2013-04-09, 01:11 PM | #1 |
EJ18
Real Name: steve Join Date: Aug 2011
Location: NW Reno
Posts: 43
Car: 05 Forester XT
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Dyno Time
Hey guys,
I recently moved away from the Reno area but thought Id still throw up a tech question. I have an '05 forester xt. Sti : turbo, intercooler, up-pipe, fuel pump, cat-back. Invidia catted downpipe. I recently moved to Fayetteville NC elevation about 300 ft. The tune I have is from Matt at K-speed, I feel like its a pretty good tune but I got it dynoed here just to see what kind of numbers I was making. in case its hard to see: it says 226 whp/ 238 wtq/ AFRs hang out around 10.5/ boost peaks at 18.3lbs I was expecting closer to 250-260 whp... I was looking for issues that might be hindering my power. My thoughts: -I am running a tune for 91 gas -I am tuned for a way different elevation -Would an intake help that much? I thought subaru stock intakes werent too restrictive till bigger power numbers -Tuner recommended a EBC to keep boost up later in the rev range -Cat back cant be that restrictive...?? from unabomber: "Which exhaust diameter is best? Exhausts have 3 diameters: 1. 2.5": Good for 300-350 HP 2. 3.0": Good for 500-600 HP 3. 3.5": Good for 600HP + " Thanks in advance guys! Last edited by scubasteve; 2013-04-09 at 01:32 PM. |
2013-04-09, 01:38 PM | #2 |
EJ22T
Join Date: Sep 2003
Location: Reno
Posts: 9,445
Car: '93/'01 GF6, mostly red
Class: 19 FP
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That power is spot on for a VF39/VF43 and a conservative tune. Exhaust diameters don't make more power, they just permit it. Muffler design is just as important as pipe diameter, if not more. A 2.5" Stromung exhaust is less restrictive than a stock 2.5" STi catback for example.
I do not recommend going to an EBC at all personally, and you 100% will need a retune if you do. The reason the boost tapers off is the STi turbo isn't really big enough for the 2.5 liter engine, and there's nothing any tuner can do about that. An EBC can improve spool up at lower RPMs to a small extent, but it doesn't help the top end. You need a bigger turbo or better fuel for that.
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2013-04-09, 02:19 PM | #3 |
EJ18
Real Name: steve Join Date: Aug 2011
Location: NW Reno
Posts: 43
Car: 05 Forester XT
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Interesting, thanks Kevin.
I agree that switching to a 3" catback wouldnt increase power but do you feel that the Sti catback/muffler is restrictive for my setup? Matt also mentioned that he tuned it to lower boost at the top of the rev range to keep it a little "safer" as well... Im not too sure exactly what that means My end goal is to get somewhere closer to 300 whp, at least on the other side of 250 haha... Are you suggesting a larger turbo as the best way to get closer to my goals? along with injectors and possibly exhaust.... thanks again |
2013-04-09, 02:26 PM | #4 |
EJ22T
Join Date: Sep 2003
Location: Reno
Posts: 9,445
Car: '93/'01 GF6, mostly red
Class: 19 FP
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Yes. If you want to approach 300whp, you need something like a 20G or larger I think. The turbo needing to taper boost is a bit complicated if you don't have a decent background in physics to understand some basic fluid dynamics and thermodynamics, but if you have studied the Law of Diminishing Returns for economics, that is a good approximation. You can keep cranking up the boost, but it gets more and more "expensive" for lesser and lesser returns.
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FWD is the new AWD |
2013-04-09, 02:37 PM | #5 |
EJ18
Real Name: steve Join Date: Aug 2011
Location: NW Reno
Posts: 43
Car: 05 Forester XT
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20g sounds kinda like a build motor...hmmm not sure Im up for that quite yet
Ive read enough to get the idea that continuing to increase boost also increase heat which makes a less dense air charge = less that will fit in a cylinder.... but for the rest of it, I will take your word for it. Whats your take on aftermarker upipe, maybe PNP headers to get a few more ponies? |
2013-04-09, 02:54 PM | #6 |
EJ205
Join Date: Jan 2006
Location: Reno, NV
Posts: 1,840
Car: Impreza and an Impreza
Class: AS / CRS PerfStock
"pedal on the right"
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Not to thread jack, but Kevin have you dynoed your Crazy/Awesome NA 2.5 build ? wondering what your whp/wtq numbers are ?
