Mike, do you think the STi cast pistons are unable to hold up to 350 whp, or is it just the forged pistons' additional det resistance that makes it easier/safer? I know of an EJ257/SOHC head hybrid making over 400whp on 91 octane. Or maybe 92... it's in Colorado. Just curious, as I'll eventually be running a stock EJ257 block regardless.

 

The gist of this thread seems to be that you can't get over 350 whp out of the STI without a 'built' engine... Yet several of the tuning sites and car mags claim to have achieved 400+ with just bolt-ons. Are these just works of fiction, or are the monster STIs these shops are building doomed to a short life?

Here's an example -- read the Stage 4 "viper killer" specs and chart:

http://www.dyno-comp.com/subaru.php?view=subaru

Only bolt-ons and ECU, no engine mods...

 

yes, hitting 400whp on the STI bottom end is no prob, making it live a long life is another story

There have been many failures with STI bottom ends pushing around 400whp and the weak link in most of them has been the Hypereutectic pistons/or rings. If you plan on running upwards of 400whp your going to want to at least run forged pistons, Im running around 350whp but I'll be swapping them anyways since I plan to have my motor trans out soon.

 

To be honest I have not witnessed the limits of the stock pistons first hand, We do have Jeremy's car running consistent 330whp+ on our dyno at 18psi and can't turn up the wick due to needing a bigger MAF housing.

From what I have seen of the internals (I have a couple of blocks here and some pistons) if it were me building a motor I would put in some forged pistons while I was at it, if I had a STI with the motor already in the car I would probably leave alone if my goals where simply 350whp on pump gas (91) and just have it tuned at a load based facility then when done run it to a place with a dyno jet.

That car you mention in Colorado is pretty impressive even for corrected dyno jet numbers, would be interesting to see how it fairs down at sea level on a Moostang or Dyno Dynamics.

I would imagine 400whp is possible (well that's a given as it has been done before) but as Jeremy mention not sure about the longievity of it but I would imagine if you had 400whp and managed to get 20,000 miles out of it you would not be too dissappointed.

Your looking to track the hell out of you car right Kevin? If so I would most certainly put in the forged pistons seeing as your setup needs to be put together somewhat anyway. I would also use some of the other bits mentioned by Mr. Impreza above (thermostat based oil cooler, Fail open colder thermostat, better radiator and so on).

Mike

 

Yeah by the time I have this motor built, my RS will pretty much be on a track, or on its way to one. I've planned on the failsafes you mentioned, already have the Crucial 160 degree t-stat, planning on a Koyo radiator, but I hadn't considered the oil cooler. I think that's worth it for the added capacity alone. I had previously decided against forged pistons when I was planning on keeping the car daily driven, but it's pointless now. You recommend the Weiscos, hands down? Or are there other very very good alternatives?

And for what it's worth, the owner of the RS-T in question in CO has a habit of making crazy power out of his motors until they blow up, so he can build a new one. I'd be surprised to see this motor last a year (it's not his daily driver).

 

Currently the only forged pistons I can recommend based on experience are the CP units, however after talking in depth to Weisco (I have always liked the Weisco stuff, with coatings and such) we are going to be building 3 motors here for testing purposes so I should be able to give you some form of qualified response by the end of Febuary (not sure how that works with your build time frame).

When building/buying your oil cooler make sure it is a Thermostat based setup not a simple sandwich adaptor going to a 11-13 row cooler. Mocal makes a really good 180 degree (I think or 160 perhaps) sandwich adaptor based thermostat and if I recall it's about $35.

Mike

 

Cheap insurance. Thanks Mike.

 

I have not asked them if its ok that i talk about the shop on the forums yet...i do not want to cause any conflicts at this point.

I have learned some things from my forums adventures....LOL.

Mark

 

good info mike

BTW i'm gettin a GT30-12 along with some new mods on my STI...the greens going away....
I think we are gonna go with CP pistons on my car....

 

Thats why we pretty much skipped the machine shop costs and went directly to Subaru of America for a new shortblock, which now will be taken apart and made stronger...
It was nice pullin it apart little to get some idea of where all that noise was comin from.

 

Glad your all sorted now mate, just wondered what engine management and fuel your going to use on the GT varient (sorry I have no idea what the -x means as I only hear it mentioned on the turbo's cast for stock pipe fitment never on the GT 4 bolt Garrett units that we use)

I actually think the green is comparable to smaller GT30 turbo so understand why a lot of folks use them on the STI especially as they are a bolt on.

Yea CP seem common the STI and I have only heard good things, I run CP on my car (with a little compression bump ) but am itching to get the new Weisco's we have inbound.

Mike

 

As far as E.M., i may use something akin to ur system for the STI beta car setup.

On street i must agree the green is a good turbo...good on CA 91 for sure where boost is limited to around 17-19#'s, but once u start goin up in boost say past 23-24#'s...on a bigger STI motor along with the right mods, then it (the green) starts showin its true colors compared to a MED. to Large GT30 turboe'd setup.

I know that my setup ran out of breath..@ that 371/395 torque level on the DD DYNO...runnin 26-27#'s

I know that if boost was turned up, Krinkov would hit 400+ WHP no problem...maybe i'll have to loan him out my motor.., or maybe he can loan me his turbo...cough, cough...

As i'm a avid racer typa guy, i should have dyno/track times after my gt30's in.

 

The GT30-12 is a "56 trim" with 55lb/min compressor wheel...not quite a strong as the turbo Gruppe-S sells,,,but ill give this one a shot for now.

I will retain the spearco topmount..and i'll try to coat the turbo heatshiled and wrap it...to keep under hood temps down...and see how it goes.

 

Sounds decent, are you sticking with the Xede and doing dual maps or are you switching to something else?

Mike

 

Check ur PMs