Factory says 'no' to sports exhaust?
Discussion
Steve -
Interesting - your notes indicate 90-93dB whereas mine, tested at 4000rpm, measured over 98. I'm sure it is the original exhaust, although I did notice big differences in noise levels between supposedly identical spec Griff and Chim 500 cars when test-driving. Anyway, thanks for the advice. I don't want to risk it next time so I shall contact Tower View for more info.
Interesting - your notes indicate 90-93dB whereas mine, tested at 4000rpm, measured over 98. I'm sure it is the original exhaust, although I did notice big differences in noise levels between supposedly identical spec Griff and Chim 500 cars when test-driving. Anyway, thanks for the advice. I don't want to risk it next time so I shall contact Tower View for more info.
simpo one said:
What if one took the other route to more noise and removed all 3 cats, but left the baffles etc untouched? Could this lead to longer term problems, and if so what?
Providing the car's ECU is modified, the exhaust is more or less the same as the 4.x Griffith. You still get back pressure from the exhaust as the cats are surprisingly free flow.
alan_d said: Steve -
Interesting - your notes indicate 90-93dB whereas mine, tested at 4000rpm, measured over 98. I'm sure it is the original exhaust, although I did notice big differences in noise levels between supposedly identical spec Griff and Chim 500 cars when test-driving. Anyway, thanks for the advice. I don't want to risk it next time so I shall contact Tower View for more info.
Yes but measuring cars is a bit of an art. There is also the fact that the silencers loose their efficiency over time as well. It also appears that every Chimaera owner has this desire to cause permenant hearing damage judging from the comments here. So you may have a noisier nonstandard standard exhaust.
Steve
I am no engineer but when I look at my Chimaera exhaust a few layman's questions occur to me. The main back pressure surely comes from the cats the silencer is yonks further on and must be relatively ineffective anyway so replacing the perforated tubes by straight-through surely has a minimal effect on the sound or the back pressure or I would think the power--it is not like a tuned header. Also if scavenging was too effective so as to reduce efficiency surely you would know by the backfiring. I am sure it is not as simple as this so please you experts put me in my place. One last point---several dealers do this conversion which would be grossly irresponsible if they even suspected possible engine damage.
One the cat is pretty free flowing because of its design. It needs surface area to work which means good gas flow.
Two: The exhaust does provide the main amount of back pressure - otherwise how do decatted cars get it? Same exhaust system.
As for dealers... they are only doing what their cutsomers ask them...
Two: The exhaust does provide the main amount of back pressure - otherwise how do decatted cars get it? Same exhaust system.
As for dealers... they are only doing what their cutsomers ask them...
jason said: I am no engineer but when I look at my Chimaera exhaust a few layman's questions occur to me. The main back pressure surely comes from the cats the silencer is yonks further on and must be relatively ineffective anyway so replacing the perforated tubes by straight-through surely has a minimal effect on the sound or the back pressure or I would think the power--it is not like a tuned header. Also if scavenging was too effective so as to reduce efficiency surely you would know by the backfiring. I am sure it is not as simple as this so please you experts put me in my place. One last point---several dealers do this conversion which would be grossly irresponsible if they even suspected possible engine damage.
The correct method (the one the Dealers do) is to replace perforated tube with solid tube, this dosn't effect performance & does increase noise (the only reason for doing this) I personally don't offer this sevice, but will stick up for the dealers that do. Just to labour the point and this is the wrong way to do it,=leaving the perforated tube in an empty vessel is no good as you get a damping effect, as air can travel through the perforations. I think this is the talking point.
Tim
A packed exhaust with perforated pipes won't create enough back pressure to make a difference on an exhaust the diameter of a TVR system provided they are "staight through" as Griffiths are, they only absorb noise. Yes if you put enough flow though them there would be a small effect but we're talking much more than what a TVR could produce.
