The boxer engine - why such low specific output?
Discussion
it's as easy as this
they protect 911 sales which they make a lot more money from and the 911 branding is "the car to be seen in"
the new 981 Boxster engine is the same block as a 420 BHP 991 engine.
If Caymans and Boxsters had 400BHp they would sell less 991's which are double the price but cost in real terms the same to build.
Also the mid engine platform would be faster which cannot ever happen , again to protect the 911 branding.
they protect 911 sales which they make a lot more money from and the 911 branding is "the car to be seen in"
the new 981 Boxster engine is the same block as a 420 BHP 991 engine.
If Caymans and Boxsters had 400BHp they would sell less 991's which are double the price but cost in real terms the same to build.
Also the mid engine platform would be faster which cannot ever happen , again to protect the 911 branding.
I hope this response is not regarded as too simplistic - but the basic Boxster/Cayman engine could easily be built into a 3.6 or 3.8 with almost all the original internals. The extra capacity would therefore be running with almost the same general internal mass and resistance yet have increased airflow rates and greater efficiency.
Since specific output is related to the internal resistance and capacity it is inevitable if an engine is designed to cover a wide capacity range that the smaller versions will be carrying a little more weight than absolutely necessary or else the larger version would simply blow apart.
Another way of looking at it is taking a smaller engine and increasing the capacity - which usually results in an engine with greater bottom end output (as air flow rates increase at lower revs) but often is restricted at the top end but still provides more output because of the increased capacity.
Or alternatively take a bigger engine and scale the capacity down without reducing the internals mass etc - and obviously it will not be as efficient as if it was designed for that capacity anyway.
However because the larger capacity versions have pushed the reliability window closer to the limit - they seem less reliable and suffer more failures while the smaller capacity versions seem more reliable - so there are pros and cons to both issues.
For a small specialist manufacturer (as Porsche were before the takeover by Volkswagen) investing in tooling and machinery to make a basic engine to cover a wider range of capacities was important for survival and worked well for them but it would never be individually as good as designing and building an engine for one specific output and capacity.
Baz
Since specific output is related to the internal resistance and capacity it is inevitable if an engine is designed to cover a wide capacity range that the smaller versions will be carrying a little more weight than absolutely necessary or else the larger version would simply blow apart.
Another way of looking at it is taking a smaller engine and increasing the capacity - which usually results in an engine with greater bottom end output (as air flow rates increase at lower revs) but often is restricted at the top end but still provides more output because of the increased capacity.
Or alternatively take a bigger engine and scale the capacity down without reducing the internals mass etc - and obviously it will not be as efficient as if it was designed for that capacity anyway.
However because the larger capacity versions have pushed the reliability window closer to the limit - they seem less reliable and suffer more failures while the smaller capacity versions seem more reliable - so there are pros and cons to both issues.
For a small specialist manufacturer (as Porsche were before the takeover by Volkswagen) investing in tooling and machinery to make a basic engine to cover a wider range of capacities was important for survival and worked well for them but it would never be individually as good as designing and building an engine for one specific output and capacity.
Baz
ge0rge said:
Could someone please direct me to some read on the boxer engine, its development within porsche and maybe some sort of explanation as to why it produces such low power/litre and why porsche have stuck with this engine other than the gravity benefits?
Which model produces a low power/litre ratio and compared to what?ge0rge said:
...why porsche have stuck with this engine other than the gravity benefits?
If you give it some thought it is a bit of a daft question. Until recently the bulk of the company history has seen it underpinned on selling 911s for half a century, and the whole design of that fits around a flat engine (even though there are actually ways of getting a small V in the engine bay if it is compact enough). Also consider the Boxster - the flat engine confers a packaging advantage over many rivals as the folded roof can sit directly on top of the engine. This simplifies the roof design and removes compromise in the weight distribution of the car (compare to a folding hard top coupe like an E93 BMW where you can actually feel quite distinctly how far back the CoG moves with the roof back in the boot when driving it).But it is mostly a marketing advantage based on the heritage of the 911 which will see it as worth continuing with.
Your specific output question is thoroughly baffling though. With the old cars it was low as they were air cooled rather than because they were flat. With the new cars there are already 2 cars with 125 normally aspirated hp per litre that have been produced and that will increase when the 991 RS hits the market...
ge0rge said:
I was referring to the cay/boxster.
Still baffling. One of the best engines out there all things considered is the turbocharged BMW 3 litre 6 cylinder used in many models (including the 335i) which has almost the same specific output as a non-turbocharged entry level Cayman. Both have the convenient side effect of tax band friendly emissions and long range fuel consumption to keep their marketing teams happy too. As for normal aspiration - the E9x M3 only has about 3bhp/litre more than a 2.7 Cayman and that is widely considered one of the greatest engines of the last decade.What were you using as your basis for comparison? Things like the S2000 perhaps (which was driven out of production as it couldn't be made to comply with emissions laws and had nothing like the linearity of power delivery of a Cayman)? Or maybe you were comparing an entry level Cayman to a Ferrari 458?
...'cause I'd hate to think that this thread was just a terrible attempt at a troll...
Edited by DiscoColin on Friday 26th July 21:55
ge0rge said:
Could someone please direct me to some read on the boxer engine, its development within porsche and maybe some sort of explanation as to why it produces such low power/litre and why porsche have stuck with this engine other than the gravity benefits?
http://www.amazon.com/Porsche-911-Engine-History-Development/dp/0760307024The output is not that low.
By way of comparison, a previous car I owned had a 4.6l SOHC V8 that produced around 210hp, a few hp less than my 02 Boxster's 2.7l engine produces (217hp IIRC). Another carI owned had a 6.0l OHV V8 and it produced just 400hp (a bit less than my 3.6l Turbo engine produces (420hp)).
Porsche obviously hasn't stuck with this engine for everything. Remember the 924, the 944, the 968, the 928, the Cayenne, and the Panamera? Oh and the Carrera GT (V10!).
It is horses for courses.
To use a different engine layout would require a considerable redsign of the car's chassis/body. And it would mean throwing away its 50+ years of history of the flat 6
And just to throw another spanner in the works it is also important to remember that it is the rear wheel torque through the gears that accelerates a car and although the same basic engine with bigger or lower capacity may well reach similar peak specific power output - the bigger capacity engine also enjoys a fatter torque curve and therefore the area under the rear wheel torque graph in each gear is greater - leading to higher performance against a similar weight/mass and resistance.
Baz
Baz
mrdemon said:
best engine I have had was the 2.5 litre pushing 430bhp in my TTRS and having over 400lb/ft from less than 2k revs
a great engine and I see the xbow has taken it on now.
Also some cars are now pushing 600bhp with that 2.5 lump.
That's turbocharged which is an entirely different ball game.a great engine and I see the xbow has taken it on now.
Also some cars are now pushing 600bhp with that 2.5 lump.
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