M70 mixed with M50 heads

[Yaninnya]

In one of other topics I found this:

Dips this is what you need



http://www.boggbros.co.uk/gallery2.html

Jason

Anyone is sitting on details of this engine (who done it, what problems he solved, etc.)?
Cheers,
Jan

[WillG]

look on some 8 series forums i seen info a while ago but cant remember where

[Turbo-Brown]

Surely that can't be a V12 block with two M50 heads. If it was, the exhaust of the left hand head would be firing at the inlet of the right hand one, unless they swapped the end the cams are driven from on one of the heads that is.

[Yaninnya]

Surely that can't be a V12 block with two M50 heads. If it was, the exhaust of the left hand head would be firing at the inlet of the right hand one, unless they swapped the end the cams are driven from on one of the heads that is.

For 99% it is. It is nothing unusual to change the sides in cylinder head (IN in place of EX and vice versa).
Check the other photos on that site.

[Turbo-Brown]

What, drawing air in through what used to be the exhaust ports on one of the heads?!

[Yaninnya]

What, drawing air in through what used to be the exhaust ports on one of the heads?!

Exactly. When you are porting the head and fitting bigger valves there no any disadvantages to do this.

[ian332isport]

What, drawing air in through what used to be the exhaust ports on one of the heads?!

Exactly. When you are porting the head and fitting bigger valves there no any disadvantages to do this.

I don't think you would ever get both banks to run the same though.

One cylinder bank would have 33mm inlet valves and 30.5mm exhaust valves. The other bank would be the other way around. Even with porting and larger valves, you will never get both banks balanced. There's just not enough space in the combustion chamber to do it.

Nice idea, but I can't see it ever running properly. Running yes, but not very well.

Ian.

[WillG]

what about if they put cam in from wrong end but bolted it down so it was driven from same side as other cam, would need a custom cam grind and machine work on one of the ends of the heads to hold cam in place but then it would use the correct ports? looking at my m20 head looks easly doable, would need cam grinder to just swap inlet and outlet lobes over and then you need to have block of ally welded to end of head and have it milled and 2 threads tapped either side

[Turbo-Brown]

Don't see why it'd need a custom grind unless the bearing journals are different on the M50 as they are with the M20.

Would probably need to machine the head to let the drive assembly in, but other than that, some kind of bolt on attachment for the normal cams would seem sensible

[stonesie]

it makes sense to me that they would make a different mould for casting the heads of 1 bank with the only difference being the basic port sizes (swapping inlet for exhaust) that way all other parts would be interchangable between heads including rocker covers

[Turbo-Brown]

Except that the plugs need to swap sides and so forth.

Makes much more sense just to design a head and cam system that can be driven from either end. That way you only need one head casting and the bank it's attached to determines which way round it's bolted.

No idea if that's what they actually did though!

[jaistanley]

The above engine would run fine... The different shape and size of the exhaust and inlet valves will mean each bank has a different volumetric efficiency at given RPMs. You might think this would lead to a mis-balance but it wont, each bank will simply be contributing differing ammounts of torque. Don't forget these banks are on a common crankshaft.

At lower RPM one bank may be producing higher torque, at higher the other might. Being attached to the same crankshaft will mean that the torque from the bank with the higher vol eff will contribute to the pumping of the other. This wont mean they will always be making same power but I put it to you that the pumping losses from the lesser bank will be fairly minimal.

I'd hazard a guess that the engine will produce the average of each banks' torque at any rpm. Also, with head design the size of the valves really isn;t the be-all-and-end-all. The port shape and valve geometry has a massive impact of vol eff.. The head could be flowed such that the once exhaust ports have the same eff as the inlets and vice versa. This would probably mean doing a 'bad job' (though one that'd require loads of skill) on the non-inverted head and a 'good job' on the inverted one.

I think the real problem here is the fuelling and spark. I'd personally run two completely separate ECUs and HT systems. Then whilst mapping, map each bank independantly. You could even limit fuel to the non-inverted side to balance torque but at the expense of extra heat generation. I'm no wizard at mapping/calibration so maybee someone could suggest how?

I do like the idea of running one head the wrong way though, engineering a pulley system for the cams. Hell of a lot of work though!

Just my thoughts..

Jai

[Turbo-Brown]

Hmm, with regard to the banks contributing different amounts of effort:

When I finally developed a decent adjustment system for the butterflies on my TBs, I borrowed Andy335's airflow gizmo and set the balance.

