SM Head Modifications on a budget
So two tests this morning. First was full removal of head bolt bulge. After leaving off yesterday convinced that the area at the apex was the major limiting factor to flow gains, it seemed reasonable to remove the rest of the HB bulge. That still fits in our initial step 1-5 plan. I did cheat a little on removing the bulge and used a burr. That was a huge time saver, but it could have been done equally well with a 1/2" cartridge roll. At the same time that I felt the bulge was 100% removed, I broke through to the brass tube. That can just be seen at the blue arrow in one of the pics. If the head bolt hole is not tubed, I think 100% removal of the bulge is not possible, certainly not wise. Flow test was test number 618. While peak flow did go down, average cfm went up a little and the shape of the curve improved. I do not see a downside to removing the bulge completely if the hole is tubed.
Second test was adding 4 cc clay to the port roof to try to reduce some flow area during/after the short turn. The thinking was that this may help reduce separation in the turn. Flow numbers were down across the board. The one positive from adding the clay is the shape of the curve improved. Peak flow was at 850 lift instead of 500 lift. It really didn't hurt flow at all at the highest lifts. 4 cc is a lot of clay and a lot of volume reduction. I intentionally chose this spot for the clay because at high lifts and high air speeds this part of the port becomes 'dead' anyway. The flow wants to window and follow a straight line from port opening to valve opening. It does not want to follow a curved roof, at least not on the cyl center side of the port.
My takeaway from these two tests is this. Yes, more area is needed at the apex as PBR often preaches in his posts. At the same time, PRH has repeatedly said that the SSR is in control. I'm not sure the two can be separated. To reshape and lower the SSR the area at the apex will increase. I also don't think there's much improvement to be had until the SSR/apex area is addressed. I included a picture of the port mold to show the abrupt/tight short turn. It's easy to see why air wants to jump the turn.
As far as next steps. I think we are moving on to step 6, whatever that is. Would it make sense at this point to clean up the ridges in the chamber a little and lay back the areas that Brian suggested? That's still a fairly easy step.
So two tests this morning. First was full removal of head bolt bulge. After leaving off yesterday convinced that the area at the apex was the major limiting factor to flow gains, it seemed reasonable to remove the rest of the HB bulge. That still fits in our initial step 1-5 plan. I did cheat a little on removing the bulge and used a burr. That was a huge time saver, but it could have been done equally well with a 1/2" cartridge roll. At the same time that I felt the bulge was 100% removed, I broke through to the brass tube. That can just be seen at the blue arrow in one of the pics. If the head bolt hole is not tubed, I think 100% removal of the bulge is not possible, certainly not wise. Flow test was test number 618. While peak flow did go down, average cfm went up a little and the shape of the curve improved. I do not see a downside to removing the bulge completely if the hole is tubed.
Second test was adding 4 cc clay to the port roof to try to reduce some flow area during/after the short turn. The thinking was that this may help reduce separation in the turn. Flow numbers were down across the board. The one positive from adding the clay is the shape of the curve improved. Peak flow was at 850 lift instead of 500 lift. It really didn't hurt flow at all at the highest lifts. 4 cc is a lot of clay and a lot of volume reduction. I intentionally chose this spot for the clay because at high lifts and high air speeds this part of the port becomes 'dead' anyway. The flow wants to window and follow a straight line from port opening to valve opening. It does not want to follow a curved roof, at least not on the cyl center side of the port.
My takeaway from these two tests is this. Yes, more area is needed at the apex as PBR often preaches in his posts. At the same time, PRH has repeatedly said that the SSR is in control. I'm not sure the two can be separated. To reshape and lower the SSR the area at the apex will increase. I also don't think there's much improvement to be had until the SSR/apex area is addressed. I included a picture of the port mold to show the abrupt/tight short turn. It's easy to see why air wants to jump the turn.
As far as next steps. I think we are moving on to step 6, whatever that is. Would it make sense at this point to clean up the ridges in the chamber a little and lay back the areas that Brian suggested? That's still a fairly easy step.