924Board.org

[Smoothie]

I'd read a while back that the 931s' OE catalytic converter had a "metal substrate" instead of the more common ceramic substrate. -The substrate being the material (aka- "monolith") that's coated with the catalyzing metals palladium, rhodium and platinum.
In the absence of any more information on metal substrate cats and why they were used in the 931, my best guess had been that the metal substrate was more durable and required in the 931 because of the increased flow from the turbocharger and possibly due to the full throttle fuel enrichment.
-But just today, I found this metal substrate cat from JCW - metal'Cat™ <click> -As far as I can tell now, the advantage of a metal substrate is only improved flow with the monolith design of 200 cells per square inch vs. a ceramic monoliths' 400 cells per sq.inch. -So durability may not be the advantage as I'd been guessing and we may as well save some bucks by using a higher capacity, lower priced ceramic cat. Anyone know if I'm guessing correctly now?
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Raceboy]

I think the ceramic cat has to be too much bigger to compensate it's worse flow capabilities. If the given numbers are correct, the difference is pretty big (though I'm not aware of the flow of the 931 OEM metal cat).
But one thing is for sure, more backpressure reduces performance on turbocharged cars (that's news, dh )
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'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche

[Smoothie]

Here's their (JCW's) $69.99 ceramic monolith "UNIVERSAL CATALYTIC CONVERTER" <click>. They claim it's good for engine sizes up to 5.9L, so I'm guessing that's big enough for the 931 with unmodified to conservatively uprated boost.
I wish they'd gone into a little more detail though. I need to know if it's a 2-way or a 3-way converter (I just barely passed emissions testing this week with NOx of 1313 (limit=1323) with no cat.) - plus it would be nice to know the actual flow rate.
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Smoothie]

I just stumbled on some more info in one of my Bosch/SAE books..
From Bosch's "Automotive Electric/Electronic Systems" 1st ed. 1988 -
"Metallic monoliths
Metallic monoliths are at present only infrequently used. They are primarily installed near the engine as so-called pre-catalysts, supplementing the main catalytic converter, in order to provide more rapid catalytic conversion after cold starts. Their application as main catalysts is primarily impeded by excessive costs."
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Tigger937]