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Old 09-27-2020, 05:09 PM   #2351
BrandonDrums
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Quote:
Originally Posted by Max Capacity View Post
I'll agree ^ these engines should not be using a "energy saving oil"

I could be mistaken but, if the timing is not optimal, the cylinder pressure becomes, "out of phase" so to speak, there by putting unequal pressure on the rod bearings.

That may be over simplified, but hopefully it may start a discussion...am I on the right track ?
Yup, on the right track for sure. Bad timing is not good for any engine FWIW - as you point out it can cause the mechanical force from the fuel burn on the piston to ram parts together. Think of riding a bike and trying to push at the wrong time and just hurting your foot vs. getting the crank to turn. Oil quality is a bit like wearing better shoes so if you do make this mistake the shoes can absorb the impact more. EC oil - not to mention keeping it at 5w30 which is too thin to start with will break down to an even thinner rating after getting absolutely roasted inside a nearly red-hot turbocharger so spikes in pressure can push through the film easier causing metal to metal contact. Think smacking your hand against a wall above ground, vs. doing it under water. Viscosity matters and maintaing that viscosity over a few thousand miles of abuse is just as important.

While this has been explained and debated a lot on this very thread, it's buried in almost a hundred pages so worth revisiting - In a Subaru EJ this is compounded because it has such a short Rod to Stroke ratio (bore and stroke ratio aside, having a stubby rod) make the rod bearings and piston rings see more lateral stress mid-stroke than most engines which are inline or vee configurations and just naturally have a longer rod to stroke ratio. So even without a knock/ping event - just having the combustion force max out a little too early or too late can be compounding the stress the piston rings and rod bearings experience more than an engine with a more optimized geometry. So if there's not enough protection between the metal, bang zoom you've got a shredded bearing or a cracked ringland as the ring grabs the bare metal cylinder wall and tries to rip itself out.

Additionally, the piston's rate of acceleration to and from TDC (and BDC) is higher as the Rod to Stroke Ratio decreases. This also affects how long a piston 'dwells' at TDC at the peak of the compression range so there's a lot of finicky business finding the right ignition timing to avoid ping. But, some engines may choose low rod to stroke ratios just to reduce rotational mass which can also be a benefit...

...it's a tradeoff....

And just to avoid rehashing a huge debate on this topic - i'll mention this discussion came up because some performance engines like the Honda S2000 engine(s) have an even shorter rod to stroke ratio and spin to 8 and even 9 thousand RPM giving those mechanical components more overall stress than even a 400hp EJ engine with a 6500 RPM redline. However, there's just a lot more chemical and heat energy entering the combustion chamber when you boost an engine so a knock event is both more likely and more potentially devastating on the turbocharged car. You gotta keep a wider margin of safety when you boost, you can wind out a naturally aspirated engine a lot more towards the edge because there's just less danger in a knock event happening...and that knock event being large enough to matter. And nevermind the fact that the cooling system on a lower output engine doesn't have to work as hard and the oiling system would inherently be engineered for the higher rotational stresses out of the box. Subaru Engines aren't designed to rev that high, they make their power through increasing torque which actually reduces some operational stress just by making peak power at a lower RPM range than say an engine spinning at 9 grand. But at the expense of a higher likelihood to knock and that knock event having more mojo....

I know this is getting pretty technical but basically modding a turbocharged EJ Subaru engine vs. other similar engines in it's class like a Mitsubushi Evo engine or a Civic Type R or Ford Focus RS might require a bit more attention to detail regarding fluid quality and the tune itself. Let's hope the next Generation STI has much more bespoke considerations in design with fueling, cooling, oiling and component quality (like forged pistons and rods with more rod bearing surface area) to improve reliability. A tuner car should be a little more hardened IMO even though I love these freakin cars.

A couple quick references:



https://www.hpacademy.com/previous-w...tio-explained/
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Last edited by BrandonDrums; 09-27-2020 at 05:38 PM. Reason: I'm obsessed with making a perfect post.
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Old 09-27-2020, 05:17 PM   #2352
Max Capacity
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Thank You for explaining that.

Again, thanks to my Tuner.
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Old 09-28-2020, 10:40 PM   #2353
Ptkacik
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My brothers four engines in 135,000 miles have been bone stock from the dealer. No modifications. New short blocks so pistons, bearings, cylinders are always new.

I hear the talk about heavier weight oil but that bothers me in that it would modify the cam timing due to flow problems in the cam timing advance systems. That is, it may put thicker oil on the rod bearings but it wont flow the same through the cam timing orifices.

So what is it that the engine designers at Subaru have missed? With four engines from the dealer, if it was bearing material, you think they would have caught that.

Peter
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Old 09-29-2020, 01:12 AM   #2354
BlueSTI4Me
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Brandondrums, glancing at what you explained versus inspecting rod bearings I have seen wear in the middle of the rod cap side of the bearing. It has always bothered me, but I never measured the difference. I'll have to run that thought by someone I know who measures bearings.
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Old 09-29-2020, 07:15 AM   #2355
Zak6182
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Ptacik -- When they replaced the short blocks did they reuse the oil cooler and pump? Is this the same shop doing the work every time? After my 2nd engine I'd very skeptical about going back and I'd definitely be asking about the oil cooler and getting specific answers as to how they were cleaning everything.

Also, its widely accepted to run 40 weight oil, especially if its being driven hard or in high temps. I believe its even in the owners manual to use for severe conditions. Find an oil with good resistance to shearing like Redline or Motul. It also wouldn't hurt to get an oil sample done during oil changes to see whats happening.

You say he drives like a "teenager". Someone else mentioned it a few posts back but a good oil pickup and baffle (iag or Killer B) will help with keeping the oil in the pan so the pump doesn't starve. This can happen in high G situations, hard corners, doughnuts or hard launches.
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Old 12-27-2020, 08:37 PM   #2356
Zvejniex
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Hello,
had a nr 2 rod bearing failure on my 02 rex. Picked it up with already having signs of something that might ruin the engine, knocking noise at 4k steady rpms, that I did not notice during the purchase. It held better than I expected though. Hard to say exact milage, but it could be around 5k. Did a few pulls here and there, nothing crazy and it finally finished her

Some what recently i've rebuilt it (not myself).

Couple of Q for seasoned vets here: Could it be possible that STD main bearings can be used with used block halves and new crank? Machine shop said that halves don't need to be machined except for the cylinder hone. Im a bit worried something can go wrong here, but I do not know how old is the block, all I know it's been split previously and it also had STD bearings everywhere.
Cars dash shows around 280k km.

Whats your take on used halves? Standard procedure?

I did my best by changing crank, rods, bearings, pickup, pan, oil cooler and pump, so it would be very silly to have it all fall apart because of reused halves.

Currently around 1k miles in and all is well.
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Old 01-02-2021, 12:00 PM   #2357
Seangraz
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Quote:
Originally Posted by Ptkacik View Post
My brothers four engines in 135,000 miles have been bone stock from the dealer. No modifications. New short blocks so pistons, bearings, cylinders are always new.

I hear the talk about heavier weight oil but that bothers me in that it would modify the cam timing due to flow problems in the cam timing advance systems. That is, it may put thicker oil on the rod bearings but it wont flow the same through the cam timing orifices.

So what is it that the engine designers at Subaru have missed? With four engines from the dealer, if it was bearing material, you think they would have caught that.

Peter
Heavier weight oil in Subaruís is good for them. The only reason Subaru recommends 5w-30 in the US is for fuel efficiency. Iíve always run 5w-40 with no issues.
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