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Old 08-27-2009, 05:55 AM   #11
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Originally Posted by bobc455 View Post
Again, not so easy - since many turbos spin at 30,000 to 60,000 RPM (and I've heard of some at 100k+ RPM)
If you look at the flow chart I posted above, the (mostly) horizontal curves with the big numbers next to them are RPM values. The map starts at 56,400 RPM. A super-60 T3 (60 referring to the .60 A/R value) is a middle of the road to slightly large turbo for automotive applications. Larger turbos may spin slower, smaller ones may spin faster.
The ovals are regions of efficiency if I recall correctly. The closer to the middle oval, the more efficient the compressor will be operating.
Pressure ratio refers to how much boost the compressor is producing. 1.00 = atmospheric pressure x 1 = no boost. 2.00 = atmospheric pressure x 2 = ~14.7 psi. The chart maxes out at about 2.8, or 26 psi of boost.
Air flow in lbs/min along the bottom will depend on your engine's displacement and volumetric efficiency (how efficient it is at moving air) as well as how much boost you're running.
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Old 08-27-2009, 06:21 AM   #12
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I'm not quite sure the compressor info will help him much, since that's the intake side.
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Old 08-27-2009, 07:00 AM   #13
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Use an optical tach. No weight addition and you can just read off the compressor shaft.

That link isn't exactly what you are looking for but it's close.
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Old 08-27-2009, 09:01 AM   #14
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Originally Posted by RoadWarrior View Post
I'm not quite sure the compressor info will help him much, since that's the intake side.
Yeah, but unless you've got some horrific blow-by issues or a boost leak, the air flow being fed to the engine should be directly related to the exhaust flow coming out. A properly sized turbine and compressor pair should be able to drive each other, again assuming there are no mechanical or design issues with the engine.
The question the flow map really addresses is how well paired would the turbo be with a given engine... How much boost will it take to shove a given flow rate of air through said engine and how efficient will the turbo be under those conditions. Once you've figured out where you will be on the map, reading off the shaft RPM is easy.
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Old 08-29-2009, 08:54 AM   #15
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i think garrett has full explanations and guides on selecting a turbo and all the math involved on their web site. very well written out as i remember
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Old 01-07-2010, 08:06 AM   #16
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Use an optical tach. No weight addition and you can just read off the compressor shaft.

That link isn't exactly what you are looking for but it's close.
I thought of capturing the turbine sound with a microphone and a small circuit to detect the main frequency.
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Old 01-07-2010, 06:17 PM   #17
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That should work or magnitize a single blade on the intake fin and use a hall or inductive pickup to measure the rpm that way. Heat is one of the problems however for the sensors. Depending upon the diameter and weight of the impeller the speed can be pretty high.
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Old 01-08-2010, 06:47 AM   #18
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Originally Posted by zero_gravity View Post
i think garrett has full explanations and guides on selecting a turbo and all the math involved on their web site. very well written out as i remember
Correct, I also suggest studying the Ferrari F-40 engine.

They utilized turbos that offer varying amounts of boost throughout the RPM cycle. We looked at their design for the layout of some 4.7L Dodge Dakota turbo setups.
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