Discountconvert cat, part II

["Giller,Bruce C." <bgiller@domain.elided>]

	As you might recall, I had installed a Discountconverter cat on my '86
Spider last weekend only to have fitting problems at either ends.  Both
gaskets leaked and I was getting exhaust fumes in the cabin...along with
puff-puff exhaust sounds.  I had all week to think about the problem and
decided to remove the cat for inspection.  Also, the new cat appeared to
be lower than stock since I was scraping over things in the road that I
didn't hit with the stock unit.

	Upon inspection of the downpipe mounting flange gasket, the leak
appeared to be only on one side; the side between the gasket and the
cat.  I discovered that the cat flange was not flat across its' width;
there was about 1/32" gap on the side that was leaking.  The stock unit
was dead flat.  Applying the tender mercies of my angle grinder, I took
down the high spot (the ridge between the two openings) and checked at
other positions.  I polished up the whole flange with a flapper disc. 
It wasn't perfectly flat but much better than before.

	The center muffler (Stebro) has a 51 mm OD round protrusion that fits
into the cat (for a depth of 4.5 mm or so) to help seal the two
together.  The new cats' opening was slightly less than 51 mm which
meant the the cat and the center muffler never seat properly.  The stock
unit had a perfect 51 mm opening and the correct depth.  Using a
combination of die grinder bits, I enlarged the opening and deepened it
as well.

	Then I compared the two cats, side by side with the downpipe mounting
flanges clamped to a piece of steel.  The new cat will extend  about
1/2" lower than stock when mounted on the car.  This, I think is due to
how they mounted the O2 sensor.  The stock sensor is mounted at an
angle, pointing toward the front of the car to clear the front of the
drivers' side pan.  The new cats' sensor is mounted at 90 degrees to the
pipe which means that it must be lower than stock to allow the top of
the sensor to clear the body.  No wonder the attachment strap on the cat
did not align correctly with the tranny support bracket.

	After working on both connection flanges, the exhaust no longer leaks. 
But I still have a clearance problem: since I have lowered my Spider,
every mm counts in regards to exhaust pipe clearance to the road.  My
idea here is to mimic the stock O2 angle by removing the the bung on the
new cat, welding on a short piece of angled tubing and welding the bung
on top of that.  (The stock cat accomplishes this by an angled
depression in the tubing.)  Then have the cat's down tubes bent to match
the original angles (using the stock piece as a template) to regain my
missing ground clearance.

	Bruce

	'86 Spider
	'73 GTV which should be out of the shop this week.

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