[GoingTooFast]

Originally Posted by bradleyland

The CLA AMG is a full-blown AMG. It should be priced higher, just like the M2 will be. I don't prefer the CLA. It's a fine car, but I think some of its proportions are ungainly, and the character of the engine isn't to my tastes.

So, in your opinion the N20 engine's character is better than the AMG turbocharged inline-4 as I seem to recall that you drive a N20 engined vehicle, am I right?

Originally Posted by bradleyland

I think most enthusiasts would have loved for the M3/M4 to stick with a V8, or at least a naturally aspirated I6. Just look at all the people who continue to cry out for a high-revving, N/A engine in cars like the M2, despite repeated clarifications from BMW that N/A engines are a thing of the past.

Turbocharging is necessary in order to meet fuel economy requirements. No matter what you do, a turbocharged engine cannot match the throttle response of a naturally aspirated engine.

Precisely my point... the use of a turbocharged inline-6 engine is pure marketing because it doesn't present any meaningful technical advantage over smaller, lighter, equally powerful, more fuel-efficient modern-days turbocharged inline-4.

Originally Posted by bradleyland

In order for the turbine portion of a turbocharger to operate efficiently, you need a smooth series of exhaust impulses. Generally, you want 3 or more cylinders feeding a single spool. Any less than that and efficiency falls at low RPM.

This means the yield in improvement of throttle response for an I4 is not optimal when you add a second turbo. I'm not saying it's never done, and I'm not saying BMW won't do it, but I would expect them to stick with the current twin scroll design, rather than to move to a twin turbo system on the N20/S20.

The twin-scroll concept was first introduced with inline-4 engines precisely to mimic the use of two turbos by taking advantage of the separated exhaust flow plumbing from two cylinder pairs in order to maximize the 180º apart (for one combustion cycle) exhaust gas pulses energy recovery with a single turbine.

You can enhance this effect by using two effectively separated low innertia turbochargers instead of just a bigger one in order to reduce the turbo lag even further.

[bradleyland]

Originally Posted by GoingTooFast

So, in your opinion the N20 engine's character is better than the AMG turbocharged inline-4 as I seem to recall that you drive a N20 engined vehicle, am I right?

The character of these two engines is difficult to compare. The N20 is a relatively low-boost engine at 16-18 psi. The M133 (the CLA45 AMG powerplant) breaths at 26 psi. The M133 delivers much more punch than the N20 in it's standard trim, but to do so, it trades throttle response.

From a pure character (throttle response/driving feel) perspective, I would say yes, I think the N20 is better. From a performance standpoint, it's a no-brainer. The M133 is a runaway winner.

Originally Posted by GoingTooFast

Precisely my point... the use of a turbocharged inline-6 engine is pure marketing because it doesn't present any meaningful technical advantage over smaller, lighter, equally powerful, more fuel-efficient modern-days turbocharged inline-4.

You have to stop doing this. Seriously. I like having a spirited discussion, but it's really obnoxious to have you constantly mischaracterizing what I say. You're clearly not listening. You're just scrutinizing my words, trying to twist them around to your viewpoint. Stop it, or I'm taking my ball and going home. Make your own points; don't take what I say and try to twist it around to your viewpoint. It's sophomoric and annoying to constantly have to correct you.

To say something is "pure marketing" is to say it has no benefit outside of a bullet point in a marketing brochure. That is categorically false. Just because I would prefer a N/A engine doesn't make all turbocharging decisions equal. Again, you could benefit from a more subtle understanding of how a turbocharger works.

An engine makes it power from burning an air-fuel mixture. The more you burn, the more power you make. Because gasoline engines rely on a stoichiometric ratio of around 15:1, you must add air proportionally with fuel. This means that in order to make more power, you must move a greater volume of air. Your options are:

• Rotate the engine faster - loses efficiency to laminar flow issues at high velocity
• Increase the displacement of the engine - results in poor fuel economy because of wasted heat energy at lower loads
• Force more air in to the engine - requires additional energy to increase intake pressure

Turbocharging "cheats", because it uses wasted exhaust gas energy to drive the compressor, which increases intake pressure. However, there is only a limited amount of this exhaust energy available for a given displacement. This means that the more pressure you try to generate, the longer you'll have to wait for boost. That is the very formula for poor throttle response.

