psycho1122
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posted August 16, 2009 05:54 AM
Question....why noy just put a gauge right off the main oil feed?
I feel the oil light acts more like a "change engine light". 
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entropy
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posted August 16, 2009 07:03 AM
quote:
Question....why noy just put a gauge right off the main oil feed?
I feel the oil light acts more like a "change engine light".
Like my ole Mom used to say: "great minds run in the same gutter..."
(theory makes my head hurt, put a gauge on it, better yet, log oil pressure)
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Shane661
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posted August 16, 2009 07:06 AM
 Edited By: Shane661 on 16 Aug 2009 15:22
Presumably oil pressure will read lower due to the evacuated crankcase. So, determining what the acceptable pressure range would not be as simple as a gauge reading.
The mystery is what effect the lower pressure # in psig would have on oiling, if any at all. As stated earlier in the thread, atmospheric pressure is no longer the reference in an evacuated crankcase.
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entropy
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posted August 16, 2009 08:35 AM
Shane,
me thinks you are "out-science-ing" yourself.
IMO no matter what the crankcase pressure is, spec for oil pressure is at the oil galley.
No matter if the crankcase is evacuated or not, if you get the right pressure in the galley, you are getting the right pressure within the bearings.
simply put a gauge on it and/or start logging oil pressure.
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Shane661
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posted August 16, 2009 08:45 AM
Edited By: Shane661 on 16 Aug 2009 16:48
I don't know. But I do know that I am right back to where I started.
I am giving up on this (again) for now.
Many good thoughts, theories, and opinions. But not enough hard data to warrant change and/or risk.
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dougmeyer
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posted August 16, 2009 08:54 AM
Edited By: dougmeyer on 16 Aug 2009 16:55
Lots of misconception here- (Y2excepted)
In a WET SUMP system........
The oil pressure is the pressure created by the oil pump forcing the oil into a space with with a controlled leak (bearing clearances). You could just as easily consider the total area of these "leaks" as one area, so do that for now- think of it as just one hole at the end of a pipe from the oil pump. The pump drives the incompressible oil against the leak and the gauge measures the pressure in the pipe. Also, remember, the pump measures "gauge pressure' , not "absolute pressure" (more on this in a moment).
The inlet port on the pump is below the level of oil in a reservoir (oil sump) and this reservoir has atmospheric pressure on its "top" surface. The pump seems to draw oil from the sump by the suction created by the empty spaces created as the rotor rotates in the pump- it SEEMS to draw the oil with a fairly high suction or negative pressure into the pump and then packs the "pipe' with much more oil than the leak can relieve which creates the "oil pressure". However, this "suction" (any suction)is really the difference between the ambient pressure on the top of the oil and the lack of pressure in the pump rotor spaces as they rotate. At sea level, this pressure pushing the oil into the pump is roughly 14 psi. This is the ABSOLUTE pressure on the system. Note, though, that this same pressure is pushing back on the exit hole in the pipe which is in the crankcase. So, they balance. Ambient pressure is of no factor in the flow through the system and the gauge measures only the CHANGE in the pressure in the pipe-the GAUGE pressure. We could also measure and refer to the oil pressure as the absolute pressure plus the increase, say 70 psi plus the ambient of 14 and call it "87 psi Absolute" but it serves no purpose so we don't. (When would we, though? Well when the ambient pressure varies a great deal and would effect the system operation, Like with manifold pressure in turbo systems at very low or high barometers.- another discussion).
So what happens when we lower the pressure in the crankcase? Well, nothing as far as the oil pressure is concerned because the (very minimal) vacuum created by your evac system acts on both sides of the pump- the inlet and the exit of "the pipe" at all the exits. The gauge pressure does not change, but the absolute pressure does-by the amount of the reduced "ambient" pressure in the case. And to put a finer point on it, the pressure involved here is comparatively pretty low, A good shop vac can create about a 20 Kpa pressure drop against zero flow - atmospheric is 100 Kpa and this would be 20% reduction. And that would be a 20% drop in the absolute pressure. The small mechanical systems employed to create case vacuum probably are probably much less- maybe Y2 knows exactly.
But again, it matters not if the reduction in case pressure is acting on both sides of the oil flow. The case pressure DOES matter though, when you measure the pressures in the cylinder in a naturally aspirated engine because the baseline pressure here is different across the rings, the barometric pressure (Absolute pressure) above versus the pressure below the rings in the case which will be a different absolute pressure, greater from blow-by, lesser from a vacuum pumped system.
So here's a "real world" example- In the planes I fly I see about 50 psi oil pressure depending on oil temp. which is regulated by a thermostat in the oil cooler. At 18,000 feet the ambient air pressure "barometer" (absolute pressure in the crankcase) is roughly HALF of what it is at sea level. The oil pressure does not change.
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entropy
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posted August 16, 2009 08:57 AM
Edited By: entropy on 16 Aug 2009 16:59
Shane,
apart from this issue, i strongly recommend an oil pressure gauge AND a transducer so you can log oil pressure. I know you haven't gone into the motor, but getting in the habit of knowing what your oil pressure is may save you in the future
BTW, mojo kudo's on yr 211.9 at Loring!!! WTG!
I that the fastest NA 14????
