DBA @ 6500 rpm

[GT101]

In the UK most race tracks have a static noise requirement which is measured in a standard way, 3/4 of maximum engine revs, 1 metre from the tailpipe at an angle of 45deg (from vertical and horizontal)

In my experience a GT will read around 101dB with a standard exhaust under these conditions - so thats around 4900rpm. At 6500rpm you'd be way over this. This is also the same measurement process used for UK Single Vehicle Approval testing. A Borla muffler will be around 104 to 105dB. An Accufab is nearer 107dB.

When we developed the exhaust for the German market we had to introduce pneumatically operated valves into the unique muffler to achieve a drive-by noise level of 75dBA. This was a huge engineering task. It only effectively silenced the car as it went through the test conditions (otherwise the back pressure would have been too high) The key issue is a lack of muffler volume and nowhere to put any additional volume.

Dave Jones
mountune.com

 

[nz05gt]

Thanks guys
in New Zealand every track has one dedicated position to measure from on the outside edge of the circut where there are no structures near buy and is on a straight,
If I can get a Ford official measurement then I can run to that measurement

Neil

 

[nz05gt]

Does anyone know what the DBA is for a std GT @ 6500rpm, the reason I ask is that we have a race track noise restiction of 95 DBA, unless the car has a has a factory rating of above 95DBA I have to make the exhaust system keep below 95 DBA,I have already blown up 7 different exhaust systems trying to keep her below 95 DBA,most only last between 2 to 5 hours racing,
It is the pressure waves combined with heat and back-pressure that destroys the system,the muffler goes first,each system has had different mufflers some after market some custom made.
P.S. it is whipple charged making 763 rwhp and 666 rwtq.
if the GT has a higher DBA rating std,then I can make a better system.
any comments would be apprieciated
:ack:cheers
Neil
NZ05GT

 

[MR2Race]

Thanks guys
in New Zealand every track has one dedicated position to measure from on the outside edge of the circut where there are no structures near buy and is on a straight,
If I can get a Ford official measurement then I can run to that measurement

Neil

I do not think Fords official sound levels will help you?

Ford is required to drive by a sound wall @ 60 mph in high gear.
That is little more than idle in 6th gear.

Has nothing in common what happens at the track.

 

[MR2Race]

Neil

In the states auto makers have to comply with the federal sound requirements.
And the main test is measured in a drive by test. As the sound is bounced off a calibrated wall.


Sound levels at the track are even harder to predict.
As the environment and conditions play a huge role in the readings.

Where the microphone is placed inside or outside of a turn?
Along the straight away? High speed or low speed area of the track?
That along with air temperature & humidity all have large effects on sound readings.

We have been dealing with sound restrictions at the track for 20 years with the SCCA.

And I have learned that if you want to push close to the sound limits to optimize engine performance.

You will need to have flexibility built into your exhaust system.
As what worked one day (near the limit). Will be over on sound the next day.

Actually the stock FGT exhaust. That most agree is a bit too tame.
Has been known to fail the sound requirements at Laguna Saca.

 

[Indy GT]

Neil

Sound levels at the track are even harder to predict.
As the environment and conditions play a huge role in the readings.

Where the microphone is placed inside or outside of a turn?
Along the straight away? High speed or low speed area of the track?
That along with air temperature & humidity all have large effects on sound readings.

Very nice post Alex and conveys to all the multiple complexities in addressing something "simple" like exhaust noise.
It is complicated and not a one answer fits all solution...

 

[Yukonranger]

Compliance with sound regulations often requires adapting your procedures or vehicle to the specific requirement(s). When I used to fly into John Wayne airport in CA, I had to use full power for takeoff and initial climb then pull back the power over the sound sensors (their position is known.). You might be able to comply with the sound requirement with exhaust tips that point the exhaust away from the sensor(s).

Does anyone know what the DBA is for a std GT @ 6500rpm, the reason I ask is that we have a race track noise restiction of 95 DBA, unless the car has a has a factory rating of above 95DBA I have to make the exhaust system keep below 95 DBA,I have already blown up 7 different exhaust systems trying to keep her below 95 DBA,most only last between 2 to 5 hours racing,
It is the pressure waves combined with heat and back-pressure that destroys the system,the muffler goes first,each system has had different mufflers some after market some custom made.
P.S. it is whipple charged making 763 rwhp and 666 rwtq.
if the GT has a higher DBA rating std,then I can make a better system.
any comments would be apprieciated
:ack:cheers
Neil
NZ05GT