| Here is some more information that I found from the web ([ http://www.ztechz.net ]) and used as I selected which turbo setup I wanted. I ended up using the Garrett GT28R turbos also because I was happy with everything that I saw. I studied the compressor map and graphed it against our motor's airflow at different intake temperatures and liked what I saw. In theory... and again I stress "THEORY", these turbos should produce more than 600 crank hp between 6k and 7k rpms at around 120 degree F intake temperature. Many have argued that these turbos will be laggy on a TTZ... but the data, AS I READ IT, does not show they will be that bad... also, the members HakenTT and boileralum have them on cars and they say the lag is not bad. Here is what I base this info on: -Larger A/R for the turbine allows for more airflow and less backpressure... but this will increase the spool-up time (which means the turbos will be very laggy).
-Smaller A/R for the turbine allows for less airflow and more backpressure... with shorter time to spool-up (less lag).
-The GT28R turbo has a turbine A/R of .64... Smaller than the Sport700s (A/R=.64 or .86), so should spool faster than the Sport700s but not produce as much power due to airflow. -For "families" of turbine wheels (those with the same inducer diameter), larger trim usually means better flow with less backpressure but longer spool time.
-Smaller trim usually means less flow with more backpressure but shorter spool time.
-The GT28R turbo has a turbine trim of 62. Which is smaller than the Sport700s (trim=76), so should spool faster than the Sport700s but won't produce as much power due to airflow. Conclusion... I found what I liked with the GT28R turbos, so much so that I am putting them on my car. Many here do not believe they are a good match to our engine... but I believe differently. And in the end... I am the one that drives my car and has to live with the results. Good luck in choosing a turbo setup... There is a lot of work required with this and it is not a bolt on solution. I have templates of my brackets if you need help. -Jamie
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