To decat or not to decat? That is the question…
Discussion
So my buddy Adam with his Griff 500 took out his primary cats and fitted a Clive F Y piece. I thought the results were spectacular. Much deeper tone, more noise and what seemed like much freer breathing and what felt like more power and torque. All with lower under bonnet temperatures....
But that was 8 years ago and before I had my own TVR, so I'm now wondering if what I perceived is real. Also there are rumours that the police are gearing up to do more road side testing of emissions. So yes the primaries have to go (as they must be strangling the engine and are not needed to pass an MoT), but would it be better to go with a "sports cat" instead of a full decat? For better power and torque than standard, but no MoT issues and no future roadside test worries.
Has anyone measured the power / torque differences pre and post decat? Especially on a 450 like mine. Has anyone gone down the "sports cat" route?
But that was 8 years ago and before I had my own TVR, so I'm now wondering if what I perceived is real. Also there are rumours that the police are gearing up to do more road side testing of emissions. So yes the primaries have to go (as they must be strangling the engine and are not needed to pass an MoT), but would it be better to go with a "sports cat" instead of a full decat? For better power and torque than standard, but no MoT issues and no future roadside test worries.
Has anyone measured the power / torque differences pre and post decat? Especially on a 450 like mine. Has anyone gone down the "sports cat" route?
No you didn’t dream it. 8-10 years ago de catting first the original Y but better still using Clive or ACT Y piece could gain you 10 hp on a good engine. That’s thrashing the pants off it so not a huge increase but does help keep under bonnet temps down.
Increasingly difficult regs suggest de cat is not so easy to maintain.
I’d go for Clive Catted sports system then if your spending that kind of money get a new Ecu while your there and map the car to the pipes. Max power and efficiency with both fitted.
Leave silencer box alone or you’ll be deaf as a post in no time.
I had a complete straight through exhaust. I sold it after my hearing was effected
Cherry bombs fitted where the silencer box goes produces a very raspy race sound and very nice. Loud though.
I tire of the noise so I went back to a standard exhaust and Catted Y set up but removed the pre cats from manifolds which remove a restriction straight away, reduces heat and gives better power than with them in place.. but it is louder and slightly more drone like
My car in that configuration produced just shy of 300 hp using Powers MBE Ecu
If the average gain is 5-10 hp fully Catted my car is producing closer to 310 bhp but I can’t live with the extra noise so removed the de cat Y the car still produces 300 hp which is more than enough as most the time the car wafts along at 5% throttle.
I’d expect Clive's Catted system to produce almost as much power at a non cat system to be honest and less intrusive.
The power gain is marginal unless your hammering it.
Increasingly difficult regs suggest de cat is not so easy to maintain.
I’d go for Clive Catted sports system then if your spending that kind of money get a new Ecu while your there and map the car to the pipes. Max power and efficiency with both fitted.
Leave silencer box alone or you’ll be deaf as a post in no time.
I had a complete straight through exhaust. I sold it after my hearing was effected
Cherry bombs fitted where the silencer box goes produces a very raspy race sound and very nice. Loud though.
I tire of the noise so I went back to a standard exhaust and Catted Y set up but removed the pre cats from manifolds which remove a restriction straight away, reduces heat and gives better power than with them in place.. but it is louder and slightly more drone like
My car in that configuration produced just shy of 300 hp using Powers MBE Ecu
If the average gain is 5-10 hp fully Catted my car is producing closer to 310 bhp but I can’t live with the extra noise so removed the de cat Y the car still produces 300 hp which is more than enough as most the time the car wafts along at 5% throttle.
I’d expect Clive's Catted system to produce almost as much power at a non cat system to be honest and less intrusive.
The power gain is marginal unless your hammering it.
Edited by Classic Chim on Thursday 1st February 08:21
Corr blimey that’s a lovely build.
The holy grail of exhaust set ups but fully de cat.
That’s a problem for some.
