Removing pre-cats
Discussion
Hi all,
I am about to remove the precats but am slightly concerned about a couple of things.
Firstly the noise. At the moment it has an ACT Y piece and small aftermarket silencers. It is loud but in my opinion just right. Obviously this is going to increase the noise but will it be significant? I have a friend with a fully decatted and sleeved 5l which is too much for me with a hollow tinny noise upfront which I don't like.
Also I dont have a catted Y piece for the MOT man, do I have any other options but to buy/borrow one for MOT time? I don't really have the cash spare to buy one at the moment unless its cheap cheap.
I am about to remove the precats but am slightly concerned about a couple of things.
Firstly the noise. At the moment it has an ACT Y piece and small aftermarket silencers. It is loud but in my opinion just right. Obviously this is going to increase the noise but will it be significant? I have a friend with a fully decatted and sleeved 5l which is too much for me with a hollow tinny noise upfront which I don't like.
Also I dont have a catted Y piece for the MOT man, do I have any other options but to buy/borrow one for MOT time? I don't really have the cash spare to buy one at the moment unless its cheap cheap.
On an RV8 you get more pops and bangs if:
1. Your car is over fuelling and you lift off suddenly from high revs
2. Your ECU has been tuned to give them
3. Your exhaust is faulty
4. You have one or, ideally, two cylinders misfiring, resulting in unburnt fuel in the exhaust at low speed.
I think my best pops and bangs came with a very hot engine and a faulty exhaust, accelerating hard in second gear up to 6000rpm, then backing off sharply for a tight corner. The friend following me into Barn Corner at Cadwell Park at 60mph said I did a passable impression of a flame thrower to go with the very loud bang. Since I changed the exhaust I have had fewer issues with track day noise limits, but have woken up fewer spectators.
1. Your car is over fuelling and you lift off suddenly from high revs
2. Your ECU has been tuned to give them
3. Your exhaust is faulty
4. You have one or, ideally, two cylinders misfiring, resulting in unburnt fuel in the exhaust at low speed.
I think my best pops and bangs came with a very hot engine and a faulty exhaust, accelerating hard in second gear up to 6000rpm, then backing off sharply for a tight corner. The friend following me into Barn Corner at Cadwell Park at 60mph said I did a passable impression of a flame thrower to go with the very loud bang. Since I changed the exhaust I have had fewer issues with track day noise limits, but have woken up fewer spectators.
It's interesting to note, I've just had a new aftermarket Ecu and bespoke mapping,,,
My car still does the same as Bobfather suggests,,
Shut off from any revs, cuts fuel and no pops until down below 2000 revs,,
If I squeeze the right foot a tad,, then pops introduced,,,
Does exactly as it says on the tin
The only real difference in pops and bangs going from CUX to Mbe Ecu etc is they are more pronounced, crack more,, but their still there which is the important thing,,
If you have no pops and bangs maybe your AFR is a bit lean maybe?
My car still does the same as Bobfather suggests,,
Shut off from any revs, cuts fuel and no pops until down below 2000 revs,,
If I squeeze the right foot a tad,, then pops introduced,,,
Does exactly as it says on the tin
The only real difference in pops and bangs going from CUX to Mbe Ecu etc is they are more pronounced, crack more,, but their still there which is the important thing,,
If you have no pops and bangs maybe your AFR is a bit lean maybe?
QBee said:
On an RV8 you get more pops and bangs if:
1. Your car is over fuelling and you lift off suddenly from high revs
2. Your ECU has been tuned to give them
3. Your exhaust is faulty
4. You have one or, ideally, two cylinders misfiring, resulting in unburnt fuel in the exhaust at low speed.
This, after my last service two plug leads were swapped over. It sounded awesome, ran like a dog. 1. Your car is over fuelling and you lift off suddenly from high revs
2. Your ECU has been tuned to give them
3. Your exhaust is faulty
4. You have one or, ideally, two cylinders misfiring, resulting in unburnt fuel in the exhaust at low speed.
T
I do slightly miss the lovely bangs my car used to make with the faulty exhaust, right outside the cafe at Cadwell Park as I backed off for the Hall Bends. Always made me giggle as I made the mums and dads and small kds jump. I'm just a superannuated juvenile t
t, my daughter tells me,
Just like you then, Alun
ClassiChimi said:
If you have no pops and bangs maybe your AFR is a bit lean maybe?
My AFR is a tad rich, at about 12.0 to 12.5 all the way up. So not the reason. Pops and bangs require a lump of unburnt fuel in the exhaust, mine runs too evenly unless I provoke it. I do slightly miss the lovely bangs my car used to make with the faulty exhaust, right outside the cafe at Cadwell Park as I backed off for the Hall Bends. Always made me giggle as I made the mums and dads and small kds jump. I'm just a superannuated juvenile t
t, my daughter tells me,Just like you then, Alun
Hi,
I have a Chimaera 500 and I am to believe that my exhaust was standard, until my last service when I had ceramic coated decatted manifolds and decatted “Y” piece fitted. The items are not by ACT: I bought them from E-Bay but sent them to ACT to have the flanges machined (they were quite pitted when I got the exhaust) and also for ACT to supply all the gaskets / screws, etc… Tim from ACT told me that the system I bought was made by a guy called “Graham” based in the West County and use to be sold by peninsula, so not sure if anyone knows this system.
