Hello EVO owners. I was looking at both the STI and the EVO power capabilities using 100% stock internals ("valve cover down"). This means only gains with upgraded bolt on performance. I saw a threads on the STI that said they have made over 400+whp w/no problems and others that share stories saying how there piston melted at 350whp or rod snapped at 370whp. So right now STI owners are saying the "reliable" power limit for the STI is around 350WHP/400CHP. So my questions for you EVO owners are what kinds of problems have the EVO's come across and what seems to be the "reliable" limit on the EVO stock internals?? Also how is the tranny holding up to these power conditions?

Please no stupid remarks like EVO's rock and STI's suck and EVO=900whp and STI=broken engine BS.

 

I can't comment on the STI as I have no first hand knowledge.

The 4G63 motor is very reliable and has seen HP figures in the 500 range on stock internals. Does this mean that it is daily driven reliable hp? No, but it is very possible with the right tune that you can achieve these numbers with some margin of safety.


Some where in the range of 375 to 450 is very common on stock internals for these motors.

I would recommend getting some ARP head studs for this kind of power though.

 

Define stock internals... Stock bottom end? Or stock from the valve cover all the way down?

I believe I've seen posts here reporting over 400 WHP with a totally stock engine. No clue on reliability, though...

I remember reading that the rods in the Evo engine are good to 24 PSI boost, and that 26 PSI is too much. I think that 24 PSI at redline would equate to 400 - 425 WHP. At that power output and boost, you would definitely want to replace the head studs, and in order to get there, you're probably looking at a cam swap.

 

One common upgrade for EVO's is cams so if you wont let the tuner lift the valve cover you will cripple the ideal tune path. The STi's have big problems above 17 psi. With a basic round of mods (IN, EX), the STi will boost creep badly and cause engine damage if not addressed. The whp limit based on common full round of mods (IN, EX, FMIC, fuel) with engine management and an upgraded turbo is around 350+ whp at around 1 bar.
The 4G63 has been shown to handle 450 without immediate concern. HP is a bit misleading since the EVO's can flow the air to hold torque much higher in the rpm band (and thus give high HP numbers) compared to STi's. Again, headwork and cams will yield significant improvements; it's just part of the EVO's mod path, but it doesn't really alter the reliability of the vehicle.

 

We've tuned a bunch of STis and they win the torque battle hands down. Haven't played around with upgraded turbos yet so they've been limited to 350-380bhp range, depending on octane. They've exhibited to reliability issues either. We've just started to get into upgraded turbos and fuel systems so higher hp testing is just around the corner. If they are like other motors in the EJ series, they should put up with the stress just fine as long as you don't rev those big pistons too high/fast.

EVOs are also proving to have very strong motors as we've made a conservatively rated 550--570bhp on completely stock internals (okay, it had cams and adj cam gears). Stock head studs, stock rod bolts, stock head, etc,. No issue during the hundreds of dyno pulls and the thousands of miles we pounded on it. Of course, this is on race gas so det was pretty much taken out of the equation. And we only revved it to 7780rpm which probably helped a bit. Still, that kind of reliable power on a little 2 liter is unusual.


Regards,
shiv

 

No more input??? I thought this would be a good topic...

 

Everybody replaces the cams in the EVO and you specified stock from the valve covers down.... not many people have experiance with a modified EVO that is keeping the stock cams. Hell, you can make 500 wheel HP on the stock "from the cam covers down" engine if you want to try...but nobody is going to do it when cams are so easy to do and not very expensive for the gain you get.

Keith

 

I guess we all have to wait for a 1 or 2 to really know how reliable the evo8 vs. the sti battle for power. Many tuners have claimed 450whp range, but none really have their evo beyond 40-50K miles range. Only time will unveil the winner. I hope the 4g63 will win, hhehe, bc I own one!!! Peace...

 

anybody know if the STi comes with forged rods? I know the piston are cast....

