Is this a stock valve spring?

[i3igpete]

I just noticed that this guy is asymmetrical when I measure from 0-720 degrees of helix angle.

Does anyone know the spring height when the valve is closed, or the seat load?

[i3igpete]

So it looks like the later year 6g7* SOHC engines use a different spring that has a 4mm longer free length and a ~25% higher spring rate. Thats huge bump in installed seat load. I'll dig into this further.

found a source with values that line up with my spring.
http://www.dairally.net/jason/files/...ns%20h,j,k.pdf

Free Length
Standard ........................... 1.830" (46.48 mm)
Limit .............................. 1.790" (45.47 mm)
Installed Height ..................... 1.492" (37.90 mm)

Stealth316
Valve lift = 0.350" = 8.89mm
Compressed spring height = 37.9-8.89 = 29.01 mm


measured free length: 46.6 mm
measured wire diameter: 3.7 mm
measured coil OD: 26.7 mm
R-Phi-Z helix profile:
R(center) Phi Z(center)
11.5 0 0
11.5 180 1.03
11.5 360 3.5
11.5 540 5.75
11.5 720 8.57
11.5 900 12.15
11.5 1080 16.25
11.5 1260 19.8
11.5 1440 24.15
11.5 1620 27.79
11.5 1800 31.99
11.5 1980 35.45
11.5 2160 39.75
11.5 2340 42.85
11.5 2520 45.85
11.5 2700 46.6

[i3igpete]

So here's what I did. First, I modelled the spring using the caliper measurements to get the spring profile. From basic spring theory, you can get the stiffness of an arbitrary section of coil. For those of you that know electrical circuits, you can think of coils-in-series is analogous to capacitors-in-series. As you compress the spring, you knock out active coils/capacitors. This gives you the rate vs. compression profile. Here's a simple online calculator that gives the equations:
Compression Spring Constant (k) Calculator - Engineers Edge

force-compression.jpg
First check, do the values at installed and max lift match the reference data? I get 57 lbs, the reference data gives 61 lbs. So we're on the right track.
reference.png

While we can, let's look at the stress in the spring. Again, nothing special, just basic spring theory (you can google wahl-corrected spring stress). When a coil touches it's neighbor, it gets "knocked out" and cannot carry any more load. Using the electrical analogy again, imagine you charged up a series of capacitors, and took one out. It would "remember" it's state when you removed it.
stress.jpg fatigueline.png
The fatigue curve tells me that Mitsubishi used using a proprietary steel slightly above SAE 9254, a common spring steel for low-load applications like suspensions.

The reason I made the post was, I wanted to figure out what happens when you flip the spring upside-down during installation. Why does this matter if the spring puts the same load in both directions? The screenshot above gives some clue. With a correctly installed spring, the bunched coils are on the cylinder head side. That means that when the valve moves, they dont contribute to the reciprocating mass. When the bunched coils are on top, that is more mass that essentially lumped into the retainer. What I did next was take a snapshot of the spring at the installed and max height positions, and tracked the motion of each section of coil.

nodedisplacements.jpg

The motion of each section was divided by the total valve motion (0.350 inches, or 8.9mm stock valve lift). This fraction is then multiplied by the coil section mass, and summed together to give an effective total mass. I did this both in the correct and upside-down configurations. Stock spring weight came out to be 43.5 grams, which

TOO LONG DIDN'T READ.
When the spring is in the correct orientation, the effective mass is 17.23 grams. When it's upside down, the effective mass is 26.27 grams. That's a difference of 9.04 grams.

For comparison, DSM stock spring retainers are ~14 grams, and titanium retainers will save you about 50% weight.

Next up, how will this affect the valve float speed?

[i3igpete]

correct-incorrect.png

asdfasdf

[Keyan]

maybe i completely missed this but you said its a SOHC spring...do they fit in DOHC heads? or is this all fun science for the sake of science?

[i3igpete]

So it's confirmed, this is a stock DOHC valve spring.

The SOHC spring being thicker makes sense now that I've seen picture of the rocker arm; the rocker shaft support is pretty beefy, and the valve socket is massive. adds up to a pretty heavy rocker.

[Boost4VR4]

So it's confirmed, this is a stock DOHC valve spring.

The SOHC spring being thicker makes sense now that I've seen picture of the rocker arm; the rocker shaft support is pretty beefy, and the valve socket is massive. adds up to a pretty heavy rocker.

This is mainly why the SOHC has a redline of 6800 due to the rockers being huge and the rocker support. The one modification that would be advantageous in the SOHC is replacing the rocker springs on the rocker supports to something stronger to prevent the rockers from sliding side to side too much so the redline could be increased

The only reason why I say this is because I am working on a turbo SOHC and I have seen some others putting a turbo on the SOHC with success but everyone complains that the powerband is small and the turbo really tries to thrash the engine past redline.

[i3igpete]

can anyone weigh the stock intake valve, retainer, and spring?

[i3igpete]

springinstall.jpg

So if you ever wondered why this picture was in the factory service manual, even though the spring fits either direction... now you know.

For those of your rebuilding engines and don't see the marking, make sure that the bunched coils face down.

For those of you electrical engineers... think of the valvetrain as an RLC circuit. The smaller the spring mass on the retainer side, the smaller the step function.

[DocWalt]

Pete, I love your threads. Though it appears you're asking questions nobody has ever bothered asking before... Which is great