MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGF Technical - Question about CAT Bypass

I'm after an improved exhaust note but not worried about increasing performance. Can I achieve this with a CAT Bypass only, or do I need to buy a complete exhaust? I'd rather spend 40 than 400!!
Neil

Neil

For the extra sound yep a cat bypass will work

Maybe someone else can answer this question:

In the workshop manual on the 2000F it shows a sensor
past the CAT which isn't on the pre 2000 F
will fitting a cat bypass tube affect anything?

-matt
M66 MAT
Neil

How much difference to the sound does the bypass make with the standard exhaust?
Neil

Neil,
the cat will only make a few HP different, it will make the exhaust note harsher.
For the best sound (IMHO) the K&N cant be beaten, with 15BHP on VVC and 8BHP on MPi improvement, the best value around. Also, there is not really any extra noise when cruising down the motorway when the extra noise can be a pain.
Cheers
G
Gareth

Neil,

Are you driving an MPi or a VVC?

- Andy
S6 AJG
Andrew Gilhooley

"In the workshop manual on the 2000F it shows a sensor
past the CAT which isn't on the pre 2000 F
will fitting a cat bypass tube affect anything?"

I haven't looked into the specs, but yes is the probably answer.

Japanese spec cars are fitted with what is aclled a 'catalyst overheat sensor' that sits in the exhaust immediately after the cat and which looks just like the familiar Lambda sensor, only smaller. This simply measures the exhaust temp and detects when there is an internal problem with the cat, say whjen it about to melt down when Dirk is driving. (Sorry Dirk, but I recall one of your early problems!)

As we move deeper into exhaust emiissions there will be pre and post cat lambda sensors actively monitoring the exhaust gas content and so any remoavl of the cat will clearly have a direct impact with the operation of the engine managment system. I suspect that the effect will be many times more loss that the cat removal will gain!

As a matter of interest I have been doing some testing on road going Rover 200/25 based cars with modified engines. One a BRM with just s mild head clean up and Janspeed exhaust has made 152 bhp at the wheels and held that. The standard cat was retained and clearly from the power delivery and rpms there was little or no loss of power.

Another well modified Rover 200 based car, with what is described as a High Torque 160 bhp engine spec, (MPi based) made 145bhp at the wheels last Monday using the same exhaust and sports cat. In this case there was more indication of potential exhaust restriction than with the standard set up. However that doesn't stop that car from being a real pleasure to drive.

Unless your on the track, anything less than a 10% increase in power is really not worth the time discussing, as less is at best only going to make the car feel sharper.

Rog
Roger Parker

Andy,

It is an MPI. Does this make a difference?

Neil.
Neil

Neil,

It appears to. With the MPi you may gain a bit, but as Roger says, nothing that you'd notice (1-2BHP max).

As everyone else does, I'd reccommend a K&N 57i kit - you'll get a better noise, about 5BHP (MPi) and better throttle response. Bolt the filter directly onto the plenum chamber, ditching the big rubber tube (this only appears to work properly on VVCs). It'll set you back about 80 + P&P, and is straightforward to fit - you will not regret it!

- Andy
S6 AJG
Andrew Gilhooley

Andy,

If only I could!! My insurance co. will not allow any air filter mods, but I can do what I like to the exhaust - seems a bit strange to me!!

Anyway, I just want a slightly sportier exhaust note - not too worried about power. So, if the cat bypass will achieve this I'll do it, otherwise I guess it'll be 300 for an SP from B&G.

Neil

Neil

I reckon you'd get a better sound from a sports exhaust- and the SP has a particularly pleasing wail. Don't forget Mike Satur's systems that sounds simply excellent, as do the Trevor Taylor Fxtreme exhausts. As a group, we all voted Mike's system as best sounding, and incedently, this system also proved to be the most powerful (5 bhp + 5 lb.ft). Might as well get the most bang for your buck!

Rob
Rob Bell

So would I be wasting my time with the cat bypass or would I get a noticable sound difference?
Neil

Depends on whether you are after volume or sound quality. With a bypass tube, you are basically just amplifying the noise from the existing exhaust system.

I have heard a standard system with a cat bypass- I just can't remember exactly how it sounds. Maybe that is a clue... Not particularly memorable ;o)

Rob
Rob Bell

Neil,

Change your insurance company, mate!

I must admit, I've never heard a stock exhaust with a bypass tube. You'll definetely get a sound difference.

- Andy
S6 AJG
Andrew Gilhooley

advantages of a cat bypass:

1. your (expensive) cat doesn't wear out
2. more noise, at 7000rpm in a tunnel big time grinning !
3. more bhp (a few, BUT ONLY in combination with a (freeflow) performance exhaust)
4. lower engine temp
5. you may push the accelerator when starting, since there's no cat, nothing to ruin
6. less risk of HGF/manifold catastrophy since you don't risk a blocked cat

disadvantages of a cat bypass:

1. mother nature will suffer a bit more, think of all those little animals out there
2. your neighbours might get a headache, go tell them it's not your problem ;-)
3. you cannot pass MOT unless you refit the cat. Golden tip is to buy the Mike Satur cat saver nuts (only a few quid)

So for about 350 quid you got a noisier, more responsive & less-risky F.

I read once on this BBS the increase in noise of a cat bypass and std exhaust was almost zero! not really the case with SP fitted :-))

Da choice is yourz.
Dirk

This thread was discussed between 23/03/2001 and 27/03/2001

MG MGF Technical index

This thread is from the archive. The Live MG MGF Technical BBS is active now.