Herm:
Remember it will only hit 4000 rpm when you cruising at 100mph (or going uphill with a full load), wind and tire noise will drown it out.. its not like an ICE car that you have to rev up to get good acceleration.. the acceleration power needs of the Volt are met by the buffer of the battery.. the ICE may be loping along at 2000 rpm and meanwhile you got the throttle floored while you merge into a hwy.I think it will be a rare occasion that you will notice the genset running.  

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Well I hope you’re right. It’s a good point that the battery serves as a buffer for hard acceleration. Just to be difficult, I will point out that in my personal experience, going fast enough on the highway for the engine to hit 4000 RPM results in some significant engine noise that is not drowned out by the road. But cars are all different, and the Volt will be more different than most! Hopefully that translates to quieter.

Your answer to whether the Volt 1.4 liter normally aspirated engine is running Atkinson cycle is a question so far un-explicitly answered by GM. But any competent Sherlock Holmes can deduce whether it is so or not.

The published ratings for the normally aspirated Family 0 1.4 liter, VVT, DOHC, engine was 90hp or 66Kw @ 5600 rpm and 125 N-m of torque at 4000 rpm in 2003. A later version, in 2006, is rated at 100 hp or 75 kw. Neither version is DI; the first SPI, the second improved to MPI.

The Cruze 1.4 l Family 0 engine built in America is a VVT, DI, turbo version, same bore and stroke but rated at 140 hp. Presumably the VOLT engine will be manufactured on that same Flint engine line. Presumably it also will be DI but normal aspirated. That usually means it Hp would increase to perhaps 104-110 Hp.

The published Hp requirements for the Volt are that it must be sufficient to power a 53 Kw or 71 hp electrical generator at 4000 rpm.

Opel Amptera however publishes the specification of the engine in the engine generator of the Amptera supposedly an identical Voltec drive European version of the VOLT as 1.4 liter Family 0 normally aspirated engine @ 82 HP.

Taking an engine rated @ either 100 Hp, or in older form 90 Hp, and only obtaining 82 hp from it, means it has been detuned. How & Why? Well it is well known that running Atkinson cycle, the thermal efficiency goes up, but the Hp produced goes down.

Given that you can control the valves such as by VVT, which the 1.4 l already has, the only change to create Atkinson cycle is a revised cam, and altered software in the ECU. Probably a two day job for an engineer, or a backyard mechanic.

Therefore Sherlock Holmes deduces that the VOLT engine is running on Atkinson cycle — just like the 28% larger displacement Prius engine.

QED.

PS Wikipedia says that GM has demonstrated the same 1.4 l, Family 0 , VVT, DI engine with some modifications such as cylinder sensors for the Demonstration engine for running HCCI mode. The engine was modified to have turbo assist and simple VVL, along with an alternate ECU and the already mentioined cyclinder senors. The HCCI engineer at the Demonstration said that the HCCI engine is particularly useful for applications like an engine generator in a Voltec powertrain and saves significant amounts of fuel, making it the the equal of a diesel, but much lighter and cleaner.

Which is neither here nor there. Apropos of nothing, but potentially significant.

George S. Bower: Dr. Ibringdo hits the nail on the head. In a direct comparison between a series hybrid (Volt) and a series /parallel hybrid ( Prius) this article gets the picture straight. The supposed sweet spot advantage of the series hybrid (Volt) just went away. The Volt engineers are programing an operating LINE not a sweet SPOT. The operating line is programmed along the peak efficiency points (min SFC) on the ICE engine map. They are doing EXACTLY what the Prius engineers did. Therefore the series (Volt) setup should suffer some penalty in MPG since instead of running the power directly to the rear wheels they are running it thru a generator/inverter/ motor. The only way they can beat or tie the Prius MPG in CS mode is to do it with things like drag coefficient and tire rolling resistence. I think the best we will see is the volt with an MPG that ties the Prius. That is if they were able to make that 1.4L into an Atlinson-Miller cycle which we don’t know yet. That may be some more disappointing news—-That the Atkinson cycle is for the next generation not first release.

Another way of looking at this problem:

What would be the fuel efficiency of this same 1.4 litre engine if it were deployed using Toyota’s drive chasis?

Also, what is going to happen to the fuel efficiency when a person is carrying passengers plus luggage, heading up an interstate incline at 60 miles an hour, and has to step on the throttle to pass a truck? Will there not be an even greater loss of efficiency from not having the motor directly connected to the chasis?

Respectfully,

Dr. Ibringdoh

Herm: It all depends on the ICE, GM has to tune the exhaust /intake manifolds, muffler, the cams and the timing to optimize the ICE for those sweet spots.. they probably just found out where the ICE needs to operate in the recent long distance testing so now they go back and tweak the ICE..Most likely they calibrate their computer models and so the next generation of the Voltec will be improved without needing so much testing.

Just to make sure I understand what you’re saying: You’re suggesting that if GM calibrates the manifold, exhaust, valves, and timings for the RPMs that the engine utilizes in real use, this will be enough to overcome 2nd Law issues incurred when the motor is not engaged to the drive train?

Respectfully,

Dr. Ibringdoh

Rashiid Amul: Gotta be, my friend.

+22 now. Stretching out the lead!