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Always Remembered RIP
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520 Posts
Discussion Starter #1
As I’m having little luck finding a good R107 300SL so I’ve decided to look at some larger V8s with the view to converting to LPG if and when the fuel costs get too high. As there’s little difference in the cost of insurance I’ve decided to look mostly at either the 450 or 500s from the early ‘80s.
Which is considered the better engine?
I’ve read that some of the 500s have a single timing chain. Is their anyway of telling?
As the 500 has an alloy engine does this mean it will also have hardened valve seats and be able to run on unleaded fuel with out any modification? What about the 450?
Has anyone converted to LPG and found it worth while? (I’m thinking of a multi-point system)
For a general guide line, what MPG do these return? Are the 350, 380s etc. any better?
 

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350SLC, 500SLC, 300TE, 190E2.3 Sportline
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690 Posts
Re V8s and LPG

All the V8 engines used alloy heads regardless of whether iron or alloy block. I'm not sure about the UK deliveries but the 450s delivered to Australia had sufficiently hard valve seats for unleaded fuel from 1976 onwards (ie. CIS or K-Jetronic injection as opposed to earlier electronic D-Jetronic).

My general feeling is that the iron block versions of the M116 & M117 (ie. 350 & 450) may give a longer life than the alloy versions (380, 420, 500 & 560). Others may disagree with me. Some of the very earliest 380s had a single row chain, not sure about the 500s. All others including the older 350 & 450 ran double row chains (which still need periodic replacement).

Quite a few 350s and 450s get around Australia running on LPG.
 

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Always Remembered RIP
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520 Posts
Discussion Starter #3
Apparently the 500 originally came with a simplex chain but it was altered to duplex and...

Apparently the 500 originally came with a simplex chain but it was altered to duplex and a recall was offered for those still under warranty.

Looking in various books I've noticed that the 500 is quoted to return almost 18mpg Urban compared to 14-15mpg in the 450. This figure feels a bit optimistic or is it because of the newer auto box and weight (I believe the 500 also has some alloy body panels)?

I'm going to view both a 450 and 500 tomorrow so if all goes well I may get lucky.
The 500 sounds good as it’s a late '85 with one owner, full history and is for sale at a garage with a good reputation that specialises in Mercs. As it seems a bit over priced I was wondering if the 500s generally fetched more.
 

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E430T + 300SL (W107)
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346 Posts
A conversion using diesel engine hasn´t crossed your mind? [:D]...

A conversion using diesel engine hasn´t crossed your mind? [:D]
 

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1972 350SL Auto
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17 Posts
My '72 350 returns 18 mpg (Imperial) no matter how it is driven. However, last week it sur...

My '72 350 returns 18 mpg (Imperial) no matter how it is driven. However, last week it surprised me and did 18.2! As it is such a heavy car, the larger engines probably work less and return similar figures.
It is believed that the valve seats for all V8' are of such quality that unleaded will not be a factor unless you are really unlucky. I run mine on unleaded most of the time with a special treat once a month of LRP.
 

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Always Remembered RIP
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Discussion Starter #6
Re: My '72 350 returns 18 mpg (Imperial) no matter how it is driven. However, last week it sur

I run mine on unleaded most of the time with a special treat once a month of LRP.
I'd be a bit weary of using LRP as there's no specific guidelines as to what they use for the lead replacement and some are supposed to react badly with others.
Leaded fuel is still available in the UK and if you look at the topic further down 'what fuel to use?' there's a link to all the garages within the UK which sell it
 
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