3L33ter New Reader
1/3/18 4:13 p.m.

I have (among other cars) a 1974 Mercedes 280. It has the M110 2.8L straight-six. I'm new to this engine, but they say it's very performance oriented (for its day), and I can tell it likes to rev because down low it's just OK, but over 4000 it wakes up and starts to sing.

It has an awful exhaust manifold with like 2 inch runners going to a collecter at the FRONT, turning 180 degrees and going into a big juicy catalytic converter. '74 is smog exempt here in CA but I guess MB put cats on them back then. I've already sourced a set of headers from an earlier model.

Now I'm looking at the intake. This car is carbbed, and I don't care about carbs at all, so I don't want to bother learning about them and how to tune them. Particularly this Solex 4A1, which is apparently a headache and not very good for power. Some people have done TBI conversions on these carbbed engines. The factory also made 2 fuel injected versions, an EFI and MFI, so there are 3 very different intake manifolds to choose from.

So I'm thinking of what I want to do, but to start with I definitely want EFI with megasquirt. I'm not against a turbo, but I like the simplicity (especially in this simple car) of an NA straight six. Anyway, which manifold would you choose, and why?

Note, the injector ports are IN THE HEAD (for injected models) so all manifolds lack injector ports. I can weld them in if I wanted to go to port injection.


I'm not really asking for advice (but I welcome it!), I was mainly interested in starting a conversation on the different manifolds, what each one would be better for, and which one you would choose / what you'd do with it. In the end I think I'll just start with a TBI conversion on my current carb-manifold, and evolve/change it as time goes on.

Dr. Hess
Dr. Hess MegaDork
1/3/18 4:23 p.m.

I would go with Manifold #2, weld on injector bungs and a throttle body on the front.  Add Megasquirt.

dean1484 MegaDork
1/3/18 4:26 p.m.

I would say door number two as well. 

RossD MegaDork
1/3/18 4:32 p.m.

The longer intake tract length leads to more low rpm torque and less high rpm horsepower. At least I think I have that right!? I would choose which (Short/medium/long intake runner length) makes more sense to change in your current car and pick the one that will accentuate your intentions.

barefootskater Reader
1/3/18 4:43 p.m.

The top picture looks like a typical gm spread-bore 4bbl pattern and would be easily and cheaply adapted to a gm tbi unit, though I'm not really sure if it is the best option for making the most power. A $20 adapter and any junkyard gm truck/van from 1986-1994ish and you should have everything you'd need. 

MrJoshua UltimaDork
1/3/18 4:46 p.m.

I would go with number 2. I like the equal length runners of 2 and 3 but 3 has an odd mix of joined inlets on the middle runners with separate inlets on the outside two that seem like they could vary the flow between cylinders. Number 1 is a carb manifold with varied length runners etc. so I would skip it.  

Edit-Does #3 have 2 separate plenums with 3 runners each? If so it's an interesting option that probably is tuned for a torque bump.

oldeskewltoy UltraDork
1/3/18 4:55 p.m.

tough to say... can't really get an idea of plenum volume in #2... but I'd pick #2, then #1, and finally #3

mad_machine MegaDork
1/3/18 5:20 p.m.

3 would be good for boosted power, the long runners should bump up the torque.

GameboyRMH MegaDork
1/3/18 5:43 p.m.
RossD said:

The longer intake tract length leads to more low rpm torque and less high rpm horsepower. At least I think I have that right!?

Yep, and shorter means more high RPM power and less low RPM torque.

#1 is a rather old-school design that might not spread fuel around that evenly, clearly made for a carb. #2 looks like a safe choice. It's hard to see what's going on with #3, it could be a good choice too but it looks like the chamber that all the runners connect to may be more restrictive than #2.

Driven5 SuperDork
1/3/18 5:51 p.m.

In reply to GameboyRMH :

That's what I was thinking...#2 is the obvious answer, but #3 may have more to it than meets the eye.

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