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Grahaml

Replacement Sports Cats (DIY)

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With huge acknowledgement to Gunter who gave me the idea and advice.

I had a problem with stuttering/holding back from about 4,000 RPM which I eventually traced to a broken cat which was restricting the exhaust.  The story is in the Engine section (as I was looking at other options initially) but I thought it might be interesting to others to see the conclusion - in the correct section now.  The previous story is here:

Looking at a pair of replacement cats - the cost of around £350 each seemed a lot so I was interested in what Gunter had done before - basically to cut open the existing cat pipe, knock out the old cat innards and "simply" insert generic sports cats into the space then weld it all up again - looks original, meets MOT requirents (to be tested tomorrow!!),  gives more power (200 cell sports cat rather than 400 cell standard) and  costs a lot less.

I will try and put in pics and narrative as I go!

Remove cats - I had already knocked out the original ones - one of which as badly broken up and blocking the exhuast.  I cut it open - so I could get an accurate(ish) size to source a generic sports cat.  There are many available on eBay.  I cut the first cat just before the second O2 sensor boss but then thought if I cut after it I could still put the cats in past it so I cut the second one further up.  As it turns out neither were the best option.

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after measuring inside dimensions I was looking at cats around 98mm wide and sourced them from eBay.  They are stainless steel (made in China) and had a metallic core rather than ceramic.  I ordered the smallest size of bore on each end of the cat as they are less expensive yet the cat itself is exactly the same and I was going to cut the conical sections off anyway.

Using an angle grinder I ground down the welds and cut the new sports cats up to fit into my exhaust;

The I thankfully found they were a very tight fit for my exhaust needing hammered in.  At this stage I found that the cuts I made in my exhaust were in the wrong places and there were overlapping joints and seams that stopped the cat getting in.  I had to make other cuts to fit them in.  The fisrt one I did I eneded up makeing two more cuts and later for the second exhaust I cust the section on the existing wels where it meets the curved section (what I should have done in the first place;

 

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Mt welding skills are far from good but with my home MIG welder I managed to get it all stuck together again.  After attacking it with the angel grinder fittes with an abrasive flap wheel it didn't look so bad.  I painted the cat section with exhaust paint (which won't last long at all I suspect) to make it look a little better and refitted the exhausts.  A brief test run confirmed it is running well - It goes for MOT tomorrow so we will see if the cats are good enough to pass the emmision test.

 

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The cost?

Cats were £140 for the pair plus a little bit for welding consumables - but I had them already.

I figured it was worth trying - it's not too much to lose even if it does fail the emissions and I have to buy new proprietery ones.  Even then I might just fir them to pass the MOT then remove them and run "my" sports cats until next MOT time.

Thanks again to Gunter for inspiration and advice.

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update: MOT passed.  A bit marginal but I have a friendly and helpful MOT tester who took a bit of time and rerun tests untill it passed.  I will run a bottle of Redix in the tank and clean the fuel system/ injectors  as a precaution anyway.  Use isn't very high (1,500 miles last year) so I'm sure it will benifitr anyway.

Thanks @Günter

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I found Lucas oil injector cleaner to be very very good 


Only here once

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Thanks Barry - I wasn't sure which was "best".  Looked at a review on Youtube where Fith Gear tested the effect of Redex which appeared pretty good so I have ordered that.

I'm also doing a full service and I just replaced plugs and leads so I will hopefully be getting the full effect (as shown in the Youtube video).  Not that I am likely to notice - that Lotus V8 has so much power anyway :)

Graham

 

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On 04/04/2017 at 01:15, Grahaml said:

Mt welding skills are far from good but with my home MIG welder I managed to get it all stuck together again.  After attacking it with the angel grinder fittes with an abrasive flap wheel it didn't look so bad.  I painted the cat section with exhaust paint (which won't last long at all I suspect) to make it look a little better and refitted the exhausts.  A brief test run confirmed it is running well - It goes for MOT tomorrow so we will see if the cats are good enough to pass the emmision test.

 

IMG_20170329_163450.jpg

IMG_20170329_170446.jpg

IMG_20170329_170446.jpg

IMG_20170330_150949.jpg

The cost?

Cats were £140 for the pair plus a little bit for welding consumables - but I had them already.

I figured it was worth trying - it's not too much to lose even if it does fail the emissions and I have to buy new proprietery ones.  Even then I might just fir them to pass the MOT then remove them and run "my" sports cats until next MOT time.

Thanks again to Gunter for inspiration and advice.

I'm going to be getting mine done similarly, but I wondered if it would be better to cut out the top half of the pipe and "drop" the catalyst in, then replace the "lid" and weld it back up?

that way the integrity/shape of the exhaust would be kept, and I wouldn't worry about losing the bend/angle of the setup. There's also be less chance of damaging the catalyst with hammering it into place.

 Thanks!

Edited by LotuStuart

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Quick question:

Was it a two way ora three way catalyst that you used?

Thanks 

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Hi - I haven't a clue to be honest there was no mention of either that I can recall.  I just now looked on eBay for "sports cats universal" and this is what came up.

Ebay link...

I'm not saying these were the ones I fitted but they looked like that.

It's worth noting that unfortunately I think I will need to fit proper cats for MOT next year as I only passed this year thanks to a very understanding and helpful (mate) MOT tester.  Like a lot of these cars it doesn't get used a lot - about 1K miles a year and so maybe theres other things I could do to get through emmisions test but it was very well warmed up before the test.

 

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Thanks Graham

I went with a 400 cell in the end, which I am assuming is a three way cat...

It should be fitted this week and MOT after-will update on how it goes. 

 

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On ‎11‎/‎12‎/‎2018 at 09:36, LotuStuart said:

Thanks Graham

I went with a 400 cell in the end, which I am assuming is a three way cat...

It should be fitted this week and MOT after-will update on how it goes. 

 

Any update on the 400 cell cats? I'm looking to do mine before the end of March. Stuart, where did you get your cats from & how much did were they if you don't mind me asking.

Cheers

Jon

Edited by maydharm

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Hi Jon

in the end I decided against it. The 400 cat I bought (ebay, £50 odd) was about an inch of catalyst-which is why, no doubt, these cheAp "sports" cats just manage to scrape a car through the emissions test. 

I bought a bunch of second hand OEM cats and fitted two. Sailed through MOT and I'm confident it will next year and the year after...

has also reduced the noise. Previously with a straight through pipe it was Armageddon. Now although it is not as raucous through tunnels, I can drive longer distances without the noise becoming unbearable. (Which it risked before)

Am happy with decision. Sent ebay cat back so not much worse off,

cheaper using second hand oem, without the fear of after market badly fitting barely legal ones. 

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Stuart

Thanks for the info, I've seen new cats on ebay for £300 ish and a par of second hand ones for £350 one of which sounds shot. Phone round time I think.

Cheers

Jon 

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