SM Head Modifications on a budget
This could be the last test in this series of trying to find the low hanging fruit when porting a Speedmaster head. I have prepared 3 ports in the same head with different valve jobs. All three ports have had the pushrod pinch enlarged until the brass tube was reached. All three ports have had the head bolt bulge fully removed. All three ports have had the chamber deshrouded to the gasket line on the long side.
Here's the differences in the ports:
Test 628 is port 3/6 with a 15/30/45/60/70 valve job and a 2.055 valve. This is the port used throughout this entire post.
Test 634 is port 2/7 with a 35/45/60/75 valve job and 2.055 valve.
Test 635 is port 1/8 with a 40/50/65/75/80 valve job and 2.02 valve. The intake valve on this port has been shifted 0.060" and the exhaust port has been shifted 0.080".
Flow results are attached. I think it's safe to say that in the hands of a novice porter like myself, 260-265 cfm is about all that is available from this head until the apex/short side areas are addressed. That was PBR's estimate from the beginning. He thought that there was 15 cfm available from some simple(ish) modifications. That proves to be exactly right.
It is interesting to note the areas in the flow curve where each of the three ports pull ahead of the others and also lag behind the others.
As time allows I plan to make simultaneous modifications to all three ports and track the progress. It will most likely happen in a new thread.
This could be the last test in this series of trying to find the low hanging fruit when porting a Speedmaster head. I have prepared 3 ports in the same head with different valve jobs. All three ports have had the pushrod pinch enlarged until the brass tube was reached. All three ports have had the head bolt bulge fully removed. All three ports have had the chamber deshrouded to the gasket line on the long side.
Here's the differences in the ports:
Test 628 is port 3/6 with a 15/30/45/60/70 valve job and a 2.055 valve. This is the port used throughout this entire post.
Test 634 is port 2/7 with a 35/45/60/75 valve job and 2.055 valve.
Test 635 is port 1/8 with a 40/50/65/75/80 valve job and 2.02 valve. The intake valve on this port has been shifted 0.060" and the exhaust port has been shifted 0.080".
Flow results are attached. I think it's safe to say that in the hands of a novice porter like myself, 260-265 cfm is about all that is available from this head until the apex/short side areas are addressed. That was PBR's estimate from the beginning. He thought that there was 15 cfm available from some simple(ish) modifications. That proves to be exactly right.
It is interesting to note the areas in the flow curve where each of the three ports pull ahead of the others and also lag behind the others.
As time allows I plan to make simultaneous modifications to all three ports and track the progress. It will most likely happen in a new thread.