That’s how you do it mind. What a bloke
L/h drive?
In answer to Marks question a set up like above might add 20-25 hp on a strong engine with decent compression.
Induction on a 450 is probably more of a restriction in power.
The holy grail of exhaust set ups but fully de cat.
That’s a problem for some.
That’s how you do it mind. What a bloke
L/h drive?
In answer to Marks question a set up like above might add 20-25 hp on a strong engine with decent compression.
Induction on a 450 is probably more of a restriction in power.
Edited by Classic Chim on Thursday 1st February 08:58
CharliesTTS said:
Indeed they are..from ACT...went for the stainless radiator as well!
Full bore your getting it job. Fantastically exciting.
I nearly plumped for one of those but considered it extravagant until I see this fantastic car.
I’ll forever remember your car everytime I look but mine were painted by powers when they re freshed my engine so I quite like them and the paints lasted years.
What colour is the body as thats quite a departure from standard chassis colour although I think it looks great.
As an object I find them endlessly fascinating at this stage of the build.
And so so easy to work around.
CharliesTTS said:
Thank you..however I can’t claim the credit..I’m just saying what I want and paying for it! 
No, Rhd..work by TVR101
That’s a great advert. No, Rhd..work by TVR101
Im liking that rack paint. Looks like shadow chrome or similar.
I lacquered my rack years ago and it’s been quite effective but that looks a step up I must say.
Plenum on the right side. Of course it’s not fitted yet. Just keeping crud out of inlets.
That’s a great job. You must be very happy with it so far.
Edited by Classic Chim on Thursday 1st February 09:27
I'd leave the standard dustbin cat in place.
The money is best spent elsewhere ie cam refresh, aftermarket ecu should you wish to spend some money.
I preferred the sound with pre cats removed and standard cat in place.
If you want more sound I'd go Act cherry bomb system, it's the best RV8 tone I've heard.
The money is best spent elsewhere ie cam refresh, aftermarket ecu should you wish to spend some money.
I preferred the sound with pre cats removed and standard cat in place.
If you want more sound I'd go Act cherry bomb system, it's the best RV8 tone I've heard.
For what little it’s worth, here’s my 2p;
My Chimera was running the factory exhaust when I bought it. When I had the body-off chassis refurb I had de-catted stainless Y piece made by RT Racing and the main cars removed.
The sound was heavenly and perhaps it was a slight placebo effect, but the engine felt to spin up a little quicker. So would I recommend de-catting? Yes. Absolutely !
Here’s a little fly past of it at Elvington in the pouring rain at 155.
https://youtu.be/m5FKfGgN0AY?si=McbiD546EI9QlxkG
My Chimera was running the factory exhaust when I bought it. When I had the body-off chassis refurb I had de-catted stainless Y piece made by RT Racing and the main cars removed.
The sound was heavenly and perhaps it was a slight placebo effect, but the engine felt to spin up a little quicker. So would I recommend de-catting? Yes. Absolutely !
Here’s a little fly past of it at Elvington in the pouring rain at 155.
https://youtu.be/m5FKfGgN0AY?si=McbiD546EI9QlxkG
I'm not in this spot just yet, but when I come to replacing the manifold gaskets, I'm seriously considering removing the precats.
I'm very happy with the sound as is, but like the idea of the engine breathing more happily.
I saw a thread or vid of someone doing it with a long drill bit to break them up, then when they finally collapse, just chipping it out.
Then rinsing it through to get dust and cr@p out. Probably take the lambda sensors out too.
Is that right?
I'm very happy with the sound as is, but like the idea of the engine breathing more happily.
I saw a thread or vid of someone doing it with a long drill bit to break them up, then when they finally collapse, just chipping it out.
Then rinsing it through to get dust and cr@p out. Probably take the lambda sensors out too.
Is that right?
PabloGee said:
I'm not in this spot just yet, but when I come to replacing the manifold gaskets, I'm seriously considering removing the precats.
