Race engine oil orifice sizing.

[sprint48]

Yes I have all the formulas and no this isn't a school project but this is critical enough that I'd like some expert opinions please.
I'm building a "Racesaver" 305cuin small block Chevy. This is a sprint car series 'spec' motor and I will be documenting it in Engine Builder magazine - hence asking the right folks!
Rules call for solid lifter cam. Keeping the lifters oiled at 7000 rpm is sometimes a problem. Old NASCAR engines put a tray under the cam that filled with oil, splash lube.
I'm looking to drill and tap the oil passages above each cam lobe. I can get orifice nozzles that will thread in.
Since there are 16 of these little buggers and another that lubes the timing chain, I need to be pretty accurate on sizing. Sketch attached.
The oil will be a 5w30 synthetic,(11cSt @100C) engine temp about 200F, the wet sump oil pump puts out about 70 psi at 7000 rpm.
I can get thread in misting nozzles as small as 0.2mm (0.008")diameter for about $20. The 0.003" lab grade ones would add almost $300 to the build. So I need to balance that. I think my rough calcs showed the 0.008 would flow around 2gpm total which could starve the bearings.
This whole thing might not be worth the effort but it's one of the article items. If this deal makes it to press, I can come back and add the link
THANKS FOLKS!!

 

[Artisi]

First up, this is probably better in the automotive forum. Secondly, if you are not reinventing the wheel - why not ask around other race engine builders.
If something completely new then you have some serious engineering calcs' to look at - - what is the pressure loss from the pump to the camshaft, what is the flow
output from the pump, the nozzles closest to the pump will have higher flow than the more distant nozzles - just a couple of random thoughts, probably many more to consider.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[ornerynorsk]

I don't have a valid answer, but my first thought would be is the oil really going to be, or stay, clean enough to tolerate those small orifices? I would expect to see most of them plugged after the first teardown. Would it be feasible to run a separate system with dedicated (clean) supply? It's been 25 years since I've gotten my hands dirty on a small block chevy build, so this is just a "what-if".

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[romke]

in theory i think the system can work, although with very small orifices blockage might occur once the oil gets contaminated. "the system can work" in this case thus meaning: "a large enough oil supply". whether that would actually improve lubrication/reduce wear is another question. the contact between a cam and a lifter is very small (a thin line that somewhat changes temporarily into a elliptic shape under load)that is under such a load that only elastohydrodynamic lubrication is possible. even then, the oil wedge between lifter and cam will be very small and can be as thin as 0.1 micron. most of the oil you can get there thus is squeezed out anyway, the actual "lubrication" is mostly taken care off by the antiwear components in the engine oil that form a thin layer at the mating metal surfaces that when worn off, can be replaced by new antiwear components bonding to the then temporarily virgin material.

thus, you do not really need that much oil there (other then perhaps for cooling purposes). you need to make sure that the oil used has a proven performance in terms of cam/follower lubrication as can be demonstrated by the various engine tests in the API an ACEA oil test sequences and also that it scores well in the special viscosity test at 150 deg C incorporated in the SAE viscosity grading system. In that particular test at 150 deg C the oil is put under very high shear conditions, more or less reflecting what happens in cam/follower contacts.

 

[sprint48]

Thanks for the responses. I posted here rather than the automotive threads because hyd/fluid engineers typically have much more experience with tiny orifice flow than the car guys.
Clean oil - full flow filter Wix filters which are rated at 25 microns. I know the smallest flake of RTV silicone can screw it all up.
Romke - excellent points. The synthetic we use is designed for solid lifter interface. Your point on the oil wedge is spot on, I was looking for additional cooling.
Meantime I did some extra research on this, in regards to what others are doing. Instead of restricting the oil flow to the lifters and rocker arms, which the roller cams do, I'm going to let the components meter the flow. The pump I ordered today will handle that and more. 8qt pan, plus the filter will have enough reserve.
Which brings me to what is an easier solution, to open the block area above the cam, direct the oil that drains back from the heads to flow on the cam. While this may increase windage loss slightly, it should provide more that enough for the lifter/lobe interface. This can also be channeled by raising a small lip around the main drainback holes in the block to hold about half a quart in the lifter valley. Sloppy splash lube, but it works.
Yes, the KISS principle is at work here. But you all know that once an engineer - ANY engineer - gets an idea stuck inside the head we have to at least explore it, right?
My co-driver in the picture has her own opinions.
Thanks again to all of you!!
Bob