Catalytic converters delete on GEMS D1

terryjm1

Well-known member
Jan 23, 2011
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Aside from removing the cats and replacing with welded in pipe, is there anything else that is needed?
 

Harv

Well-known member
There is of course the argument that you shouldn't delete the cat's, but it's probably too late to suggest that. For the downstream O2 sensors, you could install them with extenders, spark plug non-foulers. This pulls them out of the exhaust stream, giving them a different reading than the upstream sensors, which makes the ecu happy, thinking the cat is doing something, and not giving a cel. I've also heard of people just ty-wrapping the downstream O2 sensors away, not installing them in the exhaust at all.
 

fishEH

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Jan 26, 2009
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Lake Villa, IL
Are you subject to emissions testing? Removing the cats could throw some codes making passing tough. The D1 O2 sensors are a bastard size thread, so finding non-foulers to fit is a pain.
 

terryjm1

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Jan 23, 2011
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No emissions or any inspection at all where I will register it. Just wondering if any ECU mods are needed to keep fuel mixtures accurate.
 

p m

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Apr 19, 2004
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No emissions or any inspection at all where I will register it. Just wondering if any ECU mods are needed to keep fuel mixtures accurate.
None required. ECU uses the front O2 sensors for closed-loop fuel adjustment, and only uses the rears to monitor catalyst performance.
But the lack of cats may trigger the CEL.
 
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squirt

Well-known member
Nov 13, 2008
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Los Angeles
No cats? Where do you live? Tijuana?

10 years ago, I used to live in Minnesota. At the time(maybe still now) there was no inspection, emissions or otherwise. I had several vehicles that were V8 swapped, using custom exhaust with no cats, and there was never any concern.
 

terryjm1

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Jan 23, 2011
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What is your goal with removing the cats? That helps determine whether you'll achieve it by simply cutting them out.
I have a y-pipe in great shape that has no cats that came with a parts truck. I am buying a D1 with a y-pipe in poor condition with cats. I just don’t want to spend the cash on a new y-pipe with cats for a vehicle that will see about 1000 -2000 miles of use a year. However, my immediate goal is to make the truck quiet as the current y-pipe leaks a lot of exhaust and noise. My neighbors tolerate my garage noise and too many vehicle disease well. Figure I should avoid making it worse with an obnoxious loud exhaust.
 

Tugela

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May 21, 2007
4,754
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Seattle
If it helps, I just bought a D1 Y-pipe with cats off ebay for under $300. That's more than $0, but it's not bad. It hasn't shown up yet so I have nothing to report in terms of quality or performance, but I wanted to throw that out there as an option that might achieve your goals for not a ton of money. Sell the cats from the crappy Y-pipe to a metal recycler, I plan to do the same with the ones I'm removing.
 
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terryjm1

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Jan 23, 2011
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If it helps, I just bought a D1 Y-pipe with cats off ebay for under $300. That's more than $0, but it's not bad. It hasn't shown up yet so I have nothing to report in terms of quality or performance, but I wanted to throw that out there as an option that might achieve your goals for not a ton of money. Sell the cats from the crappy Y-pipe to a metal recycler, I plan to do the same with the ones I'm removing.
Please do report back.
 

simondewing

Well-known member
Feb 10, 2020
59
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Texas
If you look at any of the UK discount parts suppliers there is a non cat variant of the range rover classic efi exhaust system these are very cheap <$100.
Down pipes and Y piece should be a direct fit no cutting / welding etc required (just addition of bungs for O2 sensors assuming you plan to keep your stock ECU).
Have this set up for my 110 with 4.0 disco engine conversion; just needs to be extended by a couple of inches to fit that.
 
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squirt

Well-known member
Nov 13, 2008
824
13
Los Angeles
I have a y-pipe in great shape that has no cats that came with a parts truck. I am buying a D1 with a y-pipe in poor condition with cats. I just don’t want to spend the cash on a new y-pipe with cats for a vehicle that will see about 1000 -2000 miles of use a year. However, my immediate goal is to make the truck quiet as the current y-pipe leaks a lot of exhaust and noise. My neighbors tolerate my garage noise and too many vehicle disease well. Figure I should avoid making it worse with an obnoxious loud exhaust.

Got it. Make the swap and tie up the rear O2's. You won't have an issue other than CEL.
 
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