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Old 02-17-2013, 01:10 PM   #51
wrx1392
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from what i have gleaned from these threads , the rods are fed from the mains...if the mains are too loose the oil does not feed the rods what they need to live with all this power and boost.so yeah i'd say flow is better than pressure with more bearing clearance...thats why i went with the 11mm pump.less drag with more clearance ??? makes sense worth a try on a race motor. too much work for a DD that goes 100+ miles a day .
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Old 02-17-2013, 01:31 PM   #52
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I know a shop that does .002 mains and rods. The mains do feed the rods but the oiling is interrupted each time the oil hole of the crank passes over the ungrooved part of the main. So looser mains can alleviate a little of the interruption. With the full 360 groove xpg's I think you can still go pretty tight on the mains because the rods won't have interrupted flow. Also keep in mind the aluminum block expands more than the steel crank so clearance on the mains will loosen a little at operating temp.
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Old 02-18-2013, 10:06 AM   #53
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nothing wrong with the clearance. theres always positives and negatives.

i set my rods to .002 +-.0002

and mains to .0015
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Old 02-18-2013, 03:38 PM   #54
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This thread has some good info in it!

I had talked to john 1badSTI about rod and main clearances in another thread. Right now I have an ej251 NA that was rebuilt by a friend who has built other ej series engines with good success. The rods and mains are at around 0.002". John suggested that I add a shim to my new wrx 10mm oil pump which is what I am going to do. The engine will have some aggressive cams in it so revving close to 6k rpms at times. Once I break it in, not sure if I should use a 10w30 or a 10w40 for break in (going to add the ZDDP additive), I will be using a good 5w40 oil after that.

From other reading that I have done and the info that is in here, the factory rod and main clearances are too tight for even a stock turbo engine. NA might be fine though. Dom @ Maxwell power in Seattle likes to do 0.0016- 0.002 for the rods and mains but tweaks the wrx 10mm oil pump to flow 30% more oil. I could see using the sti 11m pump for single or dual avcs heads though. I agree with this because pressure makes things heat up while the right amount of flow has better cooling ability. Too much flow obviously is bad too but a little more flow is still better than a little more pressure overall.

Not to hijack this thread, but am I on the right track?

Last edited by subi400; 02-18-2013 at 03:54 PM.
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Old 02-18-2013, 03:42 PM   #55
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Yep sounds good I spin to 8000-8500. And run a jdm 12mm oil pump
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Old 02-19-2013, 08:38 AM   #56
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Sorry for neglecting the thread for the last several days...

Quote:
Originally Posted by kakarot09 View Post
So killerbee in your opinion high oil pressures are an issue because of the bypass valve flow characteristics. If you increase the bypass pressure would you see an issue with higher pressure then?
Flow and pressure are relative to each other here. For a SB with rods and pistons (OEM crank bearings and/or bearing clearances) there is zero reason to increase anything. The OEM setup will provide PLENTY of oil. The OEM pump, as-is, has a surplus of flow capacity.

When clearances get opened up the flow requirements (a bigger hole to push the oil through) get marginally increase, but is still within the capabilities of the OEM pump.

Something often not taken into consideration when increasing clearnaces is a REDUCTION in flow requirements when going from an OEM Journal Bearing to a Ball Bearing turbocharger that has a smaller oil restrictor.

Enough on the preamble, or pre-ramble

Now lets talk about how the bypass comes into play in this role. When pressure is to high (lets use the STi 04-07 10mm pump as an example, 85psi), the bypass opens. It's a fairly simple concept most all of us have a good understanding of. The opening point varies by RPM, viscosity and the clearances used, but gererally this is in the 2,000-3,000RPM range for OEM. So this means anything above the 'opening pressure RPM' the bypass is open. For example, if pressure stops rapid climbing at 2,500RPMs and levels off, anything above 2,500RPMs you are recirculating oil back into the pickup side of the pump.

This is not generally bad but it should raise some questions: Do I need 85psi at 2,500RPMs, is it benefitial? When RPMs double (to 5,000RPMs) almost HALF of the oil pump's flow is being bypassed, what are the downsides and are there any upsides? What happens if I open clearances and increase power, a LOT. And it should raise questions, or awareness, everytime an oiling related thread (spun bearing, short longevity, consumption, etc., etc.) pops up.

IMO, putting in a shim just opens a can of worms. You are asking the entire oiling system (spring, pump, lines, seals, etc.) to withstand a higher pressure than it was designed for, when really there is already adequate pressure already and more than enough flow.

