The OEM rod bearings debate

[nelsmar]

Originally Posted by arghx7

Well I'd have to see the exact text here. NA engines simply can't get more than maybe 16-17 bar IMEP (work before pumping and friction is subtracted). Boost can do a lot more than that, but has knock issues on pump gas so how do you compare? The same relationship I described earlier still exists. If the combustion is significantly retarded for knock relief, the peak pressure will be lower and display the "double hump" characteristic shown here:




while an MBT pressure trace at the same given torque looks more like this:




Are you asking how combustion speed is affected by charge air/load at a fixed rpm? Generally speaking I'll say that the burn delay (0-10%) is longer in the low speed low load range, which requires earlier spark timing for a given combustion phasing (location of 50% burn and peak pressure). Otherwise it's too complicated of a question and depends on too many things like valve timing, mixture motion, spray pattern.

2 things.
1) isnt the double hump showing the first hump being the compression stroke, and hte second being combustion? So you arent actually "gaining" pressure, that pressure would exist regardless of spark or not. So this isnt actually showing that positive atmosphere would increase power by using retarded timing correct?

2) Lets go more hypothetical, i am just talking about a fuel burn rate regardless of combustion engine. Say we take a 1 liter canister. Fill it full of stoich mixed E85 and atmosphere. Ignite at the top and calculate the burn duration & time until shock hits the bottom of canister. Now lets take the same canister but fill with the same mixture but in a pressure of 2bar (so twice the density, twice the mass). Will the burn rate & shock rate change?

[nelsmar]

So now to make a post on topic. Does anyone have any photos of bearings that have been damaged? Does anyone have any logs of oil pressure? (Slim chance!). @cf6mech were you running an oil cooler? If so how long were your lines, how large of a unit. I am really leaning towards oil & tuning and starting to lean towards using some OEM bearings to test my self. A lot of people are using oil coolers which can lower the overall oil system flow.

[arghx7]

Originally Posted by nelsmar

2 things.
1) isnt the double hump showing the first hump being the compression stroke, and hte second being combustion? So you arent actually "gaining" pressure, that pressure would exist regardless of spark or not. So this isnt actually showing that positive atmosphere would increase power by using retarded timing correct?

That first hump is from the compression. If the spark is advanced enough, you have one big hump, instead of a small hump and a second bigger one to the right. As you advance the spark from the retarded position, the second hump moves left, closer to the first one, and eventually you get one big hump. If you advance past MBT, the hump "leans" to the left. Go back to my first post in this thread and look at the picture.

At a fixed rpm on a dyno, it is conceivable that you could be running a lot higher load (say more boost) with retarded combustion and still have lower peak pressure than running lower load at MBT. Peak pressure in terms of magnitude (say having 90 bar vs 70 bar max) can be highly sensitive to combustion phasing. So that means burn rates and spark advance.

2) Lets go more hypothetical, i am just talking about a fuel burn rate regardless of combustion engine. Say we take a 1 liter canister. Fill it full of stoich mixed E85 and atmosphere. Ignite at the top and calculate the burn duration & time until shock hits the bottom of canister. Now lets take the same canister but fill with the same mixture but in a pressure of 2bar (so twice the density, twice the mass). Will the burn rate & shock rate change?

that's sort of a textbook problem... I suppose you could say it goes faster at higher pressure, but that's kind of a useless answer. It's like in school physics talking about dropping a rock from a plane and only talking about gravity, neglecting the air it would be falling through. That's your simple "free fall" problem. But then try taking that simple discussion and using it to understand how a real bomb falls out of a plane. There's a whole lot more going on.

In a real piston engine, the instantaneous pressure and volume is always changing as the piston is going up and down. What you are asking and trying to understand is really what 3D modeling is for, and to a lesser extent optical single cylinder engines with high speed photography. When you look at modeling software output it will give you heat release, pressures, etc on a degree-by-degree basis to answer those kinds of questions.


Now that we've gone down that tangent... I too would like to see pics of a messed up bearing.

[nelsmar]

Thanks and yes I just wanted to know the basics for personal knowledge. I understand it is minimal in the scheme of things. I just wasn't sure if a higher density increased or decreased burn rate.

I have another question to add bit too much to yor from my cell phone. Ill type it in the am. I'll pull the bearings out of my block hopefilly bymmidndecember once I catch up at then office but no confirmation that was my failure point. I would likened seenither users who are currently assuming failure at bearings.

