Increasing engine Displacement

[ajsimpson]

The general consensus of 350SLC (euro) vs 380SL (U.S) seems to be pretty is would be pretty much comparable but, gives a slight nod on the power side to the 350SLC (euro) model.

I find it strange that as much as I have searched through different message boards and such, I've yet to come across discussions centered around increasing engine displacement or, specific recomendations for increasing the combustion chamber in the heads, porting and, things of that nature.

What does anyone know about increasing engine displacement in the 350, 380 or, the general beefing up of these engines?

Thanks, A.J.

 

[TJ 450]

It's not a very well explored area, because people tend towards engine conversions and things like that, otherwise they purchase a car with the larger displacement engine already installed. I suspect that the alloy engines are also less modification friendly due to the special hardening of the cylinder walls, for example.

Tim

 

[B13]

When the W126 hit the market in 1981 or so, MB explained their new lightweight alloy V8 engines with 4-speed auto boxes thusly:

The 380 M116 is considered comparable in performance to the old 450 M117

The 500 M117 is considered comparable in performance to the old 6.9 M100

and the 420 M116 and 560 M117 came along later to satisfy the quest for a decent power increase in the W126-update models and also recover some of the performance that smogged vehicles lost during their development.

I don't wish to start a debate on how true the above statements are, but it was what MB were aiming for.... the end result varies from country to country, obviously a Euro 500SEL with no smogs is going to give a California 560SEL fully smogged a run for its money etc...

Since the outside dimensions of a 420SEL motor would be almost the same as a 380 motor, and the fuel injection is the same, the most logical choice for me if I were in your shoes would be a 420SEL engine coupled to the 350SLC 4 speed manual box.

That and the fact that 420SEL engines are cheap and plentiful, can be had for under $1500 in Aus, probably cheaper in the USA.

I.

 

[John S]

There are a number of ways of getting power out of a motor, the easiest way normally is to increase capacity by over-boring or increasing stroke by crankshaft modification (weld up one side then grind off-centre to increase stroke). Boring out an aluminium Mercedes or Porsche motor is not advised as the specialised material used to cast the block has no liner, but is actually etched to expose silicone molecules which give the bore it long lasting qualities. I haven’t heard of anyone stroking a Mercedes motor. Modifying the head may not achieve much, but you may be able to increase compression a bit. With electronic ignition there is probably not a lot to be gained by mapping the advance curve either.

It's probably much easier and cheaper to swap to a 420 or (even better) a 500 (some euro engines are available) engine plus the matching gearbox and then have a lot of reliable fun.

 

[ajsimpson]

There are a number of ways of getting power out of a motor, the easiest way normally is to increase capacity by over-boring or increasing stroke by crankshaft modification (weld up one side then grind off-centre to increase stroke). Boring out an aluminium Mercedes or Porsche motor is not advised as the specialised material used to cast the block has no liner, but is actually etched to expose silicone molecules which give the bore it long lasting qualities.

I'm not talking about stroking the engine on one of these aluminum blocks. Let me clarify. I'm speaking about making mods to one of the older cast iron blocks.

I'm ignorant to the specs between models. For example: what are the differences between the heads of the 350, 450, 380 and, 560? Can these heads be interchanged with favorable results? Are there any known bottle necks in any of the heads that can be reshaped in order to increase combustion chamber turbulance? The heads are usually the place to turn to when you really want to make things happen.

Increasing compression can yield disastorous detonation effects if you don't know what your doing. I don't know enough about these engines so, that's why I'm asking these questions.

As far as electronic ignitions are concerned, I'll beg to differ with you there. There are enormous gains to be had, between taking control of the fuel injection system, controlling the ignition system and, firming up proper AFR you can make these cars way more efficient then Mercedes ever could with these antiquated J/K systems. There's a huge difference between analog and, digital. As far as remapping the advance curve goes, there would be gains there if it were handled automatically through an electronic ignition system. Not to mention the fact that for all your trouble you'd probably end up getting better gas mileage.

