Clipping will help out somewhat, but the overall bore and diffuser area will still remain untouched and the wheel will still be a significant restriction. The biggest reason I can see to clip the Turbine wheel in this application is not so much for the marginal airflow increase, but more for protection against compressor surge. Every compressor wheel has a flow map (or flow chart) where you can see a line on the far left side, called the surge line. The map is a measurement of wheel performance documenting its ability to produce Pressure vs. Airflow, and bigger wheels generally react very poorly to High pressures vs. low engine airflow. The clipping of the TD03L Turbine wheel on your turbos is thus doing two things to aid with this:
1) Slightly increasing airflow per a given pressure level, mostly at higher airflow levels.
2) Slowing down the turbines response to exhaust heat and pressure so that it will not as easily make the compressor produce intake pressure (ie. laggier response) and thus keeping the compressor to the right of the surge line (ideally). Some wheels have a more friendly surge line than others, and this is where wheel choice becomes of importance.
The TD03L Turbine also appears to have been designed with a form of clipping as part of its original design from MHI, and I believe there was likely alot of research into the blade design to make it perform optimally (alot more physics than I am qualified to speak about). Overall when you start modifying a wheels construction, it really comes down to some trial and error. In some instances, you just find that you can only mismatch a compressor vs. turbine SOO much and there comes a point where you need to keep them sized appropriately for one another. My gut tells me that the OE compressor is sized very well for the OE turbine, and going bigger is only pushing the envelope. However my gut instinct only means so much whereas real world testing means so much more, so I will stay tuned to see what you come up with out of these.
As for the ASR/RD Turbos not being water cooled, I dont know what to say as to why they both chose that path when all Water Cooling functionality is in place on this platform and Garrett readily offers Water Cooled CHRA's that would appear to work (aside for simplicity of adaptation/cost reduction).
I do know that ball bearing turbos use only a little oil for lubrication, so don't count on much cooling from the Oil either. This leaves you solely with the air cooling, but considering the environement our turbos are in I think the coolant flow would be very advantageous (or at minimum ALOT of Oil flow). These turbochargers are really crammed in a tight location with the direct presence of both Turbine housings, exhaust manifolds, very close engine block, and Both downpipes' Radiant heat 24/7... which surely doesnt help those casting "fins" to do much to expel the heat. If I went the ASR/RD Turbo route (just my personal thoughts) I would at least wrap the Downpipes as much as possible to help with radiant heat.
Please note I am far from a Garrett Turbo Engineer, but I'd think the only way to know precisely how well they would perform long term is to know the facts on the CHRA's ability to fight off heat vs. Ambient Temps. Surely Garrett has some documentation on ideal ambient and operating temp ranges that these CHRAs could be subjected to and still perform as intended, but I am not privy to it nor have I measured the temps in that region of the compartment to compare.
Rob
Quote:
Originally Posted by E92Fan
Thanks for your input. I can see the point you're making about volume of air going through the turbo and the restriction of the exit side. However I believe that Turbo Dynamics have modified the exhaust turbine wheel to increase the speed of expellation, or flow rate, and this should mitigate the apparent restriction of the exhaust turbine size.
Also, do you not have a concern that the ASR/RD turbos will suffer from heat soak issues given the CHRAs aren't water-cooled? ASR state that the new Garrett cores are so robust that they don't require water-cooling, yet when you look at the Garrett website which lists all the available CHRAs, the vast majority are all water-cooled (especially in the GT28 and GT35 ranges)
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