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Old 09-07-2021, 06:48 PM   #8
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Member#: 508105
Join Date: Nov 2019
Chapter/Region: NWIC
Location: Greater Seattle Area
2002 WRX - Link ECU
being installed :)


Originally Posted by WRXnick16 View Post
I'd wait for the FA24 in the 2023+ STI. My bet is a simple downpipe (j-pipe), ethanol sensor & flex fuel tune will easily net ~375-400+ whp depending on the dyno. Then you'll still get the STI drivetrain, Brembos & hopefully Recaros. No need to upgrade the fuel system because the stock injectors have plenty of overhead.

The EJ just doesn't respond as well to ethanol and basic bolt-ons as the FA. The FA24 will produce more torque and be more responsive (longer 86mm stroke, higher compression ratio, low mount twin scroll turbo, etc.). Not to mention, it'll also get better fuel economy as an added bonus.

Here's a pretty fair-ish EJ257 vs FA24DIT dyno comparison (same turbo, similar mods, same dyno, same tuner). Keep in mind that this is the FA24DIT engine from the Ascent SUV.. not whatever special bits the STI-tuned version may receive.

The FA24 dominates in area under the curve and makes more torque everywhere despite the old EJ having a slight displacement advantage. It has the potential to be a monster if Subaru doesn't ruin the rest of the car.

FA24DIT (from Ascent):
Power: 537 whp
Torque: 490 wtq (lb-ft)
Fuel: E56 blend
Boost: 22 psi
Displacement: 2387cc (2.4L)
Bore & Stroke: 94mm x 86mm
Bore/Stroke ratio: 1.09 (oversquare)
Rod/Stroke ratio: 1.5
Compression: 10.6:1
Effective compression: 26.5:1
Injection: Direct
Turbo: Low mount, twin scroll, ball bearing, 22 psi
Specific output: 225 WHP/L (~265 HP/L)
BMEP: ~41 bar (~242 lb-ft/L)

EJ257 ('19 STI Series.Gray):
Power: 463 whp
Torque: 448 wtq (lb-ft)
Fuel: E85
Boost: 26 psi
Displacement: 2457cc (2.5L)
Bore & Stroke: 99.5mm x 79mm
Bore/Stroke ratio: 1.26 (oversquare)
Rod/Stroke ratio: 1.65
Compression: 8.2:1
Effective compression: 22.7:1
Injection: Port
Turbo: Single scroll, ball bearing, 26 psi
Specific output: 188 WHP/L (~222 HP/L)
BMEP: ~36 bar (~215 lb-ft/L)

Turbo specs for both setups:
FP XR Blue 73HTZ ball bearing turbocharger
Flow rating: 57 lb/min
Compressor wheel: 52.6mm inducer/73mm exducer
Turbine wheel: 60.8mm inducer/54mm exducer
CHRA: Xona Rotor ball bearing
Turbine jousing: EJ is single scroll, FA is twin scroll

Fair point but the FA20 is pretty capable as it is and he currently owns a car with one.
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