A good, healthy euro 500 engine is really what I'd like to get my hands on because, the sad truth is, (as far as I can tell) rebuilding these engines is way too expensive for my blood. Unless I'm way off the mark, I estimate that a total rebuild on one of these engines has got to be in the neighborhood of $5,000 and, that's with me doing all the work. Mercedes prices the internal engine parts as if they were selling gold. Call me crazy but, I've never felt comfortable with getting used engines and, not rebuilding them. After all, irrespective of milage, you can't know how the other guy treated the engine.

I'm going to keep my eyes open and, if I can come across something that's reasonable I'll reevaluate at that time.

Thanks, A.J.

 

[John S]

ajsimpson, I can advise you that the Aluminium 380, 420, 500 and 560 blocks will not take a 350 or 450 head. If you can finds a good 500 use that as the cost should be very reasonable, not a lot of people being after them at the moment.

 

[s class]

You might rebuild a cast iron M116/7 for $5000, but the alloy ones would run you 2 to 3 times as much for a proper rebuild.

 

[ajsimpson]

ajsimpson, I can advise you that the Aluminium 380, 420, 500 and 560 blocks will not take a 350 or 450 head. If you can finds a good 500 use that as the cost should be very reasonable, not a lot of people being after them at the moment.

I'm keeping my eyes open for a 500.

Thanks for the info John,
A.J.

 

[ajsimpson]

You might rebuild a cast iron M116/7 for $5000, but the alloy ones would run you 2 to 3 times as much for a proper rebuild.

I wonder why it is that these parts are so expensive? I can rebuild an aluminum V12 Jag engine for $2,500-$3,000. During the same time period Jaguar was the team winning the races.
Oh well, I guess if I want to pursue a rebuild, I'm just, going to have to bite the bullet and, pony up the dough because, complaining about it, is not going to make the prices any cheaper.

A.J.

 

[BAR]

Iron block vs Alloy block! That is the question, but not just the answer in this instance.

The alloy motors, would if installed complete with the gearbox from the W126, certainly boost performance, top speed and economy compared with the iron block engines of lesser displacement. Other benefits would be fuel economy and quiter ride at sustained mid to high speed running due to the overdrive 4th gear and reduced engine revs.

3.5 vs 4.5 engines, well if my memory serves me correctly the bore for both is the same and MB got extra capacity from a longer stroke, thus increasing capacity, power and fuel consumption.

Together with the alloy block the W126's got better fuel injection and true engine management computers. This also assisted in reducing emissions and improving performance and economy.

THere are those who would suggest that the 3 speed aut is a stronger and longer lasting unit than the 4 speed unit.

I have long ago abandoned the idea of a better engine managment system [timing, fuel distribution and improved ignition] as a way forward as it would cost more money than the repective economy that would be derrived, although there is a slight gain in performance.

All in all, in my opinion, given the true value of the W116's it is better to make the best of what one has. If looking for better performance an negligible reduction in economy, get rid of your 350 or 450 and trade up to a 6.0. Mercedes has done all the hard work for you.

If all this doesn't really matter and your after performance / power then lengthen the stroke, drop the compression ratio and get a turbo charger installed!

If economy is your target, park the W116 and go out and buy a cheap 4 cyl car for the cost of the conversion: you will have the best of both worlds and also take big leapforward in preserving the condition of the W116. Drive the cheapie to the supermarket and you will find that dents and chips won't be so painful if afflicted on it.

If

 

[s class]

If economy is your target, park the W116 and go out and buy a cheap 4 cyl car for the cost of the conversion: you will have the best of both worlds and also take big leapforward in preserving the condition of the W116. Drive the cheapie to the supermarket and you will find that dents and chips won't be so painful if afflicted on it.

There is a lot of sense in that. Being the sort who likes to have my cake and eat it, my solution is a 280SE daily driver that does heaps of mileage, plus 6.9s for kicks on the weekends.

 

[SELfor50]

Eh.... sack that. Put the turbo on the engine!!!!!