So what happens when you open up clearances and use the OEM size pump? Idle pressure will be lower, possibly below OEM spec, since the hole you're pushing oil through is marginally bigger. Often times builders and shops will bump idle pressure anyway to improve low RPM oiling anyway. Plus the extra flow provided by the larger clearances improves oiling despite the lower pressure, because the loads are too low for pressure to have and significant effect. What else will happen? The pressure rate of climb will be lower. The pressure gauge needle will not pop up and peg to 85psi at such low RPMs. It will climb more gradually and top out another 1,000 RPMs higher (say 3,500 RPMs). This means cruising around town the bypass is not open, opens less, and bypasses less oil when it is open. You still get the bypass (full) pressure at upper RPMs where it's needed to maintain rod oiling, and because the clearances (the hole the oil goes through) is larger, there is better oiling.

How is the pump flow increased and what are the downsides? Pump flow capacity is increased one way and one way only, with larger rotors. Can the inlet and outlets be massaged to improve flow? Of course, it will have the same effect of porting anything, marginal increases in performance. The ultimate flow is determined by the pump gears. Bigger gears push more oil. Going from a 10mm to a 11mm pump increases flow capacity ~35%. That is HUGE. Putting this on an engine (especially an OEM clearanced engine) can and does have significant negative effects. Even putting the one-up pump on marginally higher clearanced engine can have more downsides than up. To accept the flow/pressures properly (on a pre-08/non-dual AVCS engine), oil passages need to be opened, bearing passages need to be opened, and clearances increase to loose. Basically, pump and engine are 'matched' to each other.

So why not use the one-up sized pump (11mmpump) on and older non-dual AVCS car. For one, you don't have dual AVCS . Why does this matter? Drive a dual AVCS car, bring the RPMs up and lift the throttle. What you'll see is a 20psi drop in pressure This is normal and the pump still has enough flow to provide the proper lubrication. Another reason is the pressure capacity of the 11mm pump is ~10psi lower. This is (I'm guessing a bit here, because the OEM redline is lower 2008+). The lower bypass opening pressure and the higher flow capacity can be a major problem if the engine is not properly modified for it. In this case, not only will the bypass open at a lower pressure, it will bypass even more.

So why is bypassing bad? It recirculates back into the pump's inlet. If you are bypassing 50% (80% with an oversized pump), that oil potentially goes through the pump over and over and over. Everytime it goes trough the pump it gets SQUEEZED as part of the pumping process, and this adds heat. This isn't what happens cruising around town, it's what happens when the RPMs aren load are high, which is not ideal. Also, the bypass flow characteristics are terrible. About as good as if you were trying to regulate the pressure out the end of your garden hose using a block of wood. The bad flow characteristics lead to aeration and that can be devastating to any components that rely on a solid steady stream of oil. What happens when the pump aerates? Bubbles are created by turbulence out the bypass valve and get sucked into the pump, and because air is compressable, the pressure and oil flow out the pump drops, bypass closes, aeration stops, pressure climbs and you get aeration again. How fast does this happen? F-A-S-T! You won't see the occilations on a gauge, but you will see it on a high end data logger with a good sample rate. Pressure will climb nice and neat then you will see occiliations, significant ones. The bypass when woprking properly will occilate as it opens and closes, regulating pressure, but aeration will look different and have spikes and drops far beyond where it shoud be.

How can I tell I'm having aeration and should I panic if I do? It can be done with a decent gauge, but an inexpensive datalogger would be better. Watch the gauge with RPMs. It should rapidly climb to the bypass opening pressure (roughly what you see chart, but variations depend on setup, sensor location, etc.), from that point on is where you really want to pay attention. Output volume of the pump is roughly linear with RPMs, so the bypass opens at 85psi and flow still increases, so the bypass opens more. Pressure after 85psi is dictated by the spring rate of the bypass. So as it compresses by more and more flow the pressure will climb, although at a MUCH lower rate. I like to see 7-15psi climb from opening to redline depnding on the setup. If you see less than 5psi of the pressure stops climbing with RPM, there is likely aeration.

Quote:
Originally Posted by ckyguy68 View Post
Is there actual proof that these larger pumps 11mm+ and higher pressures are actually causing aeration issues and/or damage to the engines?
I consult with builders and race teams all over the world. Before I even wanted to get invloved with the pumps it was brought to my attention that it's widely accepted to open and port the bypass to eliminate aeration. On track it generally becomes a short term problem above 8K RPMs. On track, finishing a race is more important than long term street reliability. Oiling shortcomings for the long term reliability are less of a concern because the engines are being torn down every 40 hours anyway and the oiling setups just have different needs/demands.

