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BBC oil restrictors

General engine tech -- Drag Racing to Circle Track

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70MC
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Re: BBC oil restrictors

Post by 70MC »

69chev496 wrote: Wed Jul 15, 2020 10:49 am Let me share my experience. I have a 598 with AFR 335 CNC "S" version heads. I found there was not enough ventilation holes drilled in the heads. What happened is the blow-by escaping the sump into the valve covers to exit the breathers was blocking the oil flow return from the valve covers to the sump and the valve covers were filling with oil during a hard run. This happened under load when the blow by was greater. When the engine returned to idle, the blow by was reduced allowing the oil to return to the sump. I ended up drilling additional holes in the heads to allow ventilation solving my issue. I see the AFR heads were a change you made. Not sure what vintage heads you have. I believe AFR fixed this issue with their newer heads. I can find some pictures if needed.
My head's were changed a while ago. The only change I made this last time was oil pump and pan.
But my head's are 5-6 years old and this version just came out, actually had to wait for them, they are the V2 if memory is correct. I have seen other manufacturer heads that have the area in the center at top be wide open. Mine are not like that. I can see what you are saying, and that may be happening in my case. There is not much room around the push rods since I am using 7/16 pushrods.
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Re: BBC oil restrictors

Post by af2 »

70MC wrote: Wed Jul 15, 2020 3:34 pm
af2 wrote: Wed Jul 15, 2020 10:42 am I had a similar pan that on my 431" would kill the pressure at 6000. I cut that radius out and added a 2" kick-out on the right side under the starter and fixed the problem. I shifted it at 8000 with no drop in pressure. I can see with the stroke you are running the pressure drop would be sooner like it is.
I understand what you're saying.

If you look at the bottom pictures that has the oil pump sitting in the pan you will see how the oil is going past it. Shit there is hardly room for the pump!.
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af2
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Re: BBC oil restrictors

Post by af2 »

69chev496 wrote: Wed Jul 15, 2020 10:49 am Let me share my experience. I have a 598 with AFR 335 CNC "S" version heads. I found there was not enough ventilation holes drilled in the heads. What happened is the blow-by escaping the sump into the valve covers to exit the breathers was blocking the oil flow return from the valve covers to the sump and the valve covers were filling with oil during a hard run. This happened under load when the blow by was greater. When the engine returned to idle, the blow by was reduced allowing the oil to return to the sump. I ended up drilling additional holes in the heads to allow ventilation solving my issue. I see the AFR heads were a change you made. Not sure what vintage heads you have. I believe AFR fixed this issue with their newer heads. I can find some pictures if needed.
What pan are you running?
GURU is only a name.
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Re: BBC oil restrictors

Post by 70MC »

Update. I ran the motor yesterday on the Dyno and the problem I was having is gone. Oil pressure on the last pull was 69psi at the start of the pull at 4000rpm and gradually rose to 72 at 6500 and then dropped to 70psi at 6600, 68at 6700, 64 at 6800, 62 at 6900, 62at 7000 and 62 at 7100. All our pulls ended around 7000 since power ended at 6900- 7000.
At the start, the drop started a few rpm sooner, and seemed to drop a few more psi maybe 10-12psi. We added another quart on the last pull for a total of 7 1/2 quarts and it seemed to be a tiny bit better. But, on the last pull he switched from his analog gauge to his digital gauge for more accuracy, so I can't exactly compare the last pull to the other pulls.
What do you make of the drop in psi?
BTW, the motor made 892hp at 6900 and 764tq at 5500.
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70MC
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Re: BBC oil restrictors

Post by 70MC »

Here is what I did to try to correct the problem. I removed the lifter valley screens, made the oil drain back holes in the head twice the size by drilling another 7 1/6 hole above the existing hole and removed the material between the holes to make one large oval drain back hole. These heads did not have any holes in the center of the heads at the top near the valve cover, where the heat riser is in a stock head. I called AFR to see if I could drill a hole there. AFR said to drill 4, 7 1/16 holes there. I have the early V2 version head, and he said they now come with holes there. So I drilled 4, 7 1/16 holes there. I added restrictors, they came with a center restriction of .060 with 2 side feed holes of .046, I drilled the center to .093 and the side holes to .070. My oil pan did not have a trap door so I put a trap door in the center of the sump. As I may have said before, the oil pump was sent back to be checked and it was found to be in perfect working condition.
A bad day of racing is better than a good day of work
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