Quantifying equal length header noise change
 

In reading the various Vektor header reviews, change in exhaust noise is a prominent mention.
To quote basic666: The sound is glorious. Plenty of spooling sound on acceleration. Overall lots of increase in the deeper end. Coming out of a corner with the windows down is almost TOO LOUD. It's hard to capture the sound on video, so imagine its about 10-20% louder IRL than in video.
To quote flickroll: When I first started the car after installation my reaction to the sound was ‘holy sh**, this thing sounds GOOD!’. And then during the first drive the butt dyno told me there was more. And my ears told me the exhaust system was flowing lots better as I was hearing sounds I had not heard before, mainly a lot of detail with the sound of the turbos.

Sound is a measurable thing. So I found a dyno vid from Fabspeed with their 991.2 with just their bypass pipes. Then I compared it to flickroll's dyno which has the Vektor Performance headers paired with Soul 200 cell cats. I used an App called Spectroid to capture the noises from the dyno vids.

The red line in the upper plot is the max value and the yellow line is the instantaneous measurement. You can probably guess the Vektor header plot is on the right. The headers added a lot of volume in the ~60hz-200hz range, so the 'increase in the deeper end' basic666 mentioned. The histograms below show the full dyno pulls, so you can see the lines moving upwards in frequency as the engine speed increases. The brighter the lines, the higher the db level. With the equal length headers as opposed to the stock log type, you can see the exhaust noises are much better defined by the more intense few lines compared to the many lines of similar intensity with the stock headers. Looking at the stock headers, you can see how all the exhaust pulses don't have a clean flow path which I think muddies the noise. Plus the stock headers are double-walled steel which I'm sure muffles the noise even more.


https://cimg9.ibsrv.net/gimg/rennlis...729d3d3caa.jpg


I took this screen shot part way thru the dyno pulls while the engine speed is still accelerating. You can see the better defined peaks with the Vektor header from ~700hz and lower. I drew in blue lines going from the bright lines of the histograms to the representative peaks in the top plot.

https://cimg4.ibsrv.net/gimg/rennlis...df004e89d3.jpg



Just for fun, this is a Ferrari 458 with its NA V8 and 9k rpms.
https://cimg3.ibsrv.net/gimg/rennlis...acda1c30ee.jpg

I've always told people our headers make the exhaust sound more detailed and refined, less muddled. Nice to see real data to backup what I always thought was fairly subjective.

Thanks for posting!

Just ordered the @VektorPerformance Headers

Spdracerut - nice job doing this. Always nice to see some datapoints that re-enforce our assumptions.

Thanks! It's amazing what we can do with modern technology that we can hold in our hand (phone) these days. I got the idea from a buddy/former co-worker. He was trying to benchmark the Honda F1 turbo and figure out the turbo speed they were running. Using a similar app on his phone, he was able to determine the turbo speed just from the sound off the TV of the Honda cars going by; this was like 5 years ago. As you can see from my data, it's easy enough to determine engine speed based on the noise signature from the exhaust.