It used to shake like a jelly on a plate at idle and would shunt massively if you just put it in gear and let the idle pull you along, say in traffic. The reason for this being that different cylinders were getting different amounts of air, although they were all within 0.5kg/hour of each other iirc. It also made something of a warbling exhaust note and wasn't all that smooth at a light cruise, like around town at 30mph.

Anyway, balanced them properly and now it has a silk smooth idle, you can stick it in 1st on idle and it's like gliding along a glass table, the sound under load is much more consistent now and it's much much smoother at town speeds etc.

Basically what I'm getting at is that having massively different efforts being generated by each bank would make for a nasty, shaky, inefficient engine IMO, especially when the V12 is one of the few configurations that can be perfectly balanced (much like our I6 engines and Xplane-V8s)

If I were doing it, I would without out doubt engineer the cam drive from the other end rather than bodge it with two management systems and all that expensive porting! (That said didn't some '90s Ferrari's have two seperate engine management systems for their V8s?)

[Ant]

the M70's originally had split ECU's for each bank, and can be run as 6 cyl in limp mode on one bank only, theres a guy in the US that has 2 MsnS-E ECU's running is V12 in the same fashion.

cant see the poit in this head conversion though, for the cost and effort possibly easier to source a late Csi lump and use that to get the 4v per cyl

[Yaninnya]

cant see the poit in this head conversion though, for the cost and effort possibly easier to source a late Csi lump and use that to get the 4v per cyl

What you mean? 850 CSi was 2 v per cyl.

[Kos]

cant see the poit in this head conversion though, for the cost and effort possibly easier to source a late Csi lump and use that to get the 4v per cyl

What you mean? 850 CSi was 2 v per cyl.

true

they did develop a 48 valve version of the v12 but never put it in to production, bmw did want to get in to a power race with other manufacturers,


but a few years later they did

[Yaninnya]

they did develop a 48 valve version of the v12 but never put it in to production, ... ...but a few years later they did

Yes, but second hand N73 is expencive as hell.

[WillG]

850 csi doesnt use a m70, its uses a S70 and has 4 valves per cylinder according to http://dave.maisenhelder.com/bmw/engines_&_chassie.htm and http://www.realoem.com/bmw/ , one for sale at fab now and they say its a s70 aswell

same castings as maclaren FI engine

[Kos]

850 csi doesnt use a m70, its uses a S70 and has 4 valves per cylinder according to http://dave.maisenhelder.com/bmw/engines_&_chassie.htm and http://www.realoem.com/bmw/

same castings as maclaren FI engine

wrong

850csi sas a tuned m70, stroked to 5.4 liters, 2 valves per cylider

the mclaren f1 engine is a different beast altogether, the only thing similar to that is th s52 foung in the e36 m3 evo

[WillG]

if you look at part number for the s70 engine cylinder head and m70 cylinder head on realoem they are the same..wonder where this dave bloke was getting his info, or was he just guessing

[Kos]

because the s70 is a tuned version of the m70, its just got a few tricks up its sleve


the mclaren f1 engine is different altogether, that muppet must be guessing. look at this picture, is an 850csi camshaft, count the lobes on the cam!

http://www.realoem.com/bmw/showparts.do ... g=11&fg=25

[WillG]

already did that , so its that a maclaren F1 engine isnt a S70, that still doiesnt explain why he has all the s70 engines as having 4 valves dont think i would trust any of the v12 info on there, everything on m20's seems to be correct tho

[Kos]

god knows what they called it, but it never found its way into a bmw, well not our of the factory!!

[Yaninnya]

already did that , so its that a maclaren F1 engine isnt a S70, that still doiesnt explain why he has all the s70 engines as having 4 valves dont think i would trust any of the v12 info on there, everything on m20's seems to be correct tho

Let's get some light on V12 mistery:
- 850 CSi got S70 engine: 5576 cc, 2v per cyl, 380 BHP
- M8 prototype got S70/1 engine: around 6000 cc, 4v per cyl, around 550 BHP
- McLaren F1 got S70/2 and S70/3 engine: 6064 cc, 4v per cyl, 627 and 635 BHP
S70/2 and S70/3 engine was the base of BMW Motorsport used in BMW LM (i.e. 24 h Le Mans).