inline 6 vs V6

Originally Posted by void.crusader

Downside: space.
Means you can, say, pack 3.0-3.2L inline-6 into the bay and get 255-270hp from it.
Or you can pack 3.5-3.7L V6 into the same bay and get 300-330hp.
That's with all other things being equal - N/A and civil redline on both.

BMW was a long-time advocate of N/A engines. And for a good reasons. But when V6 competition pushed the HP envelope, BMW was forced to go turbo route. Sad.

I'd much rather have a turbocharged I-6 than a coarse large V-6. The BMW N54 is a much nicer engine than Infiniti's 3.7 liter.

Thanks, Mike.

I don't see BMW offering a larger version of their inline-6 in the future. It makes 300+ horses without drama, and it can easily be bumped to 350 hp without too much concern. At that point, there are several V8's than can pick it where the six leaves off...

Originally Posted by Emission

I don't see BMW offering a larger version of their inline-6 in the future. It makes 300+ horses without drama, and it can easily be bumped to 350 hp without too much concern. At that point, there are several V8's than can pick it where the six leaves off...

didn't BMW say that they were hitting the max displacement/cylinder?

Originally Posted by HW

didn't BMW say that they were hitting the max displacement/cylinder?

They have offered larger inline-6's in the past (3.5's come to mind), but I don't think they will go down that path again. I think 3.0 is the tops now.

This is interesting (from Wikipedia, again):

BMW introduced its first straight 6-cylinder engine in 1933. It developed its I6 engines of the post-World War II era by adding two cylinders to its four cylinder design. In 1968 it introduced a straight-6 design that had the same 30 degree slant, overhead camshaft layout, and 100 mm bore spacing as the four. It originally intended to follow up with a V8 engine line in the early 1970s, but when the 1973 oil crisis hit, BMW canceled its V8 plans and concentrated on refining and enlarging its straight-6 lineup.[9] These included a smaller straight-6 in 2.0 L and 2.3 L displacements (the "small six"), versions of the larger "big six" (as it became known) up to 3.5 L, and beginning in 1983 a series of straight-6 diesels. In 1986 BMW introduced a V12 which was essentially two 2.5 L straight-6s on the same crankshaft. Nowadays, a straight-six is used in the BMW 1 Series and BMW 3 Series.

Mercedes-Benz has used straight-6 engines in its cars for around 100 years, starting in the 1900s with a monstrous 10 L engine producing 75 horsepower (56 kW). Before and after the merger of Daimler and Benz in 1926, the combined company produced a variety of powerful straight-6 engines, culminating in a 7 L supercharged unit producing up to 300 hp (224 kW). Mercedes-Benz began the post-war era by producing straight-4s, but resumed making straight-6s in 1951 with 2.2 L and 3.0 L engines, which were the beginning of the modern era of MB straight-6s. Following that introduction, the company produced two lines of gasoline (petrol) straight-6s at any one time, a small six and a larger six, in addition to its straight-4s, straight-5s, and later V8s. Although the company has used diesel engines in its cars since 1934, it introduced its first straight-6 3.0 L diesel in 1985. In 1996 the company replaced its gasoline straight-6s with a series of 90 degree V6 engines, although it continued to produce diesel straight-6s.

Volvo produced straight-6 engines like the Volvo B30 engine for the Volvo 164 (1969-1975) and the B6304 engine for the 960/S90 (RWD). All vehicles in the Volvo lineup are front-wheel (or all wheel) driven thereafter, and yet, Volvo made it possible to mount their inline-6 engine transversely by using a very short transaxle package and relocated engine-driven accessories. In 2006, Volvo announced a new 3.2 L straight-6 for the Volvo S80 that was only slightly longer than its straight-5, achieved by moving the camshaft drive to the back of the engine and sharing the same gear train with ancillaries mounted in otherwise unused space over top of the transmission. This was not only short for a straight-6, but also very narrow. Volvo says a transversely mounted inline engine leaves more crush space to protect against frontal impacts than a (shorter) transverse V6 or a longitudinally mounted inline-6.[10]

Opel has also used a straight-6 engine since 1930s until the early 1990s, ranging between 2.5 and 4.0 L (153–242 cu in). They powered Opel's top of the line models, including the Admiral, Kapitän, Monza,the Senator, the Omega and the Commodore.

