Taking this ideology, why not to look putting 4-cyl car all exhaust in one single scroll turbo and then there are no time where turbo feels any pulses, like you have twin scroll for 8-cyl car?

I found this and is explains it better than I.

Found this here: Twin-Scroll Turbo System Design Explained

I found the very same good write up.

It looks I may go for twin scroll GT35 for my upcoming modification. I do plan to use 993 headers to have nice heater boxes. Only question is what size of waste gates shall I install?

For a car where you want heat that sounds like a potentially great idea. I think Brian (RL8) and Ben (M&K mufflers) can make that happen.

Of course equal length would be better however, it seems many of the new car makers are going for the twin Scroll without the equal part. Thus, draw your own conclusions.

It should also be a very low volume system and spool nice and fast.

Not an expert but I think two 38mm Tial's has a bit more capacity than a stock 930 WG and should work well.

That article is terrible, and the writer is using a bunch of terms that he/she does not understand.

For a twin scroll system to work, each pipe must be kept separate until they reach the turbine inlet flange in order to conserve the momentum of the pulse. This is more important than equal length. You can not have ANY wastegate pipes. When they are closed they provide volume for the pulses to expand into. The ‘secondaries’ of Brian’s headers will do the same thing, so that system is not useful. With no wastegate pipes, an integral wastegate turbo must be used.

The part about the scavenging and overlap in the article is incorrect. They have never run this engine. I know for a fact that this engine runs very little overlap, except for when they want to force exhaust INTO the cylinder for EGR purposes.

This is a picture of the exhaust manifold. It is somewhat misleading. The individual pipes are actually in layers, so the cutaway makes it look like the ports dump into a single volume. They don’t. There is an individual pipe from each cylinder all the way to the flange. Beautiful.

http://forums.pelicanparts.com/uploa...1275789976.jpg

Here is the dirty secret about divided systems. ALMOST ALL BENEFIT IS LOST WHEN THE WASTEGATES ARE FULLY OPEN. This is not a maximum power enhancing approach, it improves the low end, but the maximum power is about the same.

+1

If you do a Google search on a phrase of the article, "twin-scroll design is better pressure distribution in the exhaust ports and more efficient delivery of exhaust gas energy to the turbocharger’s turbine", for instance, you find it plastered all over the internet. Had a difficult time even finding the author who lays claim to the info. It guess if you plaster enough crap everywhere, people start believing it as fact. Ah, the power of the internet. ;)

Dave I get what you are saying and may use that technique in the future. I to was wondering where it came from and thought the artical I referanced was the first place said quote was used.


SS,

I am still learning.

It is not the best writing but thought it better than mine if you labored through it.

I will look for some more reference but that article reflects the major points I am thinking are the keys to a split system.

The big one being, it keeps there from being two exhaust valves from being open at the same time which can reduce pressure at the only open exhaust valve on that bank. In turn this makes for better cylinder filling.

The other is it creates an advantage at the turbine by how the exhaust relates to the wheel.

They get a little deep saying we can increase over lap.

My take away from that I might put like this: A C2 cam has a small amount of over lap. A 930 has none. I am guessing he is saying that if there is less pressure in the cylinder when the exhaust valve closes, they can run a little bit more overlap to a benefit. Overlap if used right should increase HP for two reasons. Longer duration and cleaner cylinder fill.

I do not think comparison to scavenging on a normally aspirated race motor made it any clearer though I get his point.


I love that picture of the BMW 6 posted.

What I see is two banks to a split turbinee. Each side has log style manifolds inside an encasement not unlike our heat exchangers to be more thermally efficient, be easer to build, and weigh less than a cast iron system.

They seem to have sized the turbine such that they can control boost by only bleeding off one bank.

All cool stuff.

What am I missing or getting wrong please.

Thanks if you can help.

Just thought, I suspect the BMW has active cam timing and can vary overlap by rpm and load.

Might be it can work with the lower residual cylinder pressures that come with a divided turbine system and get more aggressive with valve overlap at times.

I can not see how BMW or anyone could have made a lower volume manifold. Further, putting the WG in the turbo eliminates the volume of the WG circuit.

(Maybe a VAT)

I now understand why an equal length header has more even cylinder temps. More even pressures when the exhaust valves closes. This also allows a motor to be run closer to the optimum timing and AFR with out fear of having a cylinder or two detonating.

Speedy Squirrel & Dave,

You seemd to think the source I referanced above was junk.

In my effort to learn more about the new BMW motor that hits full TQ by 1200rpm (and near full boost). I found this:

See:TwinPower: Modified Shows How a Twin-Scroll System Works - BMW Monitor

He seems to think a bit more favorably of the quote and aritical. He went on and said the following that helped me further.

I am not sure if the N55 (twin-scroll) uses this but the naturally aspirated inline 6 uses Valvetronic and double-VANOS. VANOS is the varaible valve timing and Valvetronic is the variable valve lift system which eliminates the throttle.

Gee, you searched the internet found someone who agrees with you. I'm happy for you. :rolleyes:

Dave,

Once again you only seem intent on insearting yourself with emotional response's only to do this provoking thing!

Flieger,

You are right. After my comments above I did some more research and BMW's new motor variant is truly state of the art.

It is there first time combining variable valve timing, direct injection and turbo charging and some other trick technology's like controllable and variable oil pump delivery. It is able to run at over 10/1 CR on top of running a turbo.

