3 or 4 Cylinders?

[dwightlooi]

I want to keep this a simple poll so forgive me if it seems to lack the typical depth I tend to dwell into on various subjects. The basic premise is this...

• A 3 cylinder engine is more economical on fuel than a 4-cylinder
  
• A 3 cylinder engine is also more compact, lighter and cheaper to build
  
• A 3 cylinder engine is more miserly on fuel because it has 25% fewer frictional elements (valves/cylinders/bearings/rods/etc)
  
• A 3 cylinder is also easier and more efficient to turbocharge*
  
• A 3 cylinder is, however, slightly less refined than a 4 cylinder even with a Balance Shaft added
  

* The reason a 3-cylinder is easier and more efficient to turbocharge is because a 3-cylinder engine does not have the exhaust valves of two cylinders open at the same time. In a 4-cylinder engine two pistons are always at top dead center, when other two is at the bottom dead center. This means that whenever one cylinder opens its exhaust valves open at the beginning of its exhaust stroke, another cylinder is at the end of its exhaust stroke / beginning of intake stroke. This means that unless a dual scroll turbo and segregated exhaust mannifold is used, the high pressure exhaust gas from the cylinder beginning is exhaust stroke can back flow into the cylinder beginning its intake stroke. This leads to poor aspiration, emissions issues and reduced turbocharger response (due to lost exhaust energy). A dual scroll system is not only more expensive to fabricate, it also introduces additional flow restrictions into the exhaust path. Hence, with a dual scroll system you are trading a little top end flow capacity for improved response. A 3 cylinder engine does not have pistons at the top and bottom of their travel at the same time and hence does not have this problem. A 3 cylinder engine can therefore use a single scroll turbo with equal or higher efficiency a 4 cylinder using a dual scroll turbine.

The question is, if it comes down to you and your money, which engine will you prefer in the next refresh of the Cruze and/or the Sonic?

1.4 liter 4-cylinder

Iron Block, Aluminum Heads, 72.5 mm x 82.6 mm (Bore x Stroke)

Direct Gasoline Injection, DOHC-16v, Intake & Exhaust Variable Valve Timing

Honeywell-Garrett MGT15D turbocharger, air-to-air intercooling

170 hp @ 5300 rpm

170 lb-ft @ 2000~5200 rpm

6500 rpm rev limit

87 Octane Unleaded

1.5 liter 3-cylinder

Aluminum Block & Heads, 86 mm x 86 mm (Bore x Stroke)

Direct Gasoline Injection, DOHC-12v, Intake & Exhaust Variable Valve Timing

Honeywell-Garrett MGT15 turbocharger, air-to-air intercooling

170 hp @ 5300 rpm

170 lb-ft @ 1900~5200 rpm

5500 rpm rev limit

87 Octane Unleaded

[regfootball]

5500 rpm limit and less smoothness is a turnoff......you might as well put a pushrod motor in it then

[§carlet §wordfish]

With economy at the top of my priorities list and smoothness being at the top of I don't know the meaning of list, I'd go for the 3 cylinder.

[Z-06]

4 quantitative positives, vs. 1 qualitative not so negative? The answer is simple.

[riviera74]

4 quantitative positives, vs. 1 qualitative not so negative? The answer is simple.

Can GM build a really good 3 cylinder engine though? That is the question. Once upon a time, their 4cyl engines were awful in the USA. Since the Ecotec family came out of Russellheim, they are much better. Can they build a very good 3cyl? I don't know.

[67impss]

4 quantitative positives, vs. 1 qualitative not so negative? The answer is simple.

Can GM build a really good 3 cylinder engine though? That is the question. Once upon a time, their 4cyl engines were awful in the USA. Since the Ecotec family came out of Russellheim, they are much better. Can they build a very good 3cyl? I don't know.

The development was throughout GM not just Opel but then again Opel is GM. Ecotec stands for 'Emissions Control Optimisation TEChnology

Per Wiki

"Ecotec

The Ecotec name was adopted in 2000 for the new generation of Family II engines. The name was already used for the Opel GM Family II engine, Family 1 and Family 0 ranges. GM intends this new Ecotec to become its global 4-cylinder, and it has already fully replaced their OHV I4 line.

The Ecotec Family II is a DOHC 4-valve design with an aluminum block and head (L850 for 86 mm bore applications, and L880 for 88 mm bore), designed for displacements from 1.8 to 2.4 L. It was developed by an international team of engineers and technicians from Opel's International Technical Development Center in Rüsselsheim, Germany, GM Powertrain in Pontiac, Michigan, and Saab in Trollhättan, Sweden. Much of the development work on this project was carried out by Lotus Engineering, Hethel, United Kingdom. The engine uses aluminum pistons and cast iron cylinder liners. Vibration is reduced with twin balance shafts.

The current Ecotec line is manufactured in Tonawanda, New York and Kaiserslautern, Germany. Until the discontinuation of Saturn, it was also produced at a plant in Spring Hill, Tennessee."

As far if GM can build a good I 3 well they already have with Family 0 Ecotec

Per Wiki

GM Family 0 engine

From Wikipedia, the free encyclopedia

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The Family 0 is a family of inline piston engines that was developed by GM Powertrain, a subsidiary of Opel, as a low-displacement engine for use on entry-level subcompact cars from Opel/Vauxhall.

The engine was first introduced in 1996 Opel Corsa as a 3-cylinder version. It features light cast-iron engine block, aluminum cylinder head with Hollowcast camshafts and DOHC valvetrains driven by chain. Modern versions use variable intake technology.

* 1.0 L Straight-3 (973 cc): 40 kW / 55 hp, 82 N·m (60 lb·ft) @ 2800 rpm

* 1.0 L Straight-3 (973 cc): 43 kW / 58 hp, 85 N·m (63 lb·ft)

* 1.0 L Straight-3 (998 cc): 73.4 mm (2.89 in) bore, 78.6 mm (2.94 in) stroke, 10.5:1 compression.

* 1.2 L Straight-4 (1199 cc): 72.5 mm (2.85 in) bore, 72.6 mm (2.86 in) stroke, 10.1:1 compression, 75 hp (55 kW) @ 5600 rpm, 110 N·m (81 lb·ft) @ 4000 rpm

* 1.2 L Straight-4 (1229 cc): 73.4 mm (2.89 in) bore, 72.6 mm (2.86 in) stroke, 10.5:1 compression

[Drew Dowdell]

Can I ask why the 4-cylinder would remain iron block?

[pow]

I'd go for the three-banger. Less boost would be okay, too, if that lowers fuel consumption. 140 hp should be plenty in the Cruze Eco, especially with the reduced weight of the engine. Would make a nice range extender for the Volt, too.

[dwightlooi]

Can I ask why the 4-cylinder would remain iron block?

The Family Zero -- before the 1.4T --- has always been iron block engines. When they did the 1.4T they were looking for the most expedient way to field a 1.4 DOHC turbo four. It was basically the 1.4 Family Zero with a turbocharger. No DI, no Aluminum block. The only concession was they they went to a grey iron alloy which is a little lighter.

There reason you'll want to keep the 1.4T is so you can minimize capital and development costs. A 1.4T with DI added is just that. A 1.4T with an aluminum block will be a new engine.