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Rod/Piston upgrade without supporting mods?


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Hi all,

 

I'm looking at rebuilding my first ever engine. The engine is an EJ20Y from a 2007 legacy GT wagon with approx 180,000kms. The main reason for this rebuild is to replace all bearings and rings to breathe many more kms and reliability into this engine as i plan to tune it with light mods (decat, intake, fuel pump and boost solenoid).

 

I'm really chasing longevity and reliability and not necessarily high power thus why I want new bearings as they will probably go within the next 50,000kms, my last EJ spun its guts at 220,000.

 

Question time.

 

Q1. What is everyone's opinions on whether or not it's worth upgrading rods/pistons with just the light stage 1+ mods. I don't want to break the bank on this one, its my first build and 50% of this job is just for my own knowledge and experience! Will I get any gains from upgrading the rods/pistons while I'm still only using the stock turbo and stock tiny BP/BL intercooler?

 

Q2. I don't think I have the budget to upgrade both the rods and pistons so which of these two parts in a EJ20Y/X is the weakest and more in need of upgrading? What parts do you recommend? I was looking at these. https://www.possumbournemotorsport.com/k1-technologies-subaru-ej20-25-h-beam-connecting-r

 

Q2 continued. its worth noting that the previous owner ran this car on 91 octane for a decent amount of time and it ran like s***. I should expect potential cracked pistons and damaged ring lands. even if they appear okay would you replace them due to the high stress they have been subjected to?

 

Q4. What are some good factory replacement rods/pistons? should I consider some internals from a EJ207 or 257?

 

Q5. What rebuild kit is best? should I go to the dealership and get a OEM rebuild kit? I'm quite interested in some decent ACL race series bearings. so I could get a OEM rebuild kit and use ACL race series bearings. what are everyone's thoughts? what have you had good experiences with? what about head gaskets lol?

 

Q6. Is the factory oil pump sufficient? I've heard of many people upgrading to a 12mm oil pump? is this a good idea or is the factory one sufficient? will a aftermarket oil pump bother my AVCS solenoids?

 

Q7. its important that all of this rebuild will work with the factory tune/ecu as I have to travel 450km to my tuner. lets say i installed lower comp pistons from another Subaru engine, would i be safe to baby the vehicle 450km? (Nelson to Christchurch)

 

 

I'm preparing for my first ever build here so any opinions are much appreciated. 

 

Thanks for your time :)

Edited by Panda
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Q1. No, no gains, if anything you will slightly _lose_ as the aftermarket rods and pistons are potentially heavier, less well balanced, and not quite as good a fit as OEM. Assuming identical geometry, i.e. not gaining/losing compression. Stock turb and intercooler are never going to push the limits of even the stock internals if everything else is happy.

Q2. I wouldn't bother just doing one. Either it's a forged build or it isn't. As to whether you would replace the pistons.... if you buy used pistons, you have no idea of their history. If you buy new pistons they're going to cost you about $500 for a set for stockies, is it worth it? I'd say probably not.

Q4. The only factory internals I'd consider an "upgrade" are V7 STI EJ207 pistons and rods, and they're >$2000 for the pistons and around $800 for a set of rods, at which point you may as well just go aftermarket.

Q5. Head gaskets, OEM. Rebuild kit in terms of bearings? YMMV. OEM are probably going to be the most reliable at stock power levels but might cost a metric assload.

Q6. Yes, it's fine. Honestly unless #racecar where you have specific oil pressure needs, dicking about with the oil pump seems to lead to more problems than it's worth.

Q7. As long as you weren't way out I'd probably nana it to the tuner, especially if you had slightly dropped compression rather than adding it. As long as you were comfortable it was driving well enough to make that trip safely. Anything turbo is kinda fundamentally variable compression anyway because the actual resultant cylinder pressure could be just about anything.