[nelsmar]

So at this point it looks like I am going to try OEM bearings my self and spend some time on the dyno and see how things turn out. This may take until January until I can get a block assembled and installed as my work duty right now is quite hefty. But I should be able to hopefully get a block running by january and hopefully slap a turbo on there shortly after and see what I find out. I'll gladly post logs & information on as much as I can. I'll hopefully be ordering a new shortblock & internals by mid next week.

I may try treating the OEM bearings as well.

I'll ask again to bump the thread... is there anyone that still has their bearings that failed or photos of them? I would still love to see them!

I really hope I don't regret gambling for the sake of science on this. Hah.

[Calum]

Originally Posted by nelsmar

So at this point it looks like I am going to try OEM bearings my self and spend some time on the dyno and see how things turn out. This may take until January until I can get a block assembled and installed as my work duty right now is quite hefty. But I should be able to hopefully get a block running by january and hopefully slap a turbo on there shortly after and see what I find out. I'll gladly post logs & information on as much as I can. I'll hopefully be ordering a new shortblock & internals by mid next week.

I may try treating the OEM bearings as well.

I'll ask again to bump the thread... is there anyone that still has their bearings that failed or photos of them? I would still love to see them!

I really hope I don't regret gambling for the sake of science on this. Hah.

http://www.mahle-aftermarket.com/MAH...nents/Bearings

Take a look at this site, and click on the sputter bearings. Give how hard guys have claimed the bearings to be I'd wager the bearings are using this process or something similar. This leads me to believe that an additional coating or treatment might not be a good idea.

I look forward to seeing your results.

[nelsmar]

Originally Posted by Calum

http://www.mahle-aftermarket.com/MAH...nents/Bearings

Take a look at this site, and click on the sputter bearings. Give how hard guys have claimed the bearings to be I'd wager the bearings are using this process or something similar. This leads me to believe that an additional coating or treatment might not be a good idea.

I look forward to seeing your results.

Duely noted. I'll talking t over with my friend that specializes in eh builds. We may just go pure oem.

We area Los planning on attempting to modify the eom oil pump to try to get a bit more flow out of it to help offset the losses from the turbo.

[Dustin@Dynosty]

Originally Posted by cf6mech

I had bearing failure on E85 with no detonation with a very sound tune on a built motor running close to 400whp Using Amsoil 10W 40. I'm now equipped with Accelerated Performance Pauter rods with ACL bearings and at 300whp @ 10 psi with no issues.

Originally Posted by DAMotorsports

Having opened a FA20 i would not fear it. i would take your time and go over everything or use a motor builder. setting the clearances not matter which bearing takes time. and for the oiling they are a few thing you can due to improve the psi. knowing the clearances of the stock motor i would not use anything thinker then 0w-20w

I agree with DAMotorsports and would be curious to know what cf6mech's bearing clearances were to be running 10w40 oil... especially if he ran stock bearings and crank

[Dustin@Dynosty]

we have sold built motor components to several dealerships and smaller shops that have built and blown motors, here is a pic from one rod bearing that ruined a motor that we recently flew down to tune. (after they rebuilt it a second time)



proper bearing clearance is crucial on this motor, more so then many other motors that people can build with plastiguage and some how get away with them living. I wouldn't even think about plastigauging this motor for anything other than OEM power. If you do not have the proper measuring tools to build motors, I would not attempt to build this motor.

[nelsmar]

@Dustin@Dynosty

Thank you for contributing! Its great to see someone who has been building motors jump in, and especially with a picture.

edit: How did the other bearings look?

[Dustin@Dynosty]

That was the only bearing that failed on the built motor of theirs. They windowed the block with the bottom skirt of the piston coming apart and rod slung around til it exited.

[cf6mech]

Originally Posted by Dustin@Dynosty

I agree with DAMotorsports and would be curious to know what cf6mech's bearing clearances were to be running 10w40 oil... especially if he ran stock bearings and crank

You would have to ask my engine builder at AWD tuning, they build Subaru short blocks and ship them world wide. Its one guy and he is the only one that does the builds. As a whole they(AWD Tuning)pretty much stay off the forums with all the conjecture and nonsense that goes around. Didn't know they made an after market crank for the FA20. Running a Perrin oil cooler to answer a earlier question.

[Dustin@Dynosty]

^ No I apologize if I mislead in my statement about stock crank, I meant not turning it down in order to give further clearance, because with stock bearing options, there is not enough clearance in order to run a thicker oil with out turning down the crank. So I assume that is what they did.

[nelsmar]

@cf6mech do you know if your crank was machined? I didn't want to pry too much at AWD since clearances can be a topic that builders don't like to talk about (which i can respect, it is what they do for a living, and their trade). I just assumed the crank was machined for extra clearances but I didn't think to ask.