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'All-New' GM Ecotec 2.5-Liter 4-Cylinder Engine to Debut Next Year

Smooth operator chases new standards in noise, vibration and harshness.

By Andrew Wendler Sep 22, 2011 6:22AM

(UPDATE: Based on reader comments, we realized our wording was a bit sloppy in the initial post. In the name of brevity, the word "block" was omitted in a figurative reference to an increase in engine displacement. The main text has been updated to correct these changes.)GM Ecotech 2.5 (Photo Courtesy GM)

 

"All new.” Two words that have been casually tossed about for so long their literal meaning has been lost to the winds of hyperbole. So yesterday, when General Motors announced its “all-new” Ecotec 2.5-liter 4-cylinder engine, I tempered the news with my usual dose of hard-earned cynicism. “Let me guess," I said to myself, "a slightly redesigned block and cylinder head yielding an additional tenth of a liter displacement is teamed with new fuel injectors to produce a 6 percent increase in output and improved overall drivability. Oh, and wait -- we mustn't forget the 'all-new' designs molded into the plastic engine cover.”


As usual, I skipped past the soft-sell portion of the press release and zeroed in on the technical details, where I found myself wholeheartedly intrigued by the impressive list of technical specs and comprehensive refinements on display in this fully modern 4-banger-to-be.


Scheduled to arrive midsummer 2013, the new Ecotec will debut as the base engine in the Chevrolet Malibu. Early projections peg horsepower at around 190 and torque at 180 lb-ft -- about 12 and 16 percent more, respectively, than the outgoing Ecotec 2.4. Mileage is said to be more than 30 mpg highway, although the Environmental Protection Agency has yet to confirm those numbers. GM Ecotech 2.5 (Photo Courtesy GM)


The new Ecotec is touted by GM as one of the quietest engines in this segment. The manufacturer made a concerted effort to redistribute the noise, vibration and harshness that it couldn't banish entirely.


“Think of it as the difference between low-frequency coarse noise, such as a vacuum cleaner, versus a higher frequency precision noise, such as a sewing machine,” says Tom Slopsema, noise and vibration engineer. “We focused on reducing the overall engine noise level and placing the remaining noise in a higher frequency range. Specifically, the engine’s noise-frequency signature was targeted, with the aim of pushing radiated noises into a higher frequency range well above 2,000 hertz, which is more pleasing to the ear.”

 

While these are all welcome improvements, it's the top-to-bottom, stem-to-stern attention to minutiae that impresses me most. Check out some of the improvements the engineers made, likely while the accountants were at lunch:


1. Relocated balance shafts: Moved from the block to a cassette in the oil pan, the balance shafts are driven by a shorter, quieter chain to reduce noise and vibration.


2. In-pan oil-pump assembly: The oil pump has been moved from the front of the crank to the oil pan, where it is driven off the aforementioned balance shafts.


3. Camshaft drive with inverted-tooth chain: The camshaft drive chain uses a premium, inverted-tooth design that is significantly quieter than a roller-type chain. Also known as a silent chain, it virtually eliminates noise and enhances durability.


GM Ecotech 2.5 (Photo Courtesy GM)4. 2-piece oil pan: The 2-piece oil pan employs a stiff aluminum upper section to support the engine’s structure, and a stamped steel lower section to provide greater overall sound reduction.


5. Structural camshaft cover: Featuring increased ribbing and additional attachment bolts, the cover's increased stiffness helps to push the engine’s sound frequency above 2,000 hertz.


6. Acoustic intake manifold cover: Hey, if you say it works, I'll take your word for it. Then again, all of my personal vehicles have nothing but air and grease between the top of the engine and the bottom of the hood. Of course they're older models as, apparently, am I. Funny I hadn't noticed that till now.


7. Forged steel crankshaft: This is big. Anyone who has ever built a performance engine knows a forged crank is the way to go for durability and reduced deflection under stress. These same properties also reduce noise and vibration, the two primary enemies of smoothness.

 

8. Iron main bearing cap inserts: These stiffen the structure at the main bearings where the crankshaft rests. Same story as above: Stiffer equals quieter and smoother.


9. Isolated fuel rail: The injectors are suspended and the fuel rail is attached with rubber-isolated mounts. Although not new to the 2.5-liter Ecotec, injector tick can be annoying, and is often mistaken for a sticky valve lifter.


10. Structural front cover: The 2.5-liter's front cover was designed with extra ribbing and secured with extra fasteners for a stiffer, more rigid and quieter cover.

 

Will the average consumer notice these refinements and feats of technical wizardry? I have no idea. Probably not. Am I absolutely geeked that a car company, formerly in the habit of leaving engine designs in their lineup virtually unchanged for decades, is getting all proactive about NVH and efficiency? You can bet your sweet bippy I am.