 

With that out of the way.... I wouldn't bother with a rebuild to factory spec. A better option, IMO, is to just keep driving it on the assumption it will blow up at some stage, and in the meantime get another block and start building that one up properly (forged etc). Then when yours finally gives up the ghost, you have the option of throwing in a bigger turbo or something and making a bunch of power.

 

 

 

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I'd totally agree with what boon has said. I'd likely steer clear of what you are wanting to do regarding rebuild and address at the time. You'd spend a lot of time (and money if you make a mistake) just to get it to a position where you wanna do the basics to the platform. You'd wanna go big or go home if you're talking ripping into the engine and not just swapping with a donor engine.

 

If it were me with 180ks on it, I'd just do the bolt-ons like you have suggested and keep up with services (plus the tune). Keeping on-top of maintenance plus a good tune will give you the best chance on these cars. 

 

The cars really wake up with the downpipe, exhaust, fuel pump, 3 port and a tune. I've done exactly that to mine, plus some handling mods, and it's such a nice car to drive compared to stock. Only thing I wish I could do would be coilovers instead of lowering springs but I cbf with a cert or swapping them out for wofs lol

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Im in the process of rebuilding my first ej20 at the moment, its not done so I cant say what Ive done works, Im mentally prepared for it to pop on the first drive =] 

 

I ran a bearing, so I bought a donor motor and had the block cleaned and decked, with a light hone for the new rings, 

 

Im sticking with the stock pistons and rods that were in it, just new bearings and rings, and a complete gasket kit, all parts are from rockauto, and Im reusing my stock oil pump because the clearances were ok, 

 

Its just a project car so Ive been taking my time and its quite enjoyable, learning alot too,

 

Im up to the head rebuild now, but ive passed that part to a recon shop,

 

If i can help with any questions let me know! 

 

 

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On 9/02/2024 at 3:24 PM, boon said:

Q1. No, no gains, if anything you will slightly _lose_ as the aftermarket rods and pistons are potentially heavier, less well balanced, and not quite as good a fit as OEM. Assuming identical geometry, i.e. not gaining/losing compression. Stock turb and intercooler are never going to push the limits of even the stock internals if everything else is happy.

Q2. I wouldn't bother just doing one. Either it's a forged build or it isn't. As to whether you would replace the pistons.... if you buy used pistons, you have no idea of their history. If you buy new pistons they're going to cost you about $500 for a set for stockies, is it worth it? I'd say probably not.

Q4. The only factory internals I'd consider an "upgrade" are V7 STI EJ207 pistons and rods, and they're >$2000 for the pistons and around $800 for a set of rods, at which point you may as well just go aftermarket.

Q5. Head gaskets, OEM. Rebuild kit in terms of bearings? YMMV. OEM are probably going to be the most reliable at stock power levels but might cost a metric assload.

Q6. Yes, it's fine. Honestly unless #racecar where you have specific oil pressure needs, dicking about with the oil pump seems to lead to more problems than it's worth.

Q7. As long as you weren't way out I'd probably nana it to the tuner, especially if you had slightly dropped compression rather than adding it. As long as you were comfortable it was driving well enough to make that trip safely. Anything turbo is kinda fundamentally variable compression anyway because the actual resultant cylinder pressure could be just about anything.

 

With that out of the way.... I wouldn't bother with a rebuild to factory spec. A better option, IMO, is to just keep driving it on the assumption it will blow up at some stage, and in the meantime get another block and start building that one up properly (forged etc). Then when yours finally gives up the ghost, you have the option of throwing in a bigger turbo or something and making a bunch of power.

 

 

 

Very inciteful. Thank you very much for your advice. I am still keen to go ahead with a rebuild, reuse all parts except perhaps find a good set of used pistons. The local machine shop/EJ specialist (Tony Flynn) said it's worth throwing the pistons as far as you can and replacing them with used ones....even if they have known history. He said he seen denotation events cause damage to pistons that still pass the crack test. I think I will used OEM gaskets and seals (which I buy from machine shop) and a set of ACL duraglide bearings.

