Small Block Oiling System Modifications
What I want to show you is the modifications that were talked about and used by the racers of the 70 and 80s. This one in particular was used when you needed to run a hydraulic lifter cam, it was called by some the “A&W Crossover".
The crossover works by slowing the oil in the right main oil galley down so it will not over shoot the 90 degree passages to the number 2, 3, and 4 main bearings. The number 1 main passage was blocked on the right side. Then the crossover tube feeds the left side galley which then reverse feeds the number 1 main and cam bearing.
This is basically how it was explained back in the day. No details or instructions, just how it worked and if you sent them your block they would do the mods for you for a price.
What I am going to do is show and tell you how you can do this mod along with some others to make your SB Mopar live above 6500 rpm.
Block Mods
The blocks we are working with are the pre 88, basic 273, 318, 360 and the 68-73 340.
By the way these mods also work on the Polyspherical 318 sometimes called the wide block or Y block by people that don't know any better. The Poly 318 is the same block as a 340 with the exception of the two big holes in the water jacket on the top of the deck. But you can plug these if you want to run wedge heads on that block. You can even bore it out to a 340 and with a cam and head swap it becomes a wedge instead of a Poly. Here is one for you. Take the Poly 318 cam, heads and intake and put them on a 360. Better yet bore the Poly out to 4” and put a 340 stroker crank into it for a 408 Poly sleeper. By the way I believe the 318 Poly used solid lifters so you don’t plug the right front passage or use the crossover tube on them.
The oil passages from the filter mount to the right side main galley (passenger side) all get drilled to 1/2" id. You will need to remove all the plugs in the back of the block and in the filter mounting area. Don't forget the one in the passage below the oil pressure sending unit. I used a long pushrod to remove this one.
You will find that these passages were step drilled at the factory so open them up all the way to the main galley. I used a 9" cobalt and a 12" black oxide 1/2 " bit for drilling these out.
After drilling the passages use a bur or grinding stone to clean and radius the sharp corners inside where the passages meet .
OK, so much for the easy part.
Let’s work on the main bearing passages
These were step drilled also by the factory. Using a 12" long 5/16 bit, drill number 2,3 and 4 main passages from where the main bearing is fed all the way into the right oil galley. Do NOT drill number 1, on the right side because it will be plugged. Number 5 is not fed by the main galley so it doesn't need drilled either.
Drill the number 1 main passage on the left side to 5/16. It will be reverse fed by the crossover tube.
Cam Oiling Changes
Now is a good time to discuss the cam bearings and the feeding of the heads by the number 2 and number 4 bearing journals.
The purposes of these mods are to keep the oil going to the bearings instead of blowing out at the cam journal.
There are 2 ways to restrict the oil going to the cam bearing.
The first is the hardest. You go into the oiling passage from the main bearing saddles. Tap the passage to 5/16-18 then drill a 1/8" hole in a set screw and Loctite it in place. This is done on number 1, 3 and 5. Number 2 and 4 are feeding the heads so we aren’t restricting them.
The second way and the easiest is to restrict the oil by drilling a 1/8 hole in the cam bearings. Then install them so only the one hole lines up with the main bearing feed passage. This will block off the oiling to the heads. (Or just do #1,3 and 5 if you want to keep the stock head oiling.) The heads will be oiled by a mod to the passages in the lifter valley.
By restricting the oil to the cam bearings we are holding back oil to be used by the crankshaft and rod bearings while still lubing the cam bearings but not the heads.
