Question to the L4 engine building guru's re cam oiling

Engine, Transmission and related drivetrain.
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zKars
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Question to the L4 engine building guru's re cam oiling

Postby zKars » 30 Jul 2017 14:52

Today I have what might possibly be a silly question about cam oiling, and more specifically about auxiliary cam oiling,

The LZ24 block/A87 L20B headed beast in my 69 510 came with an auxiliary oiling spray bar attached to the inside of the valve cover, plumbed to a T at the oil pressure sender. Now I assumed that the cam choice (perhaps) was such that the usual internal oiling was not working/or available (not drilled) in that cam and that the external oil spray bar was required. Rebello knows best, right (cough cough…)?

So I'm now merrily at about the 6500 km mark and having a good time, but the one thing that bugs me is the consistent low oil pressure that thing has. Like 40psi at cruise on a good day. Now putting two and two together and getting L4, I realized that the -4 line feeding the spray bar is a damn short circuit to the overall oil system. You should see the oil volume floating around in the head with the oil cap off at 4K RPM. Damn impressive. Reminds me of a story a buddy told me about some fancy racy Subaru engines that had SO much oil volume up top that the drain back holes where not big enough to handle the return volume. You can imagine the result. Perfect cams and rods out the side of the block

I have also of course looked at the cam and see the oil holes. And they are flowing oil just fine. I'm assuming the spray bar is just "extra oil" for those 8000 RPM race days.

I though about moving down to a -3 size line, but instead I naturally feel the need to experiment some first. I have now put a needle valve in the line so I can play with different spray bar rates. Sure as hell, when the valve is OFF, the oil pressure idles at 60-70. yeah, I know….. and the cam is staying plenty oily all on it's own. Imagine that.

So I guess I'm asking the voices of reason and experience to confirm that the spray bar is intended as EXTRA oil, not required, and really not needed for non-race conditions. L6 motors don't have this problem, many have their own spray bars fed from the cam towers, no cam lobe oiling at all, then later ones (280zx's) dropped the cracking prone spray bars altogether and went with cam lobe oiling alone.

Pics of my rig attached.

oilcam1.jpg
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oilcam2.jpg
oilcam2.jpg (116.12 KiB) Viewed 306 times

oilcam3.jpg
oilcam3.jpg (103.4 KiB) Viewed 306 times

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bertvorgon
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Re: Question to the L4 engine building guru's re cam oiling

Postby bertvorgon » 30 Jul 2017 18:17

Only thing I can say, based on MY real world experience, of having a spray bar AND the turbo feed, that an oil pressure gauge we have assumed, sees a low INDICATED pressure, than actual pressure.

We shimmed my high volume oil pump to indicate 80" Psi cold, yet when all things hooked up, I see maybe 65 -70 cold and an indicated 60 PSI when running and 55'ish when under high combat use. With all that, in all the years, the cam is fine and I now have 14 years on the motor with no issues.
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

Keith Law
1973 2Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer

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Re: Question to the L4 engine building guru's re cam oiling

Postby Byron510 » 30 Jul 2017 21:55

Hi Jim,

Normally I take photos of just about everything i touch, but I just spent 30 minutes looking for a photo that documented a step which may not have been done in your application.

A couple of notes to confirm;

You should not take an oil pressure line "T"ed off of the line leading to the spray bar. The spray bar jets have a cumulatively larger output that the fitting feeding the line into the spray bar bared feeds at the block, so an accurate oil pressure could not be obtained from this source. When utilizing the spray bar, I take my oil pressure reading from the remote oil filter block, which is the pressure coming from the pump through the filter and then measured on the feed side going back to the engine (after passing through the filter). This gives an accurate engine feed oil pressure.

