Hello there, I am currently replacing my stock exhaust in my 75 280s W116. I removed the Thermal reactor thingy and I am installing euro manifolds..my question is should I do a Y-pipe type of system or run dual pipes into a dual pipe resonator and dual pipe muffler like I seen on the 78 79 M110's installed in the w123 chassis cars. I don't know how a true dual exhaust would sound and I remember reading somewhere that this motor needs a certain amount of back pressure or it wont have any low end power..I'm not sure how big the factory piping is but it appears to be less than 2 inches.. I don't want it totally quiet, I'm looking for a nice hum at the tailpipe.. Anyone who has a M110 in their car and has done the exhaust your input would greatly help me..

I would just run two pipes from the manifolds to the stock center muffler (this is not a resonator). From there they continue to the rear muffler, so it will be a two-pipe system all the way back.

I did this 17 years ago after the cat mysteriously fell off my 280E. There is no difference in sound or performance. The two mufflers provide sufficient back pressure.

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I hate it when stuff like that occurs.

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I'm not a doctor, but I'll have a look.

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It has nothing to do with back pressure. The diameter and length of the runners determine the resonant frequency of the exhaust system. As a result, the system will perform best at one and only one RPM. Increasing diameter usually moves the power up the rev curve. Unless you have access to expensive fluid dynamics modeling software, the only way to determine the precise outcome of an exhaust upgrade is by experimentation. And because experimentation is expensive, no shade tree engineer will ever admit they made a mistake. The only sure bet is factory stock, even though this is usually a compromise between sound and performance.

A straight six engine with typical 153624 firing order has equally spaced exhaust pulses in each bank (240 degrees), so there's no advantage to a crossover, h-pipe, or y. The characteristic straight six sound is like ripping cardboard when extended through parallel pipes. This is different from a v8. A 426 hemi has firing order 18436572. This results in uneven timing between pulses (270-180-90-180) on each bank, which explains that angry burble. So a V8 typically benefits from a balance pipe arrangement.

If you didn't lose any performance when the cat fell off, why not put it back?

That stock set up with the thermal reactor seems kind of restrictive..looks ugly too..lol...I don't like how all the cylinders dump in front and then go back..I much prefer the look of the euro mannys

After I put my 280ce back on the road recently I had to remove all the stock mufflers. I then put a dial-in dual out chambered muffler in the front area where the first muffler was and I put a dual-in, dual-out at the back of the car. The muffler at the back is a x-crossover style. I purposely built it like this because I wanted it to have good Racey tone and it does. Probably not the best for a daily driver though, it has a little bit of a drone when cruising at around 60mph. Hope this helps.