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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
If "broke his turbo" means he sheered a shaft, that is usually for from compressor stall that comes form a BOV malfunction than how much the bearings are cooled. Risk for this is increased by eliminating the de-accel valve and or running a larger than stock compressor wheel. Sometimes tubos built on a T3 frame can have smaller shafts that can make them more susceptible bit I think most the tubo's in our flow range now have more substantial shafts.

Not having a map should not be to big of a deal.

I suspect if you can find a compressor wheel that is very close in dimension to a non mapped wheel you can get pretty close to understanding the map of a non rated wheel. There may be some fine differences in efficiency that come from the fin design but I suspect it is not that much compared to other decisions or changes that effect the total package. Maybe a point or two more efficiency at close to the same flow rates.

Getting the motor on the right part of the compressor map at TQ and HP peak is probably a much bigger issue.

I just do not think there is as much magic in the fine points of the compressor impeller design as the magical turbo builders what us to think.

Other factors can quickly become more important.

I do not think one is going to find that much difference between a HF, 60-1, 62-1, or GT 35 compressor wheel if all other factors were the same. All those compressor wheels are a great fit for a 3.3 making up to 500 hp and more efficent than stock on a motor making near 400hp.

Add in ball bearings and changes to the hot side and there is going to start to be potential for a performance difference.

One of the problems with a 930 is the metering assembly adds restriction before the compressor wheel. Turbos do not like any restriction before the compressor wheel or after the turbine wheel. Restrict these and the performance will fall off quickly.

Thus, I suspect turbos with large compressor wheels and small hot sides that can work well with EFI motors, are not the best fit with CIS. We have to keep the hot to cold side ratios somewhat in ballance. Other wise we have a turbo that might start to boost sooner but takes a long time to reach full boost and end up with high header pressures as the compressor wheel's higher torque fights against the the small turbine wheel.

There are enough 930 owners that have done well with the non KKK turbos that I would have to consider trying one with proper attention to the oil supply and cool down. With this I might get up to 300rpm faster spool from the difference in bearings alone and increased potential for a more efficient turbo by matching the hot side to my goals. (Larger turbine wheel with a smaller AR housing for a big CIS street motor?)

Just my opinion for what it is worth as I have a lot to learn about Turbos.
Old 01-03-2010, 02:37 PM
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