When designing an engine, you can preserve throttle response by using a larger base displacement, and keeping intake pressure levels low. This allows you to use smaller turbos, which spool up much faster. That is why a 3.0L I6 turbo can deliver 300+ HP with better character than a 2.0L I4 turbo can.

What BMW has done is try to strike a balance between efficiency and preserving the character of an engine. I'm a BMW buyer because of this attention to balance. Yes, I would prefer a naturally aspirated engine, but in the absence of that option, I'm going to choose the manufacturer who at least prioritizes engine character.

Originally Posted by GoingTooFast

The twin-scroll concept was first introduced with inline-4 engines precisely to mimic the use of two turbos by taking advantage of the separated exhaust flow plumbing from two cylinder pairs in order to maximize the 180º apart (for one combustion cycle) exhaust gas pulses energy recovery with a single turbine.

You can enhance this effect by using two effectively separated low innertia turbochargers instead of just a bigger one in order to reduce the turbo lag even further.

Close, but not exactly. While it is true that the twin scroll turbo design separates the exhaust charges in to two streams, both inlets drive the same turbine impeller. There is no active management of the exhaust streams in a twin scroll turbo; it's just that the two inlets are optimized for different pressure levels (which equate to RPM). Both inlets flow exhaust at all RPM ranges.

The twin scroll turbo solves the exact problem I outlined above: in isolation, two cylinders can drive a turbo, but it's not optimal. If you look historically, I4 twin-turbo setups are usually sequential, and involve rather complex plumbing and actuators to route exhaust energy to the right place at the right time. The whole setup is complex, heavy, and prone to failure.

In contrast, if you look at the turbo system on the N54, the cylinders were split in the same way that the inlets are split on the N55 and N20. The difference is that with the N54, each turbo operated independently. This setup isn't used with an I4 engine, because the exhaust gas energy from two cylinders isn't substantial enough to drive an impulse turbine efficiently.

[ozinaldo]

Originally Posted by bradleyland

The character of these two engines is difficult to compare. The N20 is a relatively low-boost engine at 16-18 psi. The M133 (the CLA45 AMG powerplant) breaths at 26 psi. The M133 delivers much more punch than the N20 in it's standard trim, but to do so, it trades throttle response.

From a pure character (throttle response/driving feel) perspective, I would say yes, I think the N20 is better. From a performance standpoint, it's a no-brainer. The M133 is a runaway winner.



You have to stop doing this. Seriously. I like having a spirited discussion, but it's really obnoxious to have you constantly mischaracterizing what I say. You're clearly not listening. You're just scrutinizing my words, trying to twist them around to your viewpoint. Stop it, or I'm taking my ball and going home. Make your own points; don't take what I say and try to twist it around to your viewpoint. It's sophomoric and annoying to constantly have to correct you.

To say something is "pure marketing" is to say it has no benefit outside of a bullet point in a marketing brochure. That is categorically false. Just because I would prefer a N/A engine doesn't make all turbocharging decisions equal. Again, you could benefit from a more subtle understanding of how a turbocharger works.

An engine makes it power from burning an air-fuel mixture. The more you burn, the more power you make. Because gasoline engines rely on a stoichiometric ratio of around 15:1, you must add air proportionally with fuel. This means that in order to make more power, you must move a greater volume of air. Your options are:

• Rotate the engine faster - loses efficiency to laminar flow issues at high velocity
• Increase the displacement of the engine - results in poor fuel economy because of wasted heat energy at lower loads
• Force more air in to the engine - requires additional energy to increase intake pressure

Turbocharging "cheats", because it uses wasted exhaust gas energy to drive the compressor, which increases intake pressure. However, there is only a limited amount of this exhaust energy available for a given displacement. This means that the more pressure you try to generate, the longer you'll have to wait for boost. That is the very formula for poor throttle response.