I'm very happy with the sound as is, but like the idea of the engine breathing more happily.
I saw a thread or vid of someone doing it with a long drill bit to break them up, then when they finally collapse, just chipping it out.
Then rinsing it through to get dust and cr@p out. Probably take the lambda sensors out too.
Is that right?
I took mine out recently whilst doing the gaskets. Used a drill bit/chisel etc, but 99% of the progress was made by using a breaker bar and hammer. The breaker bar allows you to get under the cat down the side of the manifold and prise it away.I'm very happy with the sound as is, but like the idea of the engine breathing more happily.
I saw a thread or vid of someone doing it with a long drill bit to break them up, then when they finally collapse, just chipping it out.
Then rinsing it through to get dust and cr@p out. Probably take the lambda sensors out too.
Is that right?
I did take my lambdas out, used a box spanner to remove them. You'll have to remove the little connectors out from inside the plastic housing to then get the wire down the spanner.
I tried to start softly with it, but ended up hammering the bejeezus out of it to get them out. Make sure you have them in a vice ideally
Respirator and glasses mandatory as it's really unpleasant stuff
Feels good once you make progress on them mind!
Edited by bob-bobberson on Thursday 1st February 16:24
CharliesTTS said:
Yes, very pleased so far!
Car is a 4ltr supercharged..Body colour is burnt pearl orange, chassis is a McLaren orange.
Interior retrimmed and new seats as well!
Apologies to the op for the thread hijack - maybe I’ll start a new thread in due course?
Sounds excellent. Car is a 4ltr supercharged..Body colour is burnt pearl orange, chassis is a McLaren orange.
Interior retrimmed and new seats as well!
Apologies to the op for the thread hijack - maybe I’ll start a new thread in due course?
The experienced amongst us know these builds go on all the time and proof many TVR are better than ever.
The colours and ceramic coating really suit.
I’d enjoy seeing a photographic time line of the build even if you’d rather leave the technical questions to others.
Inspirational stuff.
Thanks everyone - this really helps!
Accordingly I've asked Clive F to change my order to the sports cat Y Piece and I'm going to take out the pre-cats. I think this produces (or will produce) enough noise, so I'm going to keep the rest of the system standard (at least until I try it).
I think the next piece is some ACT super flare carbon trumpets that taper down to the 38mm of the inlet manifold. Leaving aside the heads, cam and modifying the inlet manifold etc until I really need to do an engine refresh. Although the beautiful pics that CharliesTTS posted had me tempted for a minute, I have other items that will need doing sooner (a new radiator and all associated coolant pipework), because my engine seems super healthy with no cam issues ....
Accordingly I've asked Clive F to change my order to the sports cat Y Piece and I'm going to take out the pre-cats. I think this produces (or will produce) enough noise, so I'm going to keep the rest of the system standard (at least until I try it).
I think the next piece is some ACT super flare carbon trumpets that taper down to the 38mm of the inlet manifold. Leaving aside the heads, cam and modifying the inlet manifold etc until I really need to do an engine refresh. Although the beautiful pics that CharliesTTS posted had me tempted for a minute, I have other items that will need doing sooner (a new radiator and all associated coolant pipework), because my engine seems super healthy with no cam issues ....
Edited by MadMark911 on Friday 2nd February 10:40
Hoofy said:
Y not (sorry, couldn't resist) just have a straight pipe after the cat? Will sound amazing but also pass the MOT and any roadside emissions tests.
Having read your an aural addict and know that you require at least 8 cylinders to get your fix i’m not arguing with you BUT 
Firsty just disconnect the exhaust after Y section and fire up the engine. Expect to set car alarms off
Re connect exhaust with straight through pipes so this sound now comes out from behind you.
It will still set alarms off.
The decision to de cat or go ( straight through) exhaust is a personal one and to my mind based on how you use the car.
If it’s just sunny sundays and blatting about fine. You’ll be heard miles away.