Well, my personal opinion is that my car is not too loud for when I pick her up from my garage, in London (there are a few flat above my garage) and when I drive in the small streets in London as the noise reverbs on the parked cars and building.
When on the open road and I accelerate hard it soul pretty mental and sometimes if from high rev I lift off, I get some bang, not all the time, but sometimes…
I guess it’s a matter of taste and some people here say “you cannot make too much noise”, I think you can and I believe that my car is not slightly too loud for my liking… I am London based… (and I am sure some people will think “wker” when I pass by…, especially those thinking that it’s a cheap tuned boy race type car – MX5 comes in mind…)
I believe, but not sure that the 500 is lightly louder (or has a deeper sound) that the smaller engined Chimaeras and once you removed the cats they get even louder…?
Sorry I am not an expert…
I have been told by the guys servicing my TVR on a yearly basis (a really reputable company) that passing MOT with them will not be an issue (and they fitted my new system).
Frenchie
I have a Chimaera 500 and I am to believe that my exhaust was standard, until my last service when I had ceramic coated decatted manifolds and decatted “Y” piece fitted. The items are not by ACT: I bought them from E-Bay but sent them to ACT to have the flanges machined (they were quite pitted when I got the exhaust) and also for ACT to supply all the gaskets / screws, etc… Tim from ACT told me that the system I bought was made by a guy called “Graham” based in the West County and use to be sold by peninsula, so not sure if anyone knows this system.
Well, my personal opinion is that my car is not too loud for when I pick her up from my garage, in London (there are a few flat above my garage) and when I drive in the small streets in London as the noise reverbs on the parked cars and building.
When on the open road and I accelerate hard it soul pretty mental and sometimes if from high rev I lift off, I get some bang, not all the time, but sometimes…
I guess it’s a matter of taste and some people here say “you cannot make too much noise”, I think you can and I believe that my car is not slightly too loud for my liking… I am London based… (and I am sure some people will think “w
ker” when I pass by…, especially those thinking that it’s a cheap tuned boy race type car – MX5 comes in mind…)I believe, but not sure that the 500 is lightly louder (or has a deeper sound) that the smaller engined Chimaeras and once you removed the cats they get even louder…?
Sorry I am not an expert…
I have been told by the guys servicing my TVR on a yearly basis (a really reputable company) that passing MOT with them will not be an issue (and they fitted my new system).
Frenchie
ph1l5 said:
I have no cats and it pops and bangs quiet a lot. Calvin at Wilton Morgan did some old skool tuning by advancing the timing a smidge. Pops seem to work better in the summer time for my car.
P
Calvin is removing my pre cats next week so I will be straight through because I am also sleeved with a Clife F Y installed. P
I could be wrong but I thought it was sleeved exhaust that enabled the pops? Even before I fitted the Clive F Y I could get pops just with the sleeve.
I am going to see how loud it is (I know it will be very) and if its too much I will revert to a standard back box but if the above is right I am not sure if I want to loose the pops because I am a big kid and I like them.
StarmistBlue400 said:
I could be wrong but I thought it was sleeved exhaust that enabled the pops? Even before I fitted the Clive F Y I could get pops just with the sleeve.
Sleeving just makes it louder, the pops are caused by unburned fuel igniting in the exhaust system. That ignition occurs on the first hot surface it finds which is normally in the manifolds, the precats stifle the sound of those pops because the pop is caused by a sudden expansion of gas which the precats absorb. I doubt you'll get much unburned fuel reaching as far as the silencer area. Perhaps you were more able to hear the pops after sleevingbobfather said:
Sleeving just makes it louder, the pops are caused by unburned fuel igniting in the exhaust system. That ignition occurs on the first hot surface it finds which is normally in the manifolds, the precats stifle the sound of those pops because the pop is caused by a sudden expansion of gas which the precats absorb. I doubt you'll get much unburned fuel reaching as far as the silencer area. Perhaps you were more able to hear the pops after sleeving
OK, makes sense. Thanks for clearing that up.I removed mine when I was replacing the gaskets but found the now empty space they occupied makes a horrible tinny ringing sound at idle. Some exhaust wrap to deaden it down was a small improvement, but in terms of the hassle getting them out I shouldn't have bothered in retrospect. I did not notice any change in under bonnet temps tbh.
Removing the Pre cats not only lowers the under bonnet temperature but also removes 2 big restrictions in the exhaust, It may or may not improve power but it definitely allows the engine rev a little easier. You may not see a lower operating temperatures but the area around the exhaust is cooler and may prevent excess heat sink to your plugs, extenders and leads.
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