Factory says 'no' to sports exhaust?
Discussion
Just rang the factory to see if they could supply and fit a 'sports' exhaust, and as the nice man put it on the phone 'no sir' and tvr don't reccomend me getting it done elsewhere
He said the engine wasn't calibrated for one
and could fail as a result
can anyone explain why this is???
He said the engine wasn't calibrated for one
and could fail as a result
can anyone explain why this is???
quote:
Just rang the factory to see if they could supply and fit a 'sports' exhaust, and as the nice man put it on the phone 'no sir' and tvr don't reccomend me getting it done elsewhere
He said the engine wasn't calibrated for one
and could fail as a result
can anyone explain why this is???
Basically TVR got fed up with people modding the exhaust, not knowing what the hell they were doing and then returning the engine for warrenty work. Predominently AJP and Speed 6 engines but I have heard that some Rovers have failed the same way. They are now enforcing the warrenty small print which says you mod the car, you loose warrenty.
I discussed the manifold design with John Eales when building the 520 and was told that the design was quite critical and needed some back pressure to maintain the efficiency. Get this wrong and you can suffer from shock waves inside the exhaust which may or may not be responsible for some of the valve damage that is occassionally seen. Amongst the topics was the effect of modded exhaust systems on engines and the feedback was it can cause problems.
My Griff also had a sports exhaust fitted and was rolling roaded before I bought it. The power curve showed a 30 bhp loss over running with the standard system. Both were setup by Mark Adams but the loss was a real shock. It was very loud but well down on power. Don't know if it was a car specific problem but the curve was a surprise. It was taken off pretty quickly.
Personally, I would think twice but it's your car.
Steve
www.tvrbooks.co.uk
Most Rover engined TVR "sports" exhausts are nothing more than reduced silencing , keeping the exact internal dimensions. these are fine and offer no increase or decrease in performance / back pressure. However in Steves Case I believe the system was a different design, i don't know how many different types of these are available but i agree that you should be cautious.
Tim
Tim
quote:
Steve / Tim, are you both under the same thoughts about the pre cats, will they alter the pressure slightly in the manifold?
Not really as the cats are pretty well transparent which is why they are so big. They can get clogged and I think this explains some of the gains that have been claimed when they have been removed.
The main pressure is a function of the manifold and exhaust pipe design and the exhaust box which though its silencing does also provide some back pressure. Many are now putting stright through pipes which means that the exhaust contribution is not there and it is difficult to assess exactly what effect this has (except from making the car louder).
When playing with the 520 initially to get it quieter (117 db was a bit noisy) it turned out that I had virtually no baffles and the exhaust had to be replaced. This and adding a further silencer in the tail actually improved the car's response and acceleration because I had restored some back pressure. It also brought the noise level down to 105dB.
While I agree with Tim that keeping the same dimensions etc is less likely to affect anything, I do believe there is a risk involved and that some of the mods may make the car louder but could be at the cost of BHP or torque and may well be stressing the engine. I also seem to remember that when the Tuscans were quietened a few years ago, they actually gained some horsepower!
As with anything, if you mod the car, you take responsibility for it. Maybe I am getting past it but modding the car to make it louder and potentially slower doesn't appeal. Modding the car to make it go faster is a different kettle of fish.
Steve
www.tvrbooks.co.uk
I think that if you gain power on a race engine by a change of silencing and make it quieter in the process then the exhaust wasn't correct in the first place.! However it's important to work out where the power was gained. exhaust tuning stuff is an art in itself with the position and size of any silencers, expansion chambers, etc affecting the outcome. you can make large gains in one area and lose heavily in another. Removing cats does have an effect even with so called high flow versions because of positive wave reflections off the front wall of the honeycomb area (credit to richard prebble's friend at Ilmor for this info) so there's lots to think about. However having said that, of all the tvrs that I've had on dynos with just exhaust changes (or cats changes and factory chips) none has ever run lean to the point that even caused the mildest concern so difficult to see where the factory are coming from here other than the cynic in me thinking of backing out of warranty claims.
The Griffith Chimaera exhausts are on the large size to say the least, the back pressure in the standard design exhaust system is minimal whether sports or standard silencing, however in my experience the biggest restriction is blocked/ clogged Cats & mis-alignment of manifold to head,
I've looked into producing a new exhaust system myself, but as Jools & Steve have indicated its a science of its own, I always "come back" to sticking with the standard format, some have and have had good results, i prefer to play it safe.
Tim
I've looked into producing a new exhaust system myself, but as Jools & Steve have indicated its a science of its own, I always "come back" to sticking with the standard format, some have and have had good results, i prefer to play it safe.
Tim
So in conclusion are we saying that there should not be a significant effect from removing the silencer baffles and replacing with straight through pipe (other than more noise!). Or will the car need to be on the rolling road after to retune for the differing airflow? In case you haven't guessed I'm looking at having this done as a cost effective way of making more noise for minimal cost...
As your name is trackdemon and I assume you want to go on the track, don't even think about it as you will be severely limited to the tracks you will be able to attend. Even with after market silencing they are getting banned. That for me makes sports exhausts a no-no straight off.
As for the effect on the engine/power, no one really knows. I know enough that in certain circumstances it can be a problem but in others it isn't. I know my 520 does appear to be a little fussy and that the factory have had problems with sports exhaust on the Tuscan in particular. This is enough to start Robbie the Robot "Danger Danger" warnings in my head.