When designing an engine, you can preserve throttle response by using a larger base displacement, and keeping intake pressure levels low. This allows you to use smaller turbos, which spool up much faster. That is why a 3.0L I6 turbo can deliver 300+ HP with better character than a 2.0L I4 turbo can.

What BMW has done is try to strike a balance between efficiency and preserving the character of an engine. I'm a BMW buyer because of this attention to balance. Yes, I would prefer a naturally aspirated engine, but in the absence of that option, I'm going to choose the manufacturer who at least prioritizes engine character.



Close, but not exactly. While it is true that the twin scroll turbo design separates the exhaust charges in to two streams, both inlets drive the same turbine impeller. There is no active management of the exhaust streams in a twin scroll turbo; it's just that the two inlets are optimized for different pressure levels (which equate to RPM). Both inlets flow exhaust at all RPM ranges.

The twin scroll turbo solves the exact problem I outlined above: in isolation, two cylinders can drive a turbo, but it's not optimal. If you look historically, I4 twin-turbo setups are usually sequential, and involve rather complex plumbing and actuators to route exhaust energy to the right place at the right time. The whole setup is complex, heavy, and prone to failure.

In contrast, if you look at the turbo system on the N54, the cylinders were split in the same way that the inlets are split on the N55 and N20. The difference is that with the N54, each turbo operated independently. This setup isn't used with an I4 engine, because the exhaust gas energy from two cylinders isn't substantial enough to drive an impulse turbine efficiently.

Great post, great clarity

[GoingTooFast]

No, I'm not trying to mischaracterizing what you say. Here's what I'm listening from what you say and what is my view:

You are defending the turbocharged inline 6 cyl. engine solution because of its evident throttle response superiority and yet you've dropped the N54 engine for a turbocharged inline-4, the N20, both of which are clearly inferior to the AMG turbocharged inline-4 and even the theoretical throttle response advantage of the N54 wasn't meaningful enough to stop someone that puts so much importance on the throttle response quality such yourself from going with the N20 engine after living with the N54 AND certainly it isn't meaningful enough to justify the extra size, weight, center of gravity height and fuel consumption, except for marketing reasons. Like it or not.

Modern BMWs don't turn in due to an heavy front-end.

Additionally, saying that the AMG turbocharged inline-4 has poorer throttle response quality than the N20 and believe that someone would opt for the latter on that basis is completely unrealistic, thus there's no point in discussing it.

As for the twin-turbocharger solution in an inline-4, it is already used as a sequential 2-stage arrangement, with a small, single-scroll low-inertia turbocharger for low rpm combined with a bigger one for higher rpm, in BMW's high-boost diesel engines and could be easily adapted to the N20, with no or little development cost, to transform it into a better throttle quality response, higher-boosted S20 engine. Of course that the exhaust temperatures are MUCH higher on a petrol engine and that's the main issue to overcome as far as the reliability of such solution is concerned.

[pikcachu]

I can't just stop

some people are so obnoxious

[GoingTooFast]

[pikcachu]

I think this one describes it better

http://www.youtube.com/watch?v=XSsYJ_GBagQ&t=2m32s

[five3three]

Originally Posted by pikcachu

I think this one describes it better

http://www.youtube.com/watch?v=XSsYJ_GBagQ&t=2m32s

HAHAHA, love it!

It's not bad to drive by any standards. It's just mediocre really.

[golf_234]

Originally Posted by GoingTooFast

No, I'm not trying to mischaracterizing what you say. Here's what I'm listening from what you say and what is my view:

You are defending the turbocharged inline 6 cyl. engine solution because of its evident throttle response superiority and yet you've dropped the N54 engine for a turbocharged inline-4, the N20, both of which are clearly inferior to the AMG turbocharged inline-4 and even the theoretical throttle response advantage of the N54 wasn't meaningful enough to stop someone that puts so much importance on the throttle response quality such yourself from going with the N20 engine after living with the N54 AND certainly it isn't meaningful enough to justify the extra size, weight, center of gravity height and fuel consumption, except for marketing reasons. Like it or not.

Modern BMWs don't turn in due to an heavy front-end.

