Next BMW M5 will nix V10 in favor of twin-turbo V8

[prizrak]

Originally Posted by Karoug

The japanese can squeeze out almost 200hp/liter from a bike engine...

And how much torque do they get? Low torque, high HP engines are fine for bikes as they don't weight much. Cars are quite heavy these days and need quite a bit of low end torque to get moving.

[thedguy]

Originally Posted by NooDle

I love turbos, I have a turbo car, but I just think it's a "cheap" way of making power from an engine.

The Ferrari F430 gets > 100hp/l, which is fantastically difficult to make without some sort of boost (turbo or supercharger)

It also means the power delivery is more linear, and easier to handle than just a big old lump of turbo boost

which is what I like

Have you driven a (semi-)modern turbo engine? Full boost by 1800rpms and they have a torque plateau rather than a curve from that point up to 5500-6k rpms. The only engines that come close to that are rotaries.

You guys gotta remember one other thing, turbos are like displacement on demand without the friction of reciprocating pistons that are doing nothing more than pushing air in and out.

Originally Posted by prizrak

And how much torque do they get? Low torque, high HP engines are fine for bikes as they don't weight much. Cars are quite heavy these days and need quite a bit of low end torque to get moving.

I don't think that was the point he was trying to make.

[the Interceptor]

Dunno if it helps anyone, but there's an interesting fact about the BMW x35i engine.

*anorak bore to death mode on*

They didn't just make a twin turbo I6, they tried (and succeeded) to "simulate" a V8 with it. There are two small (and therefore quick) turbos, each one fed by three cylinders. Then, they put up some clever systems to keep the turbos spinning all the time to reduce lag and at the same time get them out of the way when no boost is needed. Additionally, they didn't go for peak torque or a high but narrow torque plateau, rather than smoothing the delivery out over a wide revband. So what they ended up with is an engine that basically behaves like their 4.4l V8, but is more economical, smaller and lighter. And for that very reason, I'm not really afraid of what they'll come up with for the new M5, even if I'm not a turbo man.

*anorak bore to death mode off*

[argatoga]

Originally Posted by Karoug

The japanese can squeeze out almost 200hp/liter from a bike engine...

Who cares. Power/liter ratios are worthless measurements for engines. They only exist because the Europeans and Japanese were never able to beat the Americans in power/weight.

Sits back and waits for the neg reps to come in.

[thedguy]

Originally Posted by the Interceptor

Dunno if it helps anyone, but there's an interesting fact about the BMW x35i engine.

*anorak bore to death mode on*

They didn't just make a twin turbo I6, they tried (and succeeded) to "simulate" a V8 with it. There are two small (and therefore quick) turbos, each one fed by three cylinders. Then, they put up some clever systems to keep the turbos spinning all the time to reduce lag and at the same time get them out of the way when no boost is needed. Additionally, they didn't go for peak torque or a high but narrow torque plateau, rather than smoothing the delivery out over a wide revband. So what they ended up with is an engine that basically behaves like their 4.4l V8, but is more economical, smaller and lighter. And for that very reason, I'm not really afraid of what they'll come up with for the new M5, even if I'm not a turbo man.

*anorak bore to death mode off*

It only took them 15 years to catch up to Toyota (see MKIV Supra)

[prizrak]

I don't think that was the point he was trying to make.

Maybe, maybe not, but the point I am making is that comparing bike engines to car engines is like apples and oranges. Not to mention that HP is not the only indicator of performance.

[the Interceptor]

Originally Posted by thedguy

It only took them 15 years to catch up to Toyota (see MKIV Supra)

Doesn't the 2JZ-GTE have sequential turbochargers?

[Karoug]

Originally Posted by prizrak

Maybe, maybe not, but the point I am making is that comparing bike engines to car engines is like apples and oranges. Not to mention that HP is not the only indicator of performance.

A literbike engine produces more tourqe than most smaller car engines.. And now ppl are putting them into small cars with good results on dragstrips and tracks.

[prizrak]

Originally Posted by Karoug

A literbike engine produces more tourqe than most smaller car engines.. And now ppl are putting them into small cars with good results on dragstrips and tracks.

Running a Smart with a Hayabusa engine is not the same as running an A4 or a 3 series on one. Granted smaller car engines may not be as powerful as motorcycle engines of the same size but small car engines were never developed for speed/power only economy.

Like I said you are comparing completely different things, performance car engines produce alot more power and torque than performance motorcycle engines. The designs of both are completely different and so are the purposes.

