How good is the sti engine ?


Are the subaru's stock pistons and rods as good as JE pistons and crower rods, granted Subaru's are already forged ?

 

Officer,
The pistons are not forged in the STi, despite the claim made in many of the preliminary subaru spec sheets. The newer/ updated subaru websites no longer claim to have forged pistons in the STi. The crazy thing is I recently read that the new Forester 2.5XT WILL get forged pistons. Doesn't make much sense does it?

 

Guys, by no means am I calling you guys b/s........but....I was almost certain the internals were forged in the sti


The ones overseas were !!!!


I dont see why the american versions wouldn't have forged




If they dont have forged internals.....THAT IS A SCAM !! One more thing to upgrade when going big boost !! DAMN......



Is there any credible evidence that supports it ?

 

Below is the spec listed in the subaru impreza web site which is also what was advertised in the media release.

The 2.5-liter horizontally opposed ("boxer") four-cylinder engine is based on a specially reinforced "semi-closed deck" engine block with forged aluminum alloy pistons, forged high-carbon steel connecting rods and sodium filled exhaust valves.


At some point between the launch of the STi and the delivery the specs appear to have been changed. Oddly enough I wasn't aware of this until after the purchase

The main subaru site makes no mention of forged pistons or connecting rods.


ENGINE
Type
Horizontally opposed 4-cylinder intercooled high-boost turbo with die-cast aluminum-alloy block and aluminum-alloy cylinder heads. Intercooler has driver-controlled manual water spray cooler with low-fluid indicator

Someone please correct me if I'm wrong.

 

Subaru may have only changed the description to something that sounds better. You will notice that they did not include descriptions of the hardened motor mount bushings but that doesn't mean they aren't there. They MAY have. done that. Hopefully, of course, they are forged pistons, etc.

 

I would go beyond just what the on-line description tells you, Subaru web-site, ((in brief)) about the internals. I haft to look at the brochure that I have on the Sti and see if it has more detail. One thing is for sure though, I don't think subaru would scimp on the rods and pistons just to save a couple of bucks. Plus no dealer in his right mind is going to go overboard to tell you they are forged pieces, like my dealer did, when there not. Now coming from a V8 history, my mustang had the coated cast pistons and after 50k miles I installed S-trim and put an additional 50k+ miles and still the ingine had good leak down. Yes, the Sti is box motor so even with the cast parts you would haft to abuse it to break it. Start adding more boost and other aftermarket parts and longevity will nose dive. Your going to get that anyway with a small motor.

Key point is not so much the larger turbo or nos. Its what they do and cause if not set up right that will destroy the cheap stuff as well as the good stuff. So here is an idea, until someone official comes on this web-site and says otherwise i'll go with the forgies.

 

Thanks for the responses, perhaps I should call subaru and hopefully they can clear things up.

 

I just signed on an STI and am very interested in finding out in detail the correct make up of the internals. I emailed Subaru information and asked them to forward the question to a subaru engineer or a technician who definitely knows the answer and to get back to me with the info. He replied and said he'd do that.

 

Well the brochure states that the pistons are coated. This means they are either forged or not. There is a web site set up by a Suby dealer that I found and he states the pistons are forged. I'll try and find the site. Now most of the performance makers of pistons ie: JE, Wiseco, are using polymers to coat there pistons. This will make the difference no matter the piston base. Unless your going all out racing then you'll be looking at other things as well to break down. The coating is great for the turbo motor > increased longevity and durability. Thats it....

 

Subarustore might know the answer !!!

 

http://www.thecarconnection.com/inde...57,184&sid=184

Car Connection, has a detailed write up on the internals not to mention the rest of car as well.
Peice

 

A subaru rep sent this message back to me.

__________________________________________________ __
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.
__________________________________________________ __

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.

 

JTibbitt,
Thanks for sharing that information. It's reassuring to hear that the motor is built so strong. I feel a little less concerned now about the fact that mine has frequent, but brief episode of detonation. I hope Subaru is right about it being a safe, normal variant in some STi's.