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Engine Tech Technical discussion related to all relevant engines such as KA, SR, RB, CA, 2JZ , L24/26/28, VG, VQ, and LSx series.


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Old 01-23-2023, 09:04 AM   #1
chiboy002
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KA24DE Vacuum and PCV Function

I'm playing with the idea of doing a dry sump set up on my KA but don't want to have to add more complexity to the system if I will need a vacuum pump to help pull vacuum for PCV.

Does anyone know how much vacuum the KA pulls at idle and 3000 rpm? I can't find a definitive answer and only found forum posts where people argue if vacuum is in PSI or mmHg or inHg
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Old 01-23-2023, 10:18 AM   #2
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Quote:
Originally Posted by chiboy002 View Post
I'm playing with the idea of doing a dry sump set up on my KA but don't want to have to add more complexity to the system if I will need a vacuum pump to help pull vacuum for PCV.

Does anyone know how much vacuum the KA pulls at idle and 3000 rpm? I can't find a definitive answer and only found forum posts where people argue if vacuum is in PSI or mmHg or inHg
Vacuum would be inHg. However, the entire crankcase is under a vacuum with a dry sump system, so the PCV can likely be removed.

https://motoiq.com/crankcase-ventila...n-a-edition/6/

Last diagram on the page.
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Old 01-23-2023, 06:24 PM   #3
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Dry sump systems ideally pull the crankcase down to lower pressure than the PCV system ever would. That's part of the reason they make more power. You can adjust that with dry sump speed (pulley size), or a variable breather on the valvecover.
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Old 01-23-2023, 06:39 PM   #4
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Right, I have an understanding of how to plumb the system, that isn't the issue. I'm moreso looking for data that I can use as a reference when picking a dry sump.

I'm under the impression that different styles can pull different amounts of vacuum and would like to pick one that is capable of producing enough vacuum in the appropriate range without going overboard.

For example, if the KA pulls 20 inHg of vacuum at 3k rpm then I would like to have a pump that can produce the same amount. It's my understanding that some pump designs are better at producing vacuum, like a gerotor compared to a spur gear. I can't find this info in the FSM and my motor isn't ready to be put back together for me to be able to measure it.
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Old 01-23-2023, 07:10 PM   #5
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Dry sump systems aren’t designed or built around how much vacuum an engine has at X rpm.

There are many variables to contend with, including the engine’s displacement and scope of modifications, intended RPM range, type of competition, tank capacity, and more.”

You need to consider what you are doing with the motor/car. Typical systems are 3stg, 2 scavenge and 1 pressure.
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Old 01-23-2023, 07:38 PM   #6
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I planned on going 4-stage, 3 scavenge 1 pressure.

I was speaking with someone at StockCarProducts and they mentioned that a spur gear with 5-stage might pull the same as, say, a gerotor would at 4 stages but they couldn't suggest anything since they are unfamiliar with KAs.

Making these numbers up for sake of conversation but if a KA pulls 10 inHg at 3k rpm and a 4-stage spur gear can only pull 8 inHg before it maxes out then I wouldn't use that and my options would either be adding a stage or looking at different pumps.

Sorry if I am not being clear but I'm asking so I can have a ballpark figure to know when comparing sump vacuum performance. I know some people have set ups in which they use a 3-stage + auxiliary vacuum pump but I would like to avoid that since it adds complexity. ARE's KA kit comes with a 3-stage sump but the Mazworks SR kit is a 4-stage sump, both from ARE, granted they aren't the same engines but this is what is leading me wanting info before I make a decision on which pump.
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Old 01-25-2023, 02:33 AM   #7
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To make use of a vacuum pump the engine should be built with low tension oil control rings and improved oil priority directed for wrist pins, as well as improved oil pump design and possibly pressure/volume.
Vacuum pumps have been known to create oil pumping and internal lubrication related issues at high vacuum setting.


Otherwise power gains will be marginal and there is increasing friction as oil is pulled away from the wrist pin leading to failure at high vacuum or oil flow related issue.


It is advised to avoid vacuum pumps in street applications as they increase maintenance, complexity, the pump will require disassembly, cleaning, and rebuilding.

You can measure vacuum in PSI and many other units. Use google to convert as needed.
Sea level atmospheric pressure is 14.5psi absolute so for example 1psi of vacuum is 2.03602" Hg or 2.03602 inches of mercury.


Vacuum pumps are useful in strict racing applications where minimal engine modifications are permitted to help contain oil within the engine and squeeze a couple of horses to edge out the competition where everybody is forced to use the same setup. They are also useful in racing applications where there is no limitation in funding for choosing the pump setup over traditional PCV, a vacuum pump is always superior to OEM style PCV, it simply costs more and is more maintenance (time, labor) intensive. Dry sump style scavenging is useful when oil pan ground clearance is an issue and keeping the bottom of the engine away from the ground is ideal such as the corvette which can use a shallow pan and set the engine low in the chassis. Dry sumps provide some of the benefits of the vacuum pump while providing oil supply in a manner which overcomes many of the potential issues faced when using a wet sump with a vacuum pump.

I get the feeling you do not understand how the OEM pcv system functions at wide open throttle to maintain Vacuum on the crankcase in forced induction applications.
In this video I demonstrate the proper technique, how to measure it and how to use PCV properly.
https://www.youtube.com/watch?v=0oRbfNPnHaI&t=1554s

It is possible for OEM pcv on engines 2L to 7L , 400 to 1500rwhp daily driver applications using wet sump
If you measure and set the crankcase pressure properly as I have shown in the video

I explain here more details
https://www.supraforums.com/threads/.../post-13980010
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Old 01-25-2023, 04:55 PM   #8
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Honestly, I'd never buy any other kit than a Dailey engineering kit. Dude is a legend and no external lines makes tons of sense to me.

Generally you size your pump based on how much power and rpm you're going to turn. I'm sure a few emails back and forth with Mr. Dailey and he'd have you sorted out.

https://daileyengineering.com/nissan/nissan-ka24/
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