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11-04-2006, 09:35 PM | #76 | |
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11-05-2006, 02:52 AM | #77 |
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01-04-2007, 03:09 PM | #78 |
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So with the 10 psi per 1000 HP figure... and an STI oil pump relief valve set at around 85, I'm good for at least 8k redline?..How much does "shimming" the pump raise the relief to ?
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01-05-2007, 12:45 PM | #79 |
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I don't understand this issue where people are saying that the centripedal force must be overcome in order to oil the rods. Others are saying that one of the holes may need to be blocked to stop the oil from flowing out the other hole at the main. Looking at the physics the path is longer to the rod than to the center of the crank via the main. So will spinning it faster starve the rod for oil? I can see a higher possibility of cavitation yes but the faster you spin it the more the inertia from the longer rod passage will suck. Also, 2 holes in the main are expected to be subjected to approx the same amount of pressure from the supply channel. I can't see how this would in any way cause the oil to shoot out the other side since both sides should be subjected to the same amount of pressure. Someone observed that an aftermarket drilled crank had a 3rd hole out the TDC side. To me this makes a lot of sense since the oil will be subjected to more centrifical force (passage is further from the centre of rotation) and it does not need to turn the 90 corner to exit on each side of the rod bearing. I think someone with too much time on their hands would need to install a crank in a bare block with all the other oil passages blocked, then spin it up to 10,000 rpm and see what happens to the oil supply at different oil pressure levels. If anything I could see this design starving cylinders 2 and 3 because 1 main feeds 2 rods. -Michael |
01-05-2007, 07:55 PM | #80 |
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The issue is directly due to the "sucking" force you mention (although some on the forum will dispute the use of that term).
You can only pull so hard on a liquid before the fluid column "breaks" this occurs when the suction force on the fluid gets close to the vapor pressure of the fluid, and either boils the fluid, or causes dissolved gasses to come out of solution and make the oil foam. For example you cannot lift water more than about 32 ft with suction (depending on temperature of the water and friction losses in the piping) as the water column will break and the water will flash to vapor under the high suction. In a cross drilled crank, at high rpm ( usually near 8000 rpm) the oil in the center of the cross drill is under a very low pressure as the centrifugal force trying to throw the oil out of the journal balances the the pressure supplied at the bearing by the system oil pressure. When these forces match oil flow effectively stops. Any bubbles in the oil will expand as they get to the center of the journal, filing that oil channel with foaming oil. At the same time from this low pressure area in the center of the main journal you have the rod drilling which is having the oil pulled up toward the rod journal. This "suction force" to use your term lowers the pressure in the oil enough that it begins to form bubbles of dissolved gasses. This aerated oil has much lower film strength than liquid oil. The net effect is that oiling effectivness to the rod drops substantially. Any high load at this time, like an over rev on down shift or a sharp throttle lift from high rpm, will lead to connecting rod failure as the rod bearing tries to seize an twists off the rod big end, or spins the bearing in the rod. Larry Last edited by hotrod; 01-05-2007 at 08:03 PM. |
01-05-2007, 09:33 PM | #81 | |
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Last edited by Homemade WRX; 01-06-2007 at 09:29 AM. |
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01-06-2007, 04:26 AM | #82 |
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The explanation from hotrod above is spot on!
I have been researching the cross drill design and what he says is correct. I think we have pretty much analysed what is wrong what we need now is some sort of reasonable solution to it. I dont mean suggestions like fit a dry sump or a setup that costs as much as the bottom end but a reasonable suggestion. Maybe we can investigate getting the crank drilled differently to enhance high rpm oiling. Not only by drilling another hole into the existing cross drilled hole as this doesn't really address the problem but a new passage that doesnt intersect the center of the journal. Anyone know what other 4 cylinder cranks are using for oiling systems? They all have a 180 degree throw between journals. Take for example a honda inline 4 cyl. They rev heaps thats to the cam system. What are they running? Lets try to find a practical solution that doesnt mean we have to run extreme oil pressure or dry sumps. |
01-06-2007, 09:31 AM | #83 |
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my favorite solution on the crankside is the "v" supply shown in the suzuki paper that was linked earlier in the thread...
aside from that I'm already working on the pump issue. Too bad it costs so much for a poor college kid (only 1 more semester!!) to do out of pocket. |
01-06-2007, 10:25 PM | #84 |
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Hi guys,
Here is a picture of our billet subaru crank with improved rod journal oiling. This is our solution for high power engines. No rod bearing issues. I think this upgrade is more important than upgrade rods up to 600hp. Thanks, Tomi |
01-07-2007, 03:20 AM | #85 | |
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You can clearly see the holes going into the crank on an angle. This is exactly what we've talking about. An oiling system that attempts to reduce the effects of cetrifugal force on the oil. I have no doubts that this crank couples with a well setup standard oil pump will not have any oiling problems whatsoever. Damn, why didnt subaru do them like this in the first place. Then we could have taken full advantage of the short stroke design and get some serious revs. |
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01-07-2007, 11:02 AM | #86 |
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Here is another one. Hopefully you can get the idea from this one.
