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Old 12-27-2020, 07:47 PM   #1
undyjr
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Member#: 459692
Join Date: Dec 2016
Chapter/Region: South East
Location: Hampton Roads Va
Vehicle:
2019 WRX STI
silica black

Default OEM bearings with forged rods?

As I have some gift cards burning a hole in my wallet I'm looking forward to the next phase of my build. This is where I'm at with my 2019 STi:

Blouch 20G XTR
Injector Dynamics ID1300s
Cobb Big SF intake with air box
Cobb 3 port EBCS
Cobb LF bypass valve
Cobb flex fuel kit
Grimmspeed TMIC
Grimmspeed catted downpipe
Grimmspeed EWG up pipe
Turbosmart 38mm EWG
Killer Bee holy header

380WHP and 370WTQ on a Dyno Jet

My plan is to pull the motor, delete the air pump, split the case, replace the rods and pistons, and install the motor with a new ACT clutch with streetlite flywheel. My tuner gave me a conservative tune because of the factory shortblock. Is 450-500WHP attainable on a Dyno Jet? I plan on using Manley forged rods and performance platinum series 99.75mm pistons. I will have the machine shop size the bores and gap the rings. Since the car is a DD and lives on E85 should I go with 9.8:1 or stick with 8.5:1?

Do I need to replace the rod bearings? The motor has 30K on it and my past 4 oil analyses have been perfect. It's tempting to replace EVERYTHING but I don't mind saving money where I can. Although I have a feeling y'all are going to tell me to replace the main bearings too. It goes without saying that I would install the OEM bearings back into their original position. Are ARP head studs a necessity? I foresee a retune approaching 25#s of boost. This is just the next step in my build and I strangely look forward to pulling the motor myself. Anyone local to the Hampton Roads aka Coastal Virginia area that wouldn't mind renting me some Company 23 tools feel free to pm me
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Old 12-27-2020, 09:47 PM   #2
subaru_gc8
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bearings are cheap you should replace as much as you can. honestly I wouldnt build the engine but buy a short block form Iag that should be fine. so here is the skinny on who boost works. you will make more power with more boost, so if you up the compression you cant run as much boost. I dont really think that the 20g will make much more than you are making now. change the turbo get the biggest turbine hosing you can and push that. also you are limited on your 1300 they wont make what you are looking for.
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Old 12-28-2020, 07:03 PM   #3
spoolinsti05
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Jr tuned TT Sleeved

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You can so run more boost combined with higher compression.

The subaru has such a large bore more compression will actually be a good thing.
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Old 12-28-2020, 10:20 PM   #4
Dave D.
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Old 12-29-2020, 05:17 PM   #5
cboggess
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Quote:
Originally Posted by undyjr View Post
As I have some gift cards burning a hole in my wallet I'm looking forward to the next phase of my build. This is where I'm at with my 2019 STi:

Blouch 20G XTR
Injector Dynamics ID1300s
Cobb Big SF intake with air box
Cobb 3 port EBCS
Cobb LF bypass valve
Cobb flex fuel kit
Grimmspeed TMIC
Grimmspeed catted downpipe
Grimmspeed EWG up pipe
Turbosmart 38mm EWG
Killer Bee holy header

380WHP and 370WTQ on a Dyno Jet

My plan is to pull the motor, delete the air pump, split the case, replace the rods and pistons, and install the motor with a new ACT clutch with streetlite flywheel. My tuner gave me a conservative tune because of the factory shortblock. Is 450-500WHP attainable on a Dyno Jet? I plan on using Manley forged rods and performance platinum series 99.75mm pistons. I will have the machine shop size the bores and gap the rings. Since the car is a DD and lives on E85 should I go with 9.8:1 or stick with 8.5:1?

Do I need to replace the rod bearings? The motor has 30K on it and my past 4 oil analyses have been perfect. It's tempting to replace EVERYTHING but I don't mind saving money where I can. Although I have a feeling y'all are going to tell me to replace the main bearings too. It goes without saying that I would install the OEM bearings back into their original position. Are ARP head studs a necessity? I foresee a retune approaching 25#s of boost. This is just the next step in my build and I strangely look forward to pulling the motor myself. Anyone local to the Hampton Roads aka Coastal Virginia area that wouldn't mind renting me some Company 23 tools feel free to pm me
Lets take a step back here please, and talk about a few things.

1) From a technical standpoint the factory rod and main bearings are perfectly fine. From a cost standpoint the winner is to go aftermarket which is why you see the change. The argument that a softer bearing will save your crank if a bearing fails is BS. Complete BS. Hard or soft if you kill a bearing the crank will be scored. A BNIB crank from Subaru is under $400. You'll spend that getting a worn crank ground and polished. Bottom line, Subaru cranks are disposable, and honestly for the price one hell of a bargain for what you get.