Additionally, saying that the AMG turbocharged inline-4 has poorer throttle response quality than the N20 and believe that someone would opt for the latter on that basis is completely unrealistic, thus there's no point in discussing it.

As for the twin-turbocharger solution in an inline-4, it is already used as a sequential 2-stage arrangement, with a small, single-scroll low-inertia turbocharger for low rpm combined with a bigger one for higher rpm, in BMW's high-boost diesel engines and could be easily adapted to the N20, with no or little development cost, to transform it into a better throttle quality response, higher-boosted S20 engine. Of course that the exhaust temperatures are MUCH higher on a petrol engine and that's the main issue to overcome as far as the reliability of such solution is concerned.

Not to be a stickler and i am sure you may know, but as a mechanical engineer, this would get destroyed in a formal academic or professional discussion. There is no such thing as a center of gravity, rather, a center of mass.

[bradleyland]

Originally Posted by GoingTooFast

No, I'm not trying to mischaracterizing what you say. Here's what I'm listening from what you say and what is my view:

Thank you for not trying to re-state my viewpoint. I appreciate that.

Originally Posted by GoingTooFast

You are defending the turbocharged inline 6 cyl. engine solution because of its evident throttle response superiority and yet you've dropped the N54 engine for a turbocharged inline-4, the N20, both of which are clearly inferior to the AMG turbocharged inline-4 and even the theoretical throttle response advantage of the N54 wasn't meaningful enough to stop someone that puts so much importance on the throttle response quality such yourself from going with the N20 engine after living with the N54 AND certainly it isn't meaningful enough to justify the extra size, weight, center of gravity height and fuel consumption, except for marketing reasons. Like it or not.

You're mixing a lot of reasoning here. I'm not even sure what your thesis is? A couple of things that might make things more clear for you:

Our X3 is a grocery getter. It's a point-A to point-B car. It only needs a competent power plant. The N20 is a great engine, and as I outlined in great detail before, it does not suffer from the same throttle response issues as the M133, because it uses a sane level of boost for a daily-driver.

Our X3 isn't material to this debate though, because it is neither an M235i or a CLA 45 AMG. It's design purpose, and my reasons for purchasing it couldn't be more different than the reasons I apply when deciding between two sports oriented cars.

Originally Posted by GoingTooFast

Modern BMWs don't turn in due to an heavy front-end.

Now you're just pulling stuff out of thin air. It is a fair criticism that modern BMW's have grown heavy and have lost some of their agility when compared with chassis like the E36, but there is no competitor who does not suffer the same failures as models grow in size, safety, and features. You're grasping at straws here.

Originally Posted by GoingTooFast

Additionally, saying that the AMG turbocharged inline-4 has poorer throttle response quality than the N20 and believe that someone would opt for the latter on that basis is completely unrealistic, thus there's no point in discussing it.

For once, it sounds like you understood my point. I will remind you though that you're the one that asked me what I felt about the N20 compared to the M133. I feel the same way. They're very different engines with very different goals. They're hard to compare.

Originally Posted by GoingTooFast

As for the twin-turbocharger solution in an inline-4, it is already used as a sequential 2-stage arrangement, with a small, single-scroll low-inertia turbocharger for low rpm combined with a bigger one for higher rpm, in BMW's high-boost diesel engines and could be easily adapted to the N20, with no or little development cost, to transform it into a better throttle quality response, higher-boosted S20 engine. Of course that the exhaust temperatures are MUCH higher on a petrol engine and that's the main issue to overcome as far as the reliability of such solution is concerned.

I'm not trying to be hard on you, but you're out of your depth again. You've got part of the story right, but you've tripped up on the details. It's true that diesel EGTs are typically lower than gasoline powered engines, but their exhaust gas volumes are much higher.

A diesel engine has no throttle plate. RPM is governed by the amount of fuel injected in to the cylinder. This is possible because you needn't maintain the strict 15:1 (or very close) air-fuel ration in a diesel. The full volume of air can flow through a diesel engine at all times, which is why their exhaust gas volumes are higher.

Because of this, you cannot simply swap a turbo diesel setup to a gasoline powered engine and expect things to go swimmingly. The turbine and compressor maps will very likely be mismatched to the gasoline engine.

