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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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30,429 Posts
if you read the MB requirement , the gray market cars due to higher compression ratio , and hotter cams should use premium .you can put anything you want , but that does not mean it s right .
LOL. It's true.

However...no knock, no ping....good performance...why pay more? And when I mean more...it's usually about $0.40 more per liter here.

I've run 91 AKI and 94 AKI....I really saw / felt / experienced no difference except on my wallet.
 

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1985 280SL
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320 Posts
From what I can gather, the 280 has a compression ratio of 9:1. That's well away from the trouble zone, particularly with its aluminum head. I wouldn't be concerned with any aluminum headed engine at 10:1. I've built 'em at 10.5:1 with aluminum heads, 89 octane and never a knock.

My '97 Tahoe is running 10.1:1 on pump piss, never a ping. Iron Vortec heads, LT4 cam which is very mild and works fine with the computer without a re-tune.

Octane rating is the resistance to detonation - nothing more - and is generally higher in more highly refined fuels. There is no reason to run hotter/higher octane gas than is necessary. I've seen it proven on a dyno when comparing an engine very similar to my 10:1 iron headed 355 in the Tahoe - low grade actually made more power than high octane fuel. Higher octane fuel actually burns slower.
 

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1985 280SL (Euro)
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326 Posts
If the car has been sitting for anytime at all. Two bottles of HEAT, 2 bottles quality fuel injection cleaner, and a full tank of non-ethanol premium gas. Also check throttle linkage for full throttle thru the peddle. The M110 has a fork type linkage in the engine bay that has plastic connectors that the linkage forks fit into (can not find my pics) If the pieces are missing you will only get about 75% throttle. Last new wires, plugs, and distributor cap. My 280SL will keep up with my ROW 450slc up to about 60 MPH, then the 450 will walk away from the 280.
Had a spell of smooth but low performance a while ago and it turned out to be the throttle linkage. Once fixed performance returned to normal (which is OK but a touch slow by modern standards)
 

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Outstanding Contributor
450slc5.0cab 280sl5sp 280se4.5 500se+500slAMG +250seStkW108 350sl4spdX3 500secEuro
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23,452 Posts
From what I can gather, the 280 has a compression ratio of 9:1. That's well away from the trouble zone, particularly with its aluminum head. I wouldn't be concerned with any aluminum headed engine at 10:1. I've built 'em at 10.5:1 with aluminum heads, 89 octane and never a knock.

My '97 Tahoe is running 10.1:1 on pump piss, never a ping. Iron Vortec heads, LT4 cam which is very mild and works fine with the computer without a re-tune.

Octane rating is the resistance to detonation - nothing more - and is generally higher in more highly refined fuels. There is no reason to run hotter/higher octane gas than is necessary. I've seen it proven on a dyno when comparing an engine very similar to my 10:1 iron headed 355 in the Tahoe - low grade actually made more power than high octane fuel. Higher octane fuel actually burns slower.
Newer cars often have knock sensors and will back off the timing of knocks are sensed.

The manual for all the older MB says to back off the timing if you have to run regular. I believe low octane gas burns a bit quicker I think and has less resistance to preignition due to heat. So if you car runs hotter than it should, or you coolant gets low and there’s air in your head coolant channels not cooling it as well, you may get preignition with low grade fuel.
 

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European 1974 350SLC ,'78 300CD& '80 300CD sold , '81 240D SWMBO's Car '84 300CD & Euro
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710 Posts
As mentioned, this car was designed to run on higher octane fuels than even to - day's premium so running regular guarantees it'll never run like it can .

If it's not been in regular use you'll find the mechanical fuel injection will be sluggish due to gumming of current American fuels, drive the darn thing using only top grade premium fuel and*do* add HEET or some fuel cleaner additive and once you get over 1,000 miles on it replace the fuel filter, it's under the trunk and you'll likely need to replace the short hose bits there too, whilst it's apart look in the inlet of the fuel pump ~ there's a brass screen that catches debris and American gasoline always has crud in it, you'll likely find some steel shavings in the screen, they block fuel flow and reduce pressure and flow significantly .

I just went through this on a 20 year old rig that only has 117,000 miles ~ it was glitchy off idle and didn't have much power even when revved up, after I did all the usual maintenance things it slowly got better and better until it ow runs like new again .

Sometimes it takes time as well as effort .



The valves certainly need adjusting and the timing checked, routine maintenance for these fine engines that few ever bother to do as long as it starts and runs .
 

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1985 280SL
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320 Posts
"As mentioned, this car was designed to run on higher octane fuels than even to - day's premium so running regular guarantees it'll never run like it can"

Not true - running higher octane than is needed will actually rob power since more highly refined fuels burn more slowly. Timing advance actually has to be increased to get the power back up.
The myth that higher octane makes cars run better is baloney - unless the car is built with higher compression that actually needs the more refined fuel to prevent preigntion and detonation.
I've personally seen it proven on both engine and chassis dynos. More than once.
Spending .25 - .50 more per gallon to get higher octane fuel is false economy. It doesn't work that way.
Now, if you want to spend that much on a better fuel with a better additive package - like some Shell stations carry - that is a different story. Many of these additives help clear the gummy crap from cheap, poorly refined gas. There are a few fuel additives that help but I think the majority of them are snake oil. I've always had good luck with Lucas products.
As long as you have no knock, there's no reason to run higher octane. Better gas, yes, but not higher octane.
 