18 hours ago, Boltonator said:

Regarding Q6. These cars already have a 12mm oil pump. I think its because along with supporting the usual turbos and bearings they have 4 AVCS solenoids to feed as well. 

I think your right. Local engine builder said the later EJs have a 12mm pump. He says it's a must upgrade for older engines....go to Subaru and get a OEM 12mm pump off a newer engine, they bolt right onto old EJs....they like $700 though.

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11 hours ago, Rapidcrazy said:

Im in the process of rebuilding my first ej20 at the moment, its not done so I cant say what Ive done works, Im mentally prepared for it to pop on the first drive =] 

 

I ran a bearing, so I bought a donor motor and had the block cleaned and decked, with a light hone for the new rings, 

 

Im sticking with the stock pistons and rods that were in it, just new bearings and rings, and a complete gasket kit, all parts are from rockauto, and Im reusing my stock oil pump because the clearances were ok, 

 

Its just a project car so Ive been taking my time and its quite enjoyable, learning alot too,

 

Im up to the head rebuild now, but ive passed that part to a recon shop,

 

If i can help with any questions let me know! 

 

 

Just like you, this is meant to be a wee project for me....I already have another EZ Subaru to drive around and this is just my weekend car so I don't mind if it's off the road.

 

....what are the clearances you checked in regard to your oil pump?

 

....did the machine shop check your crank, crank journals, hardness test on blocks and heads, crack test pistons, check bores etc?

....or did they only do what you said, blocks cleaned and decked with a light hone?

 

 

How much did your bill come to? I'm expecting the whole rebuild including parts and machine shop fees to come to a bit over two grand?

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10 hours ago, Panda said:

Very inciteful. Thank you very much for your advice. I am still keen to go ahead with a rebuild, reuse all parts except perhaps find a good set of used pistons. The local machine shop/EJ specialist (Tony Flynn) said it's worth throwing the pistons as far as you can and replacing them with used ones....even if they have known history. He said he seen denotation events cause damage to pistons that still pass the crack test. I think I will used OEM gaskets and seals (which I buy from machine shop) and a set of ACL duraglide bearings.

I think your right. Local engine builder said the later EJs have a 12mm pump. He says it's a must upgrade for older engines....go to Subaru and get a OEM 12mm pump off a newer engine, they bolt right onto old EJs....they like $700 though.

 

Brand new OEM 12mm pump is $150 on amayama btw :)

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11 hours ago, Panda said:

Just like you, this is meant to be a wee project for me....I already have another EZ Subaru to drive around and this is just my weekend car so I don't mind if it's off the road.

 

....what are the clearances you checked in regard to your oil pump?

 

....did the machine shop check your crank, crank journals, hardness test on blocks and heads, crack test pistons, check bores etc?

....or did they only do what you said, blocks cleaned and decked with a light hone?

 

 

How much did your bill come to? I'm expecting the whole rebuild including parts and machine shop fees to come to a bit over two grand?

I cant find excatly where I got the clearances, but it was in a subaru service manual, what I wrote in my book 

 

Rotor tips std 0.04 - 0.14 max 0.18mm 

 

Outer rotor to body 0.02 - 0.07 max 0.15mm 

 

Rotor height to bolt on cover (can measure this with a staight edge) 0.1 - 0.175 max 0.2mm 

 

Mine was just under the std upper limit with no visable damage, so good enough for me

 

They just did the work mentioned and it was $475, I checked the journals myself 

 

I just got the bill for my heads today, strip and clean, regrind/cut the valves, then reset the valve lash and install new stem seals on reassembly, and surfacing, boths head it was $1200 

 

And Ive spent about $730 at rock auto for bearings, rings, timing kit, full gasket kit and a couple little extra bits! 

 

Hope thats helps

Edited by Rapidcrazy
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