inline 6 vs V6

On this forum when other cars are compared to 3-series, I see frequent comments that the inline 6 is superior to a V6, in more ways than one. Is there some inherent advantage in the configuration? Or is it just the long experience and engineering that has gone into the BMW engine? Car manufacturers with V6's certainly aren't reticent about promoting them.

down side of str8 6(inline6).. lack of cooling of rear cylinders

Upside: Typically more efficient and smoother. Efficient because of less frictional losses (more valve gears and camshafts for an equivalent V6) and the V6 has twin cylinder banks, which = more heat loss. More heat loss = power loss.
Smoother because the inline-6 is inherently balanced (vertical and transverse forces generated from individual cylinders are completely canceled out by the other cylinders). Not so with the V6.

Downside: Space. They're loooong. Thus damn difficult (don't know if anyone's ever done it) to package with a front-drive, for example. This also makes for a large engine bay (long hood).

The I6 is referred to as Newton's engine.. I think a reference to it's smoothness and balance
What Galahad said is spot on..

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.

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 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

Everyone forgot the most obvious advantage of the inline 6 configuration: The sound!

Another couple of advantages to the I6 are
1) The straight-6 is smoother than engines with a fewer number of cylinders because the power strokes of pistons partially overlap. Since each power stroke lasts 180 degrees of crankshaft rotation, while a new piston starts its power stroke every 120 degrees, there are 60 degrees of overlap on each stroke in which one piston is finishing while the next is starting. (plagiarism alert - I copied the above from wikipedia)
2) Aforementioned minimized frictional/power-sapping losses from two valvetrains,
3) Balance advantages from all cylinders moving in the same plane

Good article here http://en.wikipedia.org/wiki/Straight-6

I believe another reason BMW has finally gone the route of forced induction is that you can bring to market a vehicle that will have the fuel efficiency of the NA vehicle while still delivering the power needed to be competitive (seemingly 300+ hp now). With good turbo/ecm management the engine can receive minimal boost in 'normal' driving, saving fuel.

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

Fuel efficiency is another motivator for going turbo. The enviro-f@#$sts in Germany is increasingly clamoring for speed limits on ALL of the autobahn

All things being equal, it's much more expensive to bring to market a high-revving engine (S54B32). The engineering, development, manufacturing, and warranty costs all go up at a much faster rate than does the horsepower. Also, on high-revving engines like these, the peak horsepower and torque comes fairly high in the rpm range of the vehicle. So while BMW certainly can development high horsepower normally-aspirated I6's, it seems the route going forward will be forced induction which they are quite good at too, see the 1986 Formula One engines they developed 1.5 liter, 4-cyl, 5.5 bar turbos making >1300bhp.

Originally Posted by brashman

I believe another reason BMW has finally gone the route of forced induction is that you can bring to market a vehicle that will have the fuel efficiency of the NA vehicle while still delivering the power needed to be competitive (seemingly 300+ hp now). With good turbo/ecm management the engine can receive minimal boost in 'normal' driving, saving fuel.

Plus for me - having just driven a few M3s - the thing I love about my 335 is that if you want to blast around you can.. but if I am in the mood to cruise around quietly .. the 335 if not in your face like M3's can be. Of course there is a attaction to the M3's in your face at any speed.. but I have gotten to old to want that all the time.

I believe dual personality ability is because of the turbo, ... Gas milage? ...on a freeway stretch I can see 32 mpg on the computer just show you how little the engine has to work to do 75mph.

craig

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.

Or you can have more space to add turbos alongside the 3.0-3.2L engine, boosting it's power back up to or beyond the 3.5-3.7L, as the V6 is particularly fat compared with the I6 - you know, long and athletic I6 vs short & stumpy V6

some great descriptions

http://www.autozine.org/technical_sc...ne/smooth1.htm
http://www.autozine.org/technical_sc..._packaging.htm

Originally Posted by galahad05

Downside: Space. They're loooong. Thus damn difficult (don't know if anyone's ever done it) to package with a front-drive, for example. This also makes for a large engine bay (long hood).

