All engine machine work, as well as the engine dyno tests, was done at Gray's Auto Machine in Tigard, Oregon.
Cylinder Heads, Cam And Intake
While the short-block has a few nice parts in it, what really makes this motor work is the Edelbrock cylinder heads. The set of heads on this motor were some of the very first heads produced by Edelbrock, and they were initially bolted on right out of the box. The nice thing about the Edelbrock heads is they are ready to make good power without any touch-up work or porting required.
We initially installed a Mopar Performance .528 solid cam in this motor just because it seemed like it would be a good match. At the time, we didn't realize how good of a match it was for our motor. After the motor had been in the car for a while, we started to test other camshafts, and we had a hard time finding anything that worked better than that old MP .528 grind.
Of course, given enough time and effort you can always find a camshaft that works better than the first one you start with, but for some reason the MP .528 works great when combined with the Edelbrock heads and cast-iron exhaust manifolds. Apparently, the wide lobe centers and the fairly mild profile of the .528 are a good match for the restricted exhaust, but we're not sure exactly why. If we fully understood why the .528 worked so well, we would be in a better position to design a cam that made even more power.
One thing we did learn in a hurry while testing other camshafts was that if you put too much duration into a motor like this, the torque curve falls right out of bed. In this particular motor we found that duration greater than 245 degrees at .050-inch lift killed the low end of the torque curve. Worse yet, the motor wouldn't make anymore power upstairs with the big cam than it did with the smaller lobe profile. We also found out that this motor doesn't seem to like dual pattern cams. One would think that with the restricted exhaust you should leave the exhaust valve open longer to blow out the spent gases, but that theory didn't work as planned when we tested it, so we're back to square one.
Manifolds And Head Pipes
When building this motor we had several sets of HP manifolds to choose from, but one particular set of castings caught our eye since they didn't have a heat riser. These castings originally came on a 400 HP motor in a '73 B-body car, but there might be other applications these manifolds could be found on. Manifold casting numbers for the set we selected were 3751068 and 3751071.
We didn't test any of our HP manifolds on a flow bench, so we don't actually know how well the various castings work. It is possible that some of the HP manifolds flow better than others, but we haven't yet gotten around to being that scientific about this project.
One thing that we didn't do is extrude hone the manifolds. The extrude hone technology is very interesting and would seem to be effective for this type of work. But the process is rather expensive, and we had heard that it didn't actually increase the power in their combinations. So we bolted our combination together with basically stock manifolds and hoped for the best.
An area that we did spend some attention on were the head pipes. We machined some special adapters out of stainless steel that allowed us to bolt 3-inch head pipes directly to the manifolds. We then built some head pipes out of sections of mandrel-bent 3-inch exhaust tubing. The goal was to get the exhaust gases out of the manifold and into a smoothly flowing big pipe as soon as possible. The last trick was to install bungs in each head pipe for the wide-band O2 sensors. We consider a pair of wide-band O2 sensors absolutely mandatory for tuning, so everything we build gets a set of the bungs welded into place.
The entrance to the manifold...
The entrance to the manifold and the plenum divider was smoothed out a little with a carbide burr.
A 2-inch-tall tapered spacer...
A 2-inch-tall tapered spacer picked up some power on the Performer RPM. If you have the room to try one of these spacers you should.
We tried this super tall Victor...
We tried this super tall Victor 383 manifold on the motor with poor results. Sometimes race stuff works on street motors, and sometimes it doesn't. With the HP manifolds, the exiting air restriction was hampering the incoming air's flow. In other words, the exhaust manifolds couldn't expel the air fast enough for the single plane intake to bring more in.
When you're going to get serious...
When you're going to get serious about making power, you should always sonic check the block before machining begins to see if the cylinder walls are thick and uniform. Skip this process, and you could end up with a very expensive boat anchor.
Our crankshaft started life...
Our crankshaft started life in a 426 wedge motor. We ground the mains down 0.125 and then offset ground the rod journals to Chevy big-block on a 3.875 stroke. The connecting rods come from Manley, and the pistons are lightweight JE forgings.
Here is a pile of Chevy parts...
Here is a pile of Chevy parts used in our Mopar stroker motor. The rings are for a 4.375 inch bore size, the piston pins are 0.990 diameter, and the rod bearings are 2.200 diameter.