Thanks, Tomi |
01-07-2007, 12:38 PM | #87 |
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Has anyone calculated the vacuum created by the centrifical force to determine if the vapour point of the oil is being crossed? Looking at the billet crank I think the holes look larger but I can't really see how the design itself will do anything to reduce this vacuum.
Another point is that whatever amount of oil pressure finds its way into the crank when raised by only a few psi should make a big difference in this flash boiling if it's even the root of the problem. I think rather than sitting around as armchair engineers someone needs to do the science to prove or disprove this theory. From the factory my EJ20K revved to 8250 before the cutoff. The rod bearings showed no sign of oil starvation after a year of kicking the hell out of it and smacking the rev limiter pretty much every day. I did some googling for the vacuum where engine oil boils but wasn't able to find anything. Even MSDS listed it as "extremely low". So for kicks I hooked up a brake bleeder vacuum pump to a glass coke bottle and wasn't able to see any "frothing" with a drop of mobil1 5w50 at 20C and 50" of Hg. Who knows how accurate this was as it was pretty crude... I also sent a message to redline oil asking for technical assistance in determining the vacuum point where their oil boils at normal engine operating temp. My background is not in engineering so maybe those who are educated in this can jump in here. -Michael |
01-07-2007, 01:22 PM | #88 |
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this will be a fun headache on my long list of things to do...
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01-07-2007, 03:41 PM | #89 | |
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Larry Last edited by hotrod; 01-07-2007 at 03:57 PM. |
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01-07-2007, 04:25 PM | #90 |
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After being involved with serious engine r&d program for a long time, we don't use cross drilled cranks on anything.
Subarus are the only ones. (Stage1&2) First when I got in to this subaru world, this was the first thing I wanted to improve, and it didn't took a long to come up with this improved crank. It's kind a pricey upgrade, but very very good one. Tomi |
01-07-2007, 09:03 PM | #91 |
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Now I see what you guys mean about the non-cross-drilled cranks. You don't get one by plugging one of the holes on the main. You get one by drilling the hole from the big end to one of the sides of the main rather than intersecting in the middle.
Reading the article at http://www.tytlabs.co.jp/english/rev..._044suzuki.pdf You can see his research shows that the "v" type oiling system is more effective. This is more of a cross between the two types. Unfortunately I can't see a reasonable cost effective way of "changing" the oiling system on a subaru crank. For the record I checked my legacy turbo crank and it is cross-drilled. That engine is rumoured to have the highest flowing oil pump of all the subie motors. Does anyone know if it bolts on to let's say an EJ20K? -Michael |
01-07-2007, 10:20 PM | #92 |
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all suby pumps are the same...the turbo legacy too...just shimmed from the factory....or so I've been told. Never measured the gears personally.
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01-08-2007, 01:07 AM | #93 | |
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The difference is the EJ22 type have gears that are 10mm wide, standard oil pumps are 9mm wide. They look identical but the internals are different. This means the EJ22 pump is capable of higher volume. |
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01-08-2007, 01:12 AM | #94 | |
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01-08-2007, 01:20 AM | #95 | |
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Add to this they are running at low speed, only 1800 rpms. I'm pretty sure if they went to a full grooved bearing shell and started to get the revs high enough for centrifugal forces to come into play they would get a different result. |
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01-08-2007, 01:21 AM | #96 | |
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Larry |
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01-08-2007, 04:19 AM | #97 |
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Hey, check out the picture of the Cosworth billet crank.
http://www.cosworth.com/shop_item.php?productid=384 It has oil passages drilled on the 2nd and 4th main journals !!!! Therefore you would have to drill the block and get grooved bearing shells. Surprising since the 2nd and 4th bearings are already so narrow, the groove would further reduce surface area. Is this the same item as on the Cobb website? The design looks identical. I wonder who actually manufactures the thing? |
01-08-2007, 06:43 AM | #98 |
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Our 75mm or 79mm stroke billet crank is $1149, 00.
Thanks, Tomi |
01-08-2007, 07:01 AM | #99 |
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Subaru has a number of different oil pumps:
7mm lastest EUDM SOHC engines 9mm all the older EUDM SOHC engines 10mm all the turbo engines and EJ25 engines (part# AA104~108, AA280) 12mm JDM dual AVCS engines The size above refers to the width of the throchoid gears inside the pump. If the stock 10mm pump is set at 100%, then you can say the 12mm pump flows 20% more oil. These 12mm pumps are a cheap upgrade compared to the JUN, Cosworth and who-knows-what pumps. The size of the pump is stamped on the left side above the crankshaft sprocket. It's visible with the belt covers installed. The SOHC pumps run at 5 bar oil pressure, the Turbo and DOHC pumps at 6 bar. All pumps are interchangable. |
01-08-2007, 11:18 AM | #100 |
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