Cats vs decats

[T40ORA]

Has anyone any numbers relating to the effects of cats vs. de-cats in terms of power and torque?

I'm considering bolting on sports cats in place of the de-cats I currently have as I think I have a chunk of missing torque. It may be a mapping issue, but I know there is a question mark over the real benefits of removing cats.

Ta!!

[Basil Brush]

There is a before and after map on Power's website somewhere.

Mine definitely felt a bit livelier without cats but the main benefit is the heat reduction in the engine bay. It's really noticeable.

[T40ORA]

Basil Brush said:

There is a before and after map on Power's website somewhere.

Mine definitely felt a bit livelier without cats but the main benefit is the heat reduction in the engine bay. It's really noticeable.

I have decats, so I'm happily aware of the better cooling. I'm questioning the wisdom in terms of performance gains. There seems a significant school of thought that there will also be a cost in terms of low down torque.

Considering trying sports cats as a replacement for the decats, but would like to see if anyone has done this already.

[Basil Brush]

T40ORA said:

I have decats, so I'm happily aware of the better cooling. I'm questioning the wisdom in terms of performance gains. There seems a significant school of thought that there will also be a cost in terms of low down torque.

Considering trying sports cats as a replacement for the decats, but would like to see if anyone has done this already.

I wasn't sure if you'd run with cats before, hence the comment.

[T40ORA]

Basil Brush said:

I wasn't sure if you'd run with cats before, hence the comment.

Yeah, but it was pre engine upgrade. So getting the whole package together it is difficult to assess where the benefits are derived from.

With all the conflicting views and opinions on to de-cat or not to de-cat I thought it would be good to see if there is anything documented.

[dvs_dave]

Well if an engine designer doesn't have to fit cats, they won't. That should tell you all you need to know.

They do not have any magical torque boosting powers; that's down to exhaust tuning which cats will actually hinder. Cats are essentially an unwanted but required restriction.

[fredd1e]

In my laymans view its not the lack of Cats that is the cause of loss of low down torque but the method of decat which creates a huge increase in exhaust pipe diameter at the decat pipe interface with the headers. If this was flowed more via say making the "decat pipe" extend the header pipes to a 3-1 or 3-2-1 collector into the exhaust pipes, this would appear to my limited knowledge of exhaust flow dynamics mind a better solution, though obviously likely to cost more and would require someone with the capability to devise appropriate pipe lengths joins etc. Alongside the mapping of low(er)rev /throttle ignition mapping to make use of it.
Problem is lack of a wide potential sales market would make this likely to be am expensive bespoke item in comparison to the simple de-cat pipes.

[T40ORA]

fredd1e said:

In my laymans view its not the lack of Cats that is the cause of loss of low down torque but the method of decat which creates a huge increase in exhaust pipe diameter at the decat pipe interface with the headers. If this was flowed more via say making the "decat pipe" extend the header pipes to a 3-1 or 3-2-1 collector into the exhaust pipes, this would appear to my limited knowledge of exhaust flow dynamics mind a better solution, though obviously likely to cost more and would require someone with the capability to devise appropriate pipe lengths joins etc. Alongside the mapping of low(er)rev /throttle ignition mapping to make use of it.
Problem is lack of a wide potential sales market would make this likely to be am expensive bespoke item in comparison to the simple de-cat pipes.

So we are sort of back to square one and what I was really after; has anyone any first hand experience and numbers of cats vs. de-cats vs sports cats on the same car.

My even more limited knowledge of exhaust flow dynamics understands that replacing the standard tubes stuffed with restrictive material with something more open is right. Because of the lack of R&D and goal oriented design though, what is the real difference between having sports cats and de-cats?

There are many, many variables to play with on our cars and we don't have enough empirical measurements to judge the efficacy of our mods by. We look at the theory, and if we like it sort of suck it and see. Be nice if we had a bit of a useful database.

