SBM Rocker Oil Flow Data

[nm9stheham]

Just FWIW.... here is a diagram of the oil flow from the LA SBM oil system up to the rocker shafts. It shows passage diameters in inches and flow areas in square inches. There is data here for the stock setup and also for the PRW PQx aluminum rocker setup (which is what I was working on at the time.)

Besides the 'oil flow interrupter' in the cam holes, the next most significant restriction is where the oil flows through the head pedestal into the interior of the rocker shaft. So that hole size is critical to some degree. It is smaller in the PRW shafts and that makes sense; they told me it was so to control oil flow rates.

The flow out of the interior of the shaft for the stock system will vary with stamped versus adjustable rockers; the adjustable rockers will have a smaller outflow area if the rockers are properly tight to the shaft. So the shaft may be more prone to filling up with the adjustables.

(Hope you can read the diagram...)

 

[toolmanmike]

The stock system is a pretty silly design but it does work. Many cams have a machined groove on the oiling journals which fixes the "interrupter" issue you speak about. It would be interesting to run a engine and quickly pull the shafts to see how much oil is captured inside the tube. It is like a reservoir I imagine. Also the correct installation of the shafts and the proper bolts is critical for the system to operate correctly.

 

[nm9stheham]

That is kind of the way I think of it, TMM. My current thinking on how this works it that the 'interrupter' puts pulses of pressure into the head passage, and the restriction from the head pedestal around the mounting bolt into the shaft creates a flow restriction to manage how much oil each pressure pulse can put into the shaft. With the 273 rockers and the very limited flow with their tight fit around the shaft, the shaft must fill right up eventually. (Not so sure about that on the stamped ones.)

If anyone has an excess flow problem, then the mounting holes in the rocker shaft become suspect.

Funny, my son looked at me sideways when I said we ought to put a pressure transducer in the end of the PRW rocker shafts just to look at this LOL

 

[justinp61]

What do you guys thing would work better than the factory set up? Push rod oiling is easy now, most all new lifters are capable of it. For a magnum type setup I'd say it's fine but I wouldn't want to chance my rockers/shafts not getting enough oil. All the aftermarket roller rocker I've looked at have a provision to oil the push rod and roller. So yes, there is pressure in the shaft and in the rocker arm it's self.

Another thing to consider is head bolts or studs, the ARP bolts I have are about .050" smaller on the shank than the ARP studs I have. The bolt holes in my Indy heads are about .525", so with a stud there is about .0125" around it for oil to go to the rocker shaft. With a bolt there is about .0375" for oil to flow to the rocker shaft.

 

[RustyRatRod]

Yall got any idea how quick the "interrupt" is? Even at idle, it is almost like constant oiling. At 2000 RPM, you probably can barely see the "interrupt" with the naked eye, if at all.

 

[justinp61]

Yall got any idea how quick the "interrupt" is? Even at idle, it is almost like constant oiling. At 2000 RPM, you probably can barely see the "interrupt" with the naked eye, if at all.

^^ This ^^

 

[nm9stheham]

Yall got any idea how quick the "interrupt" is? Even at idle, it is almost like constant oiling. At 2000 RPM, you probably can barely see the "interrupt" with the naked eye, if at all.

Good point. If everything is perfectly lined up at the cam bearing, the maximum % time when oil can flow is no more than 10% of the cam rotation time (about 30 degrees of cam rotation where the holes overlap at all). But in the first few % of that time, and in the last few % that time, there is so little overlapping of the holes, I would not expect any significant oil flow. So I estimated the flow/pressure pulse duration at 5% of the time; it might be 4% or 7% but it is not a lot. I would expect the flow to be more continuous at the rockers themselves due to the restrictions at 2 points downstream from the cam tend to smooth out the pressure pulses.

 

[nm9stheham]

What do you guys thing would work better than the factory set up? Push rod oiling is easy now, most all new lifters are capable of it. For a magnum type setup I'd say it's fine but I wouldn't want to chance my rockers/shafts not getting enough oil. All the aftermarket roller rocker I've looked at have a provision to oil the push rod and roller. So yes, there is pressure in the shaft and in the rocker arm it's self.

Another thing to consider is head bolts or studs, the ARP bolts I have are about .050" smaller on the shank than the ARP studs I have. The bolt holes in my Indy heads are about .525", so with a stud there is about .0125" around it for oil to go to the rocker shaft. With a bolt there is about .0375" for oil to flow to the rocker shaft.

The bolts in the oiling system are the rocker hold down bolts, not the actual head bolts, so I am not sure if that is what you are talking about with the ARP bolts....??? Can you explain further? It is the .525" hole that is confusing me.

And yes, we concluded that the shaft has some volume and low pressure in it, as it oiled the adjusters and pushords on our PRW AL rockers, and that hole is up high on the rocker.

