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May 11, 2007 21:18:41 GMT
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I've seen these about and most people use them to silence the car to get it past noise restrictions on track days etc but they have got me thinking and could there be another benefit to them... As i understand it back pressure is quite important to a N/A engine and as my kp has very little 4-2-1 manifold and a 2 1/2" bore exhaust would installing one of these be of any use? Added bonus would be a bit quieter on long trips  Any thought on these or am i just just going a bit crazy  Simon |
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Why people with welders shouldn't be allowed recreational drugs  |
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Retrojunkie
Part of things
The drinking team with a racing problem!
Posts: 603
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May 11, 2007 21:35:27 GMT
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I have seen a similar thing done withb turbo'd motors if I am on the right track here, basically when the engine comes out of vacuum and into boost it triggers another actuator that opens and bypasses the full length exhaust and diverts it straight out about 1ft away from the turbo enthalpy and stays 3" in diameter, when the actuator shuts the valve as it goes back into vacuum it returns the path of the exhaust gasses down what you could consider to be a normal exhaust length again. It would be of more benefit if you were turbo'd but I reckon not in your case dude  |
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 '84 Mk1 Golf GTi Cabby '99 Saab 9-5 Estate (lpg) 2.3 Turbo |
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exhaust control valvesBenzBoy
@benzboy
Club Retro Rides Member 7
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As I understand it back pressure is quite important to a N/A engine and as my kp has very little 4-2-1 manifold and a 2 1/2" bore exhaust would installing one of these be of any use? Added bonus would be a bit quieter on long trips I think if your car isn't slinging a load of unburnt fuel down the exhaust, you don't need to worry about back pressure. As for the noise, I can understand you wanting to have a bit of peace on a long journey!  |
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May 12, 2007 11:38:16 GMT
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loads of the modern superbikes have'em, yamaha's 'exup' power valve been around the longest (10 year patent)
whip one out of an old FZR1000 at the scrappie.
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May 12, 2007 12:16:58 GMT
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Its a Myth with a properly designed system you want the minimum back pressure possible Back pressure is only designed in to help with pulse tuning on certain engine/cam combinations, it s normally only done when you cant get the lengths right due to packaging constraints An Exup valve is totally different, it effectively alters primary pipe length by switching the pairing of cylinders at lower engine speeds to boost torque "Off cam" The vacuum exhaust valves fitted to Astons, Vipers etc are purely there to pass driveby noise tests, they bypass the main rear silencer on the Aston and on the Viper for Europe they divert all the flow through 2 tiny 1.5" dia pipes exiting under the car  Strangles an 8L V10 quite nicely that ;D The Aston can only pass driveby noise tests with this system and a Fitting tolerance on the exhaust turn outs of +-90 degrees ;D For the noise tests the tips are turned in and point down and inboard - Away from the noise tester ;D HTH Dom |
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