One of the first steps in our product development process is determining the specifics and geometry of existing components in an effort to understand how/why things work. To do so, we disassembled the factory 11th Gen Honda Civic 1.5L Turbocharger to collect measurements and data. Fortunately for us, our team had a factory 10th Gen Civic 1.5L (Si) Turbocharger here to use for a side-by-side comparison. It is important to note that all 1.5L Turbo models for the 11th Gen Civic now use the same turbocharger part number. For those that may have missed it, checkout our Part 1 Blog Post!
Just like Honda's 10th Generation Civic Turbo platform, the 11th Generation's L15 utilizes an integrated exhaust manifold in its cylinder head. Because of this, the turbocharger bolts directly to the cylinder head. It is important to note that the 10th Gen Civic cylinder head merges all four cylinders into one exhaust outlet port. However, the 11th Gen Civic utilizes two exhaust ports, merging two cylinders in each port, much like the 10th Generation 1.5L Turbo Accord (the cylinder head castings are actually the same between these two models). This change was most likely done to increase turbocharger response and promote exhaust flow.
A lot of folks have been referring to the factory turbocharger as a "twin-scroll turbocharger". However, after a quick inspection with the naked eye, we can see that this turbochargers is not a true twin-scroll turbocharger because the exhaust port divider only extends about 1" into the turbine housing inlet. This was most likely done to maintain response and exhaust flow from the dual-port cylinder head, effectively creating a "Tri-Y" system.
Though we did not measure the factory turbine housing at this time, the 11th Gen Civic turbocharger appears to be a bit larger in all ways. We can speculate that this turbo has a larger A/R and Volute around the turbine wheel in comparison to the previous generation - we will dive into this further down the line.
Though the compressor cover is visually different, there aren't too many notable features here, other than the bypass valve location. The 11th Gen's BPV is located on the turbocharger's compressor cover, whereas the 10th Gen's BPV is integrated into the turbocharger inlet pipe that bolts to the compressor cover. Also, the compressor outlet is rotated in a different location. Both turbochargers again feature an integrated electronic wastegate actuator - shown is the integrated 4-bolt mounting bracket.
All of Honda's factory turbochargers at this time use a journal bearing CHRA design. Comparing both generation turbochargers, we can see that though there are many similarities in functionality, each design is notably different in design from each other. This is most likely because the 10th Generation Civic turbocharger was manufactured by MHI (Mitsubishi Heavy Industries), while the 11th Generation Civic turbocharger was manufactured by IHI Corporation Turbo.
One of the first noticeable changes to the 11th Gen is its billet aluminum compressor wheel; the 10th Gen used a cast aluminum wheel. The 11th Gen's fins appear to be thinner in most areas (this is very difficult to accurately measure without scanning), and feature a smoother surface-finish, most likely to keep the weight down while increasing efficiency and response. Both generations use a 6+6 "split" 6-blade design. However, the 11th Gen uses a design referred to as "extended-tip" technology. Extended Tip wheels promote greater airflow, providing a faster boost response at lower engine speeds and increases efficiency at higher boost pressures. Basically, extended tip technology allows smaller wheels to achieve/amplify the benefits of smaller and larger wheels into one, compact design. This new turbocharger also has a different contour to the compressor wheel design, utilizing a more laid-over fin profile. Another notable change is the significant reduction in root size (about 24%), that is visually maintained throughout the entire root of the turbocharger. All of these revisions, including the increased wheel diameters, are how Honda was effectively able to increase overall efficiency of the 11th Gen Civic turbocharger.
Compressor Wheel Specs
|Inducer||Exd Ext Tip||Exducer||Height||Root|
|10th Gen Si||39.1||N/A||46||16.3||11|
Looking at both turbine wheels, we can see that while both share a 9-blade design, there are still some very notable differences. One of the first things we can see is how much taller the 11th Gen Civic's turbine is - 20mm vs 15.5mm. We can also see that this new design features quite a bit more angle to its blades. IHI's turbine also utilizes extended tip technology, just like its compressor wheel.
Turbine Wheel Specs
|Inducer||Ind Ext Tip||Exducer||Height|
|10th Gen Si||37.1||N/A||33.3||15.5|
Using our experience with the 10th Gen platform we can speculate that the 11th Gen Civic's factory turbocharger should be able to see around 300 wheel horsepower range with supporting modifications.
Our goal is to develop a 100% drop-in turbocharger upgrade using new components and does not require a core charge. We are currently looking into spacing constraints and compatible components to determine our design method.