Mercedes-Benz dropped their inline-6, and so did Lexus, in the interest of space (packaging under the hood).

Volvo shoehorns an inline-6 transversely under their hoods. In fact, the V8 in my XC90 sits transversely as well (see pic below)! Volvo is nuts, but they claim it adds "crush space" in an accident.

(37,000 miles on the Volvo engine. Yes, I keep my engines clean - that shot was taken on Sunday.)

I think the tradition behind the inline engines is the best part about them besides the sound they make.

Originally Posted by Emission

Mercedes-Benz dropped their inline-6, and so did Lexus, in the interest of space (packaging under the hood).

Volvo shoehorns an inline-6 transversely under their hoods. In fact, the V8 in my XC90 sits transversely as well (see pic below)! Volvo is nuts, but they claim it adds "crush space" in an accident.

(37,000 miles on the Volvo engine. Yes, I keep my engines clean - that shot was taken on Sunday.)

I swore Volvo cars (not the SUVs) had inline 5 cylinder engines. 5 cylinder mixtures of noramlly aspirated and higher performance turbo engines.

Originally Posted by Emission

Mercedes-Benz dropped their inline-6, and so did Lexus, in the interest of space (packaging under the hood).

Volvo shoehorns an inline-6 transversely under their hoods. In fact, the V8 in my XC90 sits transversely as well (see pic below)! Volvo is nuts, but they claim it adds "crush space" in an accident.

(37,000 miles on the Volvo engine. Yes, I keep my engines clean - that shot was taken on Sunday.)

did they do that so that they can get their 4matic to jive?

I6's are magical. I suppose part of that is how I like long hood lines and the roar of an I6. Too many V6 engines sound like coffee grinders.

There is a 3.8L I6 sitting in a jumble of parts pretending to be a Jaguar E-type in my garage. Rumor has it the real output was around 220 HP so considering a 3.0L e90 is supposed to make 255 HP that is quite an advance.

Originally Posted by chemgeek

I swore Volvo cars (not the SUVs) had inline 5 cylinder engines. 5 cylinder mixtures of noramlly aspirated and higher performance turbo engines.

Oh, they do. They still use lots of inline-5's, but they also have used inline-6's in the past (with and without turbochargers) in their sedans and SUV's. Note: Volvo just came out with another six-cylinder last year... a 3.2-liter V6.

Originally Posted by brashman

Another couple of advantages to the I6 are
1) The straight-6 is smoother than engines with a fewer number of cylinders because the power strokes of pistons partially overlap. Since each power stroke lasts 180 degrees of crankshaft rotation, while a new piston starts its power stroke every 120 degrees, there are 60 degrees of overlap on each stroke in which one piston is finishing while the next is starting. (plagiarism alert - I copied the above from wikipedia)
.

The overlap creates more torque

Short block v8s are great 1/4 mile engines, they rev fast

long block v8s are more for the track, they have power all through the band, they are forgiving of mistakes, this is the "feel" that most drivers want.

They are the "blue pill" types

Originally Posted by HW

did they do that so that they can get their 4matic to jive?

According to Wikipedia:

The first design of 4Matic (or 4Matic) system was introduced in 1986 on the W124 series (E Class) saloons (four door) and estate (station wagon) cars. It was available with the 2.6 L and 3.0 L 6 cylinder petrol (gasoline) and diesel engines.

Their inline-6 was a 3.0-liter (I think), so that would be the engine noted above. It is hard to package an inline-6, so many manufacturers just drop them these days.

Originally Posted by lao270

The overlap creates more torque

Short block v8s are great 1/4 mile engines, they rev fast

long block v8s are more for the track, they have power all through the band, they are forgiving of mistakes, this is the "feel" that most drivers want.

you mean oval tracks with only left hand turns?

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)...

I don't remember it being a model of newtonian goodness, although it was an awesome engine for around town driving

Joe

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)...

I don't remember it being a model of newtonian goodness, although it was an awesome engine for around town driving

Joe

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

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

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.