I rode in a friend’s Ferrari (1978 308) recently and while I love how it sounds… I often can not get enough of the turbocharged sound. So if you love the sound of turbochargers doing work here you go:
Link for you RSS peeps.
It may be an older video of ours, but I love it and cannot get enough.
Update: Apparently I decided to post this exactly two years after uploading it to YouTube. Odd.
Welcome back to the turbocharger series. Today’s lesson should be short and sweet; It is going to address some misconceptions I hear about size. And no, bigger isn’t better. I know I have covered turbo sizing to an extent in the second part, but I feel that there are some things that I have seen recently that I must comment on.
The first of those is about something called “Trim”. I have seen this used time and time again as a size descriptor for a certain turbo. It is not! A single turbo has two trims, one for the compressor wheel and one for the turbine wheel. Usually it is used in reference to the compressor.
So what is trim? Well, if you have read part two, you may recall that it is a ratio between the inducer diameter and the exducer diameter, Inducer²/Exducer² to be specific. Now, take note of that. It is just a ratio, nothing more. Yes, it does change the flow characteristics of the turbo a bit, but it has no bearing on the overall flow capabilities of the turbo, nor it’s size.
With that off of my chest, there is one other insane issue that I see crop up from time to time. Compressor wheel upgrades. It is often viewed as a cost effective upgarde to rebuild an engine’s stock turbo with a larger compressor wheel, without changing the turbine side at all. In some cases, this is actually a good idea.
However, in the vast majority, the stock turbo has a smallish turbine side to produce boost lower in the RPM band. When an even larger compressor is hooked up to that turbine, some not so good things can happen. First and foremost is compressor surge. The turbine has the potential to spin the compressor too fast and generate more boost than the compressor is capable of handling at that airflow, which leads to surge, which is extremely bad for the turbine.
The second is something that I mentioned in part four: Exhaust backpressure. A smaller turbine will result in higher backpressure, reducing the overall efficiency of the engine, and increasing exhaust gas temperatures. In other words, the engine’s power is reduced somewhat because it has more trouble flowing air, and is more susceptible to damage due to the higher temperatures.
Moral of the story: Before upgrading a turbo, make sure that both sides complement each other well. Flow capabilities should be similar on both sides.
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