Quote:
Originally Posted by stretchedk7 View Post
yeah wonder if having a much wider bearing would help with all the bearing issues
It wouldn't hurt! If you can get Subaru to change that it would be greatly appreciated. Although there are 'tuner' engines out there with smaller bearing pushing similar power levels just fine. Long term the next Impreza engine will have nearly the exact same bearing setup.

Quote:
Originally Posted by subi400 View Post
This thread has some good info in it!

Not to hijack this thread, but am I on the right track?
Dom knows what he's doing so definitely trust his advice.

Quote:
Originally Posted by stretchedk7 View Post
Yep sounds good I spin to 8000-8500. And run a jdm 12mm oil pump
8,500RPMs can be easily supported by OEM pumps. The JDM 12mm pumps were made for the WRC cars, aka: spec-c. Prodrive had a hand in these these engines and they are different besides the obvious crankshaft with better oiling, twin scroll turbocharger, and higher redline vs our EJ25s. Can they be used? Of course, but engine and pump need to be designed as a system to work together properly.
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Old 02-19-2013, 11:33 AM   #57
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So in a car that has the oem pump, would you be against increasing the bypass pressure using a shim? Most engine builders increase the clearances from stock, and I very rarely see any failed bearings on a well maintained stock engine even with bigger turbos etc. So if Subaru thinks the flow and pressures are matched well in a stock engine and I don't see many failures then I would agree with them. But engine builders increase the clearances anyway. So you're more or less giving the advice to use the oem pump as is because the pump is more than sufficient anyway. I think adding the shim to the pump is a good way of preventing some oil being bypassed and maintaining higher pressure with the increased clearances. I guess my original question should have been more specific and said what are the down sides to higher bypass pressure?
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Old 02-19-2013, 11:43 AM   #58
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The biggest issue is flow needs to be tested in each pump. Then also pressure needs to be checks once the motor is running. You can tailor the pump to each engine.

Even though the actual pump doesn't cavitate much the problem is when your returning gallons of oil in seconds back to the oil pan and it airates (spelling) the oil.
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Old 02-19-2013, 01:13 PM   #59
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Alrighty guys glad alot of great information has populated my thread, I hope this is as useful to me as it can be for others. Ok here's my update:

I purchased a 10mm OEM modified pump with one shim which was purchased from and modified in house by MPS. I dove in this weekend and replaced the pump which happened to be a great thing cause I found my timing belt was getting slightly shaved by my timing guide . I replaced my belt installed the new pump and changed my oil to Rotella 10-40 (non-synthetic, white bottle; previously using sae 30 amsoil break-in oil). Im at about 600 miles on this build.

With minimal testing and with the increased oil wieght I am still experiencing around the same oil pressures (slightly lower possibly). Im getting tuned this friday @ mps (whooopeeee!!!) So I will definitely talk to Dom and company about it. After reading killerB's last post this makes sense being that I'm at stock bearing cleances with a ball bearing turbo. I will update this again after the weekend to give any insight I get from Dom after he sees and operates my car in person. I'm about 4 hours away from him so all communication has been by email or phone.
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Old 02-19-2013, 01:24 PM   #60
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If an engine has been assembled with "too much pump"..IE the pressures when the engine is running are too high and bypassing a lot, could these be adjusted to some extent by choosing a different weight oil to keep pressures in check?

Couldn't this also in theory help oil drain back and flow since a lighter weight oil could be used?
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Old 02-19-2013, 02:03 PM   #61
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Quote:
Originally Posted by tachrev View Post
If an engine has been assembled with "too much pump"..IE the pressures when the engine is running are too high and bypassing a lot, could these be adjusted to some extent by choosing a different weight oil to keep pressures in check?

Couldn't this also in theory help oil drain back and flow since a lighter weight oil could be used?
To an extent I'm sure using a lighter oil could help but even a thick oil thins when hot.

One thing that hasn't been mentioned is for high rpm the small pumps will drop off pressure wise sometimes like past 8k.
That's when more pump is nice.

Kinda of a trade off. Need small pump for daily stuff but the big pumps are nice when your out turning some rpm.
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Old 02-19-2013, 02:08 PM   #62
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Quote:
Originally Posted by kakarot09 View Post
So in a car that has the oem pump, would you be against increasing the bypass pressure using a shim?
Yes. The only time would be with an 11mm pump (factor 76psi bypass) to increase the redline limit.

