Discussion
So was chatting to a fellow Chimaera owner about high engine temperatures. His recommendation was to remove the 2 pre Cats, which would help reduce engine temp but increase engine noise. (I know this has probably been discussed a thousand times previously, so apologies)
Is this worth it, and what is implication to MOT testing re omissions? Also are there any benefits from just wrapping the manifold?
I would personally just leave it all stock, but if the benefits are real, I would consider.
Is this worth it, and what is implication to MOT testing re omissions? Also are there any benefits from just wrapping the manifold?
I would personally just leave it all stock, but if the benefits are real, I would consider.
The pre-cats are for emission control at low engine temperatures, MOT emission test is done with the engine hot so the main cat is doing the work. Pre-cat removal should not affect MOT emission measurements. As for noise, pre-cat removal increases pops and bangs mostly. Also it removes gas flow restriction which frees up the engine, a few more horses to play with
My first Chimaera (4.0) was decatted and never ever overheated. MOT was never a problem because the garage that sold me the car did it every year and always had an idling petrol car close at hand.
My Cerbera always needed an understanding garage, even with the cats.
Apparently my new Chim always need a 'spirited' run before the MOT and the revs 'just right' to get through the emissions. My understanding of this is the precats have been removed. Further evidenced perhaps of a hot engine bay by the fitting of an ACT alloy radiator. I don't know this to be fact, but my suspicions are strong.
My Cerbera always needed an understanding garage, even with the cats.
Apparently my new Chim always need a 'spirited' run before the MOT and the revs 'just right' to get through the emissions. My understanding of this is the precats have been removed. Further evidenced perhaps of a hot engine bay by the fitting of an ACT alloy radiator. I don't know this to be fact, but my suspicions are strong.
Friendly MOT stations are becoming a thing of the past, with the DVLA tightening up the rules and I have heard they are going to install cameras in MOT bays.
If you are actually experiencing high engine temperatures (as opposed to an engine bay that feels hot) it might be worth making sure your cooling system is working properly and the fans are both cutting when they should.
If you are actually experiencing high engine temperatures (as opposed to an engine bay that feels hot) it might be worth making sure your cooling system is working properly and the fans are both cutting when they should.
QBee said:
Friendly MOT stations are becoming a thing of the past, with the DVLA tightening up the rules and I have heard they are going to install cameras in MOT bays.
If you are actually experiencing high engine temperatures (as opposed to an engine bay that feels hot) it might be worth making sure your cooling system is working properly and the fans are both cutting when they should.
Yes it’s just the engine bay heat, cooling system is fine, gauge reads correct, fan kicks in correctly, nice coolant levels etc. If you are actually experiencing high engine temperatures (as opposed to an engine bay that feels hot) it might be worth making sure your cooling system is working properly and the fans are both cutting when they should.
In my experience (400 HC), pre cat removal did nothing for the noise and only helped under bonnet temps.
Further main cat removal definitely improved the noise (rorty?) and further improvements in under bonnet temps but I cannot vouch for either improved performance or "pops and bangs." Definitely no "pops and bangs" as I think this really depends on your exhaust set up. Mine has also been de-sleeved but has a further small hot dog on each side AND it seems like a really long muffler on each actual tail pipe that suffocates any misdemeanours! A little bit disappointing as my Cerbera on the over run was so much fun compared to the Chimaera which is boring in comparison. It really depends what end result you want and what exhaust you have already.
Further main cat removal definitely improved the noise (rorty?) and further improvements in under bonnet temps but I cannot vouch for either improved performance or "pops and bangs." Definitely no "pops and bangs" as I think this really depends on your exhaust set up. Mine has also been de-sleeved but has a further small hot dog on each side AND it seems like a really long muffler on each actual tail pipe that suffocates any misdemeanours! A little bit disappointing as my Cerbera on the over run was so much fun compared to the Chimaera which is boring in comparison. It really depends what end result you want and what exhaust you have already.
I just had the original manifolds swapped for act manifolds (the old ones had started to crack). Having got the car back it sounds much better, although this is mainly due to the fact that the manifold leak is sorted although i would say theres a bit more rumble, havent noticed any pops and bangs, the rest of the exhaust is standard and still on the 14cux.
Under bonnet temps might be slightly reduced, but then the weather has been cooler since I have had it back. It passed mot after having the manifold swap
Under bonnet temps might be slightly reduced, but then the weather has been cooler since I have had it back. It passed mot after having the manifold swap
I've tried with and without pre-cats and main cat removal of the pre cats defiantly reduces temperature in the area around the HT leads and plugs which I see as the main benefit having cooked leads and extenders in the past. If this is your motivation for removal then you don't need to go further than the pre cats. As others have said from emissions point of view a warm engine without pre cats will meet emissions however I understand that you could fail an MOT for having visibly modified cats/precats so that may preclude the removal by cutting them open.
As far as pops and bangs I got those when the 2nd set of manifolds I bought so I could remove the precats turned out to have failed welds/fractures and therefore air leeks I guess introducing oxygen allowing unburn fuel to detonate in the exhaust.
As far as pops and bangs I got those when the 2nd set of manifolds I bought so I could remove the precats turned out to have failed welds/fractures and therefore air leeks I guess introducing oxygen allowing unburn fuel to detonate in the exhaust.
Fez887 said:
Any mileage in wrapping?
In theory wrapping the headers and exhaust gives a couple of benefits, keeps the heat in and lowers under bonnet temps, and a hotter gas flows quicker, which can help cylinder scavenging, and therefore aids filling of the cylinder when cams are on the over lap.Negatives are that often the exhausts crack, and the standard Tvr ones arnt known to be robust in that respect.
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