Difference between M117 and M116

[oscar]

Hi,
if the bore is the same then the stroke isn't , it would be longer, can't change maths! whilst the cranks may interchange (giving you a 350 instead of a 450, maybe a 450 instead of a 350??) the conrods might not. The rods in the 450 are either shorter or the piston pin is higher in the piston to make up for the extra stroke. The camshafts whilst possably being interchangeable would be different in their timing (well SHOULD be). The other bits should be interchangeable to reduce manufacturing costs and still have 2 different capacities without going to the expense of making 2 completely different engines. Perhaps have a look at the 560 and see if it even longer stroke? you may be able to use rods crank and pistons from one of them.
Roger
Ooooooooo! its also possable that the block has a higher deck height (distance between the crank centre and top of the block) meaning a 19mm higher engine? to make up for the extra stroke.

Whilst I can't find reference to the crankshafts, they must be different, they have to be to account for the extra nearly 20mm travel or stroke of the pistons in the M117.  Regardless of piston differences or conrod length, it's the rod journals and their distance from the centre of the crank that determines the travel of the piston.  Has to be.  The data for the crankshaft given in Haynes only list wear limits and standard measurements for journals and bearings for example, which would apply to both crankshafts.  Nothing is stated about the geometry of each crankshaft unfortunately.

So what about the extra stroke - firstly torana, I think you're spot on about the extra block height of the M117.  I thought it might be all in the heads that make the 450 look bigger, but compare these diagrams below of the distributor drive and socket.   Both sides of the block extends an extra 32mm!!

M117


M116 and M117



Camshaft Timing - they do have different timing.
But to complicate things, there's 6 types of camshafts listed.  I wont list them all nor the table but each shaft has a code number and have different values for timing. There's two types for the M116, three types for the M117 and one that is used for both M116 and M117.  The difference in timing can be upto 10o in some cases.  Best to check the identifying code on the shafts before timing them correctly.  I would've been oblivious to this had I attempted a job like this earlier.

combustion chamber - M116 15.85 to 16.15mm - M117 17.85 to 18.15mm

I was wondering what this means exactly?  Is this the different compression ratios? If so and there are low compression pistons available for the 350 then a whole new world of modification opens up which would be interesting to explore, turbo charging.  High compression is the scourge of reliable turbo charging, but the fuel system seems to be up to it, and you could get the M117 power or more from an 350 M116 with forced induction.

measuring the combustion chamber 



Haynes also states the combustion chamber can be reduced to a minimum of 15.35mm for the M116, and 17.35mm for the M117, after machining.

So seeing how the combustion chamber is measured in the head, those measurements do affect compression ratios, but I think they're only part to blame.   It would also be determined by piston depth and conrod length.  Not that I've been able to find other pistons on the web.  Shaving the head would obviously increase the ratio but I thought that would be a good thing.  I didn't know high compression was bad for turbo addition.

Following on from a recent discussion on cold air intakes and Pat Bateman's surprisingly high temps for a standard intake on his 6.9, I've been even more tempted to try and make a cold air/ram effect intake.  Especially after warming the car up yesterday and with the bonnet open, was surprised to feel warm air being still sucked into the standard forward facing intake.  Outside temp was around the 14oC mark.  A discrete wide scoop to provide a bit of positive pressure at speed with the cold intake might just improve things somewhat.  A turbo still sounds good though.

But it does seem that if power's the goal, I should leave the 350 alone and should get a 450 and go from there.

[gregdeklerk]

But it does seem that if power's the goal, I should leave the 350 alone and should get a 450 and go from there.

Smart man!!

[john skene]

To get the longer stroke the 4.5 engines crank was given 9.6mm extra throw. You can have your 350 crank built up and reground off centre to get a longer stroke, but you will have to watch the crank angle clearance at the base of the bore and the clearance between the piston and valves. You may have to get a special spacer head gasket (?) or perhaps use the low compression 450 pistons if they have a slightly shorter distance from the piston crown to the conrod.

[torana68]

well whilst your spending money, 380/560's use smaller rod bearings ,that makes me think they have off-centre ground the 450 crank to obtain a longer stroke, so..... off centre grind a 450 crank to increase stroke and use the 380/560 (?) rods, or fit a later engine (MUCH cheaper). the 450 pistons come in low and higher compression but its the size of the dish that is different.
Roger

[oscar]

I was waiting for a 6.9er to chime in

I'll try and find some info on w126 engines meantime but I doubt I'd touch the crankshaft.  I think giving a 350 extra stroke would be a wasted excercise because of the issues John raises.   With mods to the block like spacers for the head, I'd probably end up with a 450 sized block. So I'd be back to the "start with a 450 and go from there" comment.

It's just handy to know how many parts are interchangeable between the two.  But following on the power gain talk, I wonder if a 350 crankshaft, rod and piston setup in a 450 block would suit a turbo setup more than standard?

[Mforcer]

It's just handy to know how many parts are interchangeable between the two.

I find this discussion very enlightening and interesting. Makes me appreciate what knowledge must go into designing an engine but also makes me less inclined to make any changes to my engine.

I am happy driving a de-tuned race engine

[oscar]

I am happy driving a de-tuned race engine

Not to mention your 450SE is the most powerful short wheel base in the W116 line up   I know you want to say it, don't hold back