Multiple times it was mentioned that a 3 bolt housing was in the works so I bought the turbo and waited.
If the 3 bolt mod was such a turd an update and details would have been awesome.
Looks like I will need some headers, no biggie. Too bad twin scrolls are so expensive
I wouldn't be so quick to disregard the 3 bolt, presently a limited number are available from
www.theturboplace.com (call the number and ask for Sam). These are from the same batch of housings pictured in post #20 of this thread.
At the recent Lorenz Performance and Racing open house two GN's with 3-bolt BorgWarner EFR-9174's were dyno tested:
First car was John Schmidt's, e98, GN-1 stroker with rollers and GN-1 heads and matching intake, to the rolls it made, 822 Ft-Lbs @ 3,800 RPM and 659 HP @ 5,200 RPM on ~29 psi, this car previously ran a 9.97 @ 135 with this set up but pig rich. Leaning the car out a bit while on the dyno bumped the power from 600 to 659 HP.
Second car was Bryan Lynch's, (phoneguy) stroker, pump gas with alcohol, TAI class legal, to the rolls it made 856 ft-lbs @ 3,700 RPM and 640 HP @ 4,500 RPM
Bryan's feedback about boost response is that it comes up on boost very fast!
Another recent development (Thanks to GEE-M racing) is true twin scroll headers!! These headers were on display at the 2018 TurboBuick.com nationals along with a BorgWarner EFR 7163-G turbo. These headers should accommodate all EFR twin-scroll turbos and also many of the BorgWarner AirWerks turbos.
There are now available options for 3-Bolt, single scroll four bolt, and true twin scroll four bolt.