DIY Sports Exhaust?
Discussion
I know the idea behind the sport exhaust is to take quilting out of the back box.
Just wondering how easy it is to do a DIY job on it.
I think it is done by cutting a square out of the back box then taking the quilting out and re welding the back box up.
Is this the way or is it done another way.
Just wondering how easy it is to do a DIY job on it.
I think it is done by cutting a square out of the back box then taking the quilting out and re welding the back box up.
Is this the way or is it done another way.
Thats one way to make it sound different, the other is to put cut open the rear box and put two striaght through pipes, Also you can take the pre-cats out all which make it sound better IMO but could get u over the noise limit on Track days.
Also you have the main Cat taken out but this is needed for the MOT every year and the Emu needs remapping.
BB
Also you have the main Cat taken out but this is needed for the MOT every year and the Emu needs remapping.
BB
I think 'back pressure' and sundry principles are probably beyond yer average Piston Head; one of those topics where when all's said and done, there's a damn sight more said than done.
If it were not so, there would be more people posting "I've just fabricated a sports exhaust and gained xxx BHP", instead of "Who else has got a sports exhaust? I want one, but daren't make up my own mind what to buy." Short of some serious physics, backed up by lots of man hours, cut-and-shut pipework and extensive testing, I doubt that anyone makes the perfect exhaust. For a limited market such as a particular model of TVR, the investment wouldn't be justified. May I refer you to our learned friend David Hardcastle: in his book on tuning the Rover V8 (more riddled with generalisations than Pistonheads
) he depicts a manifold from an MG V8, saying that it was the best that could be done in the available space. Not the best that could be done full stop: merely a compromise. If one was dedicated enough, one would find the space required to allow a better exhaust. Apply this to, say, a TVR wedge, and the same must be true. My 390 has more bends in the tubing than a French horn; god knows what effect that has on gasflow efficiency (for better or worse).
It's a bit like hifi: what suits one, won't suit another.... by all means hack your pipe to bits, but try a rolling road session before and after. Then report back on here. You could start a trend... or look a tit.
Ian
If it were not so, there would be more people posting "I've just fabricated a sports exhaust and gained xxx BHP", instead of "Who else has got a sports exhaust? I want one, but daren't make up my own mind what to buy." Short of some serious physics, backed up by lots of man hours, cut-and-shut pipework and extensive testing, I doubt that anyone makes the perfect exhaust. For a limited market such as a particular model of TVR, the investment wouldn't be justified. May I refer you to our learned friend David Hardcastle: in his book on tuning the Rover V8 (more riddled with generalisations than Pistonheads
) he depicts a manifold from an MG V8, saying that it was the best that could be done in the available space. Not the best that could be done full stop: merely a compromise. If one was dedicated enough, one would find the space required to allow a better exhaust. Apply this to, say, a TVR wedge, and the same must be true. My 390 has more bends in the tubing than a French horn; god knows what effect that has on gasflow efficiency (for better or worse). It's a bit like hifi: what suits one, won't suit another.... by all means hack your pipe to bits, but try a rolling road session before and after. Then report back on here. You could start a trend... or look a tit.
Ian
James speaking:
Not an expert but the back preasure associated with the exhaust should be matched to the inlet manifold profile thus the intention is to create a preasure wave through the inlet manifold as the valves open thus having a ram preasurisation effect on the inlet fuel mixture. This is why complicated cars have the adjustable trumpet lenghts thus being able to control this wave effect.
Therfore if you change your exhaust back preasure you need to 'retune' the inlet profile the ECU and just about everything else to get back to full optimum performance. In realality a rechip takes out most of the difference.
Please can a well informed tunner correct my ramblings
Not an expert but the back preasure associated with the exhaust should be matched to the inlet manifold profile thus the intention is to create a preasure wave through the inlet manifold as the valves open thus having a ram preasurisation effect on the inlet fuel mixture. This is why complicated cars have the adjustable trumpet lenghts thus being able to control this wave effect.
