M110 Exhaust Venturis

[Frank Reiner]

The device shown in the Thumbnail appeared in the down pipes of M110 engines in the USA 1973-74, and the rest of the world until catalytic convertors were mandated. It was not used with any of the earlier six cylinder engines to my knowledge. It could conceivably function for tuning purposes, or for sound purposes. It does not appear in the FSMs, presumably because there was nothing to service.

Comments solicited:
a) Speculation
b) Trolling
c) Actual engineering knowledge from MB

[Mike D]

Huh! That's a new one on me. I've never seen the semi "H" pipe on any M110 I've ever worked on. Could it be specific to the "E" engines?

My '73 280's didn't have it and neither does my '74 280C.

The picture doesn't show but do the two header pipes merge into a single muffler inlet or do they continue back as dual exhaust?

The use of a "H" pipe is usually to compensate for the differing length of exhaust but I don't see how much effect on back pressure the placement of this would accomplish.

[Frank Reiner]

Originally Posted by Mike D

Huh! That's a new one on me. I've never seen the semi "H" pipe on any M110 I've ever worked on. Could it be specific to the "E" engines?

My '73 280's didn't have it and neither does my '74 280C.

The picture doesn't show but do the two header pipes merge into a single muffler inlet or do they continue back as dual exhaust?

The use of a "H" pipe is usually to compensate for the differing length of exhaust but I don't see how much effect on back pressure the placement of this would accomplish.

The set in the pic is for a W116, and is listed for both 280S and 280SE.

Both '73 280Cs (Calif.) that I had were so equipped. A '75 280C with a catalyst & single pipe obviously was not.

Since the pipe set shown is for a S-car a dual system goes all the way.

In the M110 FSM Group 49 are drawings of the exhaust systems for 107, 116, 123, and 126. The venturi pair is shown in all of them.

[Mike D]

I have seen that piping on the W123's but not on the W114's.

My familiarity with W116's has all been with M116's and M117's so I have never run across it.

I was wondering about the W107's. My experience with them is fairly limited. Mostly just minor repairs/maintenance and suspension work, brakes, etc.

I'd have to guess, since the pipes are on the "higher" end vehicles it has more to do with resonance than performance.

What is your take of the variance?

[Frank Reiner]

Mike,

I'm inclined to think that the device is for sound control purposes; 6-cyl W108s which did not have the device, but did have a dual system all the way, tended to drone a bit, and /8 230.6s and 250s had a single system aft of the center muffler, which dampened the "split-six" note.

[Mike D]

I'm not sure if the small diameter connection would be enough to equalize the exhaust pressure difference.

The more I look at the picture the more I am thinking it is for support to eliminate vibration in the two long exhaust runs. It would be tubular for weight/welding purposes.

Thoughts?

[Frank Reiner]

Originally Posted by Mike D

I'm not sure if the small diameter connection would be enough to equalize the exhaust pressure difference.

The more I look at the picture the more I am thinking it is for support to eliminate vibration in the two long exhaust runs. It would be tubular for weight/welding purposes.

Thoughts?

Mike, the small diameter cross connection is not what has stirred my curiosity; rather it is the existence of the apparent intentional restriction of exhaust flow that is caused by the venturi in each pipe. The down pipes from the manifolds (entering from the right in the pic) have an ID of ~41mm, and the venturis an ID of ~31mm. Downstream (to the left in the pic) of the venturis the diffuser section opens the pipe ID again to 41mm. The cross sectional area of the choke of the venturi is ~57% of the area of the down pipe; to my mind, a significant restriction. Or is it? Exhaust pulses in each 3-cylinder manifold occur at 240 crankshaft degrees (relatively large spacing), and the area of the choke is approximately that of the smallest part of the exhaust port in the cylinder head. If the configuration is intended to result in a near constant back-pressure in each manifold/down pipe, is it for sound control purposes, or for control of valve overlap flow? If the latter, it is the only example this writer is aware of.