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1985 280SL (Euro)
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326 Posts
I run very satisfactorily on mid grade (89). When I first got the car I assumed she needed hi test (91) but tried the midgrade as an experiment No difference in either performance or economy. so tried regular. She didn't cough or knock but there did seem to be some small difference - maybe only in my imagination. Still, as the expression goes "if it ain't broke don't fix it" so I'll continue with mid grade. At only around 1,500 miles per summer, it's a small price to pay for peace of mind. The owner's handbook suggests "premium fuel with minimum rating of 98 RON/88 MON"
 

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1985 280SL
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320 Posts
^ Buy the best mid-grade you can find based on additives, etc. Shell and Mobil get good marks year in, year out.

Mostly avoid price shopping and ending up at the mom & pops store with heavily watered down gasoline. They also have the dirtiest tanks since they're not refilled often and crap settles out.

I don't eat McDonald's and I won't ask my MB to :D
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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30,429 Posts
Mostly avoid price shopping and ending up at the mom & pops store with heavily watered down gasoline. They also have the dirtiest tanks since they're not refilled often and crap settles out.
Some of the isolated roads I've driven....One station every 350-400kms in Labrador and Northern Quebec.....one road in British Columbia....middle of BFN only had 1 pump with one nozzle.....good luck if you had a diesel. LOL
But....Pigs are Pigs.....they'll eat anything. :)
 

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1987 300SL
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725 Posts
I don't know how much different fuels are in Australia to other countries, America as an example, but I've always used higher octane fuels in all my cars
In the older cars, Fords and Holdens, you can feel the better acceleration between 91 and 98 octane, and get better fuel consumption too
I can't to say the same about modern cars as I have never run 'standard' 91 octane in them, as all the manuals say to run premium fuels
Ethanol fuels here have never really quite taken off, and I steer clear of them
 

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European 1974 350SLC ,'78 300CD& '80 300CD sold , '81 240D SWMBO's Car '84 300CD & Euro
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710 Posts
It's O.K. to not understand .

Today's American "premium" fuels are less than the 'regular' sold here when this was a new car and as mentioned, MERCEDES says to run high octane fuels in it .

If you're cheap or broke I understand but there's a thing called 'sub audible knock' that will do damage , just not instantaneously .

Smoking is bad for you too but most folks get to live a long life before dying a horrible and painful death from it .

As mentioned some brands have good cleaning additives, that's what I was getting at .

'Regular' gasoline in North America degrades very quickly, leaving it in the tank longer than three weeks is very bad practice indeed .

Good for Journeyman Mechanics like me, not so much for those who just want a nice old hobby car to drive now and then .
 

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1979 280 SL 4-speed, 2015 GLK 350 4-MATIC, 2012 Honda Accord Coupe V6 6-speed
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67 Posts
It always irked me that all Mercedes products seem to require premium (read the inside of the fuel filler door) fuel and my Hondas get equivalent horsepower from regular. I know it helps on high performance (usually higher compression) engines but run of the mill vehicles like a GLK 350? Oh, and back to the original question 180 (185?) horsepower doesn't seem like much nowadays but in 1979 when my 280SL was built, Mustang GT's had 165hp and the base Corvette engine was 180hp. It's a different word now. My SL is only a 4-speed but it keeps up with traffic if you visit the upper half of the tach.
 

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1983 380SL, ivory/dk brown, 46k miles, dual roller timing chain. 1986 560SL, red/white, 190K mile.
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7,608 Posts
Watch this video and think about whether this is the issue with sluggish performance with your 1985 280SL:

"The car has been completely transformed. These cars were obviously very spirited back in the day when they were new. And people are just getting around to them with barely functional poorly functioning K-jet system that is not producing the power anywhere near it should."

 
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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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30,429 Posts
My SL is only a 4-speed but it keeps up with traffic if you visit the upper half of the tach.
Petesmga's '79 - 4 speed now owned by ChiefRider ran like a raped ape at the top of the tach.....he used to drive the shit out of that thing. I drove it once or twice and he was always "yelling" at me to get the revs up.
 

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Premium Member
1986 560SL with M120 V12 Engine, 1988 560SL Stock
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11,560 Posts
According to “The SL Experience” a 280SL has a 0-60 speed of 9.2 seconds and a top end of 127 MPH compared to a 560SL 8 seconds and 137 MPH. A Euro 500SL is top banana at 7.4 seconds and 140MPH.
Samson 0-107MPH in 13.4. Top speed limited at 155MPH. Top speed unlimited about at the "p in "mph". :)
 

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1979 280SL, 1984 280SL
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5,718 Posts
Petesmga's '79 - 4 speed now owned by ChiefRider ran like a raped ape at the top of the tach.....he used to drive the shit out of that thing. I drove it once or twice and he was always "yelling" at me to get the revs up.
It still does, just not all the time as it did with Pete!
 
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