Many have modified their Rover V8 cars but in reality some are OK but they don't know as the Ok is based on "the engine is still running so everything must be OK" approach rather than anything more scientific like before and after rolling road measurements and set ups.. I know in my current car's history a sports exhaust lopped 30 bhp of the power curve and more power was obtained going to a standard system which in practice is pretty hard to beat. I also know that the optimum setup for the sports exhaust was not the optimum for the standard so that also tells me that the exhaust has some effect.
You are a big boy. It is your decision. If it was me I would leave well alone. Louder exhausts don't make the car brake/accelerate or handle better.
Steve
www.tvrbooks.co.uk
>> Edited by shpub on Tuesday 17th September 14:43
As for the effect on the engine/power, no one really knows. I know enough that in certain circumstances it can be a problem but in others it isn't. I know my 520 does appear to be a little fussy and that the factory have had problems with sports exhaust on the Tuscan in particular. This is enough to start Robbie the Robot "Danger Danger" warnings in my head.
Many have modified their Rover V8 cars but in reality some are OK but they don't know as the Ok is based on "the engine is still running so everything must be OK" approach rather than anything more scientific like before and after rolling road measurements and set ups.. I know in my current car's history a sports exhaust lopped 30 bhp of the power curve and more power was obtained going to a standard system which in practice is pretty hard to beat. I also know that the optimum setup for the sports exhaust was not the optimum for the standard so that also tells me that the exhaust has some effect.
You are a big boy. It is your decision. If it was me I would leave well alone. Louder exhausts don't make the car brake/accelerate or handle better.
Steve
www.tvrbooks.co.uk
>> Edited by shpub on Tuesday 17th September 14:43
Problem is - and here's the crux of it - I just want the car to sound better. Of course it sounds quite nice at the moment, but I'm looking for a rawer, louder noise. Lets face it a lot of people buy TVR's because of the noise, so as far as I'm concerned a little louder is better 
BUT; I certainly do want to trackdays (intended to buy Tower View silencer plugins), and more importantly I don't want to lose power (I could handle 5bhp, but 30bhp no way) or have a detrimental effect on the engine in terms of reliability. The car is a 94 4.3 'with cat' Chim and would be rolling roaded after the exhaust work - remove silencer baffles and replace with straight through pipe. Anyone have any experience of doing something like this?
>> Edited by trackdemon on Tuesday 17th September 16:41
BUT; I certainly do want to trackdays (intended to buy Tower View silencer plugins), and more importantly I don't want to lose power (I could handle 5bhp, but 30bhp no way) or have a detrimental effect on the engine in terms of reliability. The car is a 94 4.3 'with cat' Chim and would be rolling roaded after the exhaust work - remove silencer baffles and replace with straight through pipe. Anyone have any experience of doing something like this?
>> Edited by trackdemon on Tuesday 17th September 16:41
(says me who wants his own chim to sound like his old wedge!)quote:
So in conclusion are we saying that there should not be a significant effect from removing the silencer baffles and replacing with straight through pipe (other than more noise!). Or will the car need to be on the rolling road after to retune for the differing airflow? In case you haven't guessed I'm looking at having this done as a cost effective way of making more noise for minimal cost...
Yes, the effect of replacing perforated tube with solid is minimal on this system. I have dyno graphs with this type of sports system, they show no difference in power output or curve. I do agree with Steve though , thats if you intend to use it on the track.
As a matter of interest the AJP tuscans changed the exhaust system from a single tail to the Twin and gained power this was because Flat plane cranks run better with 2 separate pipes without a balance pipe, the opposite applies to the Rover V8. I don't know if it was this that you were refering to Steve ?
quote:
Huh? I can't believe the AJP tuscans EVER ran with a balance/connected pipes, since the whole point of getting power out of the flat crank design REQUIRES seperate exhausts?
Yep they ran for the first 2 yrs or so with a single tail, this was because there was no space for 2 pipes, so they later cut the near side door down to make space for an appropriate system & gained power !!
quote:
BUT; I certainly do want to trackdays (intended to buy Tower View silencer plugins), and more importantly I don't want to lose power (I could handle 5bhp, but 30bhp no way) or have a detrimental effect on the engine in terms of reliability. The car is a 94 4.3 'with cat' Chim and would be rolling roaded after the exhaust work - remove silencer baffles and replace with straight through pipe. Anyone have any experience of doing something like this?
>> Edited by trackdemon on Tuesday 17th September 16:41
I know a couple of guys who have done this and were pretty fed up after being banned from a trcak day, even using inserts.
A straight through pipe will take the exhaust to in excess of 110db possibly higher. Forget about getting anywhere near 98 to 100 db on a track even with inserts. They will bring it down a bit 5-7 db but this is not enough. The inserts are useful when you are borderline but with a straight through pipe the noise levels are very loud indeed and the inserts are limited in what the can bring under control. Noise measurement is a bit hit and miss and the readings can vary by 2-3 db with no problems so ideally you want to be well under.
A sports exhaust with reduced silencing might be a bit of compromise compared to a straight through but it is very much dependent on the car.
As for rolling roading it after the mods, unless you have a programmable ECU chip like the Mark Adams Tornado, there is little apart from making sure everything is setup that can be done to change the mapping. Especially as the cat/lambda sensor gets in the way.
You can't hear it anyway with a crash hat on
If you want to do track days, leave it is the best advice I can give.
Steve
>> Edited by shpub on Wednesday 18th September 07:20
Gassing Station | Chimaera | Top of Page | What's New | My Stuff