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Old 09-03-2019, 11:32 AM   #36
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Member#: 447898
Join Date: May 2016
Chapter/Region: BAIC
Location: W Sac, CA
2016 WRX (traded)
2019 STI CWP


Originally Posted by WideBody View Post
Unless they can somehow make it rev higher, it's going to be a miserable STI engine, regardless of the torque numbers. What I always wanted was a STI with a sub 6000RPM redline
It has the potential to rev just as high as the FA20 in the WRX or BRZ since it maintains the same 86mm stroke and overall engine design. It just depends on what Subaru decides to do. I wouldn't hold my breath for anything over 7,000 rpm..

FA redlines:
Forester XT (CVT) FA20F: 6,000 rpm
WRX FA20F: 6,700 rpm (CVT is 6,500 rpm)
BRZ FA20D: 7,400 rpm
Ascent/Outback (CVT) FA24F: 6,000 rpm

EJ redlines:
USDM STI EJ257: 6,700 rpm (same as wrx - not a high revving engine)
JDM STI EJ207: 8,000+ rpm (depending on the year/model)

The redline limitation of the WRX's FA20F & STI's EJ257 both involve head flow (ports, cams, valve springs, intake manifold, etc.) and a few other things. The EJ257 is limited by its UEL header. The FA20 is limited by its smaller turbo. The oiling system also isn't optimal for high rpms. However, these are all things that could be fixed if Subaru chose to..

Both engines have a relatively small stroke that will keep piston speeds safe at higher rpms.. just look at the EJ207's 8k+ rpm redline. Just for fun, here's an example of a EJ207 revving to 12,000 rpm.

It would be amazing if Subaru designed a "frankenstein" engine based on the existing FA platforms..
  • Head & intake manifold design from the BRZ's FA20 = more power & higher redline
  • Toyota's D4S dual injection from the BRZ = more efficient & eliminate carbon build-up
  • A good "STI" cam design that falls somewhere between the WRX & BRZ's (designed for a turbocharged engine) = more power & higher redline
  • A beefed up version of the Ascent's FA24 short block (it's already stronger than the WRX's FA20F) = more displacement & withstand more torque
  • A good EL header with a larger twin scroll, ball bearing turbo = more power & higher redline
But I'm dreaming at this point. That would easily produce an engine capable of 350-400 hp in stock form.. and probably close to 400 whp with just adding flex fuel.
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Last edited by WRXnick16; 09-03-2019 at 11:45 AM. Reason: Added what I wish Subaru would build
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