Quote:
Originally Posted by kakarot09 View Post

So you're more or less giving the advice to use the oem pump as is because the pump is more than sufficient anyway.
Yes. The OEM pump has more than enough capacity. Chevy V8 racing pumps hardly move 20 GALLONS per minute. That is a LOT of oil! Sadly, there are builders out there prescribing bigger pumps and don't even know the outputs of the OEM pumps

Quote:
Originally Posted by kakarot09 View Post

I think adding the shim to the pump is a good way of preventing some oil being bypassed and maintaining higher pressure with the increased clearances.
Adding shims does extremely little in regards to flow. The ONLY way to improve the flow is make a bigger hole for the oil to pass through (opening clearances). A shim squeezes the spring more, more than it was designed for, and requires the oil pressure to be higher before the relief cracks open. The rotors push the oil and the only way to increase flow is to use larger rotors. Just because the gauge shows higher pressure does NOT mean there is more oil going through your engine. The same oil is going through, just at a higher pressure.

Quote:
Originally Posted by kakarot09 View Post

I guess my original question should have been more specific and said what are the down sides to higher bypass pressure?
Taxing the components to withstand additional pressure, pressure spikes (cold) additional parasitic loses? The better question would be, why would you want more than 10-20psi per 1,000RPMs?

Quote:
Originally Posted by stretchedk7 View Post
The biggest issue is flow needs to be tested in each pump. Then also pressure needs to be checks once the motor is running. You can tailor the pump to each engine.
For DIYers these are calculation that need to be done. For seasoned engine builders, a lot of this is known and part of an engine build.

Quote:
Originally Posted by stretchedk7 View Post

Even though the actual pump doesn't cavitate much the problem is when your returning gallons of oil in seconds back to the oil pan and it airates (spelling) the oil.
It's actually worse than that. If this were a Honda the oil would exit the bypass and go back into the pan, which isn't too bad. On a Subaru this oportunity does not exist because the bypassed oil has noplace to go, it is directed right back into the pump inlet, which IMO is not so great.
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Old 02-19-2013, 02:08 PM   #63
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Good point, to clarify my intentions, Im running BC springs and cams and plan on raising my rpms a little but not much. 7500 is prob max I plan on taking it which doesn't really warrant more pump.
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Old 02-19-2013, 02:12 PM   #64
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Definitely more harm than good can be done with ppl thinking bigger is better all the time however of you have ever seen a motor that oil starved you know it can cost $$.

There's soapy variables. And yeah s2000 pumps flow great and those Turn incredible rpm and I believe those are 8 or tens
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Old 02-19-2013, 02:13 PM   #65
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Quote:
Originally Posted by Quiksmith View Post
Good point, to clarify my intentions, Im running BC springs and cams and plan on raising my rpms a little but not much. 7500 is prob max I plan on taking it which doesn't really warrant more pump.
Nope. Tons of ppl run 8 and 10mm pumps well past 600 whp! All about setup and clearances and oil mods.
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Old 02-19-2013, 02:15 PM   #66
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Quote:
Originally Posted by tachrev View Post
If an engine has been assembled with "too much pump"..IE the pressures when the engine is running are too high and bypassing a lot, could these be adjusted to some extent by choosing a different weight oil to keep pressures in check?
To some extent yes. Oil Analysis will tell you when you find the sweet spot and I highly recommend them for anyone wanting to experiment with oils, as oposed to what the builder or OEM recommends.

Quote:
Originally Posted by stretchedk7 View Post
One thing that hasn't been mentioned is for high rpm the small pumps will drop off pressure wise sometimes like past 8k.
That's when more pump is nice.
This is a misconception. It's well known that the 11mm pumps aerate. starting at ~7k and can be dangerously bad ~8K. Aeration is what causes pressure to drop.

The pumps in theres cars are positive displacement, so the flow is near linear. The flow will be double at 4K, then is was at 2K and double again at 8k from what it was at 4K RPMs. These same style pumps are used in superbikes reving past 16,000RPMs. They don't cavitate, they just push more as RPMs climb. The pressure problems happen from the pumps pushing too much and the bypass. You can see this pushing a 2008-current model STi past the rev limit on an OEM bottom end.
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Old 02-19-2013, 02:18 PM   #67
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Quote:
Originally Posted by stretchedk7 View Post
Definitely more harm than good can be done with ppl thinking bigger is better all the time however of you have ever seen a motor that oil starved you know it can cost $$.
This is the info I try to spread, but it's not often easy to convince someone that a larger pump will cause oil starvation issues.
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Old 02-19-2013, 02:26 PM   #68
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Quote:
Originally Posted by KillerBMotorsport View Post

To some extent yes. Oil Analysis will tell you when you find the sweet spot and I highly recommend them for anyone wanting to experiment with oils, as oposed to what the builder or OEM recommends.