2) The way your post reads is that you're going to open the case, swap your old rod bearing onto new rods, put it back together, and slap some pistons into the holes. DO NOT DO THIS!! You will be in for a world of hurt.

I have said it before and I will say it again. A Subaru case is a floppy bag of aluminum that just holds the guts in. You've cycled this motor a number of times now, and you will need machine work to make everything straight and true. By jamming new stuff into a used case you're going to be very disappointed. By jamming your old rod bearings into new rods (even if they were factory Subaru rods) you're going to be very disappointed.

Now, if you've got the money, and the time, and are willing to risk a failure all for the sake of a learning experience then by all means give it a shot. If you're like the rest of us poor schlubs, and you want to do it right then do it right and don't take shortcuts.

Quite honestly, if you're not made of money and free time you will be VERY well ahead of the game to purchase a shortblock. Some (but certainly not an all inclusive list) of places I would go are:

TiC <- I'm partial to these, but I'm a bit biased.
AR FAb
IAG
Revworks
Rallispec

My number one, never ever go there, why the F they are still in business, you'll hate life, your car, your dog, and your significant other place is GCH. Do NOT make that mistake.

Now, also along the lines of floppy aluminum please do not ignore you heads. Have someone who knows what they are doing check those over, and deck them at the very least. A proper deck. Using a proper machine. Set up to properly cut aluminum. Not Billy Bob and his Buddy with a whiz wheel on a grinder or old Smokey MaGee and his 1964 surfacer that's set up to cut old Ford cast iron heads using a graphite gasket.
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Old 12-29-2020, 06:40 PM   #6
undyjr
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silica black

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After reading the replies and even more research I've decided to purchase a built short block. Now I have to decide what HP I will want to achieve. Perhaps one day I will build my own, just not yet.

On a side note I purchased a FSM a couple of years ago for MY15 WRX and was never able to get it to work. It consists of links that show "your file could not be accessed" Does anyone know how to access the manual or know of a website to download another manual? Thanks.
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Old 12-29-2020, 11:20 PM   #7
spoolinsti05
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Jr tuned TT Sleeved

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If the bearings are clean and show no scoring and clearance out properly I don't see any issue with reusing them at all..

I will however agree with you that most aftermarket bearings are soft junk crap that can't handle any detonation what so ever. You thought a oem piston was weak hah..

Why do you think king made a new line of bearings with harder material... Because the old ones freaking are smosh. Stay away from that trim-metal junk.

I live by the if it ain't broken don't fix it. Used parts are tried and true. New parts can easily turn into a gamble. However they do work great in most cases..

The heat cycle straightness of the block thing is another thing it can or can't be in spec. You'd need to check it. Spend the money buy the tools and check it yourself. It WILL Definitely be Worth it. Ask me how I know been there done that...

Shoot even if I was rich I'd buy said block and assembly from said company and inspect it myself for piece of mind. At least I could sleep at night knowing my piston won't wobble in the bore or seize to the sidewall at high boost.

Last edited by spoolinsti05; 12-29-2020 at 11:28 PM.
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Old 01-11-2021, 01:45 AM   #8
RocketRobin
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On my latest rebuild I had to settle for OEM main bearings, as the newest line of King Racing bearings was not yet available at the time.
So I run the thick oil and take the loss in power and fuel economy.
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Old 01-19-2021, 09:01 AM   #9
undyjr
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Join Date: Dec 2016
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2019 WRX STI
silica black

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I recently became a "Scooby Specialist". How did that happen???
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Old 03-02-2021, 10:25 AM   #10
undyjr
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2019 WRX STI
silica black

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My question just became a moot point yesterday. Accelerating from a standstill radio off, windows down and next to a jersey wall I heard a faint rattle. Knowing I had done a lot of work under the car yesterday I wasn't too worried initially. Out of caution I nursed the car home and got it back up in the air. With the girlfriend blipping the throttle I became fairly certain it was rod knock. After straining the oil through a black t shirt, degreasing it, and waiting for it to dry I found no bearing material. I then cut open the oil filter and separated the pleats. I found what I was looking for, each pleat had silver flakes all with small striations.

At this point I'm going to begin pulling the motor and split the case. I will update with what I find. I'm sad but happy. This motor should've lasted longer, between the conservative tune and meticulous maintenance. I never babied this car, I refuse to be one of those guys that do a pull a week. I look forward to the work ahead and the pride of starting a motor I had a hand in building.

I will continue to utilize the vast amount of knowledge available in this forum. Please feel free to offer advice, constructive or otherwise. To anyone local in the Hampton Roads area that would like to rent me some of the proprietary to Subaru tools required PM me.
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