inline 6 vs V6

Originally Posted by jsc

So the BMW engine is more efficient at the torque peak

Agreed.

and should have a specific power curve that rises above the Porsche curve except at the highest RPMs, hence it is likely to have a better specific torque distribution under the curve than the Porsche.

Better efficiency at peak rpms doesn't mean higher torque/power at the same rpms. Extra 354cc should give GT3 an edge.

Originally Posted by void.crusader

Agreed.



Better efficiency at peak rpms doesn't mean higher torque/power at the same rpms. Extra 354cc should give GT3 an edge.

Of course, that's not what I said - "specific torque" and "specific power" are normalised values relative to the engine displacement. The BMW engine makes better specific power and specific torque at it's torque peak than the Porsche engine (hence is more efficient there). The Porsche engine has a larger capacity, so makes slightly better absolute values.

Measuring output efficiency at the power peak is less meaningful due to the much more rapid rate of change of the power curve at that point compared with the more linear rate of change near the torque peak. An engine that is peaky in it's power output (i.e. makes its maximum torque close to it's maximum power) will have a better efficiency at the power peak compared with an engine that has more torque lower down the rev range, in reality the torquey engine will perform much better (and have better output efficiency) than it's peak power rating would suggest, due to a much better spread of power across the rev range.

Bottom line, both engines are similar in efficiency to each other, one above at one point the other above at another, no great difference due to engineering.

Originally Posted by Kzang

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

One point that no one has mentioned as a disadvantage for an inline 6 is that because is a long engine you need to make a beefier (and heavier) block to reduce longitudinal bending. This weight disadvantage is somewhat offset by the fact that you only need one VANOS and other ancillary valvetrain equipment. This is one of the reasons for no inline 8's (other than packaging). That's also why BMW put so much effort on their magnesium-aluminum block.

Originally Posted by s2pidyeah

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

As BMW seems to realize now with the N54...

Originally Posted by galahad05

and the V6 has twin cylinder banks, which = more heat loss. More heat loss = power loss.

Disagree - in normal operation the problem is getting rid of the heat, not keeping it in. That's why all engines have a cooling system.

You cannot really say which engine is better at dissipating heat - since that greatly depends on the configuration of the engine compartment and location of the engine. A short V6 may not get under the bulkhead like an I6, so cooling is probably more even across the cylinders. But because it is wider, it's possible that not enough air circulates around the sides to cool it.

Originally Posted by jsc

The BMW engine makes better specific power and specific torque at it's torque peak than the Porsche engine (hence is more efficient there). The Porsche engine has a larger capacity, so makes slightly better absolute values.

Higher rpm -> more friction/heat losses -> less efficiency.

CSL hp/rpm*l = 360/(7900*3.246) = 0.01404
GT3 hp/rpm*l = 415/(7600*3.600) = 0.01517

1. GT3 is 8% more efficient when it's rpm 3.8% lower than CSL.

CSL bhp at torque peak (273lb/ft @ 4900) = 273*(4900/5252) = 254.7bhp
therefore hp/rpm*l = 254.7/(4900*3.246) = 0.01601

GT3 bhp at torque peak (298lb/ft @ 5500) = 298*(5500/5252) = 312.1bhp
therefore hp/rpm*l = 312.1/(5500*3.600) = 0.01576

2. CSL is 1.6% more efficient when it's rpm 10.9% lower than GT3.

Putting 1. and 2. together, I think that GT3 is more efficient at any given rpm.

Bottom line, both engines are similar in efficiency to each other, one above at one point the other above at another, no great difference due to engineering.

They are both good, of course. Too bad that CSL was limited run model and they don't make it anymore.

Originally Posted by void.crusader

Too bad that CSL was limited run model and they don't make it anymore.

BMW brings out the CSL model about half way through the series run as a limited edition (about 1400 E46 CSLs built in 2003), so the E92 version is due about 2010.

Originally Posted by void.crusader

Higher rpm -> more friction/heat losses -> less efficiency.

Friction is one of the variables in efficiency, there are many others such as thermodynamic heat-pump efficiency, combustion efficiency, air-flow capability, valve overlap, etc.

Originally Posted by void.crusader

I think that GT3 is more efficient at any given rpm.

