Estimated HP gains - bolt on mods and reflash?

[Dimman]

Thing with the headers and intake is that it sounds like they were used to spread out any torque gains as widely as possible. So there is probably power available with the natural caveat of the narrower powerband.

As it stands the rev limit is putting the mean piston speed ~4200 ft/min. If they over-built the bottom anticipating 8000+ rpm, then cams plus tuning the full torque peak to ~6500 should give some very nice top-end power gains.

I think this motor with a more specifically-tuned rev range will put out ~170+ lb-ft.

[fatoni]

Originally Posted by CyberFormula

i read on a review of a video drive once where the driver asked the rev limit....could be higher...but was not for reliability. So why not find out what sort of things will break ...and reenforce that.....so now we can tune the engine to rev higher? I presume you can can 220hp from this.

because that costs money and this car is supposed to be cheap. it would be nice but there are already cars that take this concept to the limit...the dont cost 25k

[Gardus@Supersprint]

You can keep the first part of the primary pipes at the correct diameter (same as the exhaust ports) and increase them downstream. We call them "step-design" headers.
Right now we make them for the Ferrari 430, Porsche GT3 3.8, Lotus Elise/Exige Supercharged, Nissan 370Z and M3 E46. We also tested one on the RS4 V8 but it didn't go into production because the tests were inconclusive, the engine wasn't reliable (the intake manifold got dirty with oil after some time and the performance dropped)

It's been developed for engines with a wide rev range, to not sacrifice either lowend torque or highend power.

We could develop one for the D-4S engine, with longer primary pipes a bigger diameters, and a single, 200 cpsi cat. It won't be cheap but it would probably be the best chance to get over 220 hp without cams or anything else.

Based on this picture:

I'd say the exhaust use a 4-2-1 manifold.
Given the revvy nature of the engine, a 4 into 1 step-design header with longer primaries and a sports cat placed where the secondary stock cat is would be my best bet.
A sleeve joint to allow the variation of the lenght of the primaries caused by the high temperature may be needed. Not as much as in the Impreza turbo header but still.

The stock header is not stainless steel but mild steel so it has a lower lengh elongation constant.

[gal1950]

Not to be negative, I've owned 25 Subaru's, and that is what you got under the hood, is a Subaru Boxer 4 N/A. I've owned WRX's, Legacy GT's, Forester XT's and several Impreza RS's , coupes and , wagons. Your N/A 2.0-2.5 boxer engines are not easily modified, and you really don't get to much performance for the money spent. Cobb used to make a Accessport for N/A engines, but they got out of the business , there wasn't enough benefit to pay over $500 to get very LITTLE gain in performance, people just quit buying them, Cobb just deals with turbo model cars. Your turbo 2.0 and 2.5 engines are totally different, so parts are not easily swapped. The only way to gain significant power out of the boxer engine is to turbo, or supercharge it. You might be able to gain 10-20 hp with items mentioned like exhaust, air intake system etc. but you will not see the same amount of gains as you would in other models, it seems Subaru doesn't leave alot on the table to make gains from ad on's. At least in my experience. There are not a great deal of parts available either, and with the limited of number of these cars to be sold, Subaru saying no more than 2500-3000 for them per year, Toyota/ Scion???? I really don't think the aftermarket is going to be very quick in getting out performance parts, since Subaru is already stating they are coming out with a turbo model within a year.
If I had a crystal ball , I would say, unless you plan on rebuilding the engine with performance parts, costing $$$$$$$, or putting a turbo on the car, those will come , may take a while !!!!! There isn't going to be alot to be had in performance parts, and when available not much power to be gained. That has been the history of Subaru's boxer N/A engines !!!!!! SAD BUT TRUE !!!! Things might change, but don't look for it, Scion folks, might hope that Toyota changes their engine offered in the FRS. Another thing, although the boxer engine is good proven engine, I believe that there were better choices to be made for this application. I'm a loyal Subaru fan, I've also owned several Toyota's, but they should have put a better engine, with performance ad-on capabilities, in this car, just my opinion, everyone has got one !!!!!

[Homemade WRX]

^^^^the FA20 is a completely different engine from the EJ, so I wouldn't start to speculate. Add that and the fact that direct injection leaves room for more power over port injection; I'm curious to see what head room was left in the engine from the factory. If you've ever tuned or built Subaru's from and engineers approach, you will know there is lots left on the table because of the factory tuning 'around' emissions.


glad to see someone else knowing what a stepped manifold is, however in the US the steeped feature, we just consider to be part of the 'primary' section of a manifold.

for those who don't know, a step is nothing more than the first section of the manifold that is the same ID as the port. It is usually kept short and then 'steps' into a larger ID tube in the primary...with a hard lip. This lip acts as an anit-reversion device. Then the primaries will come into a collect or go into secondaries (tri-y).

As a performance and emissions enigneer, the factory usually leaves a decent amount on the table because of budget and tuning for emissions.

