Lowered oil pressure with roller lifters..?

[BlackoutSteve]

Hello,
I have switched from a mechanical flat tappet to a mechanical roller and noticed a drop in oil pressure.
I have checked the main & rod bearings and all clearances are still within spec as prior to cam swap.
The pressure at idle used to be 20-25psi (hot), but is now 10-15psi.
I have my oil pressure sender tapped into the front-most main gallery plug, furthest from the pump (big block Chevrolet) as to always see the worst case scenario so, I decided to switch it to the rear-most plug, closest to the oil pump, and saw less than a 5lb difference indicating to me that I was not losing excessive pressure/oil from the bottom-end. (Fair assumption?)
I have continually used the same Mobil 1 15W50.



The only changes that were made to this engine is the installation of the roller cam.
The lifters are Isky RedZone lightweight 272-96-RHM. Because these lifters have pressure fed oiling to their rollers, is it expected they consume considerably more oil (and therefore pressure) than regular flat tappet lifters?
Is this where my oil pressure has gone?
I am lost as to why my oil pressure has dropped.
With such a drop in pressure, is my engine's health at risk?
Thank you for your time and help.

[racerguy]

Did you change oil filter brands. The cheaper fram filter could cause that problem.. I like ac and wixs.

[PackardV8]

Hi, blackout steve,

You've answered your own question. If the lifters and cam were absolutely the only things you changed, then there is where your oil pressure went.

Suggest you mic the lifters you removed and your new lifters. It is not unusual for race roller lifters, designed for short bursts at high loading/high RPM, to intentionally be made slightly undersize to insure plenty of oil around them. Add the pressure feed to the rollers and you are down 10 psi at idle.

As a side note, this is probably a good tradeoff, as no oil to the rollers at idle was what killed earlier generations of race roller cams run on the street.

Since you have had plenty of practice pulling it down, consider dropping the pan one more time and installing a high-volume pump and associated heavy-duty driveshaft. This is often the cure for low pressure caused by the roller lifter bleed-off.

thnx, jv.

[beth]

Was the distributor changed along with the cam or just the gear? Distributor to block clearances can affect the oil pressure at idle.





beth

[oldhead]

I have just replaced rings and bearings using the same part numbers for the 3rd time but this time replaced the roller lifters # 818-16 with the same number BUT this time Comp Camc changed them to pressure feed.I lost 10 to 15# thru the whole RPM range........ OLDHEAD

[540 RAT]

Pressure fed needles will certainly bleed off more oil pressure. You have 16 more places to bleed off oil (assuming one passage per lifter, but it could be more) and that doesn't even consider possible lifter to bore clearance changes. No more mystery as to where the oil pressure went. As long as you maintain the old oil pressure rule of thumb, 10 psi for every 1000 rpm, you should be OK. But personally I'd consider going to a high volume oil pump, assuming you don't already have one.

[BlackoutSteve]

Thanks for the responses guys.

Well, it seems my suspicions are confirmed. I guess I am somewhat relieved, but also disappointed.
I brought the rpm up to about 2000rpm (unloaded) and the pressure went to 40-45psi. This is good, but the pressure failed to increase from there onward. Without a tach, I am guessing, but I then brought it up to somewhere like 4-4500 where oil pressure remained at 45psi.
I am hoping when I load this on the dyno in 2 weeks it will support the 7500 redline with a good 60psi.

..and to answer your questions.
I continue to use the same System 1 filter and oil brand and weight. No changes there.
I do have a high volume pump already installed (with the ARP driveshaft) and I have shimmed the pressure bypass spring 1/4" to maintain 60psi (max) with the external heat exchanger and remote oil filter. (I realize that this has no effect on pressures below 60psi.)
The distributor is the same (MSD 85551) but I don't use the O-rings. -I can't because the block has not been machined with the necessary chamfers. The fit is quite snug, but still...

[PackardV8]

Hi, BlackoutSteve,

Just for our edification, suggest you put a good .0001" mic on your solids and the Isky rollers. Would like to know if the diameters are the same.

thnx, jv.

[BlackoutSteve]

Damn, the old (Crane) lifters are long gone, and I never measured the new Iskys. I just assumed they're all the 0.842".
Oversight perhaps?

[Ed-vancedEngines]

Is it possible that your pressure relief valve in the oil pump is sticking and is not letting you build pressure? With any kind of pump you should have a pressure relief valve that allows pressure to increase befor it is releas. If that is sticking in an open or part open position, you would not be able to build as much oil pressure.

I think everyone has pretty much covered everything else. Have you tried a different pressure guage yet. I do not remember reading that you did, but to be honest I did not just now read this.

For there to be a lack of oil pressure there must be one of two different issues. Oil pump not producing the pressure in the first place or an internal oil leak due to excessive clearances in some part of your engine.

Now, that is not considering other variables like types and viscosities of oil etc.

Ed

[BlackoutSteve]

The oil bypass is clean and functioning.
Also, during cold start up, it allows pressure to reach 60-65psi at idle before the viscosity of the oil begins to lower with heat.
That indicates to me that the valve is bypassing right where it should.

The Isky lifters have offer the "Full Spectrum 3 point Multi-Port oiling system". I guess that's 48 additional orifices (16x3) in my engine compared to the flat tappets I had before.
That's gotta make a difference right? I'm still waiting on a response from Isky about whether they think it's the reason my pressure has dropped.

[BlackoutSteve]

I have just replaced rings and bearings using the same part numbers for the 3rd time but this time replaced the roller lifters # 818-16 with the same number BUT this time Comp Camc changed them to pressure feed.I lost 10 to 15# thru the whole RPM range........ OLDHEAD

I'm just reading your post again OLDHEAD..
Do you mean to say that you're max oil pressure is now around 45-50psi? -assuming your max was 60psi..
Where does your engine redline?
Is it safe to go beyond 5000 with this much pressure?

[Cammer]

I will not add to your stress level!

Make certain you have an accurate and properly functioning gage when you dyno engine.

Monitor oil pressure on dyno to judge your next move.

____________________

[Wolfplace]

As was mentioned above by 540, this was very common with the pressure fed lifters & is one place that a hi volume pump may be desirable if the pressure does not rise with RPM
If it does I could care less if it is 10lbs at hot idle

The Isky lifters I sell have "modified oiling" which reduces this tendency as the oil to the outside of the roller is reduced while maintaining full pressure to the needles.
I was under the impression that all the lifters were being modified now but I don't know this for a fact as I always order them this way.

If you were to pull the intake & spin the pump with a drill you will instantly see where the extra oil is going

As long as the pressure goes up with RPM I do not consider this an issue but I would prefer to see a bit more than 45lbs at 7000,,
BTW, this issue is much more pronounced with the lighter weight oils.

[70MC]

I switched from a set of Crower roller lifter that did not lube the bearings, to a Crower roller lifter that did provide pressure fed bearings, along with a cam change. I had less oil pressure at an idle (5-10lbs), but my 65lb total pressure returned as rpms would rise.