I tried John Harley's Blitz Nur Spec backbox on my car yesterday and the findings were quite interesting.

They are almost at opposite ends of the spectrum for noise.

I already had a Magnex twin dump downpipe and STi/PPP decat centre section.

It is difficult to tell any difference in performance because of the amazing noise, and I don't know whether a dyno would detect anything with the usual problems of consecutive runs, heatsoak and smallish differences.

I did not think overall that the car was any quicker with the Blitz BB.

However, I did have to turn my boost controller down to avoid fuel cut when it was on and then turn it back up again when it came off so it must have make a significant difference to breathing. I have a Dawes with a 2mm bleed hole. The latter will make it susceptible to the effects of breathing mods, but the difference was about 1 PSI held boost.

Perhaps if I was not near fuel cut and was not running a boost controller it could have made quite a difference?

Of note you could fit the whole tailpipe of the PPP backbox INTO the back of the Nur Spec.

I stick with the PPP backbox though and it sounds like a flipping BMW in comparison.

 

I had a similar result when I removed my 'powerflow' back box and fitted a straight through pipe. There was no perceived change in power but my exhaust gas temperature dropped by 50 deg C.

Loud cars save lifes !! and engines it appears.

CC

 

it sounded,as well as it goes,for an hour anyway