Tim
Tim
OK I've listened to you two whizkids and i'm learning--thankyou! BUT I repeat the point that surely if there is not enough backpressure the gases go straight through and you get a backfire--not good! I cannot believe that a "honeycombe" like a cat does not create a fair sizes obstacle compared to straight through. I am also mystified as to WHY Steve lost 30bhp because of a straight through properly designed exhaust. Are you sure that the exhaust was the guilty party Steve? It is just that it seems a hell of a large figure when we are usually speaking of 5bhp order gains or losses with exhausts---you didn't have a potato in the tube did you 
jason said: OK I've listened to you two whizkids and i'm learning--thankyou! BUT I repeat the point that surely if there is not enough backpressure the gases go straight through and you get a backfire--not good! I cannot believe that a "honeycombe" like a cat does not create a fair sizes obstacle compared to straight through. I am also mystified as to WHY Steve lost 30bhp because of a straight through properly designed exhaust. Are you sure that the exhaust was the guilty party Steve? It is just that it seems a hell of a large figure when we are usually speaking of 5bhp order gains or losses with exhausts---you didn't have a potato in the tube did you
I was surprised when I saw the graph. It was done on my car before I bought it so I only have the graphs and feedback to go by. I have seen others as well where the gains have been less than value for money shall we say. I don't know why but I do know that exhaust manifolds and stuff are not top of my modification list as there does appear to be a risk of the mods not working well on a particular engine. The TVR manifold seesm to provide a consistent level of power. I am not saying that the cats do not provide some back pressure but it is not as much as you might think and how do you explain the decatted cars.
As for the popping and banging. Look through this archive and you will find plenty of reports about popping and banging with the sports exhaust that indicates to me that their mods have reduced back pressure or something else has changed.
My own car is decatted and has a standard exhaust. It does not pop and bang. I know of a couple of cars that have been decated and have a straight through exhaust that do like crazy. Conclusion is that the exhaust is doing something to prevent this. I think that is providing back pressure. Whether it is straight through or not it is absorbing energy and that must do something to the gas behaviour. I have never studied this but having experimented with aerodynamics it is surprising what a simple small think can do to gas flow.
I know on the 520 that adding a 12 inch length silencer significantly improved the response and engine pick up. I also know that an 8 inch narrower diameter one lost a bit of power. The key is that you need the right amount of back pressure. So..... my conclusions are that the exhaust and having back pressure is important and that modifying exhausts will affect this.
All this is saying to me that modifying the exhaust is stepping into the unknown and I would not do it. A recent post here indicated that the car was slower so make of that what you will. Add to that the factory clamp down and this just says "warning warning".
The topic on exhaust manifolds is related but different and depends on what state the engine is in and other factors but generally, it appears to be a bit more of a black art to get right.
The trouble is that exhaust design is very complex to get right. It can cause problems with the engine and effect its running and yet people get their welders out modifying things without really understanding the consequences. That is why I say no.
>> Edited by shpub on Monday 14th October 07:45
>> Edited by shpub on Monday 14th October 09:50
2 sheds said: My comments regarding back pressure were only relating to the silencer, Steves Exhaust was if i remember correctly lacking a balance pipe ?, it is very unusal to loose 30 bhp, without balance you normally only loose torque.
Tim
Well in the case we are talking about, the torque went up incredibly but the car ran out of puff at 4500+
We need to be careful as it was about 2 years ago and I know further work has been done. The point is that people seem to think that you can do anything you like with the exhaust system and it doesn't compromise power etc. Here is one case where it killed the car's performance. There have been many others. This should trigger the "all is not what it seems" warning button.
I know on the 520 that adding a 12 inch length silencer significantly improved the response and engine pick up. I also know that an 8 inch narrower diameter one lost a bit of power. The key is that you need the right amount of back pressure. So..... my conclusions are that the exhaust and having back pressure is important and that modifying exhausts will affect this.
I totally agree that with this kind of power using the wedge system adjustments will make a difference, you're on the limit of the exhaust capablities, the wedge has a single 2 1/2 inch bore silencer in steves case 370 odd bhp, on a griffith you have 2 x 2 inch bore with 270 bhp, in other words the griffith has little back pressure to start with, changes will have little effect, the system is probably good for 500 bhp.
Tim
Thanks for your feedback Steve.