I could be wrong. I mean, we're all guessing here, right? Maybe BMW goes all retro on us and drops a sequential setup on the rumored S20 engine, but I think that's unlikely, if only for cost reasons. The benefits just aren't great enough when compared with something like a twin scroll setup.

[bradleyland]

Originally Posted by GoingTooFast

...yet another YouTube review

I want to get out in the open that I don't think you should by an M235i. I'm not trying to convince you that the M235i is the car you should buy. What I'm trying to explain to you is that you and I may want different cars, and that's OK. You have your reasons and preferences, and I have mine. The problem is that when other people state their reasons, you call them marketing gimmicks or try to refute their subjective reasoning in some objective manner.

The CLA 45 AMG is a great car. I'm glad it exists, because it inspires competition. For my money, Mercedes Benz has prioritized some of the wrong things. That's based on my preferences though. You clearly have different priorities, and it sounds like the CLA is a great fit. You should totally buy one. I'd be thrilled for you; I really would.

[GoingTooFast]

Originally Posted by bradleyland

I'm not trying to be hard on you, but you're out of your depth again. You've got part of the story right, but you've tripped up on the details. It's true that diesel EGTs are typically lower than gasoline powered engines, but their exhaust gas volumes are much higher.

A diesel engine has no throttle plate. RPM is governed by the amount of fuel injected in to the cylinder. This is possible because you needn't maintain the strict 15:1 (or very close) air-fuel ration in a diesel. The full volume of air can flow through a diesel engine at all times, which is why their exhaust gas volumes are higher.

Because of this, you cannot simply swap a turbo diesel setup to a gasoline powered engine and expect things to go swimmingly. The turbine and compressor maps will very likely be mismatched to the gasoline engine.

I could be wrong. I mean, we're all guessing here, right? Maybe BMW goes all retro on us and drops a sequential setup on the rumored S20 engine, but I think that's unlikely, if only for cost reasons. The benefits just aren't great enough when compared with something like a twin scroll setup.

I'm enjoying how I'm being paternalized here... all of a sudden the forum is full of mechanical engineers and PhD academics.

Look, it's too much talk and very little relevant information about a very simple matter.

I'm not guessing, I'm presenting a possible solution for throttle response quality hyper concerned people like yourself, and you are indeed wrong except when you've mentioned that the main issue about a twin-turbocharged solution for a mass-market car is its cost viability, that's the reason why they came up with the twin-scroll solution, one is cheaper than two.

You see, long before being used on diesel car's engines the twin-turbocharged solution was used on no cost-object super sport cars such as the Mazda RX-7, the Toyota Supra and the Porsche 959 which were a way ahead of their time.

In fact, "the use of sequential twin turbochargers (two small KKK turbochargers) rather than the more usual identical turbochargers for each of the two cylinder banks allowed a smoother and seamless delivery of power across the engine RPM band, in contrast to the abrupt “on-off” power characteristic that distinguished the 959 engine from Porsche’s other turbocharged engines (930 and also 964 turbo) of the era. Sequential turbo charging was controlled as follows: below 4,000 rpm, as exhaust gas was not enough for driving both turbines efficiently; all the exhaust gas was fed to a single (small) turbo. This made the turbo operating earlier and therewith allowed the engine to build up boost earlier compared to using a conventional turbocharger setup. Between 4,000 and 4,200 rpm, the second turbo started “pre-spinning” (preparing for engaging soon at higher revs). Above 4,200 rpm, the two turbos operated simultaneously to provide full boost".

Also, the computer-controlled waste gates now used on the S55 engine of the M3/M4 were, naturally, already used on the 959's engine twenty five years ago.

What you find on the BMW's twin-turbocharger inline-4 diesel engines is exactly the same principle, except for the size of the second turbocharger which is bigger than the first one in order to achieve higher boost while the turbo lag is reduced even further.

So, if low inertia, exhaust manifold integrated small twin-scroll turbines on the modern turbocharged inline-4s are not enough for you as far as throttle response quality goes the above solution is what I would recommend to BMW for the S20 engine.

