Back in the late '80s I had the pleasure of working with wild man Rod Sokoloski. He is one of the best cylinder head and manifold men in the country. Back then, there weren't many affordable aluminum heads on market, so we ported the L98s.
We found that the ports really like the stock, 1.94/1.50-inch valve size. You can increase the valve diameters, but it's not worth the expense. The main thing that we found is that less is more. This head liked opening up the intake bowl to 91 percent of the intake valve size. Next, you want to match the roof of the intake port around the valveguide area. One side of the roof is much tighter to the valveguide. You want to open it up to match the pushrod wall side. Finally; remove about 0.050 inch off the pushrod wall at the pushrod restriction, and clean up the short-side radius. These minor changes will make big differences.
On the exhaust side, open up the bowl to 89 percent of the valve size. Widen the short-side radius, blend and reduce the valveguide area, and raise the roof of the port to match whatever header you're going to use. We would do most of the work on the exhaust port. Finally; lay back the chamber wall on the intake side and blend to the spark plug. Unshroud the chamber around the valves out to your bore size.
We used the standard three-angle valve job and 30-, 45-, and 65-degree angles on both the inlet and exhaust. We cut each valve 45 degrees with a 30-degree back-cut. It sounds like a lot of work, but we had it down to about 8 hours.
When we were finished, these heads responded with good numbers. The following flow numbers were produced on a SuperFlow SF600 flow bench at 28 inches of water, on a 4-inch bore plate, and without a pipe on the exhaust port.
- INLET
- 0.10 = 68cfm
- 0.15 = 99
- 0.20 = 134
- 0.25 = 159
- 0.30 = 183
- 0.35 = 205
- 0.40 = 220
- 0.45 = 227
- 0.50 = 214
- 0.60 = 213
EXHAUST
- 0.10 = 66cfm
- 0.15 = 95
- 0.20 = 114
- 0.25 = 136
- 0.30 = 154
- 0.35 = 164
- 0.40 = 179
- 0.45 = 186
- 0.50 = 191
- 0.55 = 191
- 0.60 = 194
On a ZZ4 with no other changes except for the porting, we would see 390 hp at 5,500 rpm and 430 Ib-ft of torque at 4,000 rpm. The stock ZZ4 engines recommend running 34 to 36 degrees total timing. With the ported cylinder heads you must retard the timing to 29 degrees of total timing to stay out of detonation. The porting increases the cylinder filling to the point that they will knock the intake valves right out of the engine if you don't. Believe me, we found it! These engines would run very strong, and you could never tell that it wasn't a dead stock ZZ4. Just ask Dandy Dick Landy!
Courtesy of Kevin McClelland, Performance Q&A,
Chevy High Performance magazine.
