Racer Buzz

Racer Buzz’s 405 LS2 motor fading oil pressure discussion points:

I have a full dry sump oiling system and cannot get the kind of oil pressure that I would have expected. I am seeing the oil pressure at 65#'s cold and then 30-40#’s when hot. Not good and it finally killed an expensive motor after 4 events with aprox. 7 to 8 hours of total running time. Here an overview of my dry sump oiling system:

The engine is a 405 CID 700 HP with 620 at the rear wheels LS2 with AFR heads and a 90MM FAST intake manifold.

Oil pump is a 4 stage, 1.25” wide each stage, Aviaid DS pump.

Oil pan is an ARE cast alum DS pan.

The oil pressure has always faded with time and oil temp with this setup over the past 4 race event weekends.

The 3 oil pan scavenge lines are all -10 from the pan to the oil pump. All have internal flat springs to prevent line collapse under a vacuum.

Scavenge out line from the pump’s combined outlet to the top of the oil tank is a -16. This scavenge line out of the pump goes to the top of the oil tank but passes thru a large size, fine screen, inspection filter.

Oil in line from the 5 gal Patterson oil tank (located on the pass side middle and attached to the side roll cage bars) to the pressure pump inlet is a -16 with a flat internal spring to prevent line collapse under vacuum.

The oil pressure out line from the pump to the 1st cooler is a -10 then to the 2nd cooler it is a larger -12 then a -12 out of the cooler to the in of a Canton HP 6” paper oil filter then out of the filter a -10 line to the engine inlet at the normal inlet at the LR of the oil pan rail.

Typically the oil pressure starts out at about 64 #’s (max I can get now from the Aviaid pump) and then slowly fads down to 30# over a 1 to 2 hr race length.

If the car sits and cools slightly for 30 minutes or so then the oil pressure goes back to 64 #.

The new motor has four PBOC & NASA events on it to date: PBOC @ Moroso, PBOC @ Sebring, NASA @ Homestead & PBOC @ Sebring.

The oil press adjustment screw is bottomed out and set to max available but it’s still only producing 64#. Seems like it should have a lot more available (I expected 80# to 100#) with any DS pump.

I started running Gibbs 10W30 weight racing oil then switched over to 20W50 Gibbs after the first event at Moroso.

I checked and set the pump to the max pressure adjustment at the first event while at Moroso as I was not happy with the pressure on the first outing.

During the second event at Sebring I had too many electrical problems with the engine shutting down to get any heat or runs to make any oil pressure determinations.

While at the third event at Homestead saw oil temps of 260 to 270 degrees and the oil pressure fading down to right at 30#’s over a two hour long race.

I then added a 2nd Setrab oil cooler prior to the fourth event at Sebring, ran it on a cool day at Sebring & got a max of 230 to 240 degrees oil temp and still saw the pressure fad to 30#’s during the first race on Sat.

During the last Sebring PBOC race on Sunday I saw the pressure faded to 30#’s then 20#’s over just a 20 minute period when the 20# oil pressure light came on then it went to “0” and then I shut it off coasted to a stop and watched the race.

One issue may be the larger 4.50” dia. pulley on the oil pump which may be just too big and not spinning the pump fast enough. Not sure. I believe the pulley size was set by Aviaid. The crank pulley on the engine balancer has a 2.5” dia. (need to measure it to be sure) dia. pulley.

I saw big oil pressure swings while sitting in the pits at Sebring at an idle. Pressure range was moving from 20 # to 55 # back & forth as the engine lopped at idle with an oil temp of just 220 degrees.

This 405 motor is now out and on its way back to the engine builder. He will look to see what he can find inside for clues and to also disassemble and inspect the Aviaid pump. I don’t see where the motor could have had an internal problem or it shouldn’t have lived for almost 8 hours of track time.

Looking for suggestion, clues, advice & recommendations.

Racer Buzz

TRACKMAN2

not an expert by any streach of the imagination but isnt a dry sump capable/suposed to run a lower oil pressure.. if i remember corectly the oil pressure of the nascar i drove was like 35 but i miggt be wrong....

Racer Buzz

NASCAR engine builders live in a whole other world of highly developed, low pressure, tight clearance, water thin oil viscosity for the absolute maximum HP possible. So it's quote possible that if you drove a cutting edge NASCAR engine builder's project motor you did see 30#'s.