Why is the inline-4 engine so important then?! Because with turbocharged inline 6 cyl. modern BMWs not only aren't as fuel-efficient as they could be with 4-cyl. engines but also they are too nose heavy which translates into poor turn-in characteristics, and ultimately less agility or sporty character, and less than ideal braking performance.

Bottom line, the inline-6 cyl. engines are today a marketing thing for BMW.

[pikcachu]

[GoingTooFast]

I rather trust professional drivers than professional reviewers...

[bradleyland]

Originally Posted by GoingTooFast

I'm enjoying how I'm being paternalized here... all of a sudden the forum is full of mechanical engineers and PhD academics.

Paternalized, huh? I think the word you're looking for is patronized. You should stop. You're just embarrassing yourself now.

Originally Posted by GoingTooFast

Look, it's too much talk and very little relevant information about a very simple matter.

You believe it's a simple matter. That belief is formed out of ignorance though. No amount of denial will change the physics of the matter.

Originally Posted by GoingTooFast

I'm not guessing, I'm presenting a possible solution for throttle response quality hyper concerned people like yourself, and you are indeed wrong except when you've mentioned that the main issue about a twin-turbocharged solution for a mass-market car is its cost viability, that's the reason why they came up with the twin-scroll solution, one is cheaper than two.

If I'm wrong about something I've posted, I'd love for you to point it out and offer a valid correction. I like to learn from my mistakes. I get things wrong all the time, but usually only once.

Originally Posted by GoingTooFast

You see, long before being used on diesel car's engines the twin-turbocharged solution was used on no cost-object super sport cars such as the Mazda RX-7, the Toyota Supra and the Porsche 959 which were a way ahead of their time.

In fact, "the use of sequential twin turbochargers (two small KKK turbochargers) rather than the more usual identical turbochargers for each of the two cylinder banks allowed a smoother and seamless delivery of power across the engine RPM band, in contrast to the abrupt “on-off” power characteristic that distinguished the 959 engine from Porsche’s other turbocharged engines (930 and also 964 turbo) of the era. Sequential turbo charging was controlled as follows: below 4,000 rpm, as exhaust gas was not enough for driving both turbines efficiently; all the exhaust gas was fed to a single (small) turbo. This made the turbo operating earlier and therewith allowed the engine to build up boost earlier compared to using a conventional turbocharger setup. Between 4,000 and 4,200 rpm, the second turbo started “pre-spinning” (preparing for engaging soon at higher revs). Above 4,200 rpm, the two turbos operated simultaneously to provide full boost".

You're like a never ending stream of straw men and non sequiturs. It's amazing really.

That was a nice little write up on sequential turbochargers, but the only argument I've made regarding sequential turbochargers is that I don't believe they'll use them on any upcoming I4 turbo motor in the BMW line up. I also said that I don't think it's a certainty; just that it's very unlikely. Unless I've missed something, you haven't presented any argument against that claim.

Originally Posted by GoingTooFast

Also, the computer-controlled waste gates now used on the S55 engine of the M3/M4 were, naturally, already used on the 959's engine twenty five years ago.

What you find on the BMW's twin-turbocharger inline-4 diesel engines is exactly the same principle, except for the size of the second turbocharger which is bigger than the first one in order to achieve higher boost while the turbo lag is reduced even further.

So, if low inertia, exhaust manifold integrated small twin-scroll turbines on the modern turbocharged inline-4s are not enough for you as far as throttle response quality goes the above solution is what I would recommend to BMW for the S20 engine.

A sequential turbo setup is not a cure-all for the throttle response issues of a high-boost, small-displacement gasoline engine. You keep going back to diesels, but a diesel engine responds very well to turbo charging for reasons that I've already explained (and you seem to ignore).

Originally Posted by GoingTooFast

Why is the inline-4 engine so important then?! Because with turbocharged inline 6 cyl. modern BMWs not only aren't as fuel-efficient as they could be with 4-cyl. engines but also they are too nose heavy which translates into poor turn-in characteristics, and ultimately less agility or sporty character, and less than ideal braking performance.

