Cat bypass pipes
Discussion
Hi guys,
i have done a search and there are no threads that appear to answer my question satisfactorily.
a little background info, i am putting a turbo on my MX5 and have been recommended to get a 2.5" system to reduce backpressure and decrease turbolag, all fine so far.
i spoke to the guy doing the install about a cat replacement pipe to further reduce backpressure and he agreed that it would be a good idea.
What is the legal and insurance standpoint if i were to crash and, god forbid, hurt someone with a declared cat replacement pipe fitted to the car, would the insurance pay up. Also, what is the deal with failing roadside emmisions checks, do they give you a while to rectify the problem, ie. go home, fit the cat and get retested and sail through.
thanks for your thoughts, empirical evidence would be great as opposed to pure guesswork, even though gut responses are welcomed.
Greg
i have done a search and there are no threads that appear to answer my question satisfactorily.
a little background info, i am putting a turbo on my MX5 and have been recommended to get a 2.5" system to reduce backpressure and decrease turbolag, all fine so far.
i spoke to the guy doing the install about a cat replacement pipe to further reduce backpressure and he agreed that it would be a good idea.
What is the legal and insurance standpoint if i were to crash and, god forbid, hurt someone with a declared cat replacement pipe fitted to the car, would the insurance pay up. Also, what is the deal with failing roadside emmisions checks, do they give you a while to rectify the problem, ie. go home, fit the cat and get retested and sail through.
thanks for your thoughts, empirical evidence would be great as opposed to pure guesswork, even though gut responses are welcomed.
Greg
the car is a 2003, well past the j-k age when cats came in, my point being that the car would definately fail a roadside emissions check without the cat, would that fact lead the insurance company to declare the insurance null and void on roadworthyness grounds ie me knowingly driving an unroadworthy car, even though i would, of course, declare it to the insurance company.
Any definitive answers chaps!!!!!
Greg
Any definitive answers chaps!!!!!
Greg
I put cat bypass pipes on my Audis S2 turbo (and they do make a difference to turbo response) - insurers happy, MOT man happy, as car was registered 1991. I forget the legalities (SO THE FOLLOWING MAY BE WRONG), but they're something along the lines:
If your car's fitted with a cat and registered 1992-1996 it doesn't need the cat if it passes the emissions test anyway.
If your car's registered 1996-> it must have a cat (unless exempt - SVA or something?).
If your car's fitted with a cat and registered 1992-1996 it doesn't need the cat if it passes the emissions test anyway.
If your car's registered 1996-> it must have a cat (unless exempt - SVA or something?).
Hollywood Wheels said:
My insurers are happy to cover me with a cat replacement pipe, honesty is the best policy. They don't charge me extra either...
Mine was shipped with a cat and requires one to pass the MOT.
It has a cat once a year for said MOT.
Insurers know I run with no cat, and care not.
greg_D said:It is based on first use of the vehicle. Basically if it was supplied with a cat and was bought in the UK (as opposed to a personal import) then it will need one to pass the MOT.
If your car's registered 1996-> it must have a cat (unless exempt - SVA or something?).
is this upon first manufacture or ongoing?
Anybody care to expand
Greg
sean5302 said:
This could work well for you, but may not. Probably not for the reasons you are thinking.
A roadside emissions test is unlikely. If the car doesn't smoke, why would anyone stop and test you, especially on a 2003 car? The MoT is likely to cause a failure, due to high CO and NOx. You may well need to put the cat back on for the MoT.
What will be a problem is the mixture progression.
I am a group engineering manager for a very large european car maker. I specialise in diesel technology, which has none of the mixture problems so inherent in petrol engines.
It's easy enough to set the mixture at tick-over and at full throttle. Progression is the problem area. The ecu will be programmed to take back pressure into account, along with extra injection to heat the cat following engine start.
On a turbo-charged engine you could end up with holed pistons, melted plugs etc.
