truedualws6

Just swapped the PCM and took the Accel 300+ out of the loop and the
sine wave in the dyno curve problem persists. At this point with a new
opti, coil, ICM, PCM, and spark plugs, there is not much left but to try
a different valve spring setup. It's just got to be valve float.

I would think that 120 pounds closed pressure and 295 pounds open would
be enough for the tiny, little, baby, Crane 104227. Considering that the LT4
springs with the stock cam and 1.6 rockers had 100 pounds closed and 265
pounds open, you would think everything would be fine, especially with the
beehive ovate springs. Granted they are the 26915s, but that is still a lot
more pressure than the LT4s.

So, what's the deal with spring pressures needed to stop my sine wave, yet
not be overkill so I don't wear everything out? Lets see, we have the Crane
99893, Comp 26918, 987, and 941, Manley 22410 and 221423, CM 612, K-800,
and who knows how many more. Oh yeah, the Isky 235-Ds that I paid $90
for and sold NIB for $45.

If you have any ideas, please be sure to address the entire set up and include
seats/locators, retainers, and locks with your spring recommendation.

Spinner

Your dyno graph looks nothing like valve float to me, but since there isnt much left, I'm having great luck with comp cams 985s. Just a tad stronger then the 987s. Using 730-16 titanium retainers (There is a steel retainer if you dont want to pony up for Ti) and 611-16 10 degree super locks. They fit on the heads with a spring seat that I cant remember the part # of, it's a manley seat. Shimmed .030 on the exhaust side, with the .060 seat. Great pressure, plenty of clearance to coil bind, no issues yet.

truedualws6

Thanks for the info Spinner. The 985s are 164/335# closed/open, at
1.75/1.25" respectively. The 987s, which are more typically recommended,
are 121/388# at the same specs. The spring rate is also higher for the 987
at 344#/in vs 333 for the 985. The Crane 99893 springs (listed on the cam
card for the 104227), are 168/365# at 1.75/1.25" respectively, with a rate
of 391#/in. I have read that 135-140# closed pressure is the upper limit for
longevity. How the heck do you decipher all these differences?

I'll go Ti retainers with whatever setup I choose. It's not the $$, and it's not
even the few HP, I want the setup to work correctly, have longevity, and I'm
getting really tired of the sine wave.

I checked out the Manley catalog but could not find a seat that looked good
for the 985/987 springs and stock spring pockets. If you come up with that
part# let me know.

shoebox

Are you sure it's not spark retard? BTW, lifters are part of the valve train, so don't forget to consider them in the equation.

truedualws6

Rob,
During the dyno tune session Jeff (CAM) did a pull with practically no timing in
the car and the graph looked the same. He looked at the data and said it's
definately not timing. The lifters are Comp Rs. I have set the lash twice and
have it set presently to 1/8 turn cold. This is with 7/16" studs.

The dyno graph looks like there is some kind of resonance. Have you ever seen
Comp Rs cause the distress shown in the graph?

About the simplest valve spring fix I can think of is to upgrade to the 26918s.
I'm just not real motivated to stick with the beehives at this point in time.

Spinner

Not sure where you got the numbers, but they're off. Manley seat may not still be made, the comp 4770 seat should also work for the springs. The 985s also have a spring damper, I dont believe that the 987s do. Again, I set them up with the .