Topic: Test Drive: 2010 Volkswagen Golf 2.5L

[tpl]

The more cylinders, the more firing strokes per revolution, the more power in total for a given displacement.

[Mitlov]

Good timing.  I just got my latest issue of Cycle World which had a liter-bike shootout.  Nine sportbikes, all 1000ccs.   Two V-twins (Ducati 1198S Corse and KTM RC8R), one V-four (Aprilia RSV4 Factory), and six inline-fours (BMW S1000RR, Honda CBR1000RR, Kawasaki ZX-6R, MV Agusta F4, Suzuki GSX-R1000, and Yamaha YZF-R1). 

Interesting.

I know squat about bikes, but maybe the fact that these are all "sportbikes" and (I assume) all tuned to get the very most out of their available displacement, then the differences (if any) resulting from number of cylinders in minimized?  Or put another way - in a less maxed-out state out tune (such as one would expect in volume-selling motor vehicle), is it perhaps easier to get more power from an engine with more cylinders but the same displacement?  Again, I don't claim to know. 

It's just my perception that, over time,  2.5l V6s seem to make more power on average than 2.5l 4-pots - but there are lots of variables at play.  Only 0.2l separate a 3.8l V6 from a 4.0l V8 - but I expect the output of the latter to be higher.  That may be an unfounded expectation on my part, but there you go.

Jaeger

Yep, these are all track-oriented sportsbikes, not sport-tourers or cruisers (cruisers are the two-wheeled equivalent of lowrider pickup trucks...don't get me started).  All designed to be as fast as possible within the 1000cc displacement limit, the limit of the chassis, and the limit of the company's budget for the bike's development and manufacture (Ducati can get more out of 1000ccs with their US$70,000 Desmosedici, but these bikes are all in the $15,000-$25,000 range).

I don't think that the engineering limits of i4s versus V6s has much if anything to do with the cars we're discussing, because none of them are even close to the state of tune that a modern sportsbike is.  That last point--budget for the vehicle's development and manufacture--is why I think you tend to see more performance out of 2.5L V6s than 2.5L i4s...because the 2.5L V6s are more expensive engines so the company can spend a bit more time tuning them.  

Think about it.  A base Altima or Fusion is a cheap vehicle.  The engine would similarly be very inexpensive.  A Spec V or Civic Si or Accord EX has a higher MSRP, part of which can go to engine development and manufacture, so the companies can extract more power from their four-bangers.  Cars like the IS250 and G25 are a LOT more expensive, so the car companies have a lot more funds to dedicate to engine development and manufacture, and they end up getting a lot more out of their 2.5Ls.

The ONLY car we've mentioned that doesn't fit well into this three-tier budget discussion is the new Sonata, and I think that's just a matter of it having DI, which boosts power by about 25 horsepower without a lot of extra cost, and its competitors don't have DI yet.  Once the rest of the manufacturers update their designs with DI as well, I suspect that the "cheapo" 2.5L i4s will approach 200 horsepower, the "upgrade" i4s like the Spec V and Accord EX will approach 220 horsepower, and the premium 2.5L V6s will approach 240 horsepower, and the three-tiered analysis will remain valid.

[Mitlov]

The more cylinders, the more firing strokes per revolution, the more power in total for a given displacement.

I disagree, and I think that the sportbike example from a few posts above refutes this theory.  Double the cylinder count while maintaining the same state of tune and the same displacement, and you only gain 5% peak horsepower.  If power was proportional to the firing strokes per revolution, you'd expect a MUCH bigger power gain when you doubled the cylinder count.

Think of it this way.  One day, you drink three 12-oz glasses of beer.  The next day, you drink six 6-oz glasses of beer.  You've had twice as many beers the second day, but it's not going to hit you any harder overall because each beer was half as big.

The 5% average increase in peak power between two-cylinder literbikes and four-cylinder literbikes, I think, is entirely due to the fact that the four-cylinders can rev a bit higher than the twins.  Shorter strokes for the cylinders equals higher redlines equals a bit more peak horsepower. 

[Mitlov]

Jaeger and TPL--

I just thought of another good example.  Compare the TSX and the IS250.  (1) Very similar displacements, (2) very similar price points, (3) very similar target market (so the manufacturers are aiming for the same point on the spectrum between "maximum possible performance" and "maximum possible refinement"), but (4) 50% advantage in cylinder count for the Lexus...and you have essentially identical horsepower and torque numbers.  If cylinder count played a significant role along with the other three factors, you wouldn't have similar total output.

EDIT:  To bring the analysis back to the Golf 2.5L.  Given 2.5L, a very low price point (at least in the States, the Golf 2.5L starts about $2,000 lower than a base Camry or Altima and about $4,000 less than a Civic Si), and a mass-market (as opposed to enthusiast-focused) powerband, 170 horsepower and 175 lb-ft is exactly what I would expect. 