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2013-04-09, 02:57 PM | #7 | |
The Doink
Real Name: Scott Join Date: Nov 2002
Location: Portland, OR
Posts: 20,335
Car: '09 OBXT, '02 WRX, '96 Miata
Class: PDX/TT-6
The way out is through
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Quote:
So while the 20g is a medium/large turbo, it's perfectly okay to run it at lower boost levels safe for a stock bottom-end EJ255. Because it will flow a ton more than the VF43, that same boost level is actually a bunch more power. Plus, you won't need to taper as much towards red line. I would bet a 20g at 16 or 17 psi will be over 250whp. At 18psi, close to that 300whp you're looking for. The stock STi cat-back might be a bit of a limit, but not terribly so. Your non-STi heads are far more the reason you're not getting STi power levels. Of course there will be some spool issues... the STi turbo is a wicked fast spooling turbo. So, your boost will come on a bit later with a 20g. But that can be combated with choosing the proper hot-side. If you're not racing the car, the TD05-20g is a crazy awesome turbo on a 2.5l block. Spools like the STi turbo, but will get you to that 300whp level with proper supporting mods. However, this turbo is known to run high EGTs when WOT for long periods. Both MikeK and I have run it... it's an awesome turbo, but at the track, you'll start melting stuff like timing belt covers. On the street, it's unlikely to be an issue because you're not going full-throttle lap after lap, but it's something to be aware of. The far more popular TD06-20g is a bigger hot-side version of the same turbo. It will spool later, make a bit more power, and run cooler. It's probably a little big for an unbuilt EJ255 w/ non-STi heads, but not by much. I bet there are tons of people running that turbo on the same block as you. And there are probably like 40 other variations/tweaks of similar sized turbos... I'm just not up on the latest and greatest since I'm not turbo shopping for a Forester these days.
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2013-04-09, 07:36 PM | #8 |
EJ18
Real Name: steve Join Date: Aug 2011
Location: NW Reno
Posts: 43
Car: 05 Forester XT
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Wow, thanks for the input! That is some really good food for thought!
which company did your source your turbo from? I dont plan on tracking the car, it sounds like a really interesting idea. What is the big difference with the STi heads? intake port size? cam size? |
2013-04-10, 09:51 AM | #9 |
Candy Mountain
Real Name: Cody Join Date: May 2005
Location: Californication
Posts: 7,751
Car: 03 Pussy Wagon, now with more pink!
Class: TESP
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No idea at all what is typical for your setup, but are your stock injectors holding you back? I know my tuner indicated that my stock injectors are hitting 100% IDC on a cool morning at sea level, which was never an issue at elevation...
I don't think it would be unreasonable for you to get a freer flowing CBE, an MBC (if your tuner is familiar with tuning for them) or an EBC and a retune, if others with your setup see better numbers on that dyno in similar weather. The boost controller won't increase max power, but it makes the car much more responsive (boost response), especially at lower RPMs.
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Slow and low, that is the tempo. Last edited by cody; 2013-04-10 at 09:56 AM. |
2013-04-10, 10:08 AM | #10 | |
The Doink
Real Name: Scott Join Date: Nov 2002
Location: Portland, OR
Posts: 20,335
Car: '09 OBXT, '02 WRX, '96 Miata
Class: PDX/TT-6
The way out is through
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Quote:
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2013-04-10, 10:14 AM | #11 | |
The Doink
Real Name: Scott Join Date: Nov 2002
Location: Portland, OR
Posts: 20,335
Car: '09 OBXT, '02 WRX, '96 Miata
Class: PDX/TT-6
The way out is through
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Quote:
Not only would small injectors be a huge limit on power, they'd be a safety issue unless the car's boost was drastically limited to stay away from 100% DC. And Cory... if you're hitting 100%... get some injectors! Slap a set of deatchwerk 750's in there. It should be a simple rescaling of your injector map and some minor tweaking on-road. Not a major re-tune, since the injector latencies should be identical.
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Is you is, or is you ain't, my con-stit-u-ints? Last edited by sperry; 2013-04-10 at 11:00 AM. |
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2013-04-10, 10:16 AM | #12 |
EJ22T
Join Date: Sep 2003
Location: Reno
Posts: 9,445
Car: '93/'01 GF6, mostly red
Class: 19 FP
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The EJ255 uses side feed injectors identical to EJ257 side feeds. Sometimes a fuel pump upgrade is a good idea for EJ255s though, and definitely if you go bigger than VF39/43.
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2013-04-10, 11:02 AM | #13 |
The Doink
Real Name: Scott Join Date: Nov 2002
Location: Portland, OR
Posts: 20,335
Car: '09 OBXT, '02 WRX, '96 Miata
Class: PDX/TT-6
The way out is through
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I'm so confused... I thought the '04/'05 FXT got the setup that went into the '06+ WRX. Isn't the '06 WRX top-feed, just like the STi became? Is the '04/'05 FXT it's own deal?
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2013-04-10, 11:26 AM | #14 |
EJ22T
Join Date: Sep 2003
Location: Reno
Posts: 9,445
Car: '93/'01 GF6, mostly red
Class: 19 FP
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I'm not 100% on the '06 WRX, but I think it's side feed and the '06+ STi is top feed. I know for sure that the early FXTs got side feeds.
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2013-04-10, 08:40 PM | #15 | |
Candy Mountain
Real Name: Cody Join Date: May 2005
Location: Californication
Posts: 7,751
Car: 03 Pussy Wagon, now with more pink!
Class: TESP
OMG Internet!
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Quote:
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