What are the merits of I6 engines over V6
12-19-2006, 11:05 AM
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I was just wondering of someone could enlighten me as to why BMW is sticking with its inline 6 cylinder formation when almost all the competetion are moving to V6 formation? Which is better & why?
Is it cheaper to maintain & service? renders better performance? Economy? Refined? I am just confused
as I noticed Mercedes, Lexus & Audi all doing there 6 cylinder engines in V6 shape whilst BMW is sticking with I6
Naturally all 8 cylinders are V8.
Any one has a layman answer please?
Is it cheaper to maintain & service? renders better performance? Economy? Refined? I am just confused
as I noticed Mercedes, Lexus & Audi all doing there 6 cylinder engines in V6 shape whilst BMW is sticking with I6Naturally all 8 cylinders are V8.
Any one has a layman answer please?
12-19-2006, 11:14 AM
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I believe the I6 run smoother and has a better weight distribution (to the overall car) than V6 design, but it costs more to manufacture. V6 is easier to package in the engine bay but BMW choice not to follow the crowd, probably because it will have an effect on the handling.
As to why there's no I8, maybe it will be too long to fit in the engine bay to make it a practical design?
As to why there's no I8, maybe it will be too long to fit in the engine bay to make it a practical design?
12-19-2006, 11:34 AM
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kchan almost hit the nail on the head. Inline engines are easier to make and offer better torque. The inline 6 is also very smooth, more so than a V6 but that's changing. The reason everyone else has gone with V6's is that it's easy to fit a V6 in an engine bay made for an inline 4 (or 4cyl engine). The inline 6 is a long engine but also fits well into a bay made for a V8. I-8's would be too long for modern cars. BMW also has a long tradition of building inline 6's just as Porsche has been known for their boxer engines.
12-19-2006, 11:46 AM
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BMW would claim that the inline 6 cylinder provides a smoother, more refined, more efficient performance - it's better balanced.
In a straight 6 the piston in front (1) will always be in the same position as the rear piston (6), and 2 the same as 5, etc ... perfect balance. I6 engines also are more efficient because V6 engines duplicate value gears and camshafts (more energy loss).
Any V engine requires something to balance off vibrations. Mercedes' V6s are just chopped-off V8s - they need a balancing shaft.
But V6 engines can fit in a smaller space: that's why they exist - to fit in smaller, front-wheel drive cars.
In a straight 6 the piston in front (1) will always be in the same position as the rear piston (6), and 2 the same as 5, etc ... perfect balance. I6 engines also are more efficient because V6 engines duplicate value gears and camshafts (more energy loss).
Any V engine requires something to balance off vibrations. Mercedes' V6s are just chopped-off V8s - they need a balancing shaft.
But V6 engines can fit in a smaller space: that's why they exist - to fit in smaller, front-wheel drive cars.
12-19-2006, 11:52 AM
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The merits of a Straight 6 compared to a V6 is basically everything but cost!. A straight 6 is smoother, quieter more powerful. The engine is perfectly balanced. A V6 will never be a smooth engine because of the cylinders its missing. A V8 is perfectly balanced. One of the most expensive parts in a engine is the crankshaft. A V6's crank is half the length of a straight six engine. So instant $$$ saving already. Thats why Mercedes went the V6 route....... the cost and the length of the engine!, I read somewhere it was 30% cheaper to make their V6 engine than the previous straight six engine they made. Thats one thing of many why BMW rule!.
Lets compare the two....
First BMW (3.0 litre non turbo version)
Cylinders Straight 6
Capacity cc 2996
Stroke/Bore (mm) 88/85
Max output 258bhp@6600rpm
Max torque (Nm/rpm) 300/2500
Mercedes engine same capacity but V6 layout
Cylinders V6
Capacity cc 2996
Stroke/Bore (mm) 82/88
Max output 231bhp@6000rpm
Max torque (Nm/rpm) 300/2500-5000
Looking at the two, you can see that the BMW engine has much more power and rev's higher. This is because of the short stroke of the V6 gives it a natural disadvantage. The torque is matched, but the BMW engine is down on torque very slightly top end. Over 25 more horses and much better on fuel looking at the two car makers websites, the cats in the bag already!, on which one I would have.
Lets compare the two....
First BMW (3.0 litre non turbo version)
Cylinders Straight 6
Capacity cc 2996
Stroke/Bore (mm) 88/85
Max output 258bhp@6600rpm
Max torque (Nm/rpm) 300/2500
Mercedes engine same capacity but V6 layout
Cylinders V6
Capacity cc 2996
Stroke/Bore (mm) 82/88
Max output 231bhp@6000rpm
Max torque (Nm/rpm) 300/2500-5000
Looking at the two, you can see that the BMW engine has much more power and rev's higher. This is because of the short stroke of the V6 gives it a natural disadvantage. The torque is matched, but the BMW engine is down on torque very slightly top end. Over 25 more horses and much better on fuel looking at the two car makers websites, the cats in the bag already!, on which one I would have.
