Lapping at Mosport - low oil pressure!

[fentin_fury]

I spent yesterday at Mosport and spent some time lapping the RBZ

 

I noticed on the back stretch that during sustained high RPMs my oil pressure fades away!

 

I do not starve for oil in tight turns etc but during high RPM sustained runs my pressure falls off.

 

For the experienced crowd here - my questions are:

 

Do we think this is oil pooling in the head? Will oil restrictors help?

 

I have a large 7litre pan, well baffled, deep, oil cooler etc. I am running a stock oil pump.

 

I read the australian thread

 

"On the circuit race cars we take a 5 step approach in controlling the amount of oil that is trapped in the cylinder head and/or blown into the catch can;

1.Block off one oil feed in the block (RB26’s have this standard)

2.Fit an appropriately sized restrictor to the other feed. The size of the oil pump is one of the determinates for the size of the restrictor, ie; a high flow, high pressure pump needs a smaller restrictor. Constant higher RPM needs a smaller restrictor etc.

3. Fit an external oil return from the rear of the cylinder head to the sump

4. Drill out the oil return galleries in the head and block

5. Machine around the oil return galleries to facilitate access for the oil "

I would have thought my extensive oil pan work and large capacity would have addressed this issue.

I suspect the oil pump not liking sustained high rpms - anyone concur?

Q

S30 RB26 - BNR34 long block (stock). Upgraded turbos, standalone, etc.

[RB26240Z]

My understanding from that specific thread and other reputable RB builders is to go with at least the N1 oil pump, and the return mod to the back of the head to get the oil back in the pan.

 

Don't let her smoke too much. Let us know the outcome.

 

Good luck

 

Henry

[fentin_fury]

I will upgrade the oil pump and was looking at the return yesterday. Have to figure out some plumbing.

 

Will invest in a real oil pressure gauge as well

 

keep all advised

 

q

[A. G. Olphart]

Yup, the Aussie post makes it sound like a generic problem, mostly in getting oil back to the pump. Doesn't much matter what pump a person runs if it is all trapped upstairs; in fact, a bigger pump with more pressure will just put it all up there sooner.

 

My take is that if your current pump can handle the RPM for a few seconds (5?) without a pressure drop, it is doing the job. It just needs a reliable supply of oil to chew on.

 

 

<>

[fentin_fury]

that is an interesting test - 5 seconds. Does anyone know the additional volume/pressure of the N1 pump vs. stock?

 

Q

 

to quote Matt

 

"THE VOLUME OF THE STOCK/NISMO/N1 PUMP IS FINE FOR ALL BUT SUPER DRAG MOTORS. 90% of the RB26's I have built are 9,000rpm engines and have zero oil pressure drop at the gauge due to not enough pump volume using these pumps. The HKS and JUN pumps are for serious power motors turning serious rpm's. Oil flow is what keeps the bearings cool. High power creates lots of pressure on the oil/bearing, creating lots of heat which will kill the bearings. In this type of motor, you combat this by opening the oil clearances, which in turn flows more oil over the bearings, keeping them cool. This requires......drumroll please.........a higher volume pump. If you don't have a higher volume pump, oil pressure will drop in the upper R's and the bearings will die a horrible death."

[A. G. Olphart]

With the engine and oil up to temperature, a person should be able to tell in a very short time at the target RPM (5 seconds is just a guesstimate) if the pressure is dropping off due to not enough pump. Run it a while, and causation gets iffy... might be starvation because all the oil is hiding in the valve cover. Insufficient oil cooling can also cause pressure to drop long term as the oil thins.

 

High RPM tosses off oil more rapidly due to centripetal force, which is there as soon as your RPMs are up. The looser the bearings and the thinner the oil, the larger the volume needed to keep pressure up.

 

I make no claims as to being an expert on your motor, just attempting to deal with the issues logically.

 

Oil and bearing issues have been around as long as cars... the term "Hot Rodder" is a direct offshoot of that. As Matt says, "High power creates lots of pressure on the oil/bearing, creating lots of heat which will kill the bearings".

High power is a relative term. In the days of Model 'T's and splash oiled Chevys, overspeeding an engine to go faster didn't gain much power, but it did wipe out the babbit bearings--- So speed demons became hot rodders.