This is a misconception. It's well known that the 11mm pumps aerate. starting at ~7k and can be dangerously bad ~8K. Aeration is what causes pressure to drop.

The pumps in theres cars are positive displacement, so the flow is near linear. The flow will be double at 4K, then is was at 2K and double again at 8k from what it was at 4K RPMs. These same style pumps are used in superbikes reving past 16,000RPMs. They don't cavitate, they just push more as RPMs climb. The pressure problems happen from the pumps pushing too much and the bypass. You can see this pushing a 2008-current model STi past the rev limit on an OEM bottom end.
I can tell you my 12 ported doesn't drop off at all past 8k. A smaller pump will and did. Proof is on the pudding for me.
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Old 02-19-2013, 02:30 PM   #69
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In other words, we should just stop being a smart aleck right? End of the day, go with what was originally used and that is plenty... well, looks like i've wasted my money
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Old 02-19-2013, 02:31 PM   #70
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I can see the 10mm and 11mm or bigger having pressure issues because of air at normal rpm and such.

Maybe the since I do a bunch of oil mods to the block its actually helping .
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Old 02-19-2013, 02:41 PM   #71
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Quote:
Originally Posted by KillerBMotorsport View Post
Yes. The only time would be with an 11mm pump (factor 76psi bypass) to increase the redline limit.
Exactly the situation I was thinking. Also for anything above 8k I would like to see more than 85 psi.

Quote:
Originally Posted by KillerBMotorsport View Post
Adding shims does extremely little in regards to flow. The ONLY way to improve the flow is make a bigger hole for the oil to pass through (opening clearances). A shim squeezes the spring more, more than it was designed for, and requires the oil pressure to be higher before the relief cracks open. The rotors push the oil and the only way to increase flow is to use larger rotors. Just because the gauge shows higher pressure does NOT mean there is more oil going through your engine. The same oil is going through, just at a higher pressure.
Well to get flow you need a pressure differential. If the pump outputs higher pressure then there will be a bump in flow through the restriction and less through the bypass. In this case the restriction is large with small clearance and so the flow may not increase a lot but it will still increase. Also the higher pressure in the bypass should mean a reduced chance of aerating the oil there.

Quote:
Originally Posted by KillerBMotorsport View Post
Taxing the components to withstand additional pressure, pressure spikes (cold) additional parasitic loses? The better question would be, why would you want more than 10-20psi per 1,000RPMs?
Taxing components is pretty vague. Additional parasitic losses I can understand, how much are we talking here 1hp? Meh. I would not want more than 20 psi per 1000rpms. However if I were revving the car to 8500 I would want around 100 psi or more. Supposedly 85 psi is sufficient but I wouldn't run it that low and expect it to live a long life given the oiling on these engines. Also the less it bypasses at that speed the better. The last thing you want is aerated oil at 8500+. The loads are much higher at that point than they are daily driving at 3k. If I'm going to pick an rpm to aerate if at all then it's lower. So I think adding a shim can be beneficial.

By the way I have a pretty healthy respect for you and your products, I also have the oiling stuff you make and I've recommended and purchased your headers and oiling components for a build I'm doing for someone else. So just a discussion about this stuff, I'm not trying to be an ass In case it comes off like that.
If I'm wrong so be it. I just currently think its better to add a shim than not to the 11mm pump. Also since most people want to "upgrade" to the 11mm I think it's a good discussion.
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Old 02-19-2013, 03:58 PM   #72
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Quote:
Originally Posted by kakarot09 View Post
Exactly the situation I was thinking. Also for anything above 8k I would like to see more than 85 psi.


Well to get flow you need a pressure differential. If the pump outputs higher pressure then there will be a bump in flow through the restriction and less through the bypass. In this case the restriction is large with small clearance and so the flow may not increase a lot but it will still increase. Also the higher pressure in the bypass should mean a reduced chance of aerating the oil there.


Taxing components is pretty vague. Additional parasitic losses I can understand, how much are we talking here 1hp? Meh. I would not want more than 20 psi per 1000rpms. However if I were revving the car to 8500 I would want around 100 psi or more. Supposedly 85 psi is sufficient but I wouldn't run it that low and expect it to live a long life given the oiling on these engines. Also the less it bypasses at that speed the better. The last thing you want is aerated oil at 8500+. The loads are much higher at that point than they are daily driving at 3k. If I'm going to pick an rpm to aerate if at all then it's lower. So I think adding a shim can be beneficial.

