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Re: Turbo... Posted by David in Tallahassee [Email] ![]() ![]() In Reply to: Re: Turbo..., SWEDISH DYNAMICS, Tue, 26 Feb 2008 13:14:52 Members do not see ads below this line. - Help Keep This Site Online - Signup |
I'm somewhat baffled by the consensus here on how to read a compressor map.
Garrett's own website explains that the target crank horsepower number divided by ten will give the approximate air flow in pounds per minute necessary to produce that amount of power. For an output of 250CHP you would need to move approximately 25 pounds per minute. A T3-60 or a T3 Super 60 is WAY more turbo than you need to move 25 LB MIN. As a matter of fact at a 2.0 PR (Which BTW is approximately 15PSI of boost) the T3-60 is in it's highest efficiency island at 25 LB MIN. The T3-Super 60 is even a little further to the left. A 2.0L 16V engine will ingest approximately 25 LB MIN at 5500 RPMS and 15-16 PSI boost at a 90%VE with compressor efficiency of 70% and I/C efficiency at 70%. These numbers will produce roughly 250CHP and that is on a C900. On a newgen with Trionic 5 you could expect roughly 270CHP between a little better VE and better timing management.
Sizing a turbo to put the peak HP in the center of the highest efficiency island is not necessarily a good idea. In the real world it results in a peaky powerplant with a narrow area under the curve. The ideal arrangement is to have peak torque near the surge line with peak power near the choke line. This gives the broadest spread of useable power. Certainly if you intend to maintain maximum boost pressure for long durations you might slightly oversize to keep temps from rising over long periods but fundamentally this is generally unnecessary.
Also, the outlet temp rise between 60% efficiency and 74% is VERY small. (Like 10-20F) Not NEARLY enough to impact the equation significantly in terms of power OR reliability.
If you want a nice swell of torque in the low end followed by a HP peak of 250 or thereabouts around 5500 RPMS, do yourself a favor and do a T3-50 or AT MOST a T3-60. If you do the 60, you might as well shoot for 275-300 because the turbo will move plenty of acceptably cool air to get you there.
Here's a map for fun:
http://www.rbracing-rsr.com/turbo/TurboMaps/t3-60.gif
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