In all, there efforts resulted in over 300# TQ by 1500rpm (apx 200rpm earlier than there twin turbo 6) and about a 7% increase in fuel economy.

Basically this little gem makes full boost by 1500rpm and pulls a 7000rpm red line.

It also makes more TQ and it makes it sooner than Mercedes E class diesel.

Cool stuff and it is interesting they did this by leaving the twin turbo behind for a divided turbine set up with a log exhaust system.

Dave, is the issue simply that only one reference was cited and that you need hard, empirical evidence or that you think twin scroll technology is without merit?

I think we'll all agree that anything that allows an engine to optimize intake and exhausg velocity gas velocity throughout the rev range is goodness. While I haven't read any PhD these or industry papers on twin scroll technology and variable valve train management, the overwhelming practice of these technologies by massively capitalized companies who make their money by selling optimized solutions tells the story.

The newest turbo engines from the big boys are all going twin scroll on single turbos with variable valve systems. Having talked to camgrinder at length on the effect of lobe spacing, overlap and limiting exhaust duration/lift low in the RPM band to increase boost response was an eye opening conversation.

The best minds with the deepest pockets betting the farm on these technologies are enough for me, especially since my ability to dissect the math isn't there. I accept E=MC^2 not because I can dissect the equation, but because I can understand the intuitive bases for this and also see that nuclear weapons work. I accept these automotive technologies for the same reasons.

The Mitsubishi Evo X and Bimmer turbos are the equivalent of 'the bomb' in the automotive context.

That BMW engine is a bit too hot to run at the track IIRC. Nice technology still.

Is a twin-scroll turbo system more efficient that having two separate compressor/turbine assemblies? I want to isolate the power variable here- how much waste energy is recovered. I realize that a flat-6 packages a separate system quite nicely while an inline engine would like a twin-scroll.

That is mainly an issue with the N54 two-turbo engine in the 335i. They do not put much of an oil cooler on it and at the track the temps get up to 250+F and goes into limp home mode. Dinan puts a bigger oil cooler and ducting on and makes a nice track engine.

Let me take a moment to explain the above technologies and the benefits they impart on the turbo motor and why:

Direct Injection:

• The 997 DFI injectors operate at 1750 psi. If MFI injectors used to be the holy grail in terms of atomization, injectors that operate at 5 times that pressure are a wonder.
• Additionally, injection into the combustion chamber means that the fuel's full evaporative capacity is absorbed by the combustion gases, providing better cooling of the combustion process, as well as quenching rogue combustion elements.
• With these injectors ability to control full directional trim control and withy the ability to fire more than once per cycle based on engine state, means that the fidelity of controlling warm up, knock and other variables is downright unbelievable in terms of tuning flexibility.

Variable valve timing:

• Controlling overlap by varying lobe spacing is huge: you can go from zero overlap at idle to race overlap at high RPM. At idle, you can build pressure extremely quickly as you can optimize the intake tract's VE to the needs of an engine in terms of air requirements at level that is functionally infinitely variable. This is great for emissions and amazing for power production. No more compromises on overlap means that you can have your cake and eat it.
• Controlling lift is even more valuable for turbos. By lift limiting the exhaust valve at low RPMs in relation to the intake valve, you can create a massive pressure differential on the exhaust side that creates significant dividends in the integrity of the exhaust wave heading toward the turbo. This translates into ridiculously low boost thresholds. You can basically use a full race cam, but make it pretend to be a cam that if static, would be useless above 3000 RPM, as it would choke off top end power for anything but a low revving diesel.

As far as the "log exhaust" goes:

This is an educated guess, but follow the reasoning: With variable cam timing and lift, at low RPM, the effects of a cam tuned for no-overlap and low lift can provide perfect exhaust wave resolution, then open things up higher in the RPM band for excellent HP production. In an engine like a 911 that has to compromise on a given, fixed cam timing spec, this resolution is not possible - any cam that would exhibit a good exhaust signature at low revs would run out of steam very quickly without being able to increase lift and overlap.

Thus, the reasoning is that at a low number of relative exhaust events over time (RPM), coupled with no overlap and high intake velocity (due to lower valve lift at low engine speed) allows the log type of exhaust to operate as well as a discrete, equal length system. BMW can make incredible low RPM power with a log style header that would not be possible in a fixed cam motor and by the time that RPMs rise, to make full power, the benefits of equal length exhaust tuning are gone (due to gas volume overcoming any synergistic effect that could be derived from pulse tuning/scavenging).

And that's the latest hail mary from an armchair ME wannabe... :D

You guys really need to test drive a BMW 335i to appreciate it.

I've had a variety of high-powered cars in my life and I don't impress easily, but every time I get in my wife's 335xi it impresses me, sewing machine smooth, almost instant torque, revs clean to redline. Damn fine bit of engineering!

Thanks for your input. That's exactly what I was asserting. To use the BMW engine as an example of an efficient twin scrolling exhaust system, grossly over simplifies what BMW accomplished. It's an "apples and oranges" scenario. The BMW engine has direct injection, a more efficient combustion chamber design, variable valve timing, higher compression, PLUS twin scrolling exhaust manifold/turbochargers. It's remarkable the torque this engine produces below 2000RPM...my former boss has one in his 1 Series and that thing is a rocket!!!

But let's keep in mind that engine is producing 100 horsepower per liter and most of us are already beyond that. Twin scrolling will produce more efficiency at low engine speeds, but there is no advantage to twin scrolling when an engine achieves higher engine speeds (above 3000RPM, for instance).