Here are a couple of dyno charts I managed to dig up:
http://www.dragtimes.com/images_dyno...MW-M3-Dyno.jpg
http://www.dragtimes.com/2007-Porsch...phs-11151.html

Couldn't find a CSL one, but the CSL 3.2 litre engine is just a slightly freer breathing version of the Euro S54 engine with 360bhp instead of 343bhp, so the power and torque curves should be almost identical, with the 360bhp engine getting it's last breath in a more linear fashion up to the peak power point at 7900RPM. The GT3 dyno chart seems to be for a slightly tuned GT3 (didn't indicate stock in the listing), but again, the power curve should have the same shape. As you can see the max torque is achieved at the correct specified points for both vehicles.

What I have done is transposed the torque and power curve shapes from these dyno charts on to a normalised graph of power and torque (normalised to specific outputs to eliminate engine size, aligned to the correct peak values for torque and power):



You can see the CSL Vanos inflexion in the power curve starting at 3000RPM and likewise the GT3 variable valve timing inflexion starting at 4000RPM. What this lower change point means is that the CSL engine is tuned to produce more torque lower down and is correspondingly more efficient there. Both engines are at their most efficient at ther torque peaks, as shown in this diagram:



So, overall they are both similar in efficiency, with the CSL better below 5400RPM, the GT3 above 5400RPM

Originally Posted by adc

Disagree - in normal operation the problem is getting rid of the heat, not keeping it in. That's why all engines have a cooling system.

You misunderstand.

Go ask a racing engine builder, which makes more power, an engine with Iron cylinder heads or one with physically identical Aluminum cylinder heads. They'll tell you the iron ones, hands down.

Why? Because one way to look at an engine is as just a giant heat pump. And it gets more efficient at higher combustion chamber temperatures. The higher the combustion chamber temperatures from the power stroke, the more torque (thus power) is being generated. The iron heads retain more heat, and can tolerate more heat, than the aluminum ones. On 5 liter racing V8s, this was usually good for another 15-20 HP, everything else equal.

The ideal: run as hot as physically possible without causing anything to melt/preignition/detonation. Thus--you need a good cooling system to keep the rest of the engine cool, and to keep the combustion chamber cool, when it's not doing work during the power stroke.
If you had uber-efficient cooling around the heads, it would rob power during the power stroke, cooling the extremely hot expanding gases during that stroke more than otherwise. Cooling an expanding gas cloud means you rob it of energy. More surface area around the combustion chamber means you have a more efficient radiator, right at the critical junction.


Side-note: An old-school racing engine-builder's trick was to take a standard quality cylinder head and fill (some of) the water passages around the combustion chamber with high-temp silica, to block them off. To keep the combustion chamber hotter.

Several comments on this thread have referred to the fact that a straight six is generally smoother running than a V 6. When we did a ED on a 335i last May the tech at the delivery center balanced a euro coin on edge on the running engine. A Euro is about the size of a quarter with just slightly more edge. Pretty impressive for a motor that generates 300HP!

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.

That comment has absolutely no technical ground. If that were the case Ferrari wouldn't have V12 engines (basically two inline sixes bolted together) mounted in the front with over 100HP per liter. The reason why BMW shifted to inline turbo fours like in the 328i is because of emissions regulations, not because they chose. A turbo engine of smaller capacity can have the same HP than a larger non-turbo engine, but the turbo engine will always be more torquey in comparison. The problem is that with the turbo engine you will not have the immediate response as with a non-turbo engine, simply because you have to wait for the exhaust gases to work. There might be the best turbo engine, but the character and behaviour of the engine will always be different. And with rivals Mercedes and Audi going in that directions they didn't have much option other than to succumb to market pressures.

Originally Posted by 235i

That comment has absolutely no technical ground. If that were the case Ferrari wouldn't have V12 engines (basically two inline sixes bolted together) mounted in the front with over 100HP per liter. The reason why BMW shifted to inline turbo fours like in the 328i is because of emissions regulations, not because they chose. A turbo engine of smaller capacity can have the same HP than a larger non-turbo engine, but the turbo engine will always be more torquey in comparison. The problem is that with the turbo engine you will not have the immediate response as with a non-turbo engine, simply because you have to wait for the exhaust gases to work. There might be the best turbo engine, but the character and behaviour of the engine will always be different. And with rivals Mercedes and Audi going in that directions they didn't have much option other than to succumb to market pressures.

Do you know that this thread is four years old, and that your comment is to a poster who hasn't been on Bimmerfest for 3 years, 51 weeks?

Originally Posted by DSXMachina

Do you know that this thread is four years old, and that your comment is to a poster who hasn't been on Bimmerfest for 3 years, 51 weeks?

Except he was wrong that going with the turbo 4 is to meet the emission regulations.

