Exhaust cat removal

[Marleez]

My friend has removed the cat and remapped  his is250 now has 240 hp.

 

Sounds nice.

 

What do you think?

[Texas]

Sounds very ‘Un-Lexus’ 250ish, Not for me thanks and in UK would not pass MOT ( original designed system components missing, also fail on bumper reflectors missing!) but hey in Bulgaria must be OK?

[Linas.P]

IS250 has 4 cats, 2 on each bank. I think it is possible to remove either primary or secondary cats and still pass mot.

As far as sound is concerned, on idle car just doesn't sound healthy - doesn't idle evenly (unless he somehow fitted uneven length headers). As for how it sound when revved is hard to say, maybe it is good? But video doesn't show that.

As for 240hp - stop dreaming! Not in Bulgaria, not in a dream land... to begin with the bottle-neck of IS250 exhaust isn't the cats, but rather Y section which goes under axle, besides some backpressure is needed for optimal scavenging of gasses. IS250 is obviously NA engine, so any such changes would have minimal difference and only at top end. So let's say in best case scenario +2-4hp at peak power, but maybe -20-40Nm from low-end (which is where you want your Nm) - and that is on properly engineered exhaust system, not just "cats-off". And the engine would be anyway limited by the air it could get in, so I have no idea where that power is coming from. I think overall, just removing cats will most likely make less power, but even if it miraculously makes more it will be few hp, certainly not 240hp.

Finally, on NA engine the only way to significantly increase power is either more volume, or more RPM - even if we assume the car is properly modified with cold air intake, equal length-headers and nice SS high-flow exhaust... it still won't make 240hp. The only way it could make 240hp to to lift the limiter to maybe 8000RPM, but that that point you will need to do full rebuild every 5k miles.

[Britprius]

1 hour ago, Linas.P said:

I think it is possible to remove either primary or secondary cats and still pass mot.

It is possible the car "may" still pass the MOT on emissions with 2 of the cats removed, but under MOT regulations it would still fail due to original manufacturers emissions control equipment being removed.

John. 

[Mr Vlad]

Marlon please get info on the remap your friend used to gain an extra 35bhp. Has that figure been proven on a rolling road?

As for the sound of that car, mmmmm yeah there's something real nice about it, sounds like a bigger engine sound.

[Linas.P]

There are plenty of snake oil seller who claim IS250 can be remapped with power gain - never seen any evidence of that, don't believe it exists.

[Marleez]

7 hours ago, Texas said:

Sounds very ‘Un-Lexus’ 250ish, Not for me thanks and in UK would not pass MOT ( original designed system components missing, also fail on bumper reflectors missing!) but hey in Bulgaria must be OK?

The car is a uk car. Just has Bulgarian plates on there. It is a right hand drive 2007 lexus is. 

[Linas.P]

28 minutes ago, Marleez said:

The car is a uk car. Just has Bulgarian plates on there. It is a right hand drive 2007 lexus is. 

yes, but the point that when it comes to MOT, the standards used are Bulgarian not British. You could not pass mot without cat in UK. And generally that is not great idea... not much different from throwing used tyres or oil into the forest. It is basically just polluting environment for no good reason (and I doubt it even adds power).

[Paul Brooksbank]

They do have a really good dual carriageway in Bulgaria from Sofia as far as Bansko in the South, I drove all 168 km of it in December 2019. I was so pleased to see my EU taxes being put to such good use. Not now, you'll have nowhere to use 240 bhp any time soon. 

[Mr Vlad]

I ask again Marlon please get info on the remap your friend used to gain an extra 35bhp. Has that figure been proven on a rolling road?

[Linas.P]

30 minutes ago, Paul Brooksbank said:

They do have a really good dual carriageway in Bulgaria from Sofia as far as Bansko in the South, I drove all 168 km of it in December 2019. I was so pleased to see my EU taxes being put to such good use. Not now, you'll have nowhere to use 240 bhp any time soon. 

New member actually pays disproportionately higher "members fee" and accept that most of their educated talent leaves the country, so fair trade. 

Main roads are nowadays good in that area - Poland, Hungary and even Romania... Last time I was "euro-tripping" my average speed was higher in Poland then it was in Germany, roads at least to Warsaw were actually better than Autobahn. 

6 minutes ago, Mr Vlad said:

I ask again Marlon please get info on the remap your friend used to gain an extra 35bhp. Has that figure been proven on a rolling road?

let me help you with that - no there is no proof, because that is impossible... unless substantial modifications are done to engine internals as well.

[Mr Vlad]

Linas I KNOW. I'm asking Marlon to ask his friend and no one else. It's His thread.

As for engine internals Linas our engines are just about bullet proof having forged pistons and rods and a very strong crank.

[Linas.P]

Pistons are not forged, only rods. But what I mean by substantial mods, that would be forged crank, rods and pistons, skimmed head, different valve geometry, raised rpm, ported heads, headers with good flow etc. I reckon with fully built engine you could even get like 280 maybe, but that is at least £10k for this works as it would be all custom and completely pointless as more powerful engine could be fitted for less. 

[Marleez]

I'll ask my mate and get back to you.