[Flinter]

Jaeger and TPL--

I just thought of another good example.  Compare the TSX and the IS250.  (1) Very similar displacements, (2) very similar price points, (3) very similar target market (so the manufacturers are aiming for the same point on the spectrum between "maximum possible performance" and "maximum possible refinement"), but (4) 50% advantage in cylinder count for the Lexus...and you have essentially identical horsepower and torque numbers.  If cylinder count played a significant role along with the other three factors, you wouldn't have similar total output.

EDIT:  To bring the analysis back to the Golf 2.5L.  Given 2.5L, a very low price point (at least in the States, the Golf 2.5L starts about $2,000 lower than a base Camry or Altima and about $4,000 less than a Civic Si), and a mass-market (as opposed to enthusiast-focused) powerband, 170 horsepower and 175 lb-ft is exactly what I would expect. 

I'd agree with your point on cylinder count. All other things being equal, I would expect a 6 cylinder to produce slightly less power than a 4 cylinder due to the reduced drag of fewer pistons and fewer moving parts (fewer frictional losses) in the 4 cylinder.

However, the reality in most cases is that an equivalent displacement 6 cylinder makes more power than a 4 cylinder because "all other things are not equal". Usually, the 6 cylinder is a more expensive high end engine and the design is optimized to produce more power (ie. bore/stroke ratios, cylinder head design and valvetrain, higher compression ratios, lightweight materials etc.).

One significant exception is the TSX vs IS250 that you mentioned. What is even more interesting here is that Lexus uses direct injection and can therefore get away with running a 12:1 compression ratio, while the TSX uses traditional port injection and a 11:1 compression. You would expect the IS250 make alot more HP but it doesn't. I think this is largely due to lightweight internals of the Honda Engine and the variable value timing and lift (VTEC) that allows it to rev to a redline of 7100rpm vs a redline of 6600rpm in the IS250. The Honda engine makes peak HP at 7000rpm (201hp @ 7000 rpm) whereas the Lexus makes peak HP at 6400rpm (204hp @ 6,400 rpm).

Interesting stuff 

[Jaeger]

Going back to my 3.6l V6 versus 4.0 V8 example - do others expect that they will be as close in power as their displacements suggest, or do you expect more from the V8?  Assume for the sake of argument that both are situated in premium sport / luxury sedans.

Yes, I know someone can dig up examples of close outputs and someone else can dig up more disparate examples - but my queswtion is geared toward your expectations.  Does the increased cylider count of the V8 mean you expect more from it than the V6?

Jaeger

[Sir Osis of Liver]

The first comparison that came to mind:

Porsche GT3 RS

3.8L H6 409hp@7600, 299ft-lb@5500

BMW M3

4.0L V8 414hp@8300, 300ft-lb@3900

These days, I really don't expect more cylinders to equate to more power, just different power delivery.

Back when Mazda had the 140hp 1.8l V6 in the MX-3, it was criticized for the absence of torque compared to the 240SX, which had about the same peak power, but better torque numbers.

[Jaeger]

^^^ Fair enough.

Jaeger

[Mitlov]

Going back to my 3.6l V6 versus 4.0 V8 example - do others expect that they will be as close in power as their displacements suggest, or do you expect more from the V8?  Assume for the sake of argument that both are situated in premium sport / luxury sedans.

Yes, I know someone can dig up examples of close outputs and someone else can dig up more disparate examples - but my queswtion is geared toward your expectations.  Does the increased cylider count of the V8 mean you expect more from it than the V6?

Jaeger

I wouldn't make an assumption either way until I had more information about each car.  For all I know we're comparing a 306-horsepower CTS DI and a 252-horsepower Lincoln LS V8 (okay, the Lincoln is 3.9L, not 4.0L, but you get the point).

But I'm not your typical consumer.  My mother is.  She believes that the number of cylinders is directly proportional to the amount of power, and doubling the cylinder count doubles fuel consumption (I'm not joking on that last one).  When buying an Outback, I told her to test-drive the H4, because it had the same horsepower as the Camry V6 she was selling.  She looked at me like I told her that I had eight arms; I don't think she ever believed me.  She never even test-drove the H4.  She bought an H6, and ever since, has complained that it has more power than she would ever want and isn't as fuel-efficient as she would like.

The thing is, given that we know that my mother's analysis of the importance of cylinder count is completely bogus, should we nevertheless use it to criticize a five-cylinder for not offering more power than a similar-priced, similar-discplacement four-cylinder?  I don't think we should.   As a car forum, we should seek to dispel erroneous analyses like that, not perpetuate them because that's what an ill-informed consumer would expect.