Hey guys. I have a question regarding the exhaust because I need to replace it and it's original. I have a friend who's going to custom make me one.

Right now, goal is just to get rid of the cat, center muffler and put straight pipes into the rear muffler before I can do what I really want with it (dual straights) because I don't have enough time right now to drive two hours to the junk yard and find my the non cat manifold setup and it drags and bottoms out when I have more than two people in the car.


But here's the thing.

The center resonator has a giant hole in it (it leaves a black mark on my garage floor everytime I start the car )

The sound it makes with that hole is workable...and actually I kinda like it.

Does that mean I can do 100% straight pipe?

Or should I keep the rear muffler for back pressure, also, what's the deal with backpressure, do I need it or not? Again the car is a 280S that's CARBED.

I also came across this on google. http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm

Again. Any more input would be appreciated. Most likely also going to use the V8 dimensions for the exhaust.

There's also more specifications in this thread on W116.org.
http://forum.w116.org/mechanicals/exhaust-options/

I also removed the smog pump (air injection?) because I don't require inspection for the car since it's registered as a historic vehicle. That and it made my car sound like a leaf blower.

Here's my original post modified as the questions remain the same:
So I removed the smog/air pump and the contributing charcoal canister (got rid of the leaf blower sound)

Before I removed the smog pump, I advanced the ignition timing via pivoting the distributor

When I did that I was happy. No more misfires (it still needs valve adjustments), sounded better, ran better, idled better, and delivered power better and got MUCH better fuel economy (I run it on USDOT 89 Octane btw). There was a sputter in power delivery in WOT like misfiring but i cured it by doing the latter.

Now with the smog pump off, it idles just as well, but fuel economy went back down, and there are now sputters when doing WOT when above 4k RPM. I was told this has to do something with the stage II in the carb. It happens a couple times and doesnt bog down like a fuel delivery issue...I'd be doing WOT and i'd be accelerating but it would sputter but no real change in RPM.


But after looking at the online shop manual it seems like the stage II processes were aided by the air pump.

There were also two vacuum lines on the carb where the lines to the charcoal canister went, one of which was in and the other out. I plugged the ingoing one because if I didn't, the car would stall after coming to a halt.

I'm thinking...would I be able to route a tube from the outgoing port into the ingoing port on the carb and that would fix things?

And does anyone know how to adjust the carb on the M110? Interestingly too, it's made by Pierburg but its construction is nearly identical to the Solex 4A1. It seems to be running rich cuz I can smell it. I just don't want to burn exhaust valves by running it lean.

Your help would be greatly appreciated. Thanks guys.

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1975 W116 280S - SOLD
1994 W124 E320 Coupe - Gone

CURRENT - 1974 450SEL - 1987 560SEL

bump...

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1975 W116 280S - SOLD
1994 W124 E320 Coupe - Gone

CURRENT - 1974 450SEL - 1987 560SEL

I guess you could straight pipe it, but it'll sound like ass. Going to V8 sized piping is going to hurt exhaust velocity... aka low speed power, which the I6 cars don't have much to begin with. From what I recall each pipe off the exhaust is 1-3/4", and I'd just use that.

If it was my car, I'd just replace the rear muffler and be on my way. You'll gain some sound, but it won't be obnoxious (more of a growl). If you've ever driven a straight piped vehicle before, they're cool for a bit then gets REAL old with the interior cabin drone.

Only way to really tune the carb is with a wideband today. The 4A1 style is very temperamental so if you can find out how to deal with it, my hat's off to ya. I've had it with the 4A1 and am going to the very simple 4360 Holley until I can figure out how to get GM TBI on there. I'm after reliability over all out performance. My hurdle with TBI is the pickup in the distributor... the rest is a joke.

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

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

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