Three simple steps to big flow gains
1. Our subject heads here were a set of Mopan small-block 587 castings
from the mid-1970s. Featuring 1.88-inch intake valves, these and other similar
heads were very common on the majority of LA 360 engines. The idea for our
rework was to gain the maximum performance for the least effort.
2. To quantify the results of the modifications, we used the SuperFlow
600 flow bench at Dr. J’s Performance. The same basic modifications and results
can apply to many other Mopar cylinder heads.
To
quantify the results of the modifications, we used the SuperFlow 600 flow bench
at Dr. J’s Performance.
3. Step one when installing larger valves is to set up the seat cutter
to take advantage of the increase in valve size. Dr. J’s set the fixture to
.005 inch under the major valve diameter. The actual cutter is a proprietary
5-angle tool custom made for Dr. J’s to their specifications.
4. Seat cutting equipment is the only way to go for an accurate valve
job, especially when removing large amounts of material. Old fashioned stones
have no place in this type of work.
Seat
cutting equipment is the only way to go for an accurate valve job, especially
when removing large amounts of material.
5. The cutter completes all five angles at once for a consistent form.
It’s easy to see how much larger the throat diameter has been made by the large
step remaining in the casting below the machine work.
6. The outside diameter of the seat measures 2.0115 inches, taking
advantage of virtually the valve’s entire diameter, while leaving a small
tolerance. Beware that some machinists will cut the seats significantly
undersized.
7. An additional machining step to the valve job is to sweep the
chamber with a cutter that is designed to provide a finished top-cut, and move
the chamber walls outward to further de-shroud the chambers to the vicinity of
the head gasket line.
8. Here is the completed machine work on the intake side. Note the
smooth profile running from the chamber, right into the bowl to the end of the
machine work. The large stepped-mismatch where the machining ends needs to be
blended by hand.
9. The exhaust ports on these heads retain the stock 1.60-inch valve
size, but the radius seat-cutter used by Dr. J’s enlarges the throat area below
the valve.
The exhaust ports on these heads retain the stock 1.60-inch valve
size, but the radius seat-cutter used by Dr. J’s enlarges the throat area below
the valve.
10. To
improve flow, especially at low lift, the intake valves are back-cut with a 30-degree
angle, improving the transition at the back side of the valve.
11. A basic bowl blend will smooth the transition from the bottom cut
into the port. We went a step further to gain more flow, lightly blending the
short turn on the Intake and exhaust ports. The port work was left at a smooth
carbide-cut finish, rather than pursue any additional polishing with sanding
rolls. Flow was up considerably.
12. Looking
for another incremental Improvement, the intake side was gasket port matched,
and the pushrod restriction was enlarged to give the port more area to breath.
This modification is very effective at improving flow with these particular
castings.
