MultiAir Was Dodge’s and Fiat’s Answer to VTEC
You might have seen "MultiAir" emblems on an engine or heard it referenced somewhere. Here's what that means.
Because my eyes are bigger than my stomach, I purchased two wounded Fiats to tend to. I was able to start one of them just fine, but the other might have a tricky engine problem that may or may not be related to the MultiAir actuator “brick.” Cue my Hank Hill voice: “Does it look like I know what the hell a MultiAir is?” That’s a bit of an exaggeration, as I’m more knowledgeable about engines than Hank was about computer file formats. Still, I only encountered and learned of what a MultiAir is when I purchased my Fiat 500L and Fiat 500 Abarth. Through wrenching, driving the Fiats, and watching videos, I’ve educated myself about what it is and what it does, and I’ve come here to share my learnings.
[Editor’s note: This post was updated at 2:25 p.m. on 9/24/2021. It previously stated that both the 2.0-liter and 2.4-liter Tigershark engines used MultiAir, but only the 2.4-liter engine has MultiAir. We have changed the text to reflect this.]
MultiAir, like Honda’s Variable Valve Timing & Lift Electronic Control (VTEC) or Toyota’s Variable Valve Timing-intelligent (VVT-i), is a variable valve timing system developed by Fiat. Sort of. On a basic level, all of these systems use a complex series of variables to electronically adjust the vehicle’s engine timing. The result is a more dynamic and versatile engine, an engine that can adjust for performance or economy, within milliseconds, on the fly, seamlessly. That’s MultiAir in a nutshell.
For a more granular explanation, let’s look at a typical overhead cam engine. In the top portion of your engine, you’ll find a camshaft or two. The camshaft, which is a long stick with lobes on it inside the top of your engine, rotates around, and when the tip of the lobes touch the top of a valve, the valve opens. In a single overhead cam (SOHC) engine, only one shaft controls the timing of both the exhaust valves and the intake valves. In a DOHC engine, that job is split up, with one camshaft controlling the intake valves and the other controlling the exhaust valves.
In an engine with variable valve timing, the vehicle’s computer, or ECU, can essentially alter the cam profiles, which will let the valves on the exhaust or intake to open sooner, or later, depending on the circumstances. In a lot of modern cars, the camshafts are linked to an oil-filled gear assembly that can rotate the camshaft(s) to some degree, irrespective of how fast the engine is turning, creating advanced or retarded timing. These systems use oil pressure to move the cam gearing.
Because of the nature of the design, a Single Overhead Cam engine is generally less flexible than a DOHC unit, as the timing of both the exhaust and intake are completely fixed, relative to each other. In a DOHC engine, there’s more flexibility between both intake and exhaust valves, but at the end of the day, both designs are limited by the camshafts. Although the vehicle can alter the timing to some degree, there’s still a modicum of efficiency that could be capitalized if the engine were just a little bit more precise.
That’s where MultiAir comes in. In MultiAir engines, the camshaft for the intake valves is eschewed and replaced by electronically controlled hydraulic actuators that open and close the intake valves. In this setup, the car isn’t limited to whatever the intake cam profile can do. Instead, the computer can actuate the valves to open and close as it needs, at least based upon the intake pattern lobes from the single camshaft that controls the exhaust valves and pressurizes the hydraulic actuators.
MultiAir also has Variable Valve Lift, so not only can the engine adjust when the valves open, it can also control how much they open. In a traditional engine with Variable Valve Lift, the vehicle is once again limited by the cam profile regarding when the valve opens and how long it stays open. With the MultiAir system, the hydraulic actuators can easily vary that.
Here’s where the “multi” in MultiAir comes into play. These engines have several intake valve opening modes that are based upon driving conditions. The first is Full Lift, in which the valves open and close at their full range. Typically, this is used for max power. Beyond that, there are two modes in which the valves open or close late, and one mode where the valves don’t open at all. Most interestingly, there’s a mode in which the valves open in quick succession. Fiat claims this mode greatly improves fuel economy in city or stop-and-go driving.
Stellantis, formerly Fiat Chrysler Automobiles (FCA), has used this tech on a few engines, both in the US and elsewhere. The 1.4 turbo found in Jeeps, Fiats, and other Chrysler Fiat cars got this tech. The 2.4-liter “Tigershark” that is in many small Jeep- or Chrysler-branded vehicles uses MultiAir, too. Fiat claims a cleaner, more responsive, more powerful engine compared to a traditional DOHC or SOHC VVT/VVL engine.
MultiAir is yet another tool in an automaker’s Rolodex to create a fuel-efficient, tractable, and better-performing engine. My MultiAir-equipped Fiat 500L and Fiat 500 Abarth are the best part of those cars. The Abarth is fast, torquey, and reasonably fuel-efficient. MultiAir is great.