Originally Posted by dsxmachina

do you know that this thread is four years old, and that your comment is to a poster who hasn't been on bimmerfest for 3 years, 51 weeks?

lol

Originally Posted by thekurgan

lol

.

well the inline 6's are superior. The design allows for a differ end stoke as well as a different firing pattern and crank distribution. They put inline 6's into semis for a reason, and that is because the longer stroke allows for a much more torque driven engine. That is why upgraded 335i's tend to produce so much more torque than horsepower. There's nothing wrong with v6's and companies can promote them because very little of the population knows little or nothing about engines, and how the horsepower is actually made (in term of bore and stroke) so it sounds good if its irrelevant to you.

Sent from my WX435 using Bimmer App

Originally Posted by DSXMachina

.

:

Originally Posted by 235i

That comment has absolutely no technical ground. If that were the case Ferrari wouldn't have V12 engines (basically two inline sixes bolted together) mounted in the front with over 100HP per liter. The reason why BMW shifted to inline turbo fours like in the 328i is because of emissions regulations, not because they chose. A turbo engine of smaller capacity can have the same HP than a larger non-turbo engine, but the turbo engine will always be more torquey in comparison. The problem is that with the turbo engine you will not have the immediate response as with a non-turbo engine, simply because you have to wait for the exhaust gases to work. There might be the best turbo engine, but the character and behaviour of the engine will always be different. And with rivals Mercedes and Audi going in that directions they didn't have much option other than to succumb to market pressures.

Nope. That had everything to do with ever increasing fuel economy standards, and geopolitical nonsense in more than a few countries outside of the U.S. involving taxing the crap out of any and all engines over 2.0L. A 2.0L Inline-6 really doesn't make any sense these days, hence a 2.0L turbo engine.

Originally Posted by rubberismoney

well the inline 6's are superior. The design allows for a differ end stoke as well as a different firing pattern and crank distribution. They put inline 6's into semis for a reason, and that is because the longer stroke allows for a much more torque driven engine. That is why upgraded 335i's tend to produce so much more torque than horsepower. There's nothing wrong with v6's and companies can promote them because very little of the population knows little or nothing about engines, and how the horsepower is actually made (in term of bore and stroke) so it sounds good if its irrelevant to you.

Nope! That has nothing to do with stroke and everything to do with turbo design. It's easy to get a lot more torque out of turbos because usually there's headroom there. But getting a ton of top end is typically a lot more difficult with the smaller quick spooling turbos because they start spinning so quickly that they just start blowing a ton of hot air to the point that you can't really make anymore power. Want more top-end horsepower? That's what a larger turbo is for. This is why all the guys with MkIV Supras always switched a bigger single turbo rather than the stock twin sequential setup.

You guys...

Originally Posted by 235i

The reason why BMW shifted to inline turbo fours like in the 328i is because of emissions regulations, not because they chose.

that 's the blablah I heard from the sales man as well. If you have an CO2 / HP equation, that is *not true*.

Camry V6 268HP 3.5 355g/mile ----> 1.32 [not even direct injection]
328i manual 240HP 329g/mile ---> 1.37
C350 306HP 386g/mile ---> 1.26

The 4-cyl. turbo is bettered by both V6 above in term of emissions / output.

BMW had the choice. However, the decision to go with 4-cyl. turbo is a stupid Euro fashion, aimed to not hurt public acceptance. It looks more efficient, compared to most efficient 6-cyl., however the N20 doesn't have a case objectively.

As for the I6 vs V6, I don't care about inline layout anymore. Mercedes had a great success going the V6 route and I can say that I prefer a C300 engine to a 328i N52 engine. A direct injection V6 from BMW would be just fine with me.

Nope! That has nothing to do with stroke and everything to do with turbo design. It's easy to get a lot more torque out of turbos because usually there's headroom there. But getting a ton of top end is typically a lot more difficult with the smaller quick spooling turbos because they start spinning so quickly that they just start blowing a ton of hot air to the point that you can't really make anymore power. Want more top-end horsepower? That's what a larger turbo is for. This is why all the guys with MkIV Supras always switched a bigger single turbo rather than the stock twin sequential setup.

You guys...

As this last man said, it does have a lot to do with turbos, but if you have a V6 and a l6 with similar specs which both are normally aspirated a l6 will produce more power with a less compression ratio

Here's a Car&Driver article that sheds light on the subject, entitled: "The physics of the V angle"

http://www.caranddriver.com/features...re?redirect=no

Originally Posted by Saintor

that 's the blablah I heard from the sales man as well. If you have an CO2 / HP equation, that is *not true*.