Worth it? I think not.
I have a Honda Fireblade. Do you know it will do 163mph and 0 to 100mph to 0 in "so many" seconds?
If only Micra man wasn't in front, plus 2 cameras, plus speed calming....
Erm, am i being thick here, are you saying that excess performance is not necessary on the public road and what's the point turboing the car, if so, thanks for the concern, but i reckon i will be alright, secondly, how long does micraman stay in front of you on your bike, if it's for more than about a minute, you are right, you may be better off with a step-through vespa.
**newsflash** "Tangeant of the year award goes to Sean5302" **newsflash**
Anyhoo, back to the technicalities/legalities of a cat bypass pipe
sean5302 said:
On a turbo-charged engine you could end up with holed pistons, melted plugs etc.
Worth it? I think not.
Just about every turbo lump I know runs rich anyway, so is rather unlikely to melt a piston.
I run so rich I attach a bucket to the exhaust and stop every 50 miles to pour fuel back into the tank.
I have always thought the best way to do this goes like this :
Get a broken cat from breakers. Burn and bash the matrix it untill it is clear. Fit to car.
You can claim ignorance of the broken cat to insurers and emissions people. Cats burn and break up all the time due to bad spark and fuel on them.
Re-fit your old one back for the MOT.
Get a broken cat from breakers. Burn and bash the matrix it untill it is clear. Fit to car.
You can claim ignorance of the broken cat to insurers and emissions people. Cats burn and break up all the time due to bad spark and fuel on them.
Re-fit your old one back for the MOT.
bear in mind most ecu's will relearn the finer points of mixture and timing and stuff if you disconnect the battery and leave it for half an hour, then reconnect with the CRP fitted. I have an esprit with a GM ecu and it is happy as a pig in poo providing it is given time to settle in. the knock sensor will protect it from detonation and there are various overpressure safeguards for the turbo that will bleed away the excess. I had a wastegate/solenoid type problem and it was overboosting to the ecu's max safety boost pressure. I know it was because the ignition and fuel cut out at, ahem, around 70 and WOT. This protected the engine from going BOOM!
If my 1994 (with a 1989 engine setup) can survive I expect yours will. Do check the engine actually has these sensors otherwise it might be wise to fit them ;-), as mine was a turboed one from the start. Oh and bigger injectors and fuel pump might be a good way to go too.
If my 1994 (with a 1989 engine setup) can survive I expect yours will. Do check the engine actually has these sensors otherwise it might be wise to fit them ;-), as mine was a turboed one from the start. Oh and bigger injectors and fuel pump might be a good way to go too.
Not sure how much help this will be but.... my mate had an old H reg MX5 1.6 with 130,000 on the clock - it had a cat but it had disintegrated. So we removed it , replaced with a straight through pipe. Come MOT test we crossed fingers and amazingly the emission figures were so low the tester thought his kit was broken. So he rolled another car in and checked it - nope working fine. Recheck the MX5 - still virtually zero. Class.
greg_D said:
my point being that the car would definately fail a roadside emissions check without the cat
Any definitive answers chaps!!!!!
Greg
No it would'nt, most Jap cars including many tuned ones will happily pass the emissions test without a cat. My Turbo'd 5 did, my 88 but somehow reg'd 98 Soarer does too.
Mr E said:
On a turbo-charged engine you could end up with holed pistons, melted plugs etc.
Worth it? I think not.
Just about every turbo lump I know runs rich anyway, so is rather unlikely to melt a piston.
I run so rich I attach a bucket to the exhaust and stop every 50 miles to pour fuel back into the tank.
Doesn't it depend on how much boost he's gonna run tho, more boost meaning weaker AFR untill mapped correctly.
Whats a safe amount for an MX5? With no boost controller a decat pipe would probably see boost creep with the wastegate overwhelmed. So it may be an idea to try it with the cat left on 1st, then if not enough power decat and boost controller.
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