If you tour or aim to use the car more daily I’d be very careful what I’d do.
You can ruin the ride for longer distance use by making it too noisy,
It’s not so much the noise with power on its when your cruising and have terrible resonance that gives you head aches.
It reminds me of loud race cars. Great for racing but you couldn’t live with the vibration and noise when cruising to the pub.
The positives of de cat etc is engine does spin up better and adds a bit of hp, less heat but as most owners don’t thrash them around the power gain is minimal for how often you use it compared to how often your cruising.
It’s that trade off your considering because de cat/ de muffled original piped cars can be very noisy and have a detrimental effect on when you can use the car.
At one point I had Clive’s Y and straight through exhaust. It was hilariously loud but almost unbearable.
Proceed with caution when playing with original system and make changes reversible as not all owners get on with the car made louder.
My advice is standard exhaust and Y piece with pre cats removed as that removes a huge restriction but not too loud or
Standard exhaust or with Cherry bombs fitted coupled up to Clive’s manifolds and Y because much of the drone comes from the Tvr tinny manifolds, that offers the extra noise but without drone when cruising at lower revs.
Or indeed the full ACT sports exhaust offers a raspy sound that’s louder but less boomy and works very well.
Very expensive and maybe a bit more power.
I’d go for an ECU first because of all the good it does. Get rid of the AFM air restriction, add a new big K&N filter and smooth bore air intake kit and smooth bore elbow and time it up to have more power low down and it will feel faster and induction noise is far more exciting than exhaust noise anyway.
The only noticeable difference in sound on my car after having an MBE Ecu and the ACT induction kit fitted and Dyno’d was the induction noise which was deeper and more throat like than it ever was before.
The standard pipe work from filter through the wing is a bit restrictive and the ACT purpose shaped sections are a huge improvement and the thickness of the main rubber pipe with some heat shield surrounding it ensues only cold air is going up there.
Check your old air pipe by stretching it out in the light. It will often have holes or tears in and sucking in hot air long after the filter and if the strengthening wire is corroded prone to collapsing on full throttle. The ACT set up is a once in a lifetime mod and set to last decades. Well worth it.
The car is also more powerful everywhere so better air flow and timing can add useable power.
Then you’ll definitely want the sports exhaust because you’ll gain another few % again.
I like spending other people’s money
MadMark911 said:
Thanks everyone - this really helps!
Accordingly I've asked Clive F to change my order to the sports cat Y Piece and I'm going to take out the pre-cats. I think this produces (or will produce) enough noise, so I'm going to keep the rest of the system standard (at least until I try it).
I think the next piece is some ACT super flare carbon trumpets that taper down to the 38mm of the inlet manifold. Leaving aside the heads, cam and modifying the inlet manifold etc until I really need to do an engine refresh. Although the beautiful pics that CharliesTTS posted had me tempted for a minute, I have other items that will need doing sooner (a new radiator and all associated coolant pipework), because my engine seems super healthy with no cam issues ....
Yep all good stuff. Accordingly I've asked Clive F to change my order to the sports cat Y Piece and I'm going to take out the pre-cats. I think this produces (or will produce) enough noise, so I'm going to keep the rest of the system standard (at least until I try it).
I think the next piece is some ACT super flare carbon trumpets that taper down to the 38mm of the inlet manifold. Leaving aside the heads, cam and modifying the inlet manifold etc until I really need to do an engine refresh. Although the beautiful pics that CharliesTTS posted had me tempted for a minute, I have other items that will need doing sooner (a new radiator and all associated coolant pipework), because my engine seems super healthy with no cam issues ....
Edited by MadMark911 on Friday 2nd February 10:40
The way I looked at it was, what I do now I won’t have to do later so maximising basics before eventually doing major jobs will also maximises the effect of those more serious mods or tuning later on.
I actually went the other way in having an engine rebuild then added to it later. Either way the cars never been more powerful or useable so each bit works and adds refinement.
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