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Old 08-20-2018, 09:41 PM   #1
Scooby Newbie
Member#: 490389
Join Date: Aug 2018
Default Advice selecting turbo/headers for EJ25 hybrid

So I have an EJ25 with domed and mild port EJ20 heads and stock cams (in an 03 wrx)
I forget now what the compression ratio is (either 9:1 or 9.5:1) and cast catless sti manifold/up pipe, and sti intercooler.

I briefly had a used vf39 (which failed the 1st time I ran it) and the spool was amazing, torque right from idle! (Don't know what top end was like as it failed before I ever ran it hard).
Then I slapped the stock wrx turbo back in which worked but was significantly less torquey and powerful than the VF39.

I have the engine out and am doing some work to the heads, going to have pistons coated etc. and figure this is a good time to upgrade my turbo.

As I said the spool of the cast sti manifolds and VF39 was amazing and I could just have the vf39 rebuilt (or maybe take a chance on one of those ebay CHRAs)
I like the idea of twin scroll though (and I have a stainless equal length twin scroll header that I can use already) so I was thinking of a VF36 or a Kinugawa twin scroll GT2971r.
I don't want to lose spool though. This is a twisty road/autocross/road race car, 300-400hp at most would be great.
In theory twin scroll is supposed to spool faster, but it is also a lot of extra volume in the header compared to the sti manifold. Anyone have any real world experience with this, or the Kinugawa turbo in particular?
Or any totally different suggestions are welcome as there are so many options for these cars, it is hard to consider everything.

And if anyone is wondering, the reason I am running 9+:1 compression is because I want to pull right off idle and don't plan to run super high boost levels. (I previously had a different turbo car with 8:1 and hated how unresponsive it was before the turbo kicked in).
Any input from real world experience is appreciated, thanks!
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Old 08-21-2018, 04:28 PM   #2
Scooby Newbie
Member#: 305707
Join Date: Jan 2012
Chapter/Region: International
Location: AUS
1999 WRX
WRC Blue


Dom3 twinscroll will make 200kw around 4000rpm on that set up where a vf turbo will make around 200kw peak.
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Old 08-21-2018, 09:05 PM   #3
Scooby Specialist
Member#: 375462
Join Date: Dec 2013
Chapter/Region: NWIC
Location: Portland, OR
2006 Impreza WRX STI
WR Blue


OEM - VF36 (if you have a cable throttle) or VF53 (if you have DBW)

Numerous options for exhausts, here... and most will not perform significantly better than the OEM tubular twin-scroll manifold.

Aftermarket (more work) GTX2860R

You'll be looking at custom options for the manifold in this case.

You won't suffer in terms of spool time with any of the above, but make sure you wrap any aftermarket tubular manifold.
mrsaturn7085 is offline   Reply With Quote

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