650performance
XS650 Addict
I've had several people email me asking about what they should expect in terms of added flow in a ported vs. stock, unported head. I don't claim the modified head tested here is the best ever, but it is a very good one and provides a useful comparison for anyone looking for real numbers to evaluate the success of their modifications.
Craig
COMPARATIVE FLOW NUMBERS
STOCK & MODIFIED XS650/750 CYLINDER HEADS
Test Conditions:
The stock head is not modified in any way and has been bead blasted to ensure the ports are clean and fitted with stock valves.
The modified head is the Harry Lillie modified "master"used for modeling the CNC porting program and has the modified, oversize XR valves. Both tests were conducted within a half hour of one another on the same flow bench with the same operator employing the same fixtures and procedures. Both were tested at 28"pressure.
Results:
The results are expressed as a percentage difference at each valve lift increment. I am not sending out the flow numbers because your flow numbers will be different on another bench, and I don't want to get into discussions comparing apples to oranges. However, you should see virtually identical improvement over stock (castings do differ) with your modified head. As you can see, on the IN port the mods really begin to kick in at .300"lift, while the EX porting becomes effective between .150"and .200". The numbers underscore that the EX port is the most obvious limiting feature of the head and was one of the primary reasons the OU-72 was developed.
It is important to note that the not-so-secret "trick" to make the EX flow better is to optimize its shape to both improve total flow AND to reduce turbulence within the port to the lowest possible number. Needless to say, this takes some sophisticated flow equipment to measure. By getting this balance right, the port can flow "more than its numbers," as it was described to me.
Valve lift Flow difference from stock head
INTAKE EXHAUST
.050" 0% +12%
.100" 0% 4%
.150" +2% 3%
.200" 6% 18%
.250" 6% 22%
.300" 9% 22%
.350" 19% 27%
.400" 37% 25%
.450" 46% 24%
.500" 56% 23%
Test conducted at Competition CNC on Super Flow 600 - Sept. 2008
Craig
COMPARATIVE FLOW NUMBERS
STOCK & MODIFIED XS650/750 CYLINDER HEADS
Test Conditions:
The stock head is not modified in any way and has been bead blasted to ensure the ports are clean and fitted with stock valves.
The modified head is the Harry Lillie modified "master"used for modeling the CNC porting program and has the modified, oversize XR valves. Both tests were conducted within a half hour of one another on the same flow bench with the same operator employing the same fixtures and procedures. Both were tested at 28"pressure.
Results:
The results are expressed as a percentage difference at each valve lift increment. I am not sending out the flow numbers because your flow numbers will be different on another bench, and I don't want to get into discussions comparing apples to oranges. However, you should see virtually identical improvement over stock (castings do differ) with your modified head. As you can see, on the IN port the mods really begin to kick in at .300"lift, while the EX porting becomes effective between .150"and .200". The numbers underscore that the EX port is the most obvious limiting feature of the head and was one of the primary reasons the OU-72 was developed.
It is important to note that the not-so-secret "trick" to make the EX flow better is to optimize its shape to both improve total flow AND to reduce turbulence within the port to the lowest possible number. Needless to say, this takes some sophisticated flow equipment to measure. By getting this balance right, the port can flow "more than its numbers," as it was described to me.
Valve lift Flow difference from stock head
INTAKE EXHAUST
.050" 0% +12%
.100" 0% 4%
.150" +2% 3%
.200" 6% 18%
.250" 6% 22%
.300" 9% 22%
.350" 19% 27%
.400" 37% 25%
.450" 46% 24%
.500" 56% 23%
Test conducted at Competition CNC on Super Flow 600 - Sept. 2008