Japspeed manifold

02 Jan 2018

Is anybody using one of these decat manifolds but keeping the exhaust cat, does it still pass mot?

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F160755708227

Comments

It will give you the P420 trouble code (cat efficiency too low) Not sure if it passes MOT in UK

I’m guessing that’s because the sensors are fitted after the first two cats.
Would I be better off with a less restrictive cat on the bottom end instead?

Nah the first two sensors are fitted before the two manifold cats, then the exhaust runs thru total of 3 cats, 2 per bank and then there is another sensor fitted after all the cats. The ECU compares value before and after the 3 cats and if the efficiency is too low, it gives you an engine code. 1G-FE for the win :D

Made this little diagram, maybe it explains better. Anyway there is no way around the OEM cats if you want the engine light to stay off. That said the engine light doesn’t exactly do any harm being on. Except you won’t notice potential other problems that might also trigger the engine light.

Sorry to ask so many questions but trying to decide between turbo/supercharger or keeping it n/a.
So if you ran a turbo conversion you can’t run it without a check light or do you cut the turbo into the existing manifold?

well the engine light would stay off as long as you got enough cat efficiency from the two pre-sensor to the 3rd sensor. I don’t know exactly how much that is, most turbocharged IS200 run around with the engine light on and don’t worry too much about it. With the supercharger you can keep the factory exhaust system, that’s one of the reasons why it’s more popular than the turbo.

Thanks, I was leaning towards the supercharger as I guessed it would be able to run with all three (and cause they sound ridiculous) but wasn’t sure how important the pre cats are

Yea I would definitely recommend supercharger on these cars and leave the exhaust alone if you’re after a power increase with least amount of headache.
Turbo comes with a few problems, the cats is problem 1. Next problem is the fact that there are no good turbo manifolds in production for the car.