Anyone Ever Made a Carbureted Intake for 4.5?

[rix116]

I have a 74 450 SEL w/ 260K miles. Car is o.k., but electronic
fuel injection is finicky, as you know. You've got cold start issues,
injector issues, fuel pressure issues etc. etc. and the gas mileage
even when it's o.k. is not that great.
Now I'm a little bit old school and I don't mean to offend purists,
but if I could get a carbureted manifold I know I could make this thing run great. I imagine none were made since this car came out
when carbs were going away, and there never was much of a
racing community for these that I know of.
Would anything from an older engine fit the 4.5?
Or was ther ever any aftermarket manifold that would fit?

[cth350]

i've never heard of anybody ditching fuel injection to gain performance. -CTH

[rix116]

Sounds like I offended a purist. The first Bosch electronic fuel
injection is finicky, like I said, like many others know.
And why did they go to Mechanical in 1976 or 1977 if it was
so great?
I know what you are saying theoretically, but if you drive
these old beasts, I think it would be obvious.

[j9fd3s]

you might be able to put a carby in place of the stock throttle body, prolly not the greatest setup though.

i think it would be less work to put in modern efi, but i will confess carbs are not exaxtly my strong suit

[Tomguy]

I think they swtiched to mechanical injection because incompetent mechanics screwed up the D-Jet and didn't know anything about it or how to fix it... much simpler, easier to fix.

You will NOT gain mileage or performance by going to carbeuration. You'll only suck more gas. If you have issues now, something's wrong. You might have a malaligned TPS, or bad trigger points, or a bad ignition system.

You'll be INFINETLY better off switching to modern EFI.
I have no cold start issues (fires up after 1/4 revolution), no injector issues (all my plugs are uniform in color), and no fuel pressure issues (it's consistent, and I have no leaks).

I get very poor mileage myself but I know it's because I need a new timing chain, I've narrowed it down by repairing/adjusting anything else that could be to blame. Have you checked your ignition system, or even your cams? If your oiler tubes were ever neglected, you have at least 1 flat/nasty lobe on your cams. And these have old-school adjustable (not hydraulic) ball-studs.

You might be well-off to get new points, adjust your dwell and timing, and valve clearances, and then get a CO meter and adjust your D-Jet, before you think about ruining your 4.5... it will NOT gain anything by being carbed or Benz would have put a carb on it in the first place.

[rix116]

tomguy- what modern EFI system did you go to?
Where did you get the parts and what modifications
did you do?

[tosbt]

Tomguy you went to a EFI system? You must have picked up more power.

[psfred]

Rix:

You will require a complete manifold, as the EFI one, typically, does NOT promote laminar flow, so you wouldn't get burnable mixture in the cylinders by just slapping a carb on the manifold.

MB did not, to the best of my knowledge, ever produce a V8 with a carb that has any relationship whatever to the M116/M117, so you aren't going to find a "close fit" anywhere. All the aircraft engines were inverted Vs with mechanical fuel injection, and until 1963, the "big" engines were all in-lines. Pre-war 8s were inline, with multiple carbs, I think.

As stated above, you will most likely get a performance drop with a carb, anyway, and if you DO manage to squeeze more performance out, it will eat even more gas. For better milage, change the rear end to the W109 one for the 6.3 (if you can find one, that is).

D-Jet is kinda cranky, but really you only have to have good parts and a CO meter to get it working fairly well. You are more or less forced to accept very rich cold running (since it's not adjustable short of using a fixed resistor instead of a temp sensor, a bad idea), and flooring it will ALWAYS produce some black smoke on the 4.5 (10% fuel enrichment at full throttle), but otherwise it's much better than a carb most of the time.

If you do cobble something up for a mainfold, remember that this is a fairly small engine (276 ci), so you can't use much more than a 400 CFM carb no matter what you do. I've have to look it up in the Holley book to get an exact number.

Another possibility is the K-Jet FI off a later model 450. Requries some plumbing (the fuel lines must be replaced due to higher pressure) but otherwise drops right in.

Tomguy:

Bosch mechanical injection is derived from the in-line diesel injection system, was used druring WWII on the inverted V Diamler aircraft engines. First used in a production car in 1953 in the GullWing. EFI was originally a GM idea (late 50's), adapted and made to work reliably by Bosch when solid state componenets were beefy enough in the mid 1960's --VW/Porshe were the first to use it, I think, followed by Benz and Volvo. The GM system reportedly crapped out under high tension lines, for instance.

Peter

[wbain5280]

I'm going to investigate using a modern EFI system on my 300SE. This should prove interesting.

[j9fd3s]

Originally posted by wbain5280
I'm going to investigate using a modern EFI system on my 300SE. This should prove interesting.

www.haltech.com
www.motec.com
http://www.getfuelinjected.com/index.html

theres plenty more, but those are the popular ones

[Tomguy]

Originally posted by rix116
tomguy- what modern EFI system did you go to?
Where did you get the parts and what modifications
did you do?

No, I have the stock D-Jet. I'm saying I have no cold start problems, injector problems, or fuel pressure problems with the stock D-Jet!

[tosbt]

I would love to have a modern EFI system on my 4.5 maybe I could forget about those 3.5 cams. Perhaps someone could outline what it would take. Peter I see that you suggest a K-Jet, do you think that system would increase performance by a good bit. Say 30 or more horsepower? Manta posted a link of a conversion but I really did pick it up all together. Perhaps some qualified person could write a step by step guide, a blueprint that one could generally follow.

[Tomguy]

tosbt: I dunno, personally I think it would decrease POWER... no full throttle enrichment as far as I know, and not really temp-controlled either, but good for EMMISIONS (no full throttle enrichment -> less CO)... I could be wrong since I don't know about the system but, generally, EFI is better... a while ago, someone posted a link where they upgraded a 450's K-Jet to EFI, using the D-Jet manifold...

[cth350]

On a related note, the M110 motor was in production for about 16 years. It came in several versions...
- Solex 4A1 carb
- D-jet
- CIS
Times 2x for US and Euro emissions. The one that had the highest horsepower rating was the Euro Djet. This was a result of higher compression (pistons), more aggressive valve timing (cam), different ignition timing (distributor), smarter fuel delivery (D-jet).

Every little bit helps. -CTH

PS. I'm hardly a purist. I'm going to be putting a 1991 2.6l motor into a 1967 300se/c engine compartment fairly soon. I just have to come up with a suitable air suspension solution.