12-19-2006, 11:55 AM
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It has to do with the engine balance.
A sixinline is vibressionless but the V6 needs a lot of balacing veights to try to be in balance.
The problem, if you so like, is that the R6 is a long engine.
That's the reason why so many car manufactures prefer V6 engines.
Especially in front wheel drive cars, where the gearbox has to be fitted beside the engine
and the whole package is crosswise.
In a BMW this is not a problem since the cars are basicly rear wheal drives and the engine
is assmbled lengthwise.
Still like to add, that of technical theoremas reason the ideal size of one sylinder is about 0,5 litres.
Therefore BMW is stronly committed to six in line engines with a 3,0 litre total cylindersize.
A technical ideal
Better than a 3,0 litre R6 engine is only a 6,0 litre V12 - no other engine type comes close.
A sixinline is vibressionless but the V6 needs a lot of balacing veights to try to be in balance.
The problem, if you so like, is that the R6 is a long engine.
That's the reason why so many car manufactures prefer V6 engines.
Especially in front wheel drive cars, where the gearbox has to be fitted beside the engine
and the whole package is crosswise.
In a BMW this is not a problem since the cars are basicly rear wheal drives and the engine
is assmbled lengthwise.
Still like to add, that of technical theoremas reason the ideal size of one sylinder is about 0,5 litres.
Therefore BMW is stronly committed to six in line engines with a 3,0 litre total cylindersize.
A technical ideal
Better than a 3,0 litre R6 engine is only a 6,0 litre V12 - no other engine type comes close.
12-19-2006, 11:59 AM
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Originally Posted by the_oracle' post='369223' date='Dec 19 2006, 03:52 PM
The merits of a Straight 6 compared to a V6 is basically everything but cost!. A straight 6 is smoother, quieter more powerful. The engine is perfectly balanced. A V6 will never be a smooth engine because of the cylinders its missing. A V8 is perfectly balanced. One of the most expensive parts in a engine is the crankshaft. A V6's crank is half the length of a straight six engine. So instant $$$ saving already. Thats why Mercedes went the V6 route....... the cost and the length of the engine!, I read somewhere it was 30% cheaper to make their V6 engine than the previous straight six engine they made. Thats one thing of many why BMW rule!.
Lets compare the two....
First BMW (3.0 litre non turbo version)
Cylinders Straight 6
Capacity cc 2996
Stroke/Bore (mm) 88/85
Max output 258bhp@6600rpm
Max torque (Nm/rpm) 300/2500
Mercedes engine same capacity but V6 layout
Cylinders V6
Capacity cc 2996
Stroke/Bore (mm) 82/88
Max output 231bhp@6000rpm
Max torque (Nm/rpm) 300/2500-5000
Looking at the two, you can see that the BMW engine has much more power and rev's higher. This is because of the short stroke of the V6 gives it a natural disadvantage. The torque is matched, but the BMW engine is down on torque very slightly top end. Over 25 more horses and much better on fuel looking at the two car makers websites, the cats in the bag already!, on which one I would have.
Lets compare the two....
First BMW (3.0 litre non turbo version)
Cylinders Straight 6
Capacity cc 2996
Stroke/Bore (mm) 88/85
Max output 258bhp@6600rpm
Max torque (Nm/rpm) 300/2500
Mercedes engine same capacity but V6 layout
Cylinders V6
Capacity cc 2996
Stroke/Bore (mm) 82/88
Max output 231bhp@6000rpm
Max torque (Nm/rpm) 300/2500-5000
Looking at the two, you can see that the BMW engine has much more power and rev's higher. This is because of the short stroke of the V6 gives it a natural disadvantage. The torque is matched, but the BMW engine is down on torque very slightly top end. Over 25 more horses and much better on fuel looking at the two car makers websites, the cats in the bag already!, on which one I would have.
12-19-2006, 12:13 PM
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Originally Posted by the-oneil' post='369225' date='Dec 19 2006, 08:59 PM
BMW's previous gen (M54) engines - only replaced Sep 2005 were 231bhp
12-19-2006, 12:34 PM
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Originally Posted by Ricracing' post='369224' date='Dec 19 2006, 09:55 PM
Better than a 3,0 litre R6 engine is only a 6,0 litre V12 - no other engine type comes close.
12-19-2006, 12:39 PM
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Originally Posted by the_oracle' post='369223' date='Dec 19 2006, 09:52 PM
One of the most expensive parts in a engine is the crankshaft. A V6's crank is half the length of a straight six engine. So instant $$$ saving already. .