V12 LS1 Build
04-23-2015, 06:56 PM
#601
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It's impossible to say either way without data.
I do know that when BMW wants to build a high output engine, they give each cylinder its own coolant feed or drain.
BMW's M30 and S38 inline 6's are cousins. The M30 is the SOHC 12V normal car engine and the S38 is the DOHC 24V M5/M6 engine.
The M30 has a conventional cooling system layout in which the water pump pushes water into the front of the block, the water flows up through orifices in the head gasket, flows forward through the cylinder head and out via the (recirculating) thermostat housing. It is WELL established that the rear cylinders run hotter than the fronts. When I replaced the head gasket on my '92 535i with this engine, I went back after DDing for a week to retorque the head bolts. Working from the front of the engine to the rear, each pair of head bolts moved progressively more at the SAME retorque value because the aluminum at the rear of the cylinder head moved a little more due to continuous higher operating temps.
The S38 was designed as a race engine from the get-go. It uses an exeternal coolant manifold to meter coolant flow into the cylinder head under each exhaust port. It does not have any problems with differential cylinder temperatures, has been raced in endurance events at 800 HP and built to over 1000 HP for drag racing.
Similar changes are visible between the M60/M62 production V8's and S62 V8 from the M5 & Z8.
I do know that when BMW wants to build a high output engine, they give each cylinder its own coolant feed or drain.
BMW's M30 and S38 inline 6's are cousins. The M30 is the SOHC 12V normal car engine and the S38 is the DOHC 24V M5/M6 engine.
The M30 has a conventional cooling system layout in which the water pump pushes water into the front of the block, the water flows up through orifices in the head gasket, flows forward through the cylinder head and out via the (recirculating) thermostat housing. It is WELL established that the rear cylinders run hotter than the fronts. When I replaced the head gasket on my '92 535i with this engine, I went back after DDing for a week to retorque the head bolts. Working from the front of the engine to the rear, each pair of head bolts moved progressively more at the SAME retorque value because the aluminum at the rear of the cylinder head moved a little more due to continuous higher operating temps.
The S38 was designed as a race engine from the get-go. It uses an exeternal coolant manifold to meter coolant flow into the cylinder head under each exhaust port. It does not have any problems with differential cylinder temperatures, has been raced in endurance events at 800 HP and built to over 1000 HP for drag racing.
Similar changes are visible between the M60/M62 production V8's and S62 V8 from the M5 & Z8.
04-24-2015, 09:32 AM
#602
I'm not sure how a BMW straight 6 is relevant to this conversation. 
...Unless we are talking about putting them on a pedestal for engine design. (I would not do that. I know lots of folks with chevy 8's and BMW 6's. The chevy 8's are much more durable and less prone to breaking down... and ending up at a BMW dealer.)
Everybody knows that the ancient underground salt formations in Bavaria cause relativistic gravitational anomalies that cause engine coolant to flow in odd ways there, so I'm not sure there are any issues here.
...Unless we are talking about putting them on a pedestal for engine design. (I would not do that. I know lots of folks with chevy 8's and BMW 6's. The chevy 8's are much more durable and less prone to breaking down... and ending up at a BMW dealer.)
Everybody knows that the ancient underground salt formations in Bavaria cause relativistic gravitational anomalies that cause engine coolant to flow in odd ways there, so I'm not sure there are any issues here.
04-25-2015, 08:04 PM
#606
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Water gets pumped in the front of the block, flows to the back, goes up through the head gasket into the head and flows to the front where it leaves the engine.
It could be a W18 with three banks of 6 and work the same way.
The difference is that it's 50% longer than a V8, so getting the coolant circulation right is that much harder than it is in an engine with two banks of 4.
Water and heat don't care where the metal was cast and work the same way in all engines.
It could be a W18 with three banks of 6 and work the same way.
The difference is that it's 50% longer than a V8, so getting the coolant circulation right is that much harder than it is in an engine with two banks of 4.
Water and heat don't care where the metal was cast and work the same way in all engines.
04-27-2015, 06:15 PM
#608
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04-27-2015, 08:07 PM
#609
I'm still struggling to find the relevance of BMW's cooling problems to the engine we are discussing here. Are you really trying to point out that differential cylinder temperatures are important? If so, I'd like to know more about why. (Instead of it's important because BMW is worried about it or BMW's design is so sensitive that they have to be extra-worried about it.)
07-26-2015, 04:54 PM
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Thanks, for spLing for me. I'm not sure you've made an assertion here, though.
I'm still struggling to find the relevance of BMW's cooling problems to the engine we are discussing here. Are you really trying to point out that differential cylinder temperatures are important? If so, I'd like to know more about why. (Instead of it's important because BMW is worried about it or BMW's design is so sensitive that they have to be extra-worried about it.)
I'm still struggling to find the relevance of BMW's cooling problems to the engine we are discussing here. Are you really trying to point out that differential cylinder temperatures are important? If so, I'd like to know more about why. (Instead of it's important because BMW is worried about it or BMW's design is so sensitive that they have to be extra-worried about it.)
Also, the higher volume cooling system with the same volume water pump reduces the water velocity through the system. This increases the opportunity for water to boil locally and for the resulting bubble to stay stuck in the head. in a high velocity cooling system, the bubble forms, absorbs a lot of heat in the process, but is then taken away by the speed of the water before it can sit in the head and reduce heat transfer. Reduce the speed and the bubble is more likely to stay put when it forms, reduce heat transfer, increase chamber wall temp and provoke detonation.
8 cylinder LS engines running high boost ALREADY have problems with detonation in #'s 7 & 8 when run without a high capacity four point coolant bleed system. Those problems will only be worse on a 12 cylinder.
The M engines actually have very advanced cooling systems, though. They wouldn't be able to get 430+ RWHP out of a 3.0 with a warranty if they couldn't keep it appropriately cooled.
07-27-2015, 07:27 PM
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LS1's, Gen II LT1's, Caddy Northstars and basically every engine designed since the early '90's uses this method. BMW even modified their M30's to use such a setup... and that was a 1960's design that they built until '92ish.
What you implied about the thermostat slowing water circulation hasn't been true for any engine more recent than the Gen I Small Block.
I'm going to get really worried about this when we start seeing this detonation problem pop up in at least 5% of the LS1 V-12's on the market.
Were you serious about someone putting one into a plane? I'd sure hate to pop 11 & 12 on a low altitude high speed pass...
