http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/ Autoblog Comments for http://www.autoblog.com/media/feedlogo.gif http://www.autoblog.com en-us Copyright 2008 Weblogs, Inc. The contents of this feed are available for non-commercial use only. Blogsmith http://www.blogsmith.com/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/Jan 21st 2008 1:38PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/
Also, I do see how they've swapped the intake and exhaust, but I'm not sure how it helps too much, since unlike a supercharger, a turbo needs access to both anyway. The only advantage here seems to be that after returning from the intercoolers, the air doesn't have to fold back into the valley. And in return they get a problem where the hottest part of the engine is now right under the hood where it gets no airflow and might even bake the paint off the hood!

This does show one thing, direct air-air intercooling is dead. Air-water-air is so much smaller and easier to package once you work out how to keep it fed.]]>Jan 21st 2008 1:41PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/Jan 21st 2008 1:53PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/
This setup is crazy lol. I can already see the swaps for this, 145iTT anyone?]]>Jan 21st 2008 2:02PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/
It isn't inherently shorter, it just flows the other direction. There is still a hose going from the "wrong" side of the heads (in this case the valley) around the block to the intake (in this case on the outside). Normally this would be the exhaust tube, it's just here it's an intake tube.

Additionally, I don't see why they have two turbos next to each other. Contrary to popular believe, twin parallel turbos don't decrease lag, because although the spools have less mass, they also have half as much hot exhaust gas pushing on them.

Carlos:
The turbo isn't integrated into anything, and where it is located is the exhaust manifold area. You're used to the intake being in the valley, but in this case they've reversed it.]]>Jan 21st 2008 2:35PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/
once the turbo is spooled up, it builds pressure in the intake manifold, it take a relatively short amount of time for that pressure to be felt at the intake valve.

compare that to the exhaust side where the turbo cant do anything until the hot gases hit the turbo.

if the 2 volumes were equal, then 90% of the lag would come from the exhaust side so it makes sense to trade smaller exhaust side for larger intake side.

besides, even if the turbo were right next to intake valve, you would still want to put an intercooler in there, mine as well put the turbo closer to the exhaust because you need some space for the intercooler on the intake.]]>Jan 21st 2008 2:48PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/
to go with 1 turbo, they would have to combine the flow of the 2 banks about 4 inches away from the exhaust valve. that would cause all kinds of problems i dont even want to have to think about. there are enough issues with cylinder cross talk when the intake is no where near that close, i can only imagine that they would get much much worse that close on the exhaust side of a turbo engine.

besides, more smaller turbos are more responsive (even if they have half the gas of one larger one) because the volume (length is not important) between the exhaust valve and the turbo is smaller, effectively moving the 2 smaller turbos closer to the cylinder than 1 larger turbo could possibly be.]]>Jan 21st 2008 2:58PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/Every time the blowoff/bypass valve triggers (on a shift), the intake plenum falls in pressure and you have to start again. This is not the case with the exhaust manifold, it remains under pressure all the time.

Volume-wise, the size of the intake manifold is far more critical than the exhaust manifold. It is however nice to have a short exhaust manifold length before the turbo because the longer this tube is the cooler the charge gets before it hits the spool, which decreases the energy it imparts. The difference between 4 inches and 8 matters, but not as much as you make it out.

You could easily prevent cross talk with a dual entry turbo. The air from each bank would enter the hot side via separate nozzles, but would blow on the same vanes.
]]>Jan 21st 2008 5:38PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/
the size of the intake manifold (between the throttle and the intake valve) is most definitely very important but that is different than the volume between the compressor and the intake valve which includes plumbing and intercooler. that volume is a factor in turbo response but much less so than either the exhaust or intake manifold

the intake manifold can be of any volume and is independent of the turbo plumbing.

]]>Jan 21st 2008 7:07PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/
It's not the mass of the larger turbo that matters, its the radius. Radius is second-order (ie, it gets squared) when calculating the inertia of spinning objects.

Effectively, the ratio between flow volume and resistance would be disadvantaged compared to two smaller turbos that sum up to the same mass.]]>Jan 21st 2008 7:16PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/Jan 21st 2008 7:21PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/The exhaust flow drops when the throttle plate closes. The pressure doesn't necessarily drop, although in practice I expect it does.

Both sides lose flow when the throttles close. But additionally, there is a "leak" in the intake plumbing, the BPV/blowoff valve. There is no such leak on the exhaust side. Thus the pressurization is more constant on the exhaust side.

Your argument about it taking time for hot gases to reach the turbo kind of pretends the system is starting from an off state. We're talking about a closed loop system, each part affects each other. Additionally, we're talking about a system with over unity gain. In fact, this is why it has a waste gate. To spin the turbo up, you need air from the cylinder to push the exhaust vanes, which then push the intake vanes which push more intake air, which then expands during burning and pushes on the exhaust vanes...

Having a large plenum on either side slows the response of the system. And in this way, I don't think BMW has solved any problem by switching this around. And I think we both agree that the new packaging seems to present some logistical difficulties.

Infra:
A "half size" turbo doesn't have a half-size (and thus 1/4 mass) spool. The pumping is proportional to the surface area of the vanes and turbine and thus a turbo that pumps half the air is more like 70% the size, and thus has half the mass, not 1/4.

Either of you, read "maximum boost" by Corky Bell for info on intake lag or the effects of parallel turbos. You'll kind of have to ignore the parts where he talks about carbureting and move to the later parts though.]]>Jan 21st 2008 8:44PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/
Knowing how heavy turbos, manifolds, catalytic converters, intercoolers and all the associated plumbing and braketry is, doing it this way must shift the centre of gravity of the engine way up! This should definitely stay SUV-only.

]]>Jan 21st 2008 1:49PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/
the friggin cats would be right up against the back of the hood, everything in that area (hood, paint, windshield wipers motors and lines, wiper nozzles and lines, electronics, brakes) all of that stuff has to be able to handle EXTREME HEAT

there would almost be fewer problems if you mounted the engine upside down. there is certainly a very long list of very good reasons that NO ONE has EVER had a v8 exhaust in the valley and intake on the outside.

all of this trouble for better turbo response? hardly seems worth it.]]>Jan 21st 2008 2:36PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/Jan 21st 2008 5:10PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/Jan 21st 2008 4:15PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/Jan 21st 2008 5:34PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/Jan 21st 2008 1:54PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/
One thing that can be said is that this motor probably has some pretty insane throttle response for a turbo motor considering how short all the piping is between the exhaust mani > turbo > IC > intake mani. ]]>Jan 21st 2008 2:03PMhttp://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/http://www.autoblog.com/2008/01/21/detroit-2008-bmws-twin-turbo-4-4l-v8/Jan 21st 2008 2:12PM