M117 Carb
 

This is a pretty interesting conversion done on a 75 450SL with M117.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=320682541520


It looks like the owner threw out the fuel injection and replaced with a carb.

Carb intake manifolds and port injection intake manifolds are designed differently. So a carb on a port injection manifold design may not be the best in terms of performance and efficiency. I'm surprised by his 20mpg claim, unless he lost a lot of the original power.

There is a guy who raced a W126 Coupe in Australia who had designed a carb intake for the M117. I've been tempted to go that way for my '62 5.0L project but I was told this was a real step backwards compared to injection. So now I'm having fun with Megasquirt instead.

D-Jet was used on the 4.5 instead of a carb (or carbs) for a reason. It's more economical, more powerful & easier on starting. As primitive as D-Jet may be, I'd repair it any day over tossing on a carb. It's like replacing a 200D with a Model T as your daily driver.

I'm not sure I can agree with that comment when it comes to D-Jet.

While it was a nice system back in the day. It's now becoming a pain in the butt to keep these systems going.
$700 for a fuel pump if you can find one?
$170 for an injector if you can find one?
Trigger points, ECU's and MAP sensors are becoming harder and harder to get hold of.

I agree that in general, fuel injection is better then carburetors. If there was a kit to install a decent 4 barrel carb at low cost, it would save a lot of savable cars from the crusher.

A buddy of mine just installed a 4 barrel carb and intake into my truck in about 7 hours and it runs like train and cost me about as much in parts as one new OE Bosch fuel injector. Once it goes bad, a rebuild kit will cost $40.

While I hate to compare, I bet my 5.7 liter GMC truck with a 4 barrel now has more hp and better fuel economy then my old 280SEL 4.5 :)

I spoke to the owner of this car. He told me that he machined an adapter for the carb to bold on to the intake and then blocked off the injector holes. He did not give any details as I think he is more interested in selling the car right now then me bugging him. It's a shame though, a kit like this will really save a lot of cars from the crusher.

While I agree the stuff is expensive:
- Trigger points, the MAP or ECU rarely go bad, can be adjusted if "worn" and can be sourced in good using condition by visiting a junkyard;
- The fuel pump is expensive, but there are many other fuel pumps that can produce the same volume that will fit, so unless you're a stickler for originality, not too big of an issue;
- Unless your injectors are cracked, send them out for a cleaning. Costs a lot less than a new one.

Of course, if you replaced D-Jet with a modern carb you MIGHT see a benefit (if you also had a carb manifold...) - but if you replace it with a modern EFI system like Megasquirt, you WILL see a benefit! I'd love to Megasquirt an M100 just to see what kind of power can be had from it.