In 1959, Saab had an experimental car with two transverse straight-3 engines bolted together — the Saab Monster.

Alfa Romeo used straight-6 engine in G1 and G2 models (1921-1923), RL model (1922–1927) and between 1925–1954 in Alfa Romeo 6C series road and racing cars, the 1500 version had one of the smallest straight-6 engines (1487 cc). The last Alfa Romeo model using straight-6 was Alfa Romeo 2600 (1961–1969).

Originally Posted by JoeFromPA

Just a note: Several american companies have made inline six cylinders (I'm embarassed to admit but I BELIEVE my 97 Jeep Wrangler Sahara 4.0 was an inline six)...

Yep, the 4.0 engine in your Jeep was a straight 6, based on older AMC engine designs. (You may be even more ashamed to admit it evolved from the same engine used in the AMC Gremlin!)

It was decent for around-town driving and even better for off-roading because it had good low-end torque. It was a super reliable design, too.

Originally Posted by redadair

I think you forgot the M3 3.2L at 333HP and the 2003 M3 CSL at 360HP from 3.2L BMW can also make big HP without Turbos. It's just cheaper to do with Turbos. They save the big power naturally aspirated engines for the M's.

Red

I didn't forgot. I said "with all other things being equal - N/A and civil redline on both".

8000 is hardly civil and we all know that S54 has more problems than BMW engine should have.

Originally Posted by Emission

Yes, AMC/Jeep used the same basic inline-6 from 1964 to 2006!

http://en.wikipedia.org/wiki/AMC_Straight-6_engine

It's too bad they swapped it out for that 3.7L minivan engine after all those years... (the 4.0 is kinda the core of a Jeep, right? ).

Don't forget the Chrysler slant-6 engine. My family had two Darts when I was growing up. I later had a Duster. All three had the 225 slant-6 and all went well past 100k. One Dart we sold at 190k. Very reliable and a very easy engine to work on.

Out of curiosty, Why doesn't BMW make inline 8s for their 550i, M5, 6s, 7s?

Would it just be too long and no room?

I believe BMW is getting 272hp from their latest iteration of the N-series engine (N53B30 available in EU). While 300hp would still be a significant, 10%, increase, it goes to show you how much experience/know-how they have with the 3.0l I6.

What it really makes me wish for is a 335/330 lineup with the the 335 boosted to a (apparently) feasible 340hp and a 272hp 330. Or maybe a 335/330/325 lineup? I know the additional models would add complexity costs, but hey, I'm a consumer and I like options...

Originally Posted by Bcube

Another area that BMW has used to their advantage is placement of the engine to optimize handling. If one is already "stuck" with a long hood and rear wheel drive style, then why not push the front wheels all the to front, move the bulk of the engine behind the front axle centerline, thus promoting mass centralization. And keeping the 50/50 handling that BMW markets.

The Japanese have mostly stayed with the V-6 due to their extensive experience in packaging that engine configuration in front wheel drive platforms.

That is exactly right, the length of the e4ngine allows is to aid in the 50/50 distribution of the cars. Most automakers packe a V6 in the front, along with front wheel drive and a battery all under the hood making for a completely unbalanced car.

Originally Posted by Bcube

I read an article where BMW considered 3.5L -3.7L for their inline 6 to make the requisite 300+hp NA. But the increased size of the pistons (with the elevated weight) compromised the inherent primary balance which meant counter-weight balancers, etc. Basically leading engineering down the path of over complexity in an originally perfectly balanced concept.