[old greg]

[nrclptcnsmniak]

interesting read. I never knew NA engines had such little gain with aftermarket parts and tuning. My stage II wrx was a big difference in power with such little $$$... If a factory turbocharger comes out later thatd be my approach... It seems as FI is the only way to reach 250 whp (which is where id like to be some day). One thing for sure though I am keeping power mods minimal and am going to let others do the experimenting. Really makes me wish they had used an H6 for this car. oh well.

[RegisBou]

Originally Posted by nrclptcnsmniak

interesting read. I never knew NA engines had such little gain with aftermarket parts and tuning. My stage II wrx was a big difference in power with such little $$$... If a factory turbocharger comes out later thatd be my approach... It seems as FI is the only way to reach 250 whp (which is where id like to be some day). One thing for sure though I am keeping power mods minimal and am going to let others do the experimenting. Really makes me wish they had used an H6 for this car. oh well.

Hopefully they will release an H6 version to bring in the V6 genesis prospect buyers?

300whp NA on the 3.6 should not be that difficult. Maybe they could even come out with a 3.0 or 3.2 H6 for weight savings and just run high comp and D4S like in this engine?

250whp will be attainable in NA form...but at that point street driving will be a pain as well as reliability. I mean, crazy 300+ cams, 10k+ redline with a reworked head to allow power to be made past the 7400rpm redline, titanium valves, better valve springs, shaved crankshaft, bore and stroke kit, etc...But then again the little 4ag in the AE-86 was used in formula cars back in the day and they produced 275whp NA...with less displacement!

Don't forget though...a 250whp NA car will always beat a 250whp turbo car if they are identical in weight as well as tires, suspension, etc.

[ryude]

Originally Posted by RegisBou

Hopefully they will release an H6 version to bring in the V6 genesis prospect buyers?

300whp NA on the 3.6 should not be that difficult. Maybe they could even come out with a 3.0 or 3.2 H6 for weight savings and just run high comp and D4S like in this engine?

250whp will be attainable in NA form...but at that point street driving will be a pain as well as reliability. I mean, crazy 300+ cams, 10k+ redline with a reworked head to allow power to be made past the 7400rpm redline, titanium valves, better valve springs, shaved crankshaft, bore and stroke kit, etc...But then again the little 4ag in the AE-86 was used in formula cars back in the day and they produced 275whp NA...with less displacement!

Don't forget though...a 250whp NA car will always beat a 250whp turbo car if they are identical in weight as well as tires, suspension, etc.

I try to tell people this all the time, yes my car makes 250whp... the first pull. After that heatsoak sets in and I'm lucky to be making 210whp. If you're spending enough money for the car to make it's peak whp all the time, well congratulations you could have just bought a corvette with all the money you spent.

[fatoni]

Originally Posted by RegisBou

Hopefully they will release an H6 version to bring in the V6 genesis prospect buyers?

300whp NA on the 3.6 should not be that difficult. Maybe they could even come out with a 3.0 or 3.2 H6 for weight savings and just run high comp and D4S like in this engine?

250whp will be attainable in NA form...but at that point street driving will be a pain as well as reliability. I mean, crazy 300+ cams, 10k+ redline with a reworked head to allow power to be made past the 7400rpm redline, titanium valves, better valve springs, shaved crankshaft, bore and stroke kit, etc...But then again the little 4ag in the AE-86 was used in formula cars back in the day and they produced 275whp NA...with less displacement!

Don't forget though...a 250whp NA car will always beat a 250whp turbo car if they are identical in weight as well as tires, suspension, etc.

i dont know if that last statement is true

[Mitch]

Originally Posted by fatoni

i dont know if that last statement is true

Yeah, that statement ignores a lot. 250whp is just a peak number. It's completely ignoring area under the curve, where FI engines typically outperform NA engines of equal displacement.

[Levi]

Strange that in racing we prefere the outperformed NA engines: M3 GT2, 911 GT3, R8 LMS, SLS GT3, 458 Challenge GT3, V12 Vantage GT2, V8 Vantage GT4,.....

[Homemade WRX]

Originally Posted by Levi

Strange that in racing we prefere the outperformed NA engines: M3 GT2, 911 GT3, R8 LMS, SLS GT3, 458 Challenge GT3, V12 Vantage GT2, V8 Vantage GT4,.....

Also few of those come with a FUN variant. Those that do would have to bee detuned. See the ZR1 that had to ne detuned, a GT2 RS would need to ne detuned as well...

Ask HPD why they dropped NA for a twin turbo v6 engine when the new LeMans rules came out

[Mitch]

Originally Posted by Levi

Strange that in racing we prefere the outperformed NA engines: M3 GT2, 911 GT3, R8 LMS, SLS GT3, 458 Challenge GT3, V12 Vantage GT2, V8 Vantage GT4,.....

As mentioned, those cars are running in classes where FI is penalized. Even then, for the past 11 years the winners of the 24 Hours of Le Mans have been turbocharged.