Blizzard25

Turbos Explained: Common Turbo Designations And Inducer/exducer Sizes, Trims And A/r

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Overview
Since this section is catered toward the Ralliart owners, I'll do my best to explain turbo designations starting with the stock Ralliart turbo, and I'll go from there.

The stock Ralliart turbo is the TD04HL-15T-7. The TD series are Mitsubishi manufactured turbochargers. The 03 is smaller than the 04, 04 smaller than 05 and so on.

15T describes the compressor size. 7 describes the turbine housing (exhaust gas side), with the Ralliart turbo having a 7 cm^2 housing. Very tiny.

If you choose to upgrade your turbo to a larger one, at some point you may see a designated trim and aspect ratio (A/R) of a turbo. Generally these don't actually describe overall power a turbo can make, but can be a very good indication of how high in the rpm band a turbo can make boost (ultimately determining overall power).

Turbine Wheel
To better understand how the size of each wheel creates more power/less or more lag, etc., we can start with the turbine. Many of you know that the turbo creates power by utilization of the exhaust gases to spin the compressor wheel, sucking in more air than a naturally aspirated engine can do on its own. The turbine plays a very important role in how the turbo flows. Turbines are able to spin because they are a physical restriction in the exhaust path (duh). The smaller the turbine, the greater the restriction in the flow and the faster the turbo can spool up. This however creates an increased restriction, and top end power is sacrificed. A larger and/or better flowing turbine (i.e. 9 blade vs 12 blade) creates less exhaust gas restriction, and in turn spool slower but are able to create greater top end power.

Aspect Ratio

Aspect ratio, more commonly referred to as A/R, is simply the inlet cross sectional area of the turbo divided by the distance between the center of the turbine wheel and the center of this area. You'll find that the larger the aspect ratio, generally the greater the overall flow rate of the exhaust gases (peak power increases). I'll post a photo below in the comments later to give you a better idea of what this ratio is.

Something interesting to note, it absolutely does not matter where you measure this cross sectional area. You can measure it at the opening, or you can measure it farther down the passage (how you would do this, i don't know). The aspect ratio never changes, because as the diameter decreases down the exhaust passage, the radial distance from the center of that area to the center of the turbine wheel decreases as well.


Compressor Wheel
This makes things a little more complicated. Compressor wheels are generally described by their inducers and exducers. If you look at a compressor wheel, you will see that it generally has two different diameters; a smaller one towards the front (ambient air side), and a larger one towards the back (turbo side). The smaller is the inducer (the part that initially "grabs" the ambient air) and the larger is the exducer (the part the introduces that air into the turbo).

Trim

You may have heard this term tossed around a few times. Trim just describes the relationship between the inducer and the exducer. The calculation to find trim is (inducer size/exducer size)^2*100. In short, if you keep a constant exducer size but increase the inducer size, the trim increases.

Increasing the inducer size allows a greater airflow, and thus a larger peak horsepower number. So why not just increase the inducer size to the maximum possible? Well for a couple reasons. First, increasing inducer size increases lag, which isn't a huge concern. The main concern is the possibility of compressor surge. Compressor surge is the reverse movement of the compressor wheel due to reverse movement of the air (in essence your compressed air is now flowing backwards). If you increase the inducer without increasing the exducer, it's possible to overcome the ability of a turbo to take in all that air, and it will turn around and spit it right back out.

Increasing the exducer without increasing the inducer has similar, but opposite results. Because the exducer is what inputs that air into the turbo, you decrease spool time. A larger exducer diameter mean the compressed air now exits the compressor wheel at a much greater velocity (you have a higher ratio of wheel edge speed to shaft speed)

Obviously the optimal thing to do is increase both diameters, but if that isn't possible refer to the turbo flow maps.

Common Turbos and Their Specifications

Garrett T-25 2G DSM Stock turbo Compressor Inducer 38.7mm, Exducer 52.2mm Turbine Inducer 46.5mm, Exducer 40.4mm

TD04-13G 1G Auto DSM Stock turbo Compressor Inducer 40.1mm, Exducer 50.8mm Turbine Inducer 46mm, Exducer 41.3mm

TD05H-14B 1G 5 speed DSM Stock turbo Compressor Inducer 43mm, Exducer 58mm Turbine Inducer 56mm, Exducer 49mm

TD05H-16G (Small 16G) Compressor Inducer 46.5mm, Exducer 60mm Turbine Inducer 56mm, Exducer 49mm

TD05H-16G (Big 16G) EVO VIII stock turbo Compressor Inducer 48mm, Exducer 68mm Turbine Inducer 56mm, Exducer 49mm

TD05H-155G6 EVO IX stock turbo Compressor Inducer 49.2mm, Exducer 68mm Turbine Inducer 56mm, Exducer 49mm

TD05H-152G6 EVO X stock turbo Compressor Inducer 47.1mm, Exducer 68mm Turbine Inducer 56mm, Exducer 49mm

TD04HL-15T-7 Ralliart stock turbo Compressor Inducer 42mm, Exducer 56mm Turbine Inducer 52mm, Exducer 45.6mm

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Thank for this Bro... Not that I understand this..lol

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Haha it's a great time to learn man. But thanks :thumbsup:

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My turbo question is about RPM and spooling.

I feel like I wouldn't want the turbo to kick in at highway speed, so I'd probably want no spool until 3500 RPM. However, I'm also not sure that I'd reach that RPM often under normal driving conditions. @Blizzard25 where do you spool?

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My turbo question is about RPM and spooling.

I feel like I wouldn't want the turbo to kick in at highway speed, so I'd probably want no spool until 3500 RPM. However, I'm also not sure that I'd reach that RPM often under normal driving conditions. @Blizzard25 where do you spool?

You're not going to get that unless you get a MASSIVE turbo. Even with my new larger turbo, it still starts to hit boost around 2200 rpm. Plus you have to remember, the turbo is always spinning, even at idle. Why wouldn't you want it to spool up at highway speed?

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Why wouldn't you want it to spool up at highway speed?

I feel like that is unnecessary and inefficient. When I'm at speed I don't need boost, the boost is just to get up to speed.

My train of thought could be all wrong though, I am still learning a lot about turbo

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But if the turbo already run at low speed u can save fuel a little u know

Sent from my SHV-E250S using Tapatalk

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