Firefly (GSE): Little Four Cylinder Engines for FCA

Torque figures are approximate. We are currently working on getting accurate figures. Please check back for an update.

firefly enginesWhen Fiat first acquired a chunk of Chrysler Group, both companies had a bewildering array of engine families and sizes, each developed for a special purpose. Corporate leaders quickly decided to combine as many engine families as possible, perhaps drawing inspiration from Chrysler’s decision to standardize on one V8 family, one V6 family, and one four-cylinder family.

Thus were born the Global Small Engine (GSE) and Global Medium Engine (GME). The GSE has already been named Firefly, at least by Fiat in Brazil; the Chrysler GME turbo has been dubbed Hurricane by Auburn Hills.

torque curve

Who designed the Firefly?

FCA is a single company, and most likely the GSE was created by a worldwide team with people from facilities in Brazil, Italy, the United States, and possibly India. FCA’s “chief technology officer” is Harald Wester, but most key decisions were likely made by Powertrain Coordinator Bob Lee and Aldo Marangoni, Powertrain Engineering Director for Latin America. Bob Lee has been in charge of engines and electric propulsion since 2011, and joined Chrysler in 1978, leading both the New Hemi and Pentastar V6 programs (he was likely also in the 4.7 V8 program). Aldo Marangoni had a hand in the MultiAir, FIRE engines, diesels, and the highly regarded TwinAir.

gse heads

2G 4.7

4.7 liter engine heads

Mike Volkmann wrote:

The block is very reminiscent of the E.torQ/Tritec, which was based on the Neon engine. Much of the combustion chamber design greatly resembles the 4.7 V8 engine, especially the second-generation, with the original spark plug position used as a quench point and the second plug position holding the sole plug. ... It’s really impressive for what it is, and I love that it mixes proven older designs with newer technology.

The integrated exhaust manifold came from lessons learned on the Pentastar, and helps with thermal efficiency and getting cylinder head/combustion chambers to operating temperature quicker, cutting cold emissions. The two-valve head also helps with this.


The open deck block looks like a mix of Chrysler and Fiat; it uses an offset crank like the Tigershark engine, which minimizes piston to cylinder wall loading. It has an open deck and crank bed plate, with no balance shaft, and it has unbalanced flywheel so the crank rotating assembly is internally balanced, like the Neon 2.0.

Firefly technologies and engine effiiciency

The valvetrain uses a roller finger system, reducing friction. As diagrammed in a 2014 presentation by Bob Lee (and as mentioned above), the centerline of the piston and crankshaft was offset by 10mm, to cut friction between the piston and cylinder; and a variable-displacement oil pump was adopted. The features shown in below should be used in the GME series as well.


The engine uses coil on plug ignition with 70 mJ, igniting iridium-alloy plugs that have carefully shaped electrodes. The 1.3 engines for cars with stop-start systems have a “Smart Charger” alternator, which recharges the battery while the vehicle is slowing down to avoid wasting energy on generating electricity; it also temporarily disables alternator charging when more power is needed (e.g. for passing).

1.0 liter Firefly

The design is torque-biased, with maximum power coming at lower engine speeds than the FIRE design for better driveability — one reason for the relatively long stroke and long intake manifold runners.

The oil filter is easily accessible, towards the front of the vehicle and integrated into the sub-block, with the air conditioner support protecting it from road debris. The dipstick is integrated into the cover and passes inside the motor, preventing oil leakage.

The valvetrain is supposed to last at least 200,000 km before failure, which appears to be below the usual 200,000 mile goal.

Otto vs Miller cycles: variable cam phasing taken to the next level

valve curves

Like the Hemi V8 and Pentastar V6, the Firefly uses an electronically controlled variable cam phaser (continuously variable camshaft). In the Firefly, it’s been developed to be able to delay timing by up to 60° [some sources claim 40°], so the engine can use the Miller cycle (more commonly called a modified Atkinson cycle, and normally only used by hybrids) at low loads, and move to the more-common Otto cycle when needed (as Audi does). The cam is only retarded during partial load so there should be no issue with detonation with the 13.2:1 compression ration. Under heavy load, the cam adjusts accordingly and the engine operates like a normal Otto cycle.”

1.3 liter Firefly

As a Fiat release noted, when the driver lets up on the throttle, with most engines, there are high pumping losses, so they lose efficiency. The Firefly, instead, changes the camshaft axis to delay valve opening, which slashes pumping losses. The company claims a drop of up to 7% in fuel use.

Other efficiency measures

  • The Firefly reduces low-temperature friction by using very low viscocity oil (0W20).
  • Alcohol-burning cars (e.g. in Brazil) have heaters inside the fuel rail to allow cold starting down to –5°C.
  • Valvegear is run by a chain, for lower maintenance and more precise actuation over time.

What are the individual engines?

The GSE series includes both three and four cylinder engines. One goal was to minimize variations (and hence tooling, parts, and engineering costs) within the family, as Chrysler did with the Pentastar V6 family. Thus, there is a single basic piston and cylinder design for the three and four cylinder.

 From (FIRE)To (GSE) From (FIRE)and (E.TorQ)To (GSE)
Size 1.2 1.0 (3-cyl)

Most likely, all of the non-turbocharged GSE engines will have two valves per cylinder, to optimize torque (especially in low-to-medium revs) and fuel consumption at low throttle and moderate engine speds. Despite having just two valves, peak performance is comparable to most four-valve engines; the 82 hp/liter output of the 1.3 beats all Brazilian-sale 1.2 to 1.6 liter normal-induction engines. The two-valve design also allows use of a single camshaft with almost half the torque required for valve actuation.

Peak torque and horsepower come in at lower speeds than with the old FIRE engines — for example, the 1.4 had torque peak at 4,500 rpm; the Firefly 1.3, at 3,500 rpm.

firefly blocks

Current “FIRE” engines in the EU are the 1.2 8V, 1.4 8V, and 1.4 16V, and the 1.0 TwinAir; Brazil has 1.0 and 1.4 8V versions with different tuning. There is also a 1.8 liter E.TorQ.

1.0 3-cylinder72 @ 6,00077 @ 3,25077 @ 6,25081 @ 3,250
1.3 4-cylinder101 @ 6,000101 @ 3,500109 @ 6,250105 @ 3,500
1.0 turbo120 (est)   
1.3 turbo160 (est)   

The ordinary GSE is a single overhead cam design, with an off-center crankshaft and two valves per cylinder (a four-valve version is also made). It runs at up to 13:2 compression, so far. Connecting rods are an alloy of aluminum and graphite for low weight and low friction. The engine has a durability floor of 150,000 miles, and meets Euro 6 standards.


 From (FIRE)To (GSE)To (GSE)
Size 1.4 turbo1.3 turbo1.0 turbo

A turbocharged version of the 1.3 is expected to reach 160 horsepower, the same as the current 1.4 turbo; the turbo 1.0 is to reach 120 hp, which would make the Tipo/Neon much faster. The turbos will have four valves per cylinder. Alfa Romeo’s version of the turobcharged GSE 1.3 is expected to arrive in 2018.

We make no guarantees regarding validity or accuracy of information, predictions, or advice — see the terms of use and privacy policy. Copyright © 1994-2000, David Zatz; copyright © 2001-2017, Allpar LLC (except as noted, and press/publicity materials); all rights reserved. Dodge, Jeep, Chrysler, Ram, and Mopar are trademarks of Fiat Chrysler Automobiles.

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