Valve springs are finally all installed. Doing it right takes a lot of time.
As the chart below shows I am dealing with valve springs that have a very large tolerance range from Supertech. The idea is to get the springs when installed to be more or less equal pressure/load. Simple as that. Nissan seem to prefer more spring pressure on the exhaust valves, while the intake valves have less. Exhaust valve springs are stiffer to pound the carbon deposits off the seat and also to keep valve bounce to a minimum for optimal heat transfer. That is the idea anyway. Because of the large spring variation I had to split up the springs in (2) groups, low and high spring pressures as this cuts the tolerance variation by half. For instance the intake springs range from 83 to 87 lbs, while the exhaust springs range from 87.5 to 92.5 lbs. I color coded the springs as well so I wouldn't mess up the install.
The spreadsheet basically shows how I am doing this. I first install the valve with NO spring and measure from the tip of the valve to the spring seat position. This more or less tells me the difference between the valves but ultimately not the exact "installed height". The factory valve/spring installation height spec is 38.6 mm from the service manual. I designed a custom spring seat that is about 2.4 mm thk, so the new installation height is now approximately 36.2 mm. This doesn't account for the valve job which further alters that value somewhat. To get the new "install height" of the spring I actually have to measure it with the spring installed. Before this I would have already used the spreadsheet to find the optimal valve # position to load the spring. All springs were measured on my homemade spring tester at 36.2mm compression. As I found out the actual installed spring height on the cylinder head varies from 35.77 mm to 36.81 mm due to the valve job I did plus factory tolerances. To confuse things more all the springs vary in their lengths from 48.7 mm thru 49.7 mm. Finally, since I know the spring load and approximate install height I can then calculate the spring stiffness coefficient for every spring. Supertech say these are 7.7 lb/mm rated springs. In fact they vary from 6.46 to 6.88 lbs/mm.
The purpose of the spreadsheet is to "mix and match" the springs to balance out the load differences before I install anything. Had I randomly installed the springs it would have been possible to have a 20% difference in spring loads on the extreme tolerance limits which would not be a good thing. This is what engineers call "stack-up tolerances" and this must be avoided. To measure the actual install height I'm using a digital caliper depth attachment. They sell a spring micrometer for this as well but they don't fit for our small 24-25 mm dia. size springs. Next the spring is removed and I recalculate how far off I am on the spring load I'm aiming for. Next step is to select an appropriate shim and re-install it and then I'm done for that valve. And so the process continues until all (16) springs are installed. Prior to this I would have selected the "stiffest" spring (shown in "bold italics") and strategically placed it in the "tallest/largest" install height valve position when I initially took measurements with just the valve installed in the head. All other springs are then shimmed against that value as best I can. Hopefully that makes sense, you can add material by shimming but not easily subtract material.
The spreadsheet shows in "orange" the actual measured values. "Green" are calculated values. It takes special equipment to actually measure the installed spring load on the head, but what I have is close enough. The intake valve closed pressures vary from 83.1 lbs to 83.8 lbs and the valve open pressures from 145.6 to 146.8 lbs. This is pretty darned good to get them all that close. My goal was to stay under 100 lbs closed and under 180 lbs open which I was easily able to do while keeping the values with 5 lbs of each other. For reference the stock Juke intake spring values would be 39 lbs (closed) & 85 lbs (open). The exhaust valve closed pressures varied from 92.8 lbs to 95.2 lbs and the valve open pressures from 153.5 to 157.8 lbs. Stock Juke exhaust valve values would be 85 lbs (closed) & 113 lbs (open). Unfortunately I had (1) exhaust spring that was a bit too stiff but in reality it won't make a difference being off by 3-4 lbs anyway. I bought (17) springs and probably should have bought a couple extra to eliminate any low/high rated springs but overall things worked out well regardless.
This is essentially what blueprinting an engine is about, lot's of mixing and matching stuff. But this ultimately is done to bias values to improve performance and/or reliability. Suffice it to say the Supertech conical springs I installed are a big improvement in preventing spring surge or damaging harmonics over the stock Nissan Beehive springs. The increased spring pressure and lightweight springs will help fight valve float at higher rpms and valve blow open at higher boost pressures. There is much more to the spring calculations such as clearances to the valve guide & seal as well as coil bind height which I'm not covering here. I've already calculated those values to make certain nothing crashes into each other during operation.
Next week I will get into the valve lash adjustment but for now I'm gonna take a short break and relax.