By the way I have a pretty healthy respect for you and your products, I also have the oiling stuff you make and I've recommended and purchased your headers and oiling components for a build I'm doing for someone else. So just a discussion about this stuff, I'm not trying to be an ass In case it comes off like that.
If I'm wrong so be it. I just currently think its better to add a shim than not to the 11mm pump. Also since most people want to "upgrade" to the 11mm I think it's a good discussion.
Any 10mm pump should be providing more than 85psi. Remmber the 10mm bypass is set at 85psi and the 11mm bypass is set to 76psi. AND pressure goes beyond that (another 10+psi) after the initial opening point to redline. So if your oiling system is working well, you will see ~95psi at redline, which is what you're looking for and with the smaller pump it's safer and creates less heat because you're bypassing less oil.

You're exactly right. The phyisics will tell you bumping pressure WILL bump flow. There's no way around the physics, but do the calculations and that bump in flow in miniscule compared to the +35% in flow you get from the 11mm pump. PLUS as stated before, that bypass opening RPM is so low, you've got a glut of flow/pressure by redline. More than the 85psi when it cracks open.

I don't take offence at all! If it raisines questions, maybe some that haven't been asked before and new concerns ideas, it's worth it to have the discussion. If it saves someone from getting only 10K out of their new built motor, even better!

Quote:
Originally Posted by stretchedk7 View Post
I can tell you my 12 ported doesn't drop off at all past 8k. A smaller pump will and did. Proof is on the pudding for me.
I don't like to comment about anyone's particular observations and modifications because I know nothing about them. If you can post specific clearances and any and all modification done to the passages, bearings, clearances and date plot the pressure vs RPMs I think it would be handy to disect the results for your setup. Sharing this info would be handy for the community as well.

Making a blanket statement like that could cause someone to follow and not have the same results as you, possibly worse. Or you could be pegging and outflowing the bypass because there is nowhere near enough flow capacity in the engine to support the pumps flow. This would show a pressure increase even if you were pumping air. The bottom line is, without info on the setup and output data, it's all speculative.
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Old 02-19-2013, 04:21 PM   #73
stretchedk7
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Very true.


Mains .0014-.0016

Rod bearings .002 +-.0002

I mod about ten locations on the block.

I am changing my turbo setup now and have no aem logs saved I can show oil pressure on. Very soon though I could post logs.

I in no way am saying this is the way to do it but for every engine I have built for customer/friend I may or may not change the oil pump size depending on clearances and what the engine will do.

I can without a doubt say that all of the motors see 8k or more daily. All run the block mods I do as well as ported/polished pumps. I do not usually shim the relief however.
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Old 02-19-2013, 04:23 PM   #74
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And if the pumps were pushing air I'm certain the engines would blow up rather quickly or show horrible bearing wear.
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Old 02-19-2013, 04:36 PM   #75
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Dom knows what he's doing so definitely trust his advice.

Well, I had read an article from him about his air plane engines and also the engines he builds for subarus where he talked about stock clearances and clearances that are more ideal. Since my NA ej251 engine has around 0.002" bearing clearances, which will induce a little more flow over all but slightly less pressure, and I am raising the redline to 6500 which isn't high but for these NA engines they are a little higher then I want to make sure I match the wrx 10mm pump with the clearances, and then rpm that the engine will see at times.

Whether it is a turbo engine or a modified NA engine, having the right clearances and then the pump to match that and the rpms is important.

Lets say that I cruise on the highway at around 3200 rpms but had added one shim to the wrx pump to bump the bypass valve opening psi to what 90 psi? I could cruise at 3500 rpms and still be under the bypass valve opening, couple this with the slightly looser clearances and it seems to be a win win situation. I mean most wrx and sti owners cruise at around 3k to 3300 rpm's on the freeway so having the bypass valve open at lets say 3500 - 3700 rpms would be ideal.

Another thought is this: lets say we set the rods and mains to 0.0018 - 0.002". Port the wrx 10mm port a bit to clean up the ports and then add 1 shim at first. This obviously will increase the bypass valve psi that it will open at. So, with the looser clearances, and the slightly higher psi that the bypass opens at, wouldn't the bypass valve open and close faster and for less duration?

What do you guys think?

Last edited by subi400; 02-20-2013 at 02:43 AM.
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