Decat, What BHP????

[PAULJ5555]

When looking at decat pipes the claims of increased bhp are advertised anywhere from 4 – 20 extra horses. These are different adverts but for the same pipe and for the same car.

Has anyone had any real proof/experience, eg rolling road tests?

If so, what car? and how much?

Many Thanks

[kambites]

Might help if you told us what car you're talking about.

My (limited) experience is that it makes bugger all difference to performance, although it does make a difference to the noise.

[hairykrishna]

They can make a big difference if it's turbocharged, on some cars. Not so much for NA normally. What is it?

[CraigMST]

2-5 at the most?
I don't know why people strive for the highest BHP when it is smoothness and the power delivery that counts the most.
The decat in a turbo car may remove the slight restriction that a cat converter has on the car and in turn make the turbo spool up a bit quicker.
~ my limited knowledge and info from the net.

[falkster]

On a NA car, together with a decent exhaust, it might give it a bit extra power and on a turbo car it might make a bit more. I always thought it was more about making the car breath more and help increasing power along with other modifications but not really as a mod on its own.

[DanDC5]

What car are you de-catting?

[willfinch36]

With a turbo car it makes much more difference. On my 97 MR2 Turbo it made 26bhp difference, on same rollers etc!

[PAULJ5555]

Ok its an 1993 imported MR2 turbo, the decats are £60 and as its a 1993 import it does not need the cat for the MOT.

[CraigMST]

willfinch36 said:

With a turbo car it makes much more difference. On my 97 MR2 Turbo it made 26bhp difference, on same rollers etc!

Realllllyyyyyyyyyyyyy?

[GroundEffect]

I don't see any logical reason why it would be more beneficial on a boosted car...

[DanDC5]

GroundEffect said:

I don't see any logical reason why it would be more beneficial on a boosted car...

With a turbo car any restriction is a bad thing, remove restrictions in a standard exhaust it makes big gains.

[kambites]

DanDC5 said:

With a turbo car any restriction is a bad thing, remove restrictions in a standard exhaust it makes big gains.

Surely any restriction is a bad thing in a N/A car too?

If it works better in turbocharged cars, I'd imagine it's because the exhaust gas is flowing faster so the turbo spins faster, rather than anything directly to do with breathing restrictions. Presumably the benefits from that will depend on how the ECU is set up.

Edited by kambites on Monday 6th August 16:27

[PAULJ5555]

DanDC5 said:

GroundEffect said:

I don't see any logical reason why it would be more beneficial on a boosted car...

With a turbo car any restriction is a bad thing, remove restrictions in a standard exhaust it makes big gains.

Sorry Im not being funny, we all know this.

I was looking for someone with real proof/experiance.

Anyone??????????

[intrepid44]

GroundEffect said:

I don't see any logical reason why it would be more beneficial on a boosted car...

Usually it's because the turbo then makes more boost.

[Ved]

PAULJ5555 said:

Ok its an 1993 imported MR2 turbo, the decats are £60 and as its a 1993 import it does not need the cat for the MOT.

I went from 256 to 282 with a decat, high flowing exhaust and quality filter on a GTFour so you're likely to get a similar increase. This was on Surrey's rolling road without any silly mapping etc. Torque was up by a similar percentage.

[Dactub]

intrepid44 said:

Usually it's because the turbo then makes more boost.

How would it make more boost ?

[philmots]

Depends what car it is.

My old Saab had 2 cats. Removing the first that was about 4" behind the turbo on a 90 degree bend freed up lots of power alone as it was so restrictive.

When the car was mapped without a decat fitted it couldn't be ran at the turbos full capacity because of the cat. It was so restrictive the heat build up inside the turbo was too much so it had to be pegged back.

[intrepid44]

Dactub said:

How would it make more boost ?

It then creates more exhaust gas than the wastegate can deal with, so it is diverted to the turbo, and there's the increase in boost and hence power.

[Dactub]

intrepid44 said:

It then creates more exhaust gas than the wastegate can deal with, so it is diverted to the turbo, and there's the increase in boost and hence power.

Have to try that then. My mate owns my old 20v turbo Ibiza and has been thinking about a decat as we plan to do a few track days. The only work I've done on turbos is Reno 5s , a straight through side exit did improve power on that.

[xRIEx]

Dactub said:

intrepid44 said:

Usually it's because the turbo then makes more boost.

How would it make more boost ?

This is just from running the theory through my head, so it could be complete bks:

Catalytic converters are very very hot, which they need to be in order to operate; they heat up due to the exhaust gases, taking kinetic energy away from those exhaust gases, effectively slowing them down. Without the cat, the exhaust gases are a lot hotter, therefore have more kinetic energy which is then transferred to the turbine wheel.