For those who like max noise, it seems we need to think of a way to re-introduce back pressure but without physical obstacles in the pipe. Robbie Coltrane's 'Planes & Automobiles' describes the workings of the two-stroke engine and how Walter Kaaden made an effective exhaust valve out of the exhaust gases themselves. He achieved this by placing an expansion chamber in the pipe. Quote: 'Applied skilfully it's a trick that cna double the power output of a two-stroke engine for no more than the cost of an exhaust pipe shaped like a market vegetable. The trick lies in which market vegetable you choose to model it on.' Kaaden also worked on the V1 and V2 weapons....
Two- stroke Rover V8 conversions anyone????
For those who like max noise, it seems we need to think of a way to re-introduce back pressure but without physical obstacles in the pipe. Robbie Coltrane's 'Planes & Automobiles' describes the workings of the two-stroke engine and how Walter Kaaden made an effective exhaust valve out of the exhaust gases themselves. He achieved this by placing an expansion chamber in the pipe. Quote: 'Applied skilfully it's a trick that cna double the power output of a two-stroke engine for no more than the cost of an exhaust pipe shaped like a market vegetable. The trick lies in which market vegetable you choose to model it on.' Kaaden also worked on the V1 and V2 weapons....
Two- stroke Rover V8 conversions anyone????
So there I was, exhaust system off the car again, the silencer opened ready for re packing(more scars than an open heart surgery patient) then into my head popped a Line from Ted Nugent (any one remember him?)
.....If it too loud you're too old...
What the hell, removed the perforated tubes, replaced them with solid ones. All beck together
Results:-
Sounds like an old piston engined aircraft at tick over
Awesome at full chat
Seems to be back to the old performance levels, ie pulls like a train!
Ear plugs anyone????
Simon
.....If it too loud you're too old...
What the hell, removed the perforated tubes, replaced them with solid ones. All beck together
Results:-
Sounds like an old piston engined aircraft at tick over
Awesome at full chat
Seems to be back to the old performance levels, ie pulls like a train!
Ear plugs anyone????
Simon
shpub said: Trouble is Tim that now you have no back pressure as there is effectively no exhaust and no restriction. Just open pipes
BUT--pipes are a restriction--remove the exhaust altogether and you'll get my point. With the usual type of tuned header the problem is that say cylinder X interfers with the scavenging in cylinder Y ie too much back pressure so the header lengths are adjusted to minimise this interference. This in no way applies to a V8 TVR due to the sheer gargantuan dimensions of the exhaust. In my opinion the cats act as least as much as "silencers" as the rather futile box and actually give more (but small) backpressure. The way to resolve this one is to get a manometer in place and determine the flow pattern on a standard exhaust. If anybody is worried about possible damage resulting from straight-through tubes then try a compromise--replace,say, half the length only of the perforated tube--and it would be necessary to calculate ther optimum diameter of the replacement tube (NOT necessarily the same as that of the standard)--come on you motor engineers who design these things--tell us how it's done
Jason
I'm not an exhaust designer / engineer , i have them made for me, but as there is an apparent absence of these specialists, i will just say that your comments are all valid. Regarding the pipe diameter the Griffith Chimaera would probably produce the same power with just one of the pipes i.e half the system. i used to have a 420 that produced a genuine 305 bhp through a single 2 1/2" system. i've been involved with dyno testing for many years and found that whether Griff/ chimaera have silencers or not makes no apparent difference to power curve or figure, but in all cases the exhaust layout remained the same.
The first half of the exhaust is the most important area, as this is where pulses are strongest, we are working on improved manifolds with no small/pre-Cats instead longer primaries, similar to the early griffiths. this is the area to see improvements.
Tim
I'm not an exhaust designer / engineer , i have them made for me, but as there is an apparent absence of these specialists, i will just say that your comments are all valid. Regarding the pipe diameter the Griffith Chimaera would probably produce the same power with just one of the pipes i.e half the system. i used to have a 420 that produced a genuine 305 bhp through a single 2 1/2" system. i've been involved with dyno testing for many years and found that whether Griff/ chimaera have silencers or not makes no apparent difference to power curve or figure, but in all cases the exhaust layout remained the same.
The first half of the exhaust is the most important area, as this is where pulses are strongest, we are working on improved manifolds with no small/pre-Cats instead longer primaries, similar to the early griffiths. this is the area to see improvements.
Tim
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