How about this one:
http://www.carcraft.com/techarticles/exhaust_system_installation/index.html
You endless doubter
To find out, we tested three exhaust-system configurations on Magnaflow’s in-house Dynojet. For a baseline, we ran the car with open headers and saw 333 hp at 6,300 rpm and 304 lb-ft of torque at 5,200 at the rear wheels. Next, we ran a 2-½-inch bolt-together system consisting of a BBK short off-road H-pipe designed to fit the company’s full-length headers connected to a set of race-type 2-½-inch welded mufflers with turndowns. Our Mustang’s carbureted 302 didn’t like this combo, as
power fell to 323 hp at 6,300 rpm and 295 lb-ft of torque at 5,200. The
increased backpressure also richened up the air/fuel mixture by about two carburetor jet sizes.
Finally, we swapped on the stepped X-pipe setup and were impressed to see power levels equal to the open headers: 335 hp at 6,300 hp and 302 lb-ft at 5,200. That’s a gain of 12 rear-wheel horsepower, although it turns out we weren’t really giving anything up or gaining anything extra from the open headers. So the car’s happy, and our ears are even happier!
;-)
Only because you fiddled around a with the stock 500E parts like you stated in other posts about exhausts, with and without cats and didn't see any improvement on the dyno, doesn't mean you won't get any Power gains with a
good made exhaust system.
Its the same as pushing people with broken stock 500E cats in investing any €/$ in the stock ~1800€ cats
(yes they are available again in a low batch since 3-4weeks at the dealers in germany due to increased demand - yes another myth busted that those stock cats wont break, lol) even though for that money you get a complete stainless steel 2 way exhaust from the exhaust manifold till the end, with X-pipe and 100cell metal cats, together with
(depending on company) 10 year or even life-long warranty on corrosion here in germany. In my ears that sound like nonsense to invest any money in the stock parts when something way better is available for less, honestly.
The X-Pipe before the cats sucks out exhaust gases from the opposing bank, just like GOOD MADE Headers do. Same principle at baseline... Of course this won't net you anything with the stock cats and the stock 2->1 way exhaust system after it. As i've said it has to made complete, well thought through by professionals in the exhaust business.
Again, people in Germany proved it with Dyno-Runs, Bernard, Thomas Burgmann and others
(Videos from the Dyno runs are on Youtube, dunno how often i posted it already?).
If you guys don't believe me, drop me a PM and i hand out Bernards contact details for you. I write with him at least once a week over Facebook, and he confirmed a couple of times, that a good 2 way exhaust with X-Pipe and 100cell Metal cats is worth at least around 10HP (DIN!) if not more on the dyno with 500Es. And you feel it with your ButtDyno too.
I mean, i don't know what to think everytime, in German Forums such exhaust tuning is standard and well known, yes also at the Mercedes Folks, not only M119 specific, yet still here on 500E Forums, its considered as nonsense or at least "not worth it".
Try it, invest the money, and build yourself such an exhaust or let it be build by a motorsports-company or an exhaust-tuner that knows his business.. OK wait, granted in the US you can't even have access to any "low cell-density" listing on metal cats anywhere. Its like its totally unknown in the US. I wonder why :-(
In Europe its a well known standard since ages in Motor Sports, and trust me, those guys know their handwork pretty well.
Go for instance to any of the Porsche-Cup drivers racing teams and try to tell them they should usw a crappy 400CPSI++ ceramic cat system with numerous times from 2->1 and back again pipe-design, they would outright laugh at you.
), but when there's unburnt fuel entering the cats which starts burning there, you'll find yourself shopping for new cats quickly.