(Not really germane to your engine's behavior, but it relates).

 

 

<>

[jerryb]

Did the RB20s have this same problem?...or was it a RB26 design issue?

[fentin_fury]

Did the RB20s have this same problem?...or was it a RB26 design issue?

 

 

from my research ALL RBs are subject to the same problem. Oil restrictor sizes and number are a function of oil pump, use, and hydraulic vs. solid valve pots.

 

q

[Bchappy]

so lets say for a 500 Hp RB25

 

that can be taken to lapping events what would be the ideal mods to solve the bottom end oiling problems?

 

High flow/high quality pump

restricters

and an oil rerout from the head to the sump/oilpan

along with possibly larger oil capacity

 

I have been searching

I would like to see a thread about these modifications

[Evan Purple240zt]

You need to search on the skyline forums to get more information on the oiling if there is not enough info over here.

 

I don't have an oil pressure gauge. Sounds like something I should invest in. High rpm for over 5 seconds? About anybody who drags may run into the same problems.

 

Oil restrictors and head drains seem to be the ticket.

 

Evan

[JMortensen]

How about an Accusump? Get a bigger one, like a 2 or 3 qt model and that gives you more time before you run out of oil. It would also help if you ever did starve for oil under lateral g forces, and I'm guessing it might be simpler than modding the engine, don't know for sure though...

[Bchappy]

thanks jon

I have been on the skyline forums quite a bit as of late trying to figure out...

 

but it seems it doesn't matter if it has 6 quarts or 10:icon6: that it would eventually pool in the head...

 

Im going to search in the skyline forums and post my findings in this thread if anyone is interested.

[Bob_H]

I've been following all the oil threads everywhere and am making the mods listed later to my RB26.

As I have come to understand it, and reading many setups, including those w/accusumps - it really does come down to insufficient oil in the pan - which can be from several causes - a aftermarket high volume pump,(such as the HKS I have), coupled with a stock size restrictor,(or both restrictors as the RB20's and 25's), pumps out all the available oil in the oil pan, which ends up starving the oil pump - which has led to oil pump failures,(catastrophic gear failure), or bearing failure, which can vary in its effects from minor to major.

Having spent the day today opening up the cylinder head drains - its no surprise that the stock head has issues returning oil. If you look at the openings and the way the motor leans - you would think that they would cast the larger hole on the lower side of the motor,(drivers side for the US), but it is actually SMALLER. In addition, it is very restrictive, and comes as no surprise that oil pools. Now there are small returns along the head - but they are just that, small returns that allow oil out from the valve spring areas,(they are actually on one side only, 4 holes, near the cylinder head bolts). I'm editing my photos so I can post them in my Super Datsun thread - and I'll try to put them here as well.

Bottom line as I see it now:

-Accusump is only a band-aid fix - it will work as long as it has a supply - once that supply is depleted, i.e. more is pooled up in the head, it will no longer help. This is proven by several folks who have an accusump on their RB26 and have still suffered oil starvation

-The oil in the head must be addressed - either via opening up the returns through the head and into the block, or with an external return, or preferably both.

-Higher volume pumps,(Jun, HKS, etc..), will exacerbate the problem unless steps are taken to reduce the amount going to the cylinder head - mainly a smaller restrictor in the engine block,(1.0-1.2mm, rear blocked off). And with a high volume pump, I personally would consider an external return a mandatory option if you are taking your car to the track,(circuit for the rest of the world).

-The N1 pump may be a better solution than some aftermarket pumps as it doesn't make the problem worse by drastically upping the volume it is pulling from the pan over a given period of time.

-Expanding the sump for more volume is always a good option, as is baffling to prevent pooling away from the pickup - but again, if you don't address getting that oil back into the pan, it doesn't matter.

I'm doing all of the above - I've already expanded the cylinder head and engine block returns.

I'm installing an external return.

I'm installing a 1.0mm oil restrictor,(I have the very high volume HKS pump)

I'm installing restrictors before the turbo's - again, I have a high pressure and volume aftermarket pump - and that tends to push oil out beyond the turbo seals into the intakes.

I'm building a completely custom oil pan with baffling and extra volume. I expect approx 7-8 quarts.

