[eatV8]

Engine feels different warmed up?

the topic says it all... http://www.airpowersystems.com.au/us_spec/subaru/sti/pistons/pistons.htm

 

[sakura-iro]

interesting, thanks for posting this.

 

[gforced]

This makes it sound like we basically are driving a souped up Forester. That kind of sucks. I was under the impression that we got the same STi prepped engine, but just increased to 2.5 L for the North American market. Seems kind of misleading to me. I read a review of the USDM short block on I-Speed's site and they made it sound like the block is nothing special either. Oh well, I guess we (the North American market) got screwed again. I don't understand why they cannot just bring over the real thing and make it smog legal instead of giving us this and marketing it as a true STi. I know a lot of parts are the same, but I want the STi hand-built motor also. Maybe I am asking too much.

 

[RadarOnPaws]

Oh well, I guess we (the North American market) got screwed again.

I sure don't feel that way. The JDM car has its strengths, no doubt, but this time I think we got a car that is the equal of or better than the JDM car.

Who cares if Forester has the same engine? BTW, on that topic, I noticed that it is rated at 230hp or something like that, and similar torque. Weight is the same as the STi, roughly. How is it pulling 13.8 second quarter mi. times?

 

[toyworx]

I don't buy the wrist pin argument....

 

[4MLA1FN]

yeah, i don't either. the pin carries forces on both ends (where it connect to the piston) and the middle (where it connects to the rod). so it would seem the usdm pin is better (except for the greater weight). dunno.

 

[eatV8]

i think car and driver commented on that they think the forester wasnt making the 215hp subaru claimed 13.8 is moving... an aussie mag i have here had it run 14.8 in auto (same engine) could there be 1 second difference to a manual model?
APS said subaru used these pistons etc to keep cost of the STi down, they will serve stock purposes well and even most modding most ppl would do (exhaust, ecu etc.) it will even handle slightly more as APS have shown running both SR50 and DR55 turbo upgrades. it shouldnt cost too much to put a set of decent pistons in if needed thou.
Now thinking about what i read, subaru aust is doing 300hp 2.5ltr STi models of impreza, forester and legacy... im guessing all they have to do is fit the VF39, STi intercooler, 6 speed, exhaust and ecu tweaks... makes sence to do it since engine is same.

 

[RadarOnPaws]

13.8 is moving... an aussie mag i have here had it run 14.8 in auto (same engine) could there be 1 second difference to a manual model?

Yeah, I think there probably could. I know of other models of cars where the manual/auto exhibit that kind of disparity.

Can't remember where I read the 13.8 number but I believe it was either here or NASIOC.

 

[eatV8]

it was posted on here, possibly nasioc too, but it was car and driver that run it at 13.8

 

[eatV8]

the pistons found in the 2.5ltr engine of STi and forester are suppose to be hyperteutic coated (molecular bonded) subaru claim this makes the pistons 120% stronger then previous forged items if i recall correct. Since APS seems to be one of the only companies pulling apart engines and checking things out i will email Peter Luxon about this and ask for his opinions. I will post the reply from him when i recieve it.

 

[b0rf]

You guys seem to be jumping the gun. :roll:

Probably .1% of STi owners will be pushing the limits of the 2.5l USDM STi pistons. For those .1%, if they're that financially determined to max out the stock pistons, funds will surely be available for forged pistons.

We didn't get 'screwed'. Keep in mind, you pay $32k for 300hp/300tq-- NOT aftermarket potential.

 

[eatV8]

Do it yourself Intercooler Screen

screwed is alot of the people under the belief that these pistons were forged and subaru didnt really make it easy to find out... I am one of those owners that will push the engine enough to need better internals, but since now these are not forged im inclined to do a stroker kit and bring out displacement to 2.7-2.8ltrs close the block a little more with iron sleeves and fill the engine with goodies...

 

[Agent Chobos]

We already have iron sleeves. One of the tech brochures mentions "cast iron cylinder liners".

And there was some talk a while back about the new cast pistons actually being stronger than the forged ones. I don't know what happened with that, though.

 

[eatV8]

yeah hyperteutic coating, subaru claims it to be 120% stronger then their previous forged pistons, im waiting for APS to give there view on the pistons... is still the weekend over there so there will be no reply for a couple of days.

 

[eatV8]

ok... i have a few things messed up here... the pistons are coated, but not hyperteutic... hyperteutic is a method of casting pistons which makes them stronger then regular casting. heres what APS wrote:

Hypereutectic Castings – This is a particular casting method which is stronger than conventional castings. However, it is nothing like a true forging. Is this method 120% stronger than a conventional casting? Possibly, however irrelevant. If you are building a serious engine (and it sounds like you are), then you need a forged piston.

 

[Agent Chobos]

So is it supposed to be 120% stronger than a forging, or 120% stronger than "normal" castings? There are two different things being said here.

 

[palo]

You guys seem to be jumping the gun.

Probably .1% of STi owners will be pushing the limits of the 2.5l USDM STi pistons. For those .1%, if they're that financially determined to max out the stock pistons, funds will surely be available for forged pistons.

We didn't get 'screwed'. Keep in mind, you pay $32k for 300hp/300tq-- NOT aftermarket potential.

I disagree with this. You are saying that 1 out of every 1000 sti's will have engine mods?? No way.

Anyone runing boost pressure greater than stock wants forged pistons. I am a little disapointed.

 

[WRX_XB9R]

Tapered wristpins are the way to go. If properly designed they are lighter and STRONGER than straight bore wristpins. The karting engines which we turn 19,500-21,000 all use tapered wristpins. If you use a straight one it will break along with loosing about 1,000 rpm.

Forged pistons are the way to go for boosted engines. Coatings will only go so far to help combat the stresses on the part. Eventually you get back to the orginal part structure and forging is stronger than any casting process.

 

[4MLA1FN]

Tapered wristpins are the way to go. If properly designed they are lighter and STRONGER than straight bore wristpins.

hmm. can you explain how this is so? i don't doubt you; it's just counter-intuitive how this design make a stronger pin. (i'm doing some googles.)

 

[bitabur]

I don't think the actual pin is stronger, I think what's happening is that the pin is just as strong at the points of maximum stress, and it is tapered away at other places....

The lighter weight of this pin would put less stress on the pin during high rpm's, because it wouldn't be pulling as much mass when the cylinder changes directions.....



Just a guess....