I agree that sticking with the I6 involves trade-offs. In a role where you only care about maximum performance in a track environment, the high-boost I4 makes a lot of sense. You're minimizing weight and maximizing power where it counts. On a race track, you don't care about throttle response below 3,000 RPM.

The M235i isn't that pure of a car though. It's balanced more toward a car that you can live with day-to-day. The CLA 45 AMG is a full-blown AMG car. Wait, I feel like I've said this before. Are you breaking space-time or something? Time is a flat circle. The cake is a lie!

Originally Posted by GoingTooFast

Bottom line, the inline-6 cyl. engines are today a marketing thing for BMW.

How can you keep saying that? I've explained to you in very clear terms the very real benefits of a larger base displacement. You really are an enigma. Most people I argue with on the internet at least make an attempt to refute my arguments, rather than simply repeating themselves over and over.

[pikcachu]

Don't waste your precious time bradley...... it's not worth it...

[bradleyland]

Originally Posted by pikcachu

Don't waste your precious time bradley...... it's not worth it...

Oh, I'm having a blast

I'll get tired of it eventually, but this is too entertaining.

[pikcachu]

ah ok.... it is probably worth the fun i guess then

[pikcachu]

Also hope the CLA engine is more reliable than the new Mercedes 2014 F1 turbo charged engine.... poor Lewis Hamilton

[GoingTooFast]

Originally Posted by bradleyland

A sequential turbo setup is not a cure-all for the throttle response issues of a high-boost, small-displacement gasoline engine. You keep going back to diesels, but a diesel engine responds very well to turbo charging for reasons that I've already explained (and you seem to ignore).

Right pedal response quality is one of the big issues with diesel engines because of the HUGE amount of air you have to force-feed to the cylinders in order to assure the most complete mixture between the air and the injected fuel when max. compression takes place, as it is the compression which will eventually lead to the explosion inside the cylinders (there's no spark to ignite the mixture). That's also the reason why you can't revv a diesel engine as high as a petrol engine, you start to run short on time to feed the cylinders the necessary amount of air to assure the proper mixture with the increasingly amount of fuel you demand as you try to climb up through the rev-counter. In a petrol engine, air and fuel are mixed for the entire compression stroke, ensuring complete mixing even at higher engine speeds whereas in a diesel engine fuel is injected just before the power stroke after all the air within the cylinder has been compressed and, as a result, the fuel cannot burn completely unless it has a sufficient amount of oxygen.

Therefore, a very high-boost is necessary from the turbocharging system in a diesel engine which means BIG turbochargers, which, in turn, means HIGH turbo lag.

To overcome this, BMW went as far as using not two but three turbochargers - two small, low inertia and a bigger one - that work in sequence or simultaneously, depending on the engine rpm, forming a three stage arrangement that you can find in the M35d models such as the M535d. This car costs as much as an M3. And, I can assure you that the right pedal response of the M535d is on pair with my 1M's and that it revs eagerly right to the redline.

So, if we recall that the use of sequential twin-turbochargers was first introduced on petrol cars for the very same throttle response quality reasons and it was then adopted by diesel engines for which the issue is in fact critical, it's very easy to understand why such solution makes every possible sense for an high-boost turbocharged inline-4.

This is the last time I'll try to explain to you why BMW's bigger, heavier, higher COG and less fuel-efficient turbocharged inline-6s are a marketing thing.

I'll leave your far too many personal remarks unanswered, past, present and future, for reasons I'm sure you can understand... I really don't care!

Originally Posted by bradleyland

I agree that sticking with the I6 involves trade-offs. In a role where you only care about maximum performance in a track environment, the high-boost I4 makes a lot of sense. You're minimizing weight and maximizing power where it counts. On a race track, you don't care about throttle response below 3,000 RPM.

Except that the AMG inline-4 engine's max torque, which is as high as 332 lb-ft ( just like my 1M without the overboost function), starts as soon as 2250 rpm and with most modern turbocharged inline-4s max. torque is readily available from only 1900 rpm.

So, it's a non issue really!

Originally Posted by bradleyland

The M235i isn't that pure of a car though. It's balanced more toward a car that you can live with day-to-day. The CLA 45 AMG is a full-blown AMG car.

