Noise

[Spid]

Having trouble getting below 99 for iva , seems to be mechanical noise from the engine rather than exhaust noise, have e- mailed VOSA and asked if I can can lower the rev limiter so the test will be taken at lower revs ( I would suggest to anyone filling out the form to set your rev limit to 6000 for an ls7!) I was honest as the test is taken at 75% of max revs. Going to try and sound proof the rear clip.

[Steve_D]

Spid said:

......I was honest as the test is taken at 75% of max revs. Going to try and sound proof the rear clip.

The test is taken at 75% of the revs at which maximum power is produced. This is normally some way below your rev limit.

Steve

[Gulf LS3]

not far under the 7100rpm limit Steve, if you are using the standard fuel pumps and a swirl pot switch the lift pumps off and i saw 2 db drop in noise!!! The big primaries cause issues but what can you do??

[Steve_D]

I've often wondered what difference there would be if the rear grill was panelled in with just the pipes sticking out. This should leave the tester only testing the exhaust note not the rest of the engine.

Ceramic coating the exhaust should give some noise reduction.

Steve

[Spid]

Do you think wrapping the headers will help?

[Steve_D]

Spid said:

Do you think wrapping the headers will help?

Anything will help but I would not want to leave it on as there are issue with heat and cracking of headers.


Steve

[Gulf LS3]

Steve_D said:

Spid said:

Do you think wrapping the headers will help?

Anything will help but I would not want to leave it on as there are issue with heat and cracking of headers.


Steve

bad stuff that heat wrap!!!! but if it helps its worth a try...

if it was me i would try some restrictors in the pipes just prior to the silencers, if you can break the gas flow up before it enters the silencers it will bounce round for a little longer inside the silencers.

[V8Dom]

Hi

bend some 1/2 inch wide plate into a 'c' shape...needs to be about 3mm thick...

at each end have some self tappers screwed in with pointy bits sticking outwards.

remove the tail pipes off the silencers and force the said piece inside the silencers. the tubes in the silencers have lots of little holes in them so the self tapper screws will 'help' keep it in place along with the fact you have made the part a force fit. refit the tail pipes and retry..

test before you take it down there...

drive down to the station smoothy so not to force the pieces out, do test and remove later.. the small obstruction will knock some db off but a heavy right foot could have it flying out of the back but after the test..

Dom

[UltimaCH]

I recall some years ago (70's) when I rallied an Alpine Renault A110, had a noisy (normal)exhaust. When I went to the technical inspection the car was refused. I didn't want to change the exhaust so solved and reduced temporarily the noise for the test with a nice wad of steel wool at the end of the silencer. Car passed with flying colours. The steel wool didn't stay in very long but sufficient for the db test.

[pilbeam_mp62]

Steve_D said:

Spid said:

......I was honest as the test is taken at 75% of max revs. Going to try and sound proof the rear clip.

The test is taken at 75% of the revs at which maximum power is produced. This is normally some way below your rev limit.

Steve

This is the key to the whole thing.

Who says the revs at which your engine makes maximum power ?.... YOU DO !!

My LS7 made maximum power at 6100, so it would have been tested at 4575 rpm.

It will be SIMPLE for you to make an Excel graph (from your dyno numbers, or ANY set of numbers if you know what I mean...) that shows the power curve of your engine - it is completely credible for an LS7 to make it's maximum power at well under 6000 rpm. Then show this graph to the tester - he can't argue with it.

The power curve of my engine was flat (to within 10hp) from 5700 to 6300 - so if your graph happened to show max power at 5700, you would have it noise tested at 4275 rpm. Arguably, you might even get away with Max power at 5500 rpm - IF you are good at arguing

The rule is very specifically worded - so take advantage of that.
Good luck.

Regards

[Spid]

E-mailed VOSA for advice they said the test should be carried out at 3/4 of max power, and lucky for me their data on the ultima ls7 said that was at 6000 rpm, if Ultima would confirm this my car would be tested at 4500 rpm.
Big thanks to Ted at Ultima I now conformation of this will now have another go next week

[Steve_D]

pilbeam_mp62 said:

.....It will be SIMPLE for you to make an Excel graph (from your dyno numbers, or ANY set of numbers if you know what I mean...) that shows the power curve of your engine.....

Be very careful if using false data that the two lines of your graph (Torque & HP) cross each other at 5252RPM or the tester will know you have played with the figures.

Steve