The W1 Drop-in Turbocharger Pt.4 - Bigger is Better
It is correct to say that bigger is better but that does not tell the whole story of the design of a compressor and turbine wheel for a performance turbocharger.
Let’s start with the turbine wheel as it is the turbine wheel that is the driving force of any turbocharger. The job of the turbine wheel, by definition, is to extract energy from a fluid flow (exhaust gases in this situation) via a pressure difference across the turbine wheel. This energy is converted from kinetic energy in the exhaust gases to mechanical energy via the shaft. The process of this energy extraction is mainly defined by the design of the turbine wheel…number of blades, overall size, wheel trim, and blade profile.
As you can see, the 27WON W1 turbine wheel is significantly larger than the base model turbine wheel, 61% larger based on the inducer (the larger diameter of the wheel). Along with the overall size increase, the shaft diameter has been increased for improved high RPM strength. Thus the turbine shaft seal/ring diameter is also increased (you’ll see that in the next image). Further, the webbing between the blades has been decreased to reduce weight.
Weight is critical due to the fantastic angular acceleration and deceleration rates that a turbine wheel experiences. This weight savings translates to faster boost response between gear shifts and lower spool RPM.
Since the W1 turbo is our entry level performance turbocharger for the Civic 1.5L Turbo engine, it was important to us to maintain the best boost response and lowest spool RPM possible without sacrificing the top end power potential. We decided to maintain the 11-blade turbine wheel design for this exact reason.
See the first groove just behind the turbine wheel?
This is the turbine shaft oil seal/ring. The 27WON turbine wheel features a much larger seal/ring along with a larger overall shaft diameter. This translates into better durability. Also notice how the blade height is greater than the base model OE turbine wheel and you will be able to clearly see that there is a larger side and small side of the turbine wheels; the inducer and exducer, respectively.
The increased height of the blade inducer increases peak flow potential and the overall increased blade height allows more energy extraction to be done by the turbine wheel on the exhaust gases.
The ratio of the inducer and exducer diameters defines the wheel trim. The closer the inducer and exducer are to the same diameter the higher the peak flow of the turbine wheel is. However, this same scenario reduces response so a compromise must be made between response and peak flow. The 27WON turbine features a 76.8 trim turbine wheel vs the base model OE turbine at 77.2. This provides a good balance of response and peak flow.
The compressor wheel now uses the mechanical energy from the turbine shaft to pressurize air that eventually fills the cylinders. The entire purpose of turbocharging an engine is to fill the cylinders beyond 100% volumetric efficiency. The process of ingesting and pressurizing the air going into the engine does this exactly.
Like the turbine wheel, the 27WON W1 compressor wheel is significantly larger than the OE compressor wheel, 59% larger based on the exducer. Like the turbine, the shaft diameter has been increased for improved high RPM strength, but the “nose” of the compressor wheel has not. This allows for the largest blade width possible which improves wheel efficiency and reduces weight.
Lastly, you’ll notice that the blade tips extend past the edge of the exducer. This is called “extended-tip” technology. This feature expands the compressor map width (increases peak flow) with very minimal added weight.
Viewing the side profile of the 27WON W1 compressor vs the OE compressor shows another significant difference. Just like the turbine wheel, the increase blade height allows the compressor wheel to apply more work to the incoming air. This improves efficiency and increases the peak pressure ratio (aka boost pressure) the compressor can achieve.
Wrapping up the compressor wheel design is the trim. Again this is the ratio of the exducer and the inducer diameters. The OE compressor has a 72.3 trim which is pretty large, but typical for very small compressor wheels such as the one that comes in the Civic 1.5L. The 27WON W1 compressor has a 65.8 trim which increases peak pressure ratio capacity without sacrificing peak flow.
In-fact, a 66 trim is still a fairly large trim, you’ll see in the future, that as the overall wheel diameter increases the wheel trim will decrease and hover around 52-58. There are enough details in just compressor trim for another separate blog so we can save those for later.
The last consideration is the turbine to compressor wheel ratio;
this is the ratio between the turbine wheel inducer and the compressor wheel exducer. Going beyond 1.25:1 can experience issues with boost control and unbalanced loading on the bearing system that would lead to premature turbo failure along with other concerns. The OE Civic turbo sits right at 1.24:1 vs the 27WON W1 Performance Turbocharger at 1.23:1. For the size of the W1 Turbocharger, this is gives a good balance of boost control, response, and power potential all wrapped up in a durable and reliable performance turbocharger.
We leave you with this note, The team here at 27WON felt it was of utmost important to inform and educate every single 10th gen Civic owner on the designs and physics behind turbocharger technology before just throwing out numbers and graphs. We decided to take the initiative to truly teach and help the new and old enthusiast truly understand the in's and out of the next generation of Honda turbo and GDI technology.
That being said in the next blog we will finally break into what everyone really wants to know, the power potential of the 27WON W1 Turbocharger for the Honda Civic.
Thanks for tuning in with 27WON Performance.
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