 

Ok, how about including the cams and gears. How much HP are we talking about with the stock rods, pistons, etc.

evo542, this was written in a the I-club forum:

A subaru rep sent this message back to me.

__________________________________________________
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Hello Jeff:

I apologize for the delay in getting back to you. Your patience is appreciated. I have been advised by our Technical Services Department that the pistons in the STi engine are forged steel. The conrods and crank are forged aluminum.

Thanks for the opportunity to be of assistance. If you need any future assistance, please feel free to contact us again.

Best wishes,

John J. Mergen

Subaru of America, Inc.
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The Car Connection article quotes, "The pistons beneath those valves are made of forged aluminum alloy, while the connecting rods that move the pistons are made from forged, high carbon steel."

Somebody got it wrong, but with the two similar answers, it also seems like one of these descriptions is right.

 

The STI pistons are Cast. The Japanese ones are forged though.

http://www.airpowersystems.com.au/us...ns/pistons.htm

 

Correct; the USDM 2.5L STi has poor internals; go look on NASIOC for blown STi motors. The question about EVO reliability is already answered since that exact motor has been around for many years. The EJ257 is the questionable one.

Mark
www.Quantum-Racing.com

 

How about the tranny?????? Power limits?????

 

The EJ257 uses hyperutectic cast pistons. The JDM Version 8 EJ207 also uses hyperutectic cast pistons. They switched to them this year for reasons unknown. There was a long argument with the APS guys and the GroupN homologation papers for the V8 RA engines showed they do use hyperutectic pistons in all STI models starting this year.

Longevity wise we'll see how things hold up, just have to wait and see. I think in the end people will make more power using the EJ257, but not necessarily with the stock internals. It's going to cost more to get the STI over the hump so to speak. One big thing is the turbo is too small for the engine, and doesn't really support more than about 300whp (on most dynos). I haven't seen a blown Subaru engine from a crank or rod failure without the use of nitrous. The EJ20/EJ257 do not handle detonation very well, so when cars detonate it leads to failure.

I have an EJ257 block in my WRX currently (it cost $1100) and I'm making 350+whp running around 11.25:1 AFRs, and 16.8 pounds of boost. The car makes 300 ft-lbs of torque at 3000 rpm, and 200 ft-lbs at 2400. There are a few of us using the EJ257 blocks with good success, Jeff Sponaugle on Nasioc is making 370whp out of an EJ257 and a 20G that is running out of steam at about 6000 rpm. He's been running that setup for 4-5 months now and beats on the car fairly heavily.

My opinion is with safe tuning you can get a reliable 350+ whp out of the EJ257. If you want to push it to 400-450whp you are going to have to spend more money to do so than the EVO. The 6MT/differential in the STI is much stronger than what I've seen out of the EVO8 5MT thus far. I've _never_ heard of someone breaking one, and Tomei/JUN use stock boxes in their 600+hp tuner Imprezas. I have one in my car and it handles launch control launches (12 psi of boost at the line) from 5500 RPM on Hoosier autocross tires and not a single problem. I did tear up a stock WRX rear LSD unit though.

edit: The other thing people are running into is kind of like the WRX, the STI ECU likes to fight things and it runs alot of timing stock. Guys are throwing larger turbos on the car with piggyback computers that only offset fuel and timing and I think that's where problems come in. They can run rich but they can't control timing at all. Eventually there will be ECU reflashes and better solutions to combat this, but right now everything is still in development with the STI ecu being brand new.

 

Has anyone blown an Evo motor yet(thrown rod etc.)? I haven't seen any posts about one on here. I take that as a very good sign. The only broken parts i've heard of are clutch problems and differential problems. No major motor problems yet though. I've noticed that newly designed engines are more prone to failure. I think it's because the 4g63 has had it's time to see what problems there are with the motor. Mitsu has taken notice and took care of the problems. How long has this motor been around now! This motor can take a hard beating. I hear the valves are weak but no ones complaining.

One more thing. Ecu's are hard to crack! Thank the lord this is not true for the almighty 4g63.