not designed to be a
sealing surface. I did my best with a small sanding block to make
sure that there was a flat area on the rim to mate well with the banjo's
sealing washer. We'll see how that works.
One last thing. The silencers are fairly close to the underside of
the boot floor, spaced maybe 3/4" away. The undercoating I used
has a service temperature only around 200ยบ F, and I thought the
silencers might get the coating hotter than that. The fuel feed
also was fairly close to the left silencer. I thought some sort of
radiant heat shield would be a good idea. This some thin
aluminum, which is a good infrared reflector. The little bump up
on the near corner fits around the fuel fitting. This shield of
course doesn't do much for the hot air coming off the silencers, but
should reduce radiant heat.
OK, time to put her all together. Just to show that I'm serious
about not wanting to see the silencers, I blacked out their rear
surfaces, which actually showed a little through the tunnels, with some
high temp wrinkle paint.
Looks good to me.
The re-designing of the rear of the exhaust system was quite a lot of
work spread over a couple of years. Other than the purchase of the
exhaust system, the cost was next to nothing, since I was able to just
rearrange things. I'll have to wait to see of the changes make any
difference in the sound.
Comments to ed at elhollin1@yahoo.com
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