And yet the CLA AMG offers the same, if not better with its 4 doors, day-to-day practicality.

[bradleyland]

Originally Posted by GoingTooFast

To overcome this, BMW went as far as using not two but three turbochargers - two small, low inertia and a bigger one - that work in sequence or simultaneously, depending on the engine rpm, forming a three stage arrangement that you can find in the M35d models such as the M535d. This car costs as much as an M3. And, I can assure you that the right pedal response of the M535d is on pair with my 1M's and that it revs eagerly right to the redline.

So, if we recall that the use of sequential twin-turbochargers was first introduced on petrol cars for the very same throttle response quality reasons and it was then adopted by diesel engines for which the issue is in fact critical, it's very easy to understand why such solution makes every possible sense for an high-boost turbocharged inline-4.

The D30S1 variant of the N57 is a really interesting case study in just how far BMW will go to deliver the desired engine character. Perhaps I've been too focused on how different turbocharged diesel engines are, and not focused enough on BMW's willingness to do crazy shit like put three turbos on a diesel. In that context, it certainly seems like less of a stretch to consider that BMW may release a sequential twin-turbo I4. That would stun a lot of people. Hrmm...

Originally Posted by GoingTooFast

This is the last time I'll try to explain to you why BMW's bigger, heavier, higher COG and less fuel-efficient turbocharged inline-6s are a marketing thing.

This again? Yes, there are ways to improve upon the character of a high-boost I4. Hell, Lancia coupled a supercharger and a turbo on the Delta S4 back in the eighties. That comes at a cost though. I would say that the turbocharged I6 is a compromise (as is a turbo I4). I would not say that it is pure marketing.

Originally Posted by GoingTooFast

I'll leave your far too many personal remarks unanswered, past, present and future, for reasons I'm sure you can understand... I really don't care!

I've tried not to be personal. I hope you won't take it that way. If I use a little color in my rebuttals, it's not meant to be personal. I don't argue with boring, uninteresting people. They're no fun. It's been great fun debating with you.

Originally Posted by GoingTooFast

Except that the AMG inline-4 engine's max torque, which is as high as 332 lb-ft ( just like my 1M without the overboost function), starts as soon as 2250 rpm and with most modern turbocharged inline-4s max. torque is readily available from only 1900 rpm.

So, it's a non issue really!

And yet the CLA AMG offers the same, if not better with its 4 doors, day-to-day practicality.

We could debate this all day long and not reach a consensus. The answer doesn't lie in the numbers; it is revealed when you drive the car. The CLA 45 AMG feels like a turbocharged I4. It's easy to catch it off-guard, where you have to wait for torque delivery. Dyno runs are performed at WOT the entire time. No one drives like that... well, not for long I can't say the N55 doesn't feel turbocharged at all, because it has the characteristic early torque swell, but in 3 years of driving it, I never caught the engine off-guard in my 135i.

Every comparison video I've seen from a competent reviewer has noted the difference in engine character between the M135i and the CLA 45 AMG. The CLA 45 AMG is a car to be respected. No question about it. That doesn't mean everyone has to choose it though. There are plenty of reasons to choose the M235i, and the turbo I6 is key amongst those reasons.

[GoingTooFast]

Originally Posted by bradleyland

This again? Yes, there are ways to improve upon the character of a high-boost I4. Hell, Lancia coupled a supercharger and a turbo on the Delta S4 back in the eighties. That comes at a cost though. I would say that the turbocharged I6 is a compromise (as is a turbo I4). I would not say that it is pure marketing.

Well, I don't know what BMW is waiting for... I say pure marketing!

Porsche chief Matthias Müller has disclosed plans for a four-cylinder engine to power the next-gen Boxster and Cayman duo.

(...)

We should mention Porsche has already confirmed the Macan compact crossover is going to get a four-cylinder gasoline engine "sometime in 2014, perhaps at the end." The Stuttgart-based company has also created a special turbocharged V4 engine which powers the 919 Hybrid where it works with a front axle-mounted electric motor.

http://www.worldcarfans.com/11403217...confirmed-with