GM Ecotech 2.5 (Photo Courtesy GM)

19Comments
Sep 22, 2011 9:06AM
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them plastic belt tensioner's are going to last a long time on the timing belt.

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will the pistons smash into the valves when the timing belt blows??

Sir. This engine design uses a timing chain. Timing chains do not "blow", and they very, very rarely snap. All that one needs to do is change the water pump, water pump gasket and the tensioner every 100,000 km (~60,000 mi). Timing chain designs are practically "forever".

With that out of the way, I do see one major problem with this particular engine design: can anyone tell me where on this engine the water pump is, and why that placement is problematic?
Sep 22, 2011 6:50AM
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 "a slightly redesigned cylinder-head yielding an additional tenth of a liter displacement........."

 

Should anyone who believes that redesigning a cylinder head can change engine displacement, be allowed to write an article about an engine?

Sep 22, 2011 8:28AM
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will the pistons smash into the valves when the timing belt blows??
You know, I don't see what some people's problem is with interference engines.  I actually like interference engines.  They allow a much higher compression to be used with much more agressive cam profiles.  Basically everything that benefits power.  I understand the risk is a destroyed engine if the chain jumps a tooth or two.  The price for that increased power is increased vigilance on maintenance.  Personally, I can live with that.

Sep 23, 2011 11:13AM
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Just curious Annatar,  how do you feel about the water pump maintenance now that I pointed out the headers are at the front and not the rear?  I think it should be more accessible.
Much better! This engine seems to be well designed. Steve-80 was/is angry with me because "I don't look at the whole car". One of the first things I study on a car is how easy it would be to work on, because that tells one of the quality of engineering and thinking that went into the design of the car as a system. The more inaccessible major subsystems are, the higher the chance I will fail a car.

A forged steel crank, easily accessible water pump and a timing chain instead of a belt are all major pluses for ease of maintenance and engine longevity.
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@Had it in CA:
Yes, you are correct, and no he shouldn't. Should read "and slightly shorter stroke" and/or "slightly increased bore."

@ shrimp roll:
It's a chain.
At this point GM simply states "forged."
GM did not  disclose the material of the pistons.
GM is claiming "improved knock resistance"
It's a chain, but they did not specify if it is an interference motor or not.
Yes, it probably will.
Me too!

Thanks for keeping me honest.

Sep 22, 2011 8:26AM
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of course it won't ping on low octane fuel!?
I own a car with an LAP Ecotec engine, the 2.2L model with the improved cylinder head and 11:1 compression that was used in the final couple years of Cobalts.

It does not knock on regular.  However, during the recent brutal summer I think I may have set off the knock sensor here and there.  110°F days with the air conditioner running may have been too much for such a relatively high compression gasoline engine.  I think (but I am not 100% positive here) is happening is when the knock sensor goes off the ECU automatically fiddles with the ignition advance and cam profiles to reduce knock.  The end result is that the engine in such extreme heat didn't feel quite as peppy as normal.

With this engine, I suspect they are following the same logic as well as maybe a revised piston and head design to help with knocking.

Sep 23, 2011 5:58AM
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I don't see why the water pump would be any more difficult to access then the water pump on a TDI engine (which is ridiculous to access).
Just to be clear: in the modern world of direct injected turbo diesels, TDI is just average. I would pick Mazda's DITD or TOYOTA's D-4D any day of the week over TDI. TDI might be a performant fuel mizer, but Mazda's DITD beats it in everything. Nobody here said or even implied that TDI's layout was somehow superior to the design layout of the engine above.
Sep 22, 2011 11:05AM
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thank you for clarifying the timing chain!

i would feel much safer with a (free wheel motor??).

some GM motors do need updating and hope this one will do it for the four cylinder.

i like the 4.3L V6, but it needs more horse power and updating the fuel injector system.(for pickups)

 

Sep 22, 2011 7:16AM
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them plastic belt tensioner's are going to last a long time on the timing belt.

is it a "hardened steel" crankshaft?

forged or cast pistons??

of course it won't ping on low octane fuel!?

will the pistons smash into the valves when the timing belt blows??

won't the plastic cover add height to the motor?

i hope its built some place that will be affordable to the consumers!?

Sep 22, 2011 11:56AM
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It could be the power steering pump. Looking at the parts above, one of the components looks like the water pump. Embedded into the engine!
No, you were right the first time.  As I just mentioned, GM doesn't use hydraulic power steering anymore.  And that hookup attached to it definitely looks like a coolant hose connection, not a power steering line's banjo bolt connection.

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