[thedguy]

Originally Posted by the Interceptor

Doesn't the 2JZ-GTE have sequential turbochargers?

That's what the BMW system is, I can't recall for sure if they use 1 small turbo and 1 big one, or use 2 small ones and bring the 2nd one on higher in the revs. The only thing the BMW has on the 2jz is direct fuel injection (and on the early 2jz-gte's variable timing).

[the Interceptor]

Originally Posted by thedguy

That's what the BMW system is, I can't recall for sure if they use 1 small turbo and 1 big one, or use 2 small ones and bring the 2nd one on higher in the revs. The only thing the BMW has on the 2jz is direct fuel injection (and on the early 2jz-gte's variable timing).

No, actually the turbos on the 335i are identical. I know people confuse this all the time, even magazines often have it wrong. The 335d uses two sequential turbos of a different size. The 335i uses two identical turbos working in parallel, each one fed by three cylinders.

[Wizegui]

I don't see a problem with that. Having that it's a big engine, the turbos will probably be partially inactive, meaning that it will have somewhat decent economy from a smaller engine. When that power IS needed, the turbos kick in and the power is there. With modern turbochargers being more sophisticated in their design and usage, they have eliminated a lot of the turbo lag. Plus, the benefits of a big turbo charged engine is the low down torque, so it wil probably be a lot faster than the current normally aspirated V10.

[thedguy]

Originally Posted by the Interceptor

No, actually the turbos on the 335i are identical. I know people confuse this all the time, even magazines often have it wrong. The 335d uses two sequential turbos of a different size. The 335i uses two identical turbos working in parallel, each one fed by three cylinders.

Then they just copied the Mazda RX-7 (FD) and Toyota 2jz-GTE setup.

[the Interceptor]

Originally Posted by thedguy

Then they just copied the Mazda RX-7 (FD) and Toyota 2jz-GTE setup.

These are parts of an interview with the leading engine developer from BMW, Klaus Borgmann, taken from the german car mag "AutoBild Sportscars":

Borgmann:"The primary goal in development was to combine the efficiency of a six cylinder with the dynamics of a V8. We wanted the specs of a medium sized V8, combined with the fuel consumption and - most importantly - the smoothness of our six cylinder." [specs of the new six cylinder: 306 hp and 295 lb-ft]

(...)

As a major goal were spontaneous reactions, a single turbo seemed to be too unattractive. Its reactions on accelerator movements would have been too indolent, and the characteristics too edgy at full throttle. So, the guys from Munich decided to use two turbos, each one powered by three cylinders. The advantages were much more spontaneously reactions of the smaller turbines due to smaller [and therefor lighter] rotating masses. This way, even small accelerator movements create reasonable propulsion, as little amounts of exhaust gases are enough to make the turbos spin.

(...)

To reduce the timespan between pushing the accelerator and the reaction of the turbos even more, the engineers used another trick. Using the direct fuel injection, the turbos are being kept spinning with large valve timing overlap and an air stream of unused intake air. So, even when you're cruising, the turbines are being kept spinning with some pressure.
Well sized overpressure valves are another trick to improve fuel economy. As long as you don't access power, the exhaust gases are being disposed past the turbines. The advantage: the turbos do not raise the counterpressure, the engine has an easier time pushing the exhaust gases out and uses less energy. Only when you push the accelerator, the valves close and you get the boost you need immediately.
Another part of the story when it comes to efficiency is the use of high-strength steel for the turbos. Only a few years ago, the turbos needed to be cooled with fuel, which decreased the fuel economy. Turbos made of the new steel can resist the temperatures up to 1000 °C almost without any cooling.

(...)

Borgmann:"Even when driving progressively, this engine uses less fuel than the 3.0 NA engine [this one is based on]. Due to the higher torque, you unconsciously use higher gears all the time." That reduces fuel consumption so much that it even compensates casual power runs. Put into figures, the new six cylinder uses 2 litres less on 100 km [equals a jump from 20 to 24 mpg] than the BMW 4.0 V8. Additionally, this engine weighs 70 kg less than the V8, making the car more agile.

Doesn't really sound like they copied anything if you ask me, this sounds pretty original.

[thedguy]

Variable Valve timing and turbo's have been done, it's nothing special Toyota, VW, GM and Volvo have all been at this party long ago. BMW is just being fashionably late.

I'm not saying it's a bad design, just they didn't exactly invent the wheel, they just decided to make their own.

[the Interceptor]

Originally Posted by thedguy

Variable Valve timing and turbo's have been done, it's nothing special Toyota, VW, GM and Volvo have all been at this party long ago.