As an FYI, the PRW AL PQx rockers that we have DON'T have any roller oiling holes. We added one for the roller and for the spring, and that was what led me to check this all out: to see if the added hole would cause any large loss of pressure due to a lot more flow. Turns out it did not; it only added another 15% outflow from each rocker over what was already there.

 

[justinp61]

"The bolts in the oiling system are the rocker hold down bolts, not the actual head bolts, so I am not sure if that is what you are talking about with the ARP bolts....??? Can you explain further? It is the .525" hole that is confusing me."

They are on Indy and Edelbrocks.




Another way to look at it. Lets say at 1000 rpm idle, the cam is the cam is turning 500 rpms. So the cam is oiling the rockers eight times per second.

 

[Rapid Robert]

what I did/am doing on next years' 360 stock car eng is tap the vertical crank to cam oiling holes & screw in setscrews drilled to .060" on all (5) which is plenty of cam bearing/journal oiling & I am now in the process of T ing from the oil sender 1/8 NPT port & running lines to the back of the heads and drilling in horizontle in the bolt boss then drill down at an angle in the threads in the rear pedestal(s) to oil the rockers. with that being FT oiling as opposed to cam timed oiling not sure if I should restrict the amt of flow or not. EDIT forgot to mention that I drilled/tapped/setscrew blocked the angled oiling passage at the top on each deck. purpose of all this is to minimize the wasted flow to/around the cam journals

 

[justinp61]

The bolts in the oiling system are the rocker hold down bolts, not the actual head bolts, so I am not sure if that is what you are talking about with the ARP bolts....??? Can you explain further? It is the .525" hole that is confusing me.

And yes, we concluded that the shaft has some volume and low pressure in it, as it oiled the adjusters and pushords on our PRW AL rockers, and that hole is up high on the rocker.

As an FYI, the PRW AL PQx rockers that we have DON'T have any roller oiling holes. We added one for the roller and for the spring, and that was what led me to check this all out: to see if the added hole would cause any large loss of pressure due to a lot more flow. Turns out it did not; it only added another 15% outflow from each rocker over what was already there.

After thinking about this I dug out an old J head, as I suspected it oils the same as my Indy and Edelbrocks. The oil comes from the block into the head passage which goes into the head bolt bore where it travels up around the head bolt into the port that feeds the rocker shaft. So a larger diameter bolt or stud will restrict the oil flow to the rocker shaft on a factory (non magnum) head also.

 

[teringer]

some of the mopar circle track cams I used came with groves cut on 2/4 cam journals for full rocker oiling ,but I pluged them to help lube the crank and put fitting into the rear of the shafts and oiled off the sending unit hole drilling through the valve cover. also followed the mopar engine book to improved oiling for rockers.

 

[nm9stheham]

Another thing to consider is head bolts or studs, the ARP bolts I have are about .050" smaller on the shank than the ARP studs I have. The bolt holes in my Indy heads are about .525", so with a stud there is about .0125" around it for oil to go to the rocker shaft. With a bolt there is about .0375" for oil to flow to the rocker shaft.

I am finally catching up to you on this now.....duh. Interesting.....I checked a '68 version 273 head and the head bolt hole is .540" not .525" diameter. AND, the long bolt that is going into that particular hole has a special reduced shank area....it is .445" diameter for a stock long bolt. The Edelbrock LA heads come with a reduced shank, long bolt that is intended for that hole and that has a .450" diameter reduced shank area. And the ARP bolt set for these heads supplies a long, thinned shank bolt of the same size.

Sooooo, it looks like if you are using the ARP studs, and the standard rocker oil supply system, you are putting a severe restriction in the rocker oiling system that does not exist in the stock system. And that is doubly so for those Indy heads if the head bolt holes are really .525" diameter.

It is a bit hard to exactly compute that effect restriction size with the .500" ARP studs and the Indy head, but it is likely in the range of .010-.015 square inches and that is less than half the flow restriction area up at the stock rocker shaft-to-pedestal interface. By contrast, the stock head or Edlebrock head with the stock bolt or ARP bolt has a flow area in the head bolt hole in the range of .080" square inches.

I now gotta wonder if the use of ARP studs has been an overlooked issue with rocker oiling for the stock SBM rocker oiling system.....! If I were you, I would pull that one stud out of the head bolt hole with the oil passage, and put in the long bolt with the .450" reduced shank area.

 

[justinp61]

The use of a stud instead of a bolt in the Indy heads cuts the area for oil by about 2/3. The oil passages in the heads is .201", which is the right size for a 1/4 X 20 set screw if some one wanted to run restrictors.

 

[nm9stheham]

Good data point.... the Edelbrock and stock head passage is .312". The Indy's sure seem to be different, in this area at least.

 

[Bakerlite]

What do you guys thing would work better than the factory set up? Push rod oiling is easy now, most all new lifters are capable of it.

Overseas versions of the Mopar smallblock 1970 onwards had oil through pushrods as well as the timed oiling to the shafts. With the stamped rockers you could do away with the timed shaft oiling and just run the oil through pushrods.