Its a lot of work, but this motor should be exclusively on the track - and I'd rather not pull the motor for new bearings or worse every track weekend.

 

On my edit to add pictures:

These measures matter mostly to those who will spend a lot of time at high rpms. If you are going to primarily drive your car on the street, maybe do some 1/4 mi drag races, you likely won't ever need more than what most people have done on this board - a good oil pan, a decent oil pump and no issues with your clearances/bearings/etc...

For those of us who will spend lots of time in the 5000+ rpm category, or 6-8k on the track for 20-25+ min, you have to address those issues or you can plan on pulling your motor for a bearing rebuild and/or oil pump replacement on a regular basis assuming something catastrophic such as a rod through the side of the block doesn't happen.

That is not to say you won't have issues if you drive it on the street, just that the likelihood is much less. A smaller restrictor in the block, (1.2mm), an N1 pump and you will likely be fine. If you are going to an aftermarket high volume pump such as the HKS, Tomei, and JUN, you need to look into the rear cylinder head external return. And that should solve 95%+ of peoples problems. It is that 5% of us running at high RPM's for extended periods of time that need to look further.

 

I also want to mention the following:

Modifying the cylinder head by opening up the passages in the rear is not for the inexperienced. The aluminum in the cylinder head is very soft and with a die grinder or similar it will/can take a lot of material quickly - much more than you planned. In addition, you must plan on completely disassembling the head and having it completely cleaned as those shavings will get down into the small space in the rear of the head, and down in the valve spring area of the furthest aft springs potentially causing much more significant issues when they are moved back into the oiling system after you button the engine back up and oil is moving around again. Don't do that unless you are disassembling the entire cylinder head and cleaning it afterwards!

 

The following is pulled directly from my Super Datsun thread.

(Here if you want to read/follow further: http://forums.hybridz.org/showthread.php?t=115751 )

 

The first picture is the cylinder head before any work was done. I took the head gasket and scribbed the outline of the area available.

Over the next few pictures, opened it up to that line and smoothed out the drilling.

The 5th picture is a shot into the freeze plug that is normally removed to install a head drain. You can see the side of the rear most valve spring. As you can see, the space is rather small, and it connects to both sides of the head. All the oil must drain down through what you can see in the final two pictures. The hole is for the cylinder head bolt - the opening to the drain area that I enlarged is to the left of the picture - its about as big as the end of my thumb - maybe slightly larger. Not very large..... In the first shot from above, you can see the flashing I removed which is shown in the last picture.

 

-Bob

[Bob_H]

BTW,

Do you have any pictures of your custom 7 litre oil pan? I'm very interested in the baffle setup, etc.. I didn't find it in any of your other posts.

-Bob

[Bchappy]

wow bob thank you for the crystal clear info.

 

Now do you think that a high volume pump is absolutely necessary?

 

or do you believe there is a combination of restrictors, pump, and return that would provide good oil flow to all areas?

 

Like N1 pump, external return, the right restrictor size?

 

It looks like machining the galleys will also be a must...

 

Basically everything to get the oil back to supply the pump.

 

BtW your car is amazing!

[Bob_H]

Updated the post and put the pictures in.

If your thinking about doing this mod - please read my recent addition to that post.

-Bob

[fentin_fury]

thanks for the input. I will be doing most of the mods - still debating on the external oil return. I won't be doing this until the end of the season though. I will update all as I progress.

 

Q

[Bob_H]

Now do you think that a high volume pump is absolutely necessary?

or do you believe there is a combination of restrictors, pump, and return that would provide good oil flow to all areas?

Like N1 pump, external return, the right restrictor size?

 

I don't think a high volume pump is absolutely necessary - but can help. The N1 pump only increases the pressure, not the volume. The HKS and JUN are on the lower end of the "high volume" pumps while Tomei and NISMO are on the higher end of "high volume" - (usually measured at 6000 rpm or so).

There are lots of ways to skin a cat - so several different solutions can work well.

-Bob

[Ezzie]

Who actually makes the Nismo pump? Is it Jun, Tomei or someone else??

[Careless]

Who actually makes the Nismo pump? Is it Jun, Tomei or someone else??

 

I believe it's just a regular Nissan pump with a larger pump gear