Camry V6 268HP 3.5 355g/mile ----> 1.32 [not even direct injection]
328i manual 240HP 329g/mile ---> 1.37
C350 306HP 386g/mile ---> 1.26

The 4-cyl. turbo is bettered by both V6 above in term of emissions / output.

BMW had the choice. However, the decision to go with 4-cyl. turbo is a stupid Euro fashion, aimed to not hurt public acceptance. It looks more efficient, compared to most efficient 6-cyl., however the N20 doesn't have a case objectively.

As for the I6 vs V6, I don't care about inline layout anymore. Mercedes had a great success going the V6 route and I can say that I prefer a C300 engine to a 328i N52 engine. A direct injection V6 from BMW would be just fine with me.

You may not care, but there are a lot of the BMW faithful who care A LOT. BMW will never put a V6 in their cars, because they know and appreciate the superiority of the inline six.

Originally Posted by tturedraider

You may not care, but there are a lot of the BMW faithful who care A LOT. BMW will never put a V6 in their cars, because they know and appreciate the superiority of the inline six.

Never say 'never' when profits drive engineering and design.

"Porsche will never sell an SUV." (Heard back in 1999 when the first X5 was introduced.)

"BMW will never make the M3 with an automatic transmission." (Heard back when the E30 M3 arrived.)

It would be rather easy for BMW to slice a few cylinders off the 4.4-liter V8 and create a compact and lightweight turbocharged 3.3-liter V6... making about 350 horsepower...

- Mike

Originally Posted by Emission

It would be rather easy for BMW to slice a few cylinders off the 4.4-liter V8 and create a compact and lightweight turbocharged 3.3-liter V6... making about 350 horsepower...

- Mike

Increase the bore a smidgen and say hello to the next 335i

Originally Posted by rtgirard

Increase the bore a smidgen and say hello to the next 335i

It's not possible to increase the bore on these engines. You have to increase the stroke to increase displacement.

Originally Posted by floydarogers

It's not possible to increase the bore on these engines. You have to increase the stroke to increase displacement.

Gotcha. I knew the N52/54 were really tight, but i didn't know about the V8/10.

Originally Posted by rubberismoney

As this last man said, it does have a lot to do with turbos, but if you have a V6 and a l6 with similar specs which both are normally aspirated a l6 will produce more power with a less compression ratio

Could you please provide a good solid technical explanation as to why this is? I've yet to see one that was convincing.

GM currently has a 3.0L DOHC 60* V6 with Dual-VVT cam-phasing and direct injection and 11.7:1 compression and regular fuel is making 270hp/223tq SAE certified.

Look up engine code LFW: http://www.gmpowertrain.com/VehicleE...nProducts.aspx

This is practically the same as the Euro-spec full-tilt direct-injected N53 3.0L making 272hp and 228 lb-ft torque on a higher grade of gas. The biggest limitation here is finding engines that are truly comparable.

There Inline-6 does have the advantages of lower overall friction due to only driving two cams vs four, and having a short localized timing chain run vs a V-6 where it's going all over the place, but these are very small differences. In the grand scheme of things, I think other things matter a lot more having nothing to do with engine configuration. Such as specific cam profile selected, variable timing setup and strategy, head, port, intake manifold and exhaust system design, etc. The goal isn't always to give the maximum possible power at at very high RPM (like Hondas) but rather a good overall balance of power and a good powerband with accessible torque at low to medium engine speeds.

I love the Inline-6 and would always love to have one for its sound and feel and character. It really is something special, but I'd hardly argue that one is superior to the other. The V-6 does have a lot of advantages. Much more flexible in terms of layout. Can be mounted either transversely or longitudinally, and it's far more flexible in displacement ranges. Modern V-6 engine designs like from GM and Toyota and Nissan can span 2.5 to 4.0L in displacement. The Inline-6 due to the very long nature cannot have very large bore spacings or else it won't fit into smaller cars, so it's very bore limited and ends up needing longer strokes. You can't simply "punch out" most Inline-6 engines to 3.5L or 4.0L like you can with many V-6 engines. This is why pretty much everybody else except BMW (and Volvo) produces V-6 engines instead. V-6's clearly win in the marketplace and few people care, but I do. Nothing can match the sound and feel and character and refinement of the I-6. I've had lots of V-6's but the N55 in my 335i is the best 6-cylinder engine I've ever owned. It's tough to sell refinement to people, though. I hope BMW never makes a V-6 because the I-6 really is something special.