Inline 6 engines do not need counterbalanced cranks. They are inherently balanced, regardless of the size or stroke of the pistons. BMW avoided increased displacement since they either had to increase the bore (and the length of the engine, which is a huge cost and more packaging issues) or increase the stroke (this would drastically lower the redline).

V6 I5, and I4 layouts require separate balance shafts to smooth their inherent vibration.

Cross plane v8s require counterbalanced crankshafts to smooth the engine.

Conventional straight v8s just vibrate a lot, but you'll only find these in Ferraris and race motors. In this case, vibration is a feature.

Iversonm, when you say "straight v8's" are you referring to the 180 degree cranks that folks like Ferrari use? Just curious.

V6 in RWD-based cars are well behind the axle, similar to I6.









FWD-based is another matter of course.

Originally Posted by iversonm

Inline 6 engines do not need counterbalanced cranks. They are inherently balanced, regardless of the size or stroke of the pistons. BMW avoided increased displacement since they either had to increase the bore (and the length of the engine, which is a huge cost and more packaging issues) or increase the stroke (this would drastically lower the redline).

You're right, my bad. I wish I could find that article - it had specific reasons why BMW stayed at 3 liters. Vibration, pistonspeed, etc.

Also to consider is the European tax on displacement over 3.0 L. I doubt BMW will go over this displacement.

When you look at those diagrams, the fact that BMW achieves near 50/50 weight distribution is remarkable.

Also, the front-heavy, dive tendency of the B7 Audi becomes understandable. From all reports however they have fixed this finally for the new B8.

Originally Posted by Bcube

I read an article where BMW considered 3.5L -3.7L for their inline 6 to make the requisite 300+hp NA. But the increased size of the pistons (with the elevated weight) compromised the inherent primary balance which meant counter-weight balancers, etc. Basically leading engineering down the path of over complexity in an originally perfectly balanced concept.

Another area that BMW has used to their advantage is placement of the engine to optimize handling. If one is already "stuck" with a long hood and rear wheel drive style, then why not push the front wheels all the to front, move the bulk of the engine behind the front axle centerline, thus promoting mass centralization. And keeping the 50/50 handling that BMW markets.

The Japanese have mostly stayed with the V-6 due to their extensive experience in packaging that engine configuration in front wheel drive platforms.

+1

BMW says that for them a Maximum Cylinder volume of 500 CC’s is needed to retain the smoothness that all BMW engines have enjoyed over the years. The M3 3.2L pushed this limit somewhat, but you can see that the new V8 M3 = 4000 CC’s Divided by 8 = 500 CC's each. Same reason they went to a V10 to reach 5L.

BMW has been making essentially the same Inline 6 engine since 1936, this is their Heritage engine, it's what all others are measured by as well as all other Auto makers.

This is why BMW has won more International Engine awards than any other Engine maker out there. Funny thing, 2007 was Porsches first.

http://www.ukintpress.com/engineoftheyear/

Red

Originally Posted by Kzang

Out of curiosty, Why doesn't BMW make inline 8s for their 550i, M5, 6s, 7s?

Would it just be too long and no room?

yeah, that is the reason, V-8 allows a more balanced piston firing order than a V-6. The advantage of a straight 6 over a V-6 is the balanced piston firing order that is mentioned in an earlier post. The straight 8 doesn't carry a significant advantage over a v-8 due to 4 pistons per cylinder bank. The V-8 is so much better balanced and compact over a straight 8 that the straight 8 is antiquated. Straight 8s and 10s ad 12s were used on old receprecating aircraft engines.

Originally Posted by void.crusader

I didn't forgot. I said "with all other things being equal - N/A and civil redline on both".

8000 is hardly civil and we all know that S54 has more problems than BMW engine should have.

Do you mean the N54 Engine?

What problems are you referring to? Are these problems engine problems or are they things like fuel pumps and lack of oil coolers. Because I have not heard of any engine problems.

