Porting: Usually, porting a set of heads is up to the skill of the tool operator as each intake and exhaust port is hand-milled to open them up. In many cases, this is the only way it can be done. But no matter how expert the operator, making the intake and exhaust ports match from cylinder-to-cylinder is just about impossible. And with that irregularity, you are building in variables from cylinder to cylinder that will negatively affect the engines smoothness, power, and longevity under high loads.
To correct this and improve on the hand-ported performance head, 928 Motorsports LLC has developed and uses a CNC milling program on a 5-axis mill for optimizing the Porsche 928 heads. This digital milling process guarantees not only maximum flow, but repeatability from cylinder-to-cylinder.
Now, with 5-axis CNC machining, we can confirm that each cylinder and its ports are an exact match across the head - giving you greater engine output as well as smoothness and increased safety from detonation in high-output engines.
Valves: We can also replace the stock 36mm intake valves with our Hi-Flow 39.5mm valves. The stock valve seats are removed, and new larger valve seat reliefs are milled into the head and the seats pressed in.
Our Hi-Flow valves and seats are available in both Titanium and Stainless Steel. For more information on our valves, visit the Valve Page Here.
Flow bench analysis before-and-after our CNC porting and Hi-Flow valve installation shows that you can expect the following gains:
Intake Valve Lift |
Stock
CFM's |
Ported Heads
CFM's |
+ or - |
|
Exhaust Valve Lift |
Stock
CFM's |
Ported Heads
CFM's |
+ or - |
0.150 |
142.50 |
158.90 |
16.40 |
0.150 |
124.80 |
153.26 |
28.46 |
0.200 |
187.10 |
204.93 |
17.83 |
0.200 |
169.00 |
194.50 |
27.72 |
0.250 |
225.70 |
244.13 |
18.43 |
0.250 |
190.80 |
218.52 |
27.72 |
0.300 |
248.29 |
273.83 |
25.54 |
0.300 |
210.50 |
234.78 |
24.28 |
0.350 |
261.30 |
291.06 |
29.76 |
0.350 |
220.10 |
245.63 |
25.53 |
0.400 |
267.30 |
311.50 |
44.20 |
0.400 |
223.30 |
252.01 |
29.44 |
0.450 |
267.30 |
323.96 |
56.66 |
0.450 |
226.40 |
255.84 |
29.44 |
0.500 |
297.00 |
329.30 |
32.30 |
0.500 |
229.60 |
259.99 |
30.39 |
0.550 |
297.00 |
333.75 |
36.75 |
0.550 |
229.60 |
260.94 |
31.34 |
Comparison: The 928 Motorsports LLC modified Porsche 928 heads compared to Small Block Chevy Brodix GB2000/2001 racing heads (IRL, NASCAR):
Intake
Valve Lift
|
Brodix Race Heads
CFM's |
928MS Ported Heads
CFM's |
+ or - |
|
Exhaust
Valve Lift |
Brodix Race Heads
CFM's |
928MS Ported Heads
CFM's |
+ or - |
0.200 |
157.00 |
204.93 |
47.93 |
0.200 |
109.00 |
194.50 |
85.50 |
0.300 |
238.00 |
273.83 |
35.83 |
0.300 |
152.00 |
234.78 |
82.78 |
0.400 |
302.00 |
311.50 |
9.5 |
0.400 |
205.00 |
252.01 |
47.01 |
0.500 |
353.00 |
329.30 |
23.7 |
0.500 |
232.00 |
259.99 |
27.99 |
NOTE: maximum valve lift on the 928 with the most aggressive cams possible is only .442 on the intake, .398 on the exhaust. See Camshaft Details Here
CNC Porting and Polishing:
32 v heads: $1800 per pair. Price includes surface milling, and seat milling for over-sized valve seats.
Multi-angle Valve jobs: (2-angle valve job on exhaust valves, 3-angles on intake valves)
32v heads $650 per pair
Other charges may apply as needed, such as: valve stem replacement, etc. Prices do not include parts.