Also when utilizing the external spray bar, the internal cam oiling is no longer required and needs to be blocked off. The stock oil system in the head receives oil through the oil jet in the top of the block, through the head and then into all four cam towers respectively. Cam towers 2 and 3 then feed the camshaft lobes internally through the camshaft with tower 2 feeding forward to the front 2 cylinders cam lobes and tower 3 feeding rearward to the back two cylinder cam lobes.
Mod time: This internal cam feed needs to be blocked off. I did this by machining an aluminum plug and pressing it (and then staking it) into camshaft oiling holes drilled into the journals running in cam towers 2 and 3. Otherwise over oiling of the top end - as already noted by you - will happen. In high RPM kill mode with both oiling sources to the cam operational (when using the Nissan Comp/DL Potter external oil bar), there will be so much oil in the cam cover that it will build and puke that out of the valve cover vent and make a hell of a mess! I've seen this once happen to a competitor at a local race track - not good.

Anyways, two things that I could think of to pass along and have you verify. And no I did not find the photo of the plug installed in the cam shaft - sorry. But it is relatively simple to do.

Byron
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zKars
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Re: Question to the L4 engine building guru's re cam oiling

Postby zKars » 31 Jul 2017 07:13

Thanks for the reply boys. Leaves with a couple of unanswered questions though.

First, what is the reasoning that adding a spray bar is considered necessary? Is the stock cam oiling considered inadequate in general or is this simply a race engine/high RPM/high load durability measure? It's plain that unless you exceed the heads ability to drain back the oil you're throwing at it, or your reducing oil available to rest of the engine, there is no such thing as too much oil on the cam so I get why using a spray bar is a good thing, just want to understand the initial root cause for its use.

Second I have trouble with this concept of the pressure as measured at the sender outlet not being the pressure being fed to the internals of the engine, if that's what you two are saying. I was about to call "BS!" until I looked at the L4 and compared it to the L6.

On this L4 of mine and an L20 I have gathering dust here, the sender port is left of the oil filter (downstream?) where as the sender on the L6 is before (upstream) of the filter on the block. On the L6, if I'm seeing 40 psi at the sender port, then the oil filter is only being fed 40psi. There is NO WAY there is more pressure somewhere downsteam of that. Since the sender port is after the filter on the L4, I can see, maybe, how the pressure there may not be the pressure going out to the block and head. maybe

But I also understand that the system pressure is determined not by the pump, but by the restrictions in the oil flow circuit, primarily the bearing clearances. All of the restrictions are after both the filter AND the sender port. I just don't get that if I have 40 at the sender port, where MORE pressure is available farther down stream from this point. Pressure is at a maximum at the pump outlet and can only decrease as it encounters restrictions along the way. The pump relief valve only determines the maximum pressure the pump is allowed to develop before it opens and short circuits the pump internally.

Byron, have you verified that the pressure at your remote oil mount outlet is MORE than the pressure at the sender outlet? This might put the argument to rest.

These are the confusions circulating in my brain this morning. Hope it's not causing you any headaches.

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Re: Question to the L4 engine building guru's re cam oiling

Postby 510wizard » 31 Jul 2017 08:19

To add to the above comments, Racer Brown cams have an additional oil hole drilled in certain cam lobes, because they were not drilled in the correct location from the factory ( the factory drilled them in one machine set up) All this is covered in the " Bible". I would highly recommend that those of us the haven't read the cam charter by Racer Brown do so, you will learn all that is possible on L series cam mechanics.

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zKars
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Re: Question to the L4 engine building guru's re cam oiling

Postby zKars » 31 Jul 2017 11:03

Thanks Wiz, it is time to re-read that chapter of the Bible. I read that thing about one every 10 years, which is NOT often enough to remember details anymore.

I'm assuming you mean this

http://www.datsport.com/racer-brown.html

Chapter 5 has the relavent data on cam oiling and how to improve it.