Therfore if you change your exhaust back preasure you need to 'retune' the inlet profile the ECU and just about everything else to get back to full optimum performance. In realality a rechip takes out most of the difference.
Please can a well informed tunner correct my ramblings
simpo one said:
Having cats removed would obviously reduce back pressure too - but does the associated re-chipping correct for this?
urban myth no 2345
the rechipping is because there are no lambda sensors and with no cat the fuelling can be more agrressive. Downside is that this means the emissions fail. Changes the ECU from a closed loop operation to an open loop with no feedback. This is frequently why decatting liberates power: not because of the decatting but because of the improved mapping.
The TVR cats are pretty free flowing and the main back pressure is maintained by the exhaust system and the small diameter of the exhaust ports. There is a school of thought that says the big empty chambers are a major issue and that fitting restrictors can help. Again not totally convinced. Take the exhaust out as well and you have a recipe for a major power loss. 30 to 35 bhp is not uncommon. I have seen that happen. Decatting without chipping that has produced power gains have usually been because the original cats were blocked/melted and blocking the flow. Removing them restores the power but removing them on a well set up engine will not magically give you power. It may change the noise and improve the response but extra bhp.... unlikley.
The more tuned the engine is, the more critical the exhaust and manifolds can be.The 520 was loosing some 80 bhp due to a big 4 inch hole in the exhaust box turning the exhaust into a straight through system. Adding an effective silencer transformed it.
As for the TVR manifolds... pretty good in practice. I did look at a custom one for the 520 but in the end John Eales who built the engine reckoned that the 1 or 2 bhp (0.25% increase) I might gain was not worth the £1000+ it would take for one to be designed and made. His advice was to use what was there. When asked about increasing the exhaust bore to help the flow: he was pretty forthright in saying not worth it.
>> Edited by shpub on Thursday 7th August 22:26
But Steve, my car has been de-catted, has stainless manifolds and still has the lambda sensors into the manifolds - albeit without the big barrel shaped bit where the cats sit - more like a pre-cat model?
Can you explain that? It certainly has more grunt than a standard 4.0l - but is that down to the Mark Adams chip alone?
P.s. sorry for being dim
Can you explain that? It certainly has more grunt than a standard 4.0l - but is that down to the Mark Adams chip alone?
P.s. sorry for being dim
yiw1393 said:
But Steve, my car has been de-catted, has stainless manifolds and still has the lambda sensors into the manifolds - albeit without the big barrel shaped bit where the cats sit - more like a pre-cat model?
Me too
mines got no furry pussy's at all, because the car decided to eat them and it was either replace or remove, with the blocked cats performance was pants, with them removed it instantly felt, and sounded quicker but it's no quicker than a standard car, I've also got the lambda sensors still in, the exhaust looks standard, except the big weld around the bottom of the big downpipe and I've not even had any ECU work 
Ballistic Banana said:
Thats one way to make it sound different, the other is to put cut open the rear box and put two striaght through pipes, Also you can take the pre-cats out all which make it sound better IMO but could get u over the noise limit on Track days.
Also you have the main Cat taken out but this is needed for the MOT every year and the Emu needs remapping.
BB
Ballistic Banana said:
Thats one way to make it sound different, the other is to put cut open the rear box and put two striaght through pipes, Also you can take the pre-cats out all which make it sound better IMO but could get u over the noise limit on Track days.
Also you have the main Cat taken out but this is needed for the MOT every year and the Emu needs remapping.
BB
hi bb
looked all over the car but cannot find any emu,s lurking anywhere .hopefully see you next year at le mans.
rocky
yiw1393 said:
But Steve, my car has been de-catted, has stainless manifolds and still has the lambda sensors into the manifolds - albeit without the big barrel shaped bit where the cats sit - more like a pre-cat model?
Can you explain that? It certainly has more grunt than a standard 4.0l - but is that down to the Mark Adams chip alone?
P.s. sorry for being dim
It is the Mark Adams work that provides the benefit. Mark may or may not be using the lambda sensors. If he is then I doubt that the chipping is that aggressive.
>> Edited by shpub on Friday 8th August 18:47
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