I asked flyboy what the fastest NA 14 was but he apparently thought I was being a smartass and didn't answer. pretty thin skin, but oh, well...
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Shane661
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posted August 16, 2009 09:31 AM
Edited By: Shane661 on 16 Aug 2009 17:34
Thanks Doug. I'll have to digest this information slowly....very much appreciated.
Thanks Karl. I think my run is definitely the fastest stock motor, naturally aspirated pass on a 14...in the United States. As for worldwide...I'm not sure....but it is certainly possible! The only other faster LSR 14's that I know of either had had nitrous or turbo installed.
But now that the excitement (and winds) have died down...I will be focused on hitting the 200 mph mark in the standing mile. I consider that to be an even bigger challenge considering my stock motor.
Good idea on logging the oil pressure. I would like to get my DL-32 dialed in and set up by October.
Shane
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kawasakijockey
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posted August 16, 2009 09:36 AM
Edited By: kawasakijockey on 16 Aug 2009 17:42
This is a link to a little info about vac pumps.
http://www.gzmotorsports.com/vacuum-pump-guide.html
After reading some on this it seems that oil suspension on the topends of some engines is a cause of flickering oil pressures too. The vacuum on the top slows the return to the pan because of return passage size. Could this be the case with these bike engines?
Some of the 810 ci engines pull as high as 22hg. Typical 11000rpm 4cyl race engines are around 12hg (car engines).
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Shane661
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posted August 16, 2009 10:04 AM
Edited By: Shane661 on 16 Aug 2009 18:06
quote:
This is a link to a little info about vac pumps.
http://www.gzmotorsports.com/vacuum-pump-guide.html
I like the vacuum relief valves that they offer. I had been researching similar parts.
Would it be accurate to say that any crankcase pressure beyond what is needed for ring sealing is just robbing some hp?
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dubious
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posted August 16, 2009 02:34 PM
quote:
Shane,
apart from this issue, i strongly recommend an oil pressure gauge AND a transducer so you can log oil pressure. I know you haven't gone into the motor, but getting in the habit of knowing what your oil pressure is may save you in the future
BTW, mojo kudo's on yr 211.9 at Loring!!! WTG!
I that the fastest NA 14????
I asked flyboy what the fastest NA 14 was but he apparently thought I was being a smartass and didn't answer. pretty thin skin, but oh, well...
Shane I bought AEM guages, as they have transducers with analog OP to tie in to our DL 32 data loggers( or any for that matter).
Bit pricey but I like the lighted guages, and the fact they have remote senders( no oil or fuel pressure in the cockpit) and deliver 0-5 signals with O.P. for data logging.
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NOX
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posted August 16, 2009 06:43 PM
Thank you for the post doug
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dougmeyer
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posted August 16, 2009 09:12 PM
Apples and Oranges Alert
When reading info about vacuum systems and large drag engines like the ones in kawasakijockey's link, keep in mind that there is a huge difference between those applications and ours. The engines are as much as ten times the size of ours, the oil flows are torrential, the blowby massive, and the vacuum pumps take several hp to create those very large vacuum numbers. But even then, the basic fluid pressure laws still apply.
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dubious
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posted August 16, 2009 09:14 PM
quote:
Thank you for the post doug
+2 thanks Doug.
Doug n Jim... the wizards...
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2000redrocket
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posted August 17, 2009 05:40 PM
so for my old post on changing oil. my zx12 seems to not get oil pressure till i pull off the oil fill cap and relieve the vacume.
and my thoughts on oil pressure and safe though we have the man explaining it well over my head (some of it) oil pumps are positive displacement pumps for the most part being gear pumps so volume wise it would almost have to be the same volume of oil at a given rpm through the same tolerances once primed. just weard my nings does not want to prime its self till i open the cap.
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dougmeyer
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posted August 17, 2009 09:02 PM
Stuff like that happens and we can almost always figure out exactly why, where the airlock is, why the pump doesn't pick up. But if you know how to avoid it, it's not worth the effort to figure it out. On RG's Shootout bike I had to fill every line and the filter or it wouldn't prime. On the Turbo ZRX we had to put the front wheel a foot in the air and lean the damn thing way over to the left before it would flow any water. Not worth trying to find the bubble. You just do what you need to do...........
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Y2KZX12R
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posted August 18, 2009 04:20 AM
Great post Doug.
Its been hectic here at the shop and I haven't had a chance to gather the Indians to iron out the pressure differences between an evacuated wet and dry sump system behaviors.
The oil return is an issue with a dry sump system. You have to have separate air and oil paths. Otherwise the oil is trying to gravity drain back down to the pan and the rushing of "air" up threw the engines oil return paths prevents the oil from gravity draining back. To avoid this you need multiple paths of adequate size/area and we also scavenge the cylinder heads of oil so the oil doesn't even need to drain back. Some engines we split and seal off the top and bottom of the engine. So the crankcase area is evacuated and from the lifter valley up isn't evacuated. Completely divided. That's when you must have scavenge pickups in the lifter valley and each valve cover area.
Doug, on another topic, our new port design on the SB2.2 engine is working extremely well. Our engine won Watkins Glenn in car# 72 at the SCCA TransAM race. The only Chevy powered car to win a race over the Fords all year. But unfortunately it came too late.... The Fords wrapped up the championship in the same race.
OK back to the scheduled programming.......
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