Stock pellet style converters

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DoubleV

Royal Smart Person
Feb 25, 2011
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Medina Ohio
What year did GM stop putting pellet style converters on gbodys?

Another question. I have a bone stock 78 Cutlass with 260 with the original pellet style converter and exhaust. I have a Walker replacement converter ( monolithic ) as a replacement. Is it worth my time ( which I have very little of nowadays ) to swap in the newer cat? How restrictive is an old pellet style converter on a puny 260 anyway?.... I mean if I could gain just 5 horsepower I'd do it but who knows?

P.S. Please refrain from comments pertaining to dumping the 260 or other such anti 260 nonsense. I'm not an idiot. I know what I have.
 

CaliWagon83

Royal Smart Person
Nov 12, 2017
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I honestly don't think there's any disadvantage to going with the newer style converter. From everything I know, they flow better than the old pellet-bed converters. I'd say it comes down to availability and cost. Like you said, I don't think it's going to make a huge difference one way or the other on a stock engine.
 
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DRIVEN

Geezer
Apr 25, 2009
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Agreed. Newer designs are more efficient but I wouldn't expect to notice a huge difference.
 
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bracketchev1221

Royal Smart Person
Jan 18, 2018
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I would do it. Yes it would suck because the old one is so big and the new one is probably tiny and would need fabricating of pipes. Not only is the old one is probably more restrictive based on design, but also after 40 years of oil and carbon its probably partially clogged too.
 

motorheadmike

Geezer
Nov 18, 2009
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It is less about making more power (that requires changes to the air pump itself (heads, cam, intake, etc)), and more about restoring lost performance or optimizing the existing system.

So, yes swapping out the old for new is going to have a benefit on restoring efficiency to some degree.
 
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Oct 14, 2008
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As said, if it is starting to plug, you will notice a difference. I figured out my converter was plugging on my 81 Delta 88 with the same converter when I got beat by a Mercury Mistake. I replaced the cat with a piece of pipe, it made a huge difference. He wouldn't race me again, I would have beat him, I barely lost the first time.
 
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Michael Watts

Master Mechanic
Dec 12, 2017
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They had "test tubes" back in the day.That replaced the cats. back then It depends on the state emission laws .My 1981 didn`t have a "cat" when I got it .(it had a 290 Hp 350 .With stock exhaust manifolds going into one then going into dual Flowmaster mufflers. and it still passed emissions at hat time. If you are going to replace your cat with another .You might as well get an aftermarket high flow one.It will give you a little more power and fuel mileage.
 
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Streetbu

Know it all, that doesn't
Supporting Member
May 22, 2011
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Pellet style are very restrictive, junk it and install the newer style. Don't throw it out though! Lots of precious metals inside, they are worth some $$$ at a junk yard
 
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DoubleV

Royal Smart Person
Feb 25, 2011
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Medina Ohio
The original converter has very little miles on it so I'm assuming it's not plugged but since I already have a Walker factory replacement ( I can already see I'm gonna need some longer bolts....) I figured hell if I can get ANY extra power it'll be worth it.

Maybe I'll slap on a stock 307 thermal clutch fan to replace the fixed X style one. Maybe I'll free up another 4 horsepower and then I'll be the terror of the back roads!
 
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