I demand proof.

[thedguy]

http://www.3sgte.com/1JZGTE.htm

The 1JZ-GTE engine has been modified by the addition of an Intelligent Variable Valve Timing System (continuous wide range intake camshaft phasing control system) and a new high-efficiency turbocharger (CT 15B). The engine generates 50% more engine torque at low engine speeds, and turbo lag has been reduced by 50%, while allowing a 10% improvement of fuel economy.

http://autospeed.com/cms/A_109201/article.html (plenty more in the whole article, including a break out box just on the vvt bits).

We'll apologise for rabbiting on in advance. But we've got to tell you, the post-1998 VVT-i version of the Supra 2JZ twin-turbo 3.0-litre six is - without doubt - the best production turbo engine we've ever driven.

http://www.diskdrive.co.za/new_launc..._s80_2.4t.html (Volvo S80 2.4t).

http://www.autozine.org/html/Saab/93.html (2005 Saab 9-3)

Another new addition to the 9-3 is a 2.8-litre turbocharged V6. It is derived from the Holden V6, produced in Australia but Saab involved the development of the turbocharging system, which is unique to Saab. The normally aspirated version of the 2.8-litre all-aluminum 60-degree engine has been used in Cadillac CTS. Based on that engine, Saab added a Mitsubishi turbocharger running at a light boost pressure of 0.6 bar. Because only a single turbo is employed, it chose a twin-scroll turbocharger which separate the exhaust gas from the two banks of cylinders to avoid interference. Other changes to the engine include a lower, 9.5:1 compression, sodium-filled exhaust valves (for better heat dissipation to deal with the extra heat generated by high pressure), stronger forged steel crankshaft and sintered forged con-rods. The flat torque characteristic of turbocharging allows the discard of variable-length intake manifolds, but intake variable valve timing is retained.

And VW http://en.wikipedia.org/wiki/List_of...hp_2.0_TFSI_I4

170-272 hp 2.0 TFSI I4

Engine code
BPY (North America); AXX or BWA (Rest of world)
Configuration
1,984 cc water cooled inline 4, based on the naturally aspired 2.0 FSI
Cylinders
bore × stroke 82.5 × 92.8 mm (0.89 rati), 496 cc/cylinder, 10.5:1 compression ratio
Block
CG 25 grey cast iron, 88 mm cylinder spacing, two chain driven balancing shafts
Head
four-valve, low-friction roller cam follower drive, modified inlet duct geometry for high tumble values providing superior knock resistance, continuous intake camshaft adjustment
Fuel system
Gasoline, Fuel Stratified Injection, up to 110 bar
Aspiration
0.9 bar boost turbocharger, intercooler, variable plastic controlled intake manifold with charge movement flaps adjusted by a continuous-action pilot motor

edit: Yes I know, I quoted Wikipedia on the VW, I don't know enough about, or care about VW's to actually put effort into my research on it.

[the Interceptor]

Okay, that's variable valve timing and swapping older parts for newer, better versions. But how about using valve timing to keep the turbos spinning, and actually bypassing the turbos in specific situations to lower exhaust back pressure? That's what the BMW engine is about, and that's what makes it feel like an n/a engine. Of course, turbos have improved over time, but I've never seen a system like BMW uses it before, and I didn't find it in any of your examples.

[thedguy]

It sounds like you're looking for me to find someone that says the exact same thing as the BMW engineers said, word for word.

Read the first link, or the break out box in the 2nd link. If those don't satisfy you then Point still stands. Toyota has had VVT turbo engines for 10 years, some of which even had a sequential system that the BMW still lacks.

[the Interceptor]

What I'm trying to say is that there have been many systems involved in making turbo engines, and that those engines have improved hugely over the years. But I've never seen someone try to copy the behavior of a n/a engine with a turbo model (an idea that's just growing popular with "downsizing" as the reference). So the BMW engineers combined a range of systems to make their turbo not only behave similar to their bigger n/a model, but they also made sure that you can actually not tell the difference (apart from a different sound that is).

Now I'm not saying that the engines in your examples are bad, just like you said that you don't dislike BMWs system. Still, I want to emphasize that there's a bit of a difference as well in the original idea as in its execution.

Originally Posted by thedguy

some of which even had a sequential system that the BMW still lacks.

BMW has a sequential system of two differently sized turbos in the 335d, just like I said earlier. And reading what Borgmann stated, it doesn't really sound like a sequential system would have had any advantage for the 335i.