TRACKMAN2

na just a crappy petty car

WNDOPDLR

I am certainly not an expert either, but oil preassure will drop as it heats-nature of the beast. I run a dry sump on my C4 and at ambient temp-60-100 degrees, I start off at about 60# at idle and it will drop to 30 by the end of the session. My oil pump as an external adjustment to set the preassure and my engine guy tells me that 10#per 1000RPM is the ball park to work for. I have a 6200 pill in my rev limiter and with hot oil I am running about 70# of OP at that RPM.
How hot is you oil getting? With that kind of tank, I cant imagine it is very hot. Also check for an external adjustment on your pump. Hope that helps.

mwvettec5

Buzz,

In the "old days" when we ran SB Chevys with Weaver drysumps, always had 55-60 lbs of oil pressure as long the oil temps were reasonable (under 280 or so).

Even as recently as 2003, I ran a GT-1 car with a 355 & Weaver system at Topeka in August when ambient temps were over 100 deg and had the same oil pressure (60 lbs) at the end of the race (270 deg oil) as at the start (230 deg oil).

Note that the above was with Mobil 1 15W-50 racing oil

Curiously, I've had two LS motors that have the temp related low oil pressure problems that you describe. They were wet sumps but exhibited the same lower oil pressures (20-30) after the oil got hot (over 270).

I tried heavier weight oils and all had lower pressure with more temp.

A friend has a trackday C5 Z06 w/ a freshly rebuilt motor that ran all last year with lower pressures when the oil got hot - his motor is still going strong.

It's un-nerving but seems to be "normal" for the wet sump LS motors - a local Corvette "guru" and experienced mechanic says the LS motors do run w/ less oil pressure than the small blocks we ran for so many years in the '70s and '80s.

The above doesn't apply directly to you, but the more temp/lower pressure thing seems to be pretty common - your problem sounds more like a bearing issue ???

BTW - I talked to "Paulie" before Christmas - he traded off the Beretta he worked on for years and got a ride in one of Ray Irwin's GT-1 Corvettes at a couple of races.

Take care,

Emery

Wasserott

I will offer two additional points to consider:

1) RAFTRACER suggests that the LSX engines are prone to oil bleedby through the lifter bores as the bores are aluminum and the lifters are steal which heat up at different temps. He also says that high lift cams will only make matters worse. If you are getting 620RWHP then you obvioulsy have a very aggressive cam. He says that to solve for the bleedby issue you have to sleeve the lifter bores. Say's the WC guys all do this to address their pressure issues as well.

2) I have a friend how who had a C5 in TCC that raced a large bore ~500RWHP motor that also saw pressure issues after installing an ARE Drysump set-up. He eventually discovered that the pressure problems were due to the lines from the tank to the coolers/motor were inches away from the headers with no heat protection at all. Check the placement of your lines w/r/t your headers and see if the radiant heat could be part of your problem.

Or could be like the op said just bad parts/clearance setup.

John Shiels

sounds like it was a great motor. Can you tell if it failed from oil issues or a failed part? I know you are looking at it. What happen when it did fail, damage was?

yakisoba

How do you check for foaming oil? Fluid with air in it compresses well, and would result in lower pressure. I am taking a shot in the dark here, as I know next to nothing about dry sum systems, but what you are describing sounds familiar...

Racer Buzz

Thanks all for the input and suggestions. Please keep it coming as it sound interesting that this is a universal LS engine series problem of sorts. Even with a dry sump I am surprised that the pump can't supply enough oil to compensate for any lifter bore leakage.

Emery, Good to hear from you and really glad you are still out there flogging it around the race track. I wondered what DePirro was up to. Just knew he like you and me couldn't leave it either. My low oil pressure became a bearing issue as there is now brg stuff in the screen filter. The motor is now out and on its way back to the engine shop in Ft Myers, FL.

Wasserott, Good point on the lifter bores and having an aggressive cam. Sleeving the lifter bores is something I will now discuss that with my engine builder. I made a really good effort to shield all the AQ oil lines around the headers with thermo material but I will review it again, Thanks.

John Shields, Motor is in back of the truck and will advise back to everyone on our findings in respect to which brgs went when it gets dissembled. When the pressure finally drop to "0" on my mechanical gauge I just shut it off on the front straight, no noises were apparent and certainly no large breakages.

