Alfa Romeo 8V Twin Spark (75&164) cylinder head porting

Original Alfa TS intake flows around 100 cfm @ 10” water at 10 mm lift and does not gain more with additional valve lift. That would be enough for 170 hp in an ideal setup. The flow will de-attach at the discontinuity at short side radius and transition area to the valve seat. The finishing level can be seen from the picture below. There tend to be some offset between the intake port and the valve position in some of the ports, which makes things even worse.

Std intake port

STD Alfa Twin Spark 8V intake port

 

Flow results of STD head

Flow results of STD head

The exhaust port can do the job up to around 200-220 hp with just some cleaning. After that some porting becomes essential.

The basic design of the Alfa head is not bad at all. Significant performance upgrade can be made by low budget mild porting job using standard valves and seats. To reach 200 hp power level, some more room is needed around the valve guide and the shape of the transition to the valve seat is needs attention. This can be called as “Stage 1” porting in general terms.

“Stage 1” porting job, std valves, std seats

“Stage 1” porting job, std valves, std seats

Following graph shows the difference of flow capabilities of the intake port with standard 44 mm valve and standard valve seats. The “Std with some cleaning” curve is from one certain head that came out from one race engine. It was called “slightly ported”, but in practice the head was about as good as the standard head. The ported “Stage 1” head flows near to 120 cfm and is ready for 205 hp at 12 mm lift.

Flow results of different porting jobs with std valves and seats

Flow results of different porting jobs with std valves and seats

In any real race engine, the first upgrade is to replace the valve seats to pull the valves out of the original recessions and at the same time it’s practical to move to 46 valves as well. This is called later as “Stage 2”. New raised seats and 46 mm valves give potential for better flowing head, although porting is again needed and there will be some more need for material removal compared to “Stage 1” porting.

New valve seat with radius cut for 46 mm valve, non-ported

New valve seat with radius cut for 46 mm valve, non-ported

“Stage 2” Ported head for 46 mm valves

“Stage 2” Ported head for 46 mm valves

The throat area consisting of seat and valve shapes is very important for flow capacity, but if the port shape is left alone, the gain from the new seats and bigger valves may be lost. The curve “Non-ported, 46 mm..” shows an example of this. As good as Std head.

Graph below shows the benefit of 46 mm valve. It outperforms the “Stage 1” version at all lifts and flows around 130 cfm at 10” water at 13 mm lift. This gives potential near to 225 hp. The head with 46 mm valve can be made to flow even some more at high lifts if needed, but with cost of some mid lift flow.

Flow results of “Stage 2” porting and 46 mm valves

Flow results of “Stage 2” porting and 46 mm valves.

In extreme racing applications, the valve size can be made even larger, example 48 mm. Together with extensive ”Stage 3” porting job, the head can flow around 150 cfm at over 16 mm lifts. As seen in the graph below, the extreme head with 48 mm valve rules only at high lifts. At the lower lifts the large valve is shrouded by the cylinder wall, which is standard 84 mm in this flow test. So this head asks for really high lift cams and would benefit from larger bore. The potential shows over 250 hp figures.

"Stage 3" porting with 48mm valve

Flow capability of "Stage 3" with 48mm valve

Flow capability of "Stage 3" with 48mm valve

In the case of extreme “Stage 3” big valve porting, special attention is needed to not make hole to the water passages. The offset of the intake port castings should be noted before starting removing the material.

The effect of the intake valve shrouding was studied with Stage 2 ported head with 46 mm valve. Following graph shows the flow difference when the head was moved 1 mm on each direction. The difference of 5 to 10 cfm at all lifts below 13 mm is significant for sure.

Head offset flow test

Head offset flow test

On the other hand, as the valve follows the piston after TDC, there would not be that much room for air anyway at low lifts.

Room behind the valve during overlap

Room behind the valve during overlap

Kimmo @ Alfa Tune Ltd

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