De-Catting

[BristolE30]

To decat or not too decat.

Just wondering the pro’s and cons. This is what I’ve come up with so far, but be interested hear opinions (I’m sure there’s many)

Pro:
Tasty noise
Better flow
Harvest the cat for £££

Cons:
Too loud
Bad for environment
Effort
No real performance change?

Thoughts?

[Brianmoooore]

The most noticeable change from removing it will be an increase in MPG especially on an M40.
If you care about the environmental bit, ditch the poison generating fuel you're running it on and convert to LPG. Close to zero harmful emissions and double the engine life.

[BristolE30]

The most noticeable change from removing it will be an increase in MPG especially on an M40.
If you care about the environmental bit, ditch the poison generating fuel you're running it on and convert to LPG. Close to zero harmful emissions and double the engine life.

What about on an M20B25?

Yea my brother has been banging about lpg conversions, what are they like on performance?

Thanks

[Lemon98]

I'm also following as I would like to remove my cat at some point and replace it with a resonator and a nice muffler at the back. (1990 M20B20)

I've had 2 classic mini's both of which were de-cat but they were simple as - literally bolted on each side with a flange so was cheap and easy to put in a straight pipe. But I imagine it's more complicated and expensive on these as the cat is part of quite a long exhaust section.

[Brianmoooore]

Easiest way to 'remove' a cat. is to knock the insides of it out with a steel bar.
According to BMW's official fuel consumption figures the effect on a M20B25 is much less than on a M40, but there is a worthwhile increase in performance of about 0.2 seconds on the 0-60 time.
A decent LPG conversion will have no effect on performance whatsoever over a properly working petrol version. If your engine is running with a weakened fuel mixture on petrol, as a result of injectors long past their service date, then you may well notice an increase in performance when running on LPG. The power increase is certainly noticeable on my E39 when I switch from petrol to LPG.
If you were to take advantage of LPG's 100+ RON rating by modifying your engine to suit, you could get a considerable power increase, but this would be at the expense of your engine's ability to run on petrol as well.
The real advantages of running on LPG are the vastly increased engine life, as a result on eliminating cold running bore wash and most of the hot running oil contamination, and, of course, the effect on your wallet. Secondary effects are the greatly reduced harmful emissions, allowing you to run the engine in a closed garage without harming yourself, and being able to meet the 'clean air zone' regulations in some countries. My E39 has a French 'CritAir 1 certificate (go from 0 to 5, with 0 being the cleanest). 'CritAir1 is as clean as any internal combustion engine can be. 0 is only awarded to zero emission vehicles, such as electric.

[BristolE30]

Easiest way to 'remove' a cat. is to knock the insides of it out with a steel bar.
According to BMW's official fuel consumption figures the effect on a M20B25 is much less than on a M40, but there is a worthwhile increase in performance of about 0.2 seconds on the 0-60 time.
A decent LPG conversion will have no effect on performance whatsoever over a properly working petrol version. If your engine is running with a weakened fuel mixture on petrol, as a result of injectors long past their service date, then you may well notice an increase in performance when running on LPG. The power increase is certainly noticeable on my E39 when I switch from petrol to LPG.
If you were to take advantage of LPG's 100+ RON rating by modifying your engine to suit, you could get a considerable power increase, but this would be at the expense of your engine's ability to run on petrol as well.
The real advantages of running on LPG are the vastly increased engine life, as a result on eliminating cold running bore wash and most of the hot running oil contamination, and, of course, the effect on your wallet. Secondary effects are the greatly reduced harmful emissions, allowing you to run the engine in a closed garage without harming yourself, and being able to meet the 'clean air zone' regulations in some countries. My E39 has a French 'CritAir 1 certificate (go from 0 to 5, with 0 being the cleanest). 'CritAir1 is as clean as any internal combustion engine can be. 0 is only awarded to zero emission vehicles, such as electric.

Do you own an lpg business? Really selling it!!
Jokes aside does sound very sensible and worthwhile. Further down the road perhaps.

Preferably I’d like to sell that CAT as I know it’s a worth a little, so smashing it probs not best option!?

[Brianmoooore]

No connections to the LPG business at all, although promoting it is to my advantage if it encourages forecourts to install LPG pumps. The only thing that baffles me is why the take up in the UK is so low. There's no doubt that if LPG could have been dispensed and stored efficiently and easily in the early days of motoring, then the vastly inferior and dangerous fuel that is petrol would never have caught on.
I've been running all my cars on LPG since October 2000, so have covered 150,000 - 200,000 miles on the stuff, saving me in the order of £15,000. on fuel costs.
All the value of a cat. will be in what you smash out of it, but it may be a little more difficult to actually get paid that value.

[HenryM3]

I’m with Brian on this my 4.6 x5 runs on lpg does 18mpg on a long run, price wise that 36mpg in a 2 ton truck. I’ll Defie anyone to notice any difference in performance. As to Brian’s point as to why more people don’t use it. A polish guy said to me that he can’t understand the English. You don’t use lpg because you worry that your neighbours will think that you can’t afford the petrol prices. He’s probably right to. I’ve had comments about running a big suv and can’t afford to run it properly. Long my those beliefs last, the less people use it the cheaper it stays.

[HenryM3]

Got side tracked with lpg, many years ago after the s50 b32 engine was fitted the exhaust consisted of e36 m3 center and back box. Rollingrosded at Thruxton 320hp, didn’t expect that. Binned the center box, btw no cats, Rolling roaded at 317hp and well down on torque. Back to drawing board. Fitted two Alpina resonaters and z3m back boxes (so quad exhausts now) samota cai remap this came out at 333hp. This has been on since. Exhaust can make a significant difference not just in sound.

[DanThe]

X pipe in the system makes a big difference to a twin pipe exhaust

[HenryM3]

Have to agree there. I fitted a Magnaflow custom exhaust with enclosed x pipe and 2 sesonaters NO back boxes to my 4.6. Very noticeable difference, you just want to go out for a drive,window down. Have been thinking of an H pipe on the m3

[steve_k]

X pipe in the system makes a big difference to a twin pipe exhaust

they sound really really good on a cammed 2.7 m20 with a decent 6 branch mainfold,

depending on the cam, the idle can sound like a yank V8.

[964russ]

Do it.
Dead easy to do.

Mines defo quicker, but everthing else is done as well.