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HOW MANY HORSEPOWER CAN WITHSTAND STI 2004 TRANSMISSION AND DIFFERENTIAL STOCK?

7.9K views 13 replies 7 participants last post by  Pythagorus  
#1 ·
good day bros! i need youre help!!!!!!!!!!!!!!!!!!!!!!

I'm thinking of putting forged connecting rods and pistons in my ej257 but I'm not sure how many horsepower my sti could handle without ruining my stock transmission???

The turbo (atp garret gtx 2Gen) would handle approximately 500whp, that's what I would like, but I don't know if it is wise to do so, the only thing I have planned to change in my transmission is the clucth (it will be stage 4)

WHAT DO YOU THINK???
I NEED YOUR ADVICE...
326208
 
#7 ·
It may handle it, it may not.

You are asking for it to hold 2.5 times the OEM output for which it was designed. It might be fine: the STI transmission is pretty overbuilt, but no guarantees.

Sent from my SM-G960U using Tapatalk
 
#8 ·
If we can link YouTube videos on here there’s a video of a master Subaru transmission rebuilder And if I remember correctly he says the six speed sti transmission begins to fail at 625 hp. I would assume that’s based on a solid, well functioning starting point. I’ll have to find the video to confirm what he said though. So don’t quote me.
 
#10 ·
^^ I liked this post.


To be nitpicky, the Automotive Engineers prefer to think in BMEP rather than what you have called "compression ratio," but I get your point.
 
#13 ·
I am just shaking my head. 1)I actually own a 650HP / ~570ish rear wheel HP car. It's 10L90 transmission is rated for 900 pound feet of torque. That is the manufacturer's rating. I would guess that Subaru would have a similar type of rating number that can be found for the STI. That's just a guess.

The thing about building any car is that you are always finding the next weakest link.
Brakes? What type of rotors? What type of pads? What type of brake fluid? What type of brake lines.

Cooling? What type of radiators? How many (transmission, steering, eDiff)? My Bucket of Bolts has 11 and a very tasty carbon fiber heat extractor as part of the hood. It has three radiators across the front section, alone.

Differentials, half-shafts, motor mounts, clutch, drive shafts, etc. Break one, fix it and then find the next weakest link.

Costs? Cost of the car? Cost of the build? $25,000 reserve funds to fix what breaks as they do break.

I do have just a little bit of experience with automobiles, tracks and strips. I have seen my share of professionally built cars oil tracks and strips across a fair sized piece of our country. Yes, you sit in the paddock, in your run group, waiting to cross the white line as the clean-up crew goes about the very important job of cleaning the track and making it safe for the rest of the event. I think at NCM Raceway, that cost was $1,500-$2,500. COTA is stupid expensive. You pay that before you leave.
 
#14 ·
I am just shaking my head. 1)I actually own a 650HP / ~570ish rear wheel HP car. It's 10L90 transmission is rated for 900 pound feet of torque. That is the manufacturer's rating. I would guess that Subaru would have a similar type of rating number that can be found for the STI. That's just a guess.

The thing about building any car is that you are always finding the next weakest link.
Brakes? What type of rotors? What type of pads? What type of brake fluid? What type of brake lines.

Cooling? What type of radiators? How many (transmission, steering, eDiff)? My Bucket of Bolts has 11 and a very tasty carbon fiber heat extractor as part of the hood. It has three radiators across the front section, alone.

Differentials, half-shafts, motor mounts, clutch, drive shafts, etc. Break one, fix it and then find the next weakest link.

Costs? Cost of the car? Cost of the build? $25,000 reserve funds to fix what breaks as they do break.

I do have just a little bit of experience with automobiles, tracks and strips. I have seen my share of professionally built cars oil tracks and strips across a fair sized piece of our country. Yes, you sit in the paddock, in your run group, waiting to cross the white line as the clean-up crew goes about the very important job of cleaning the track and making it safe for the rest of the event. I think at NCM Raceway, that cost was $1,500-$2,500. COTA is stupid expensive. You pay that before you leave.

Appreciate your common sense being put forward....and in terms of the 'next weakest link' ...and then there is the cost of your life passing focused on a car.