Yakisoba, Oil foaming can be a real problem with the heat it generates when the tiny bubbles get crushed when in the brgs to rods and crank mains and cause bad erosion to the brg surfaces. I will have the engine builder look for signs of erosion. The pump builder, John at Aviaid, says with a 5 gal oil tank and a total of 22+ quarts of oil in the whole system the oil should be in the 20" tall oil tank long enough to remove most of the foam / bubbles. But, who really knows for sure!! Perhaps a clear oil tank would answer that, but then again.....

Bink

Gotta hand it to you TRACKMAN2 - you say some funny ch*t.

Racer Buzz

Any other thought or suggestions out there on the problem of fading oil pressure in LS motors under load and heat.

Seems no matter whether they are stock wet sumps, Accusump inline or dry sumped the general opinion is they all lose pressure as the oil temp get to 240 and up.

Come on we can solve this problem what with a group that has the huge knowledge base of this forum. Pass the word er thread on......

Slalom4me

Is there a record of how much crankcase vacuum registers at RPM?

With three scavenge stages, there is likely to be some negative pressure.

.

0Louis @ LG Motorsports

Theres a couple things here, and some mis-information. Be careful what you read guys.

Dannys motor was prone to lifter bleed because it was a solid roller. Lifter bushs are needed when using a solid roller. we ran them in 04, and that was it. When we switched back to hydraulic rollers, we no longer needed to bush the lifter bores. High lift cams move the lifter down in the bore due to the smaller base circle on the cam, thus opening the lifter oiling hole, and allowing a fairly large leak. This is the issue with high lift cams. Its not the lift, its the result in order to get the cam to fit.

Key thing here is bearing clearances- What are the mains, and what are the rod bearing clearances? Aluminum block?

What is engine crankcase vacuum?

our WC cars run ~ 40#s on track, and can dip as low as 5-10#s idling in the pits. Remember, it only takes 4 psi to float the crank at idle.

You need to: Check the quality of the oil, find out the main and rod clearance for me, and list a little more about the valvetrain setup and I can steer you in the right direction.

Louis

Bink

good to know

craig brian johnson

Good suggestions so far.

In looking at your original post, it looks like all your lines are sized adequately. However, how are they routed? Do you have large rises and dips in your intake line that could impede the impeller draft?

When I ran my first dry sump, I didn't understand that you had to fill it when running the motor at a reasonable RPM. Instead, I filled it while the motor was slowly idling. Accordingly, I had underfilled the tank. When the was motor spun up tight, the crank would hold onto a good amount of oil (exacerbated by an improperly adjusted scraper) which did cause a couple of instances of low oil pressure.

Could underfilling or even a poor crankshaft oil scraper/windage tray be a factor?

I wonder, If your problem seems more related to an oil bleed off condition caused by or wide open hydrolic lifter holes, then why couldn't you place an appropriate oil galley restrictor?

Or, why not change the pump gearing to give you adequate oil pressure (10#/1000rpm) when the motor is hot?

Racer Buzz

ttt

OKsweetrides

Bringing from the dead....


You ever figure it out?

I know there is an oil frothing issue on my setup. But I have my tank sitting in my trunk bolted to the frame and I got some wacky heat wrap on the lines anywhere near exhaust. I don't do enduro, and have just a LS6 with heads/cam but needed the oil pressure to maintain during very very high lateral g's, so I didn't go extreme++ on my ARE setup.

KLJ

I think Yakisoba had it. I think the threshold for air entrainment damage to rod bearings is at 30% air to oil.

The LS engine is well known for air entrainment issues. The Corvette is capable of generating high Gs sufficient to make it difficult for expelled oil in the crankcase to enter the scavenge ports of a dry sump. This problem will be worse depending on how much atmosphere is present. It sounds like an equilibrium was reached for the deaeration ability in the tank and then continued use simply pushed the position higher up the equilibrium curve, i.e. more and more entrained air was allowed to stay in the oil.

There is a simple way to test this hypothesis. Simply add a fitting in the pressure line with a valve that will allow you to gradually draw off a quart or two of oil in a clear container immediately after coming in to the pits following a session where you note the pressure slowly dropping. Look for bubbles. If you delay the test then it is meaningless.

BrianCunningham

I don't suppose the crankcase being under a vacuum has anything to do with it?

the relative pressure may be the same, in the crankcase, but the gauge pressure is now lower.