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Byron510
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Re: Question to the L4 engine building guru's re cam oiling

Postby Byron510 » 31 Jul 2017 12:39

As Montey alluded, there are some inherent issues with the factory oiling in higher performance applications. Half of the lobes are drilled on the back side of the lobe to save on a machining step, which doesn't assist much with the lubrication needed on a high ramp - high lift - cam. In stock configuration - I've never seen a problem with the factory oiling, so I don't call the design faulted. However when the pressure gets greater with stiffer valve springs needed for high RPM operation, and steeper cam lobe ramps creating exponentially greater contact forces, the oil in shear needs to be well supplied to the area. Hence the need for the external spray bar arrangement.

As for your comment on oil gallery pressure - certainly it would be dropping in pressure/flow available on every corner it takes, and every fitting it passes through. I totally agree, the pressure has to be at it's highest pressure and flow exiting the pump, and drops once passing through the filter, drops again as it passes through the block. It drops significantly has it passes into the head due to the oil restriction jet placed in the top of the block.

My comment regarding reading pressure of your spray bar line is that it can't be accurate due to having very little restriction in the line itself (due to the sectional area and number of holes feeding out of the spray bar unless (you have a really high volume pump and large fitting feeding the spray bar itself). The 1/8 NPT fitting itself on the side of the block becomes the restrictor of flow, and therefor allows the building of pressure on the gallery side of that fitting. Your oil gallery no doubt has higher than 40 PSI of pressure during operation (above 2000 RPM). In fact you likely approach 55 psi with a stock pump, and 60 with a ZXT Auto/Z24 (& KA pump?) due to the higher volume available at the same pressure (60 psi max).

As a side note, many also enlarge the oil feel holes to the mains in the block, and open up the bearing holes to allow greater flow of oil into the crank. This all to get better oiling to the rod bearings and more oil cooling the piston crowns. Again this is all high load applications used in race cars, and not at all needed on mild or stock engines. What has additionally been noted in race engines over the years that are in constant operation at high RPM, the oil actually gets siphoned out of the rod journals due to centrifugal force - hence why they need to be opened up and why high volume pumps are needed for this application - just to add addition confusion to the oiling systems.

As for the head oiling, if you never sustain hi RPM you may never overcome the oil's ability to drain down into the block. Keep in mid however that there is significant flow of gas/air passing up through the block at hi RPM. Most of us with a change in carburation performed on many cars - many owners have omitted the crank case vent all together.... meaning the only place that the engine can vent is out the valve cover (which often has a hose running back under the car, or first into a catch tank before running under the car, or in many cases just a nice little chrome vent filter. This movement of gas/air can greatly hinder the oils ability to drain - hence causing the puke over of oil out the breather when it builds up high enough - that of course if the pan doesn't run out of oil first. There's lots more to consider on race engines.

Back to your case Jim, if you never sustain high RPM's and you are sure you are getting 10 psi per 1000 RPM at the crank journal galleries - your likely good to go. Less than 10psi/1000 RPM on the main/rod bearings for any sustained period of time means you will likely have a short bearing life.

If you do sustain higher RPM for periods of time, then I'd look at blocking the flow into the cam lobes from towers 2 & 3 as noted above to help control the amount of oil up top.

Hope that helps Jim.

Byron
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Re: Question to the L4 engine building guru's re cam oiling

Postby bertvorgon » 31 Jul 2017 12:59

I can attest to the issue of too much oil in the top end at high rpm.

One time on the Hope/Princeton, with my new motor, I race a Corvette. After leaving him in the dust, I saw my oil pressure gauge starting to flicker...what the Hell!? I was on my way to the Knox hillclimb.

It turned out as the oil could not drain back down that corner hole fast enough, so the air pumping velocity just took it out the valve cover breather, over flowing my catch can and making a hell of a mess. Took me two hours at the car wash to try to get it cleaned up and to this day I still have oil weep out of the frame and seams on that side of the car. At least it won't rust there.

I ended up blocking the factory oiling and just use the cam spray bar oiler as I do see high rpm.
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

Keith Law
1973 2Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer


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