Red

Originally Posted by redadair

Do you mean the N54 Engine?

I mean S54. Sierra-Five-Four at E46 M3. Engine of Damocles. The one you mention in your post with "M3 3.2L at 333HP".

http://www.google.com/search?hl=en&s...re&btnG=Search

This is why BMW has won more International Engine awards than any other Engine maker out there. Funny thing, 2007 was Porsches first.

Awards is good and all, but Porsche certainly know something others aren't.

911 GT3:
3600cc, 409hp @ 7600, 298 lb-ft @ 5500
They didn't rev it that much, didn't force-fed it, didn't even put DI. Still, somehow they got 113.6 HP per liter. Impressive engineering should be involved to get this.

Okay, may be GT3 is a bit over the top, but even lowly Caymans are putting very good HPs per liter without over-revving.

Originally Posted by Kzang

Out of curiosty, Why doesn't BMW make inline 8s for their 550i, M5, 6s, 7s?

Would it just be too long and no room?

it would look like the batmobile

Originally Posted by void.crusader

I mean S54. Sierra-Five-Four at E46 M3. Engine of Damocles. The one you mention in your post with "M3 3.2L at 333HP".

http://www.google.com/search?hl=en&s...re&btnG=Search



Awards is good and all, but Porsche certainly know something others aren't.

911 GT3:
3600cc, 409hp @ 7600, 298 lb-ft @ 5500
They didn't rev it that much, didn't force-fed it, didn't even put DI. Still, somehow they got 113.6 HP per liter. Impressive engineering should be involved to get this.

Okay, may be GT3 is a bit over the top, but even lowly Caymans are putting very good HPs per liter without over-revving.

Well, the cheaper (than a GT3) M3 CSL is close in specific output at 109.4bhp /litre @ 7,900 RPM, but produces 84.1 lb-ft /litre @ 4,900 RPM compared with 82.8 lb-ft /litre for the GT3 at a much loftier 5,500 RPM, so the M3 CSL S54 engine has a beefier torque curve than the GT3 engine for it's capacity, allowing more power to be extracted at a lower RPM (for it's capacity), so requiring it to be revved less.
If you compare the Cayman S with the Z4 M-Coupe (although the lower performing Cayman is the real competitor if comparable price is used), the following engine characteristics for the European models are:

M-Coupe:
104.1 bhp /litre @ 7,900
82.9 lb-ft /litre @ 4,900

Cayman S:
85.9 bhp /litre @ 6.250
74.1 lb-ft /litre @ 4,200-6,000

As power = torque x engine speed (RPM), the BMW will be making more specific power and torque at a given RPM than the Porsche, due to it's fatter torque curve for it's engine capacity.

The inline 6 is inherently smoother than the V-6 - less vibration modes. Years and years ago, my brother in law had a 1953 Buick straight 8. Very smooth running, but physically a monstrosity under the hood. The disadvantage of an inline block is its physical length. I had a Volvo S60R, which had all wheel drive and a transverse inline 5 engine. The shortcoming of that design was that, with the long engine and oversized wheels and brakes, there was so much stuff between the wheels that the turning circle was severely compromised. 5 and 6 cylnder inline engines create bad packaging problems if mounted transversely, but as we know, BMW 6's run fore and aft.
If you look under the E90 hood, the front axle is roughly in between cylinders 3 and 4. Th engine is far enough back that the car avoids being front heavy, at the expense of a slightly long hood. I also have a Honda S2000. In that car, the inline 4 is completely behind the front axle, which gives almost perfect 50/50 front to rear weight balance, but the hood is incredibly long for an otherwise tiny car. The E90 ends up with a weight balance around 51/49, which ain't that bad.

Originally Posted by void.crusader

V6 in RWD-based cars are well behind the axle, similar to I6.









FWD-based is another matter of course.

Those are very decieving actually.