[s5tvr]

The dyno chart below will hopefully help. The power and torque curves each have 3 lines. In each case the lowest power and torque curves represent my car totally stock (except JP exhaust). The middle power and torque curves show the impact of the first remap. The higher power and torque curves show the position post decat and remap. What would have been useful in hindsight would have been to do a power run post decat but prior to remap. So from my experience the decat gave a bit more top end power but more importantly more power and torque through the useable rev range. This was reflected in how the car drove as well.

[glow worm]

A good demonstration of the difference between at the wheels and flywheel figures .

[T40ORA]

Useful, and interesting. Thank you for posting.

[s6boy]

S5 I see you've got a T350 but does it have a 4litre engine? It's just that your power looks to be tailing off a few hundred rpm before 7k whereas mine, a 3.6, doesn't produce max power until 7150. Good example of what tuning can do +35lb/ft @ 5k must be felt.

OP it would be worth your while speaking to spitfire4v8 over the re-mapping. I was convinced when my decats went in that I'd lost some torque low to mid range. He is extremely helpful and knowlegable and explained how it would be possible to lose a little power pre re-map...although not as much as I felt I'd lost if that makes sense.

[s5tvr]

s6boy,

Here's my TDI tuning plot which interestingly shows peak power at 7,250rpm. In between the Austec dyno run and the TDI one, I changed my exhaust system completely so perhaps that has some bearing. The engine is definitely a 3.6 but it is factory Red Rose. The guys who used to service the car thought it was a 4.0 because it felt torquey to drive, but I got Jason at Str8six to check and he confirmed it as being a 3.6.

[s6boy]

please tell me that was post decat/retune, I'm starting to feel inadequate

That really does look like good 4l territory. The beauty of the TDI set up of course is there is no slip/ loss so as long as it's calibrated correctly what you see is what you get at the wheels. The date on your run looks similar to mine, but need to check as it's at work, did you go on a TVR shoot out day?

I've been around the forums long enough so should know but what exactly constitutes a red rose 3.6?

[s5tvr]

s6boy said:

please tell me that was post decat/retune, I'm starting to feel inadequate

That really does look like good 4l territory. The beauty of the TDI set up of course is there is no slip/ loss so as long as it's calibrated correctly what you see is what you get at the wheels. The date on your run looks similar to mine, but need to check as it's at work, did you go on a TVR shoot out day?

I've been around the forums long enough so should know but what exactly constitutes a red rose 3.6?

Yes the TDI run was post decat and fitting of a new exhaust system from the manifolds back but I haven't had he engine re-mapped after the exhaust change. It was part of a TVR shootout day that was organised to raise some money for charity. Factory red rose spec is larger bore exhaust, balanced bottom end and brake upgrade - there may be more but I can't remember. My car also had Tuscan S headers (larger) fitted at the factory as part of the original build.

[s6boy]

Just checked that was the same day, very good set up there..

[s5tvr]

[quote=s6boy]Just checked that was the same day, very good set up there..


For me the star of the day was Del's Griff diesel conversion.

http://youtu.be/EsXLgAOFVUk

Edited by s5tvr on Monday 9th June 21:19

[dvs_dave]

s5tvr said:

For me the star of the day was Del's Griff diesel conversion.

http://youtu.be/EsXLgAOFVUk

:ROFL: very good

[s6boy]

s5tvr]6boy said:

Just checked that was the same day, very good set up there..


For me the star of the day was Del's Griff diesel conversion.

http://youtu.be/EsXLgAOFVUk

Edited by s5tvr on Monday 9th June 21:19

GULP

OP sorry for the slight digression, but hopefully the graph S5 put up will have answered your question.

[T40ORA]

Digression is good and I'll be checking the diesel out. Yes, it is useful. There is still, in the wider community, discussion about the removal of cats though which I find interesting. I may be getting sports cats to replace the de-cats on mine simply to reduce the amount of noise, so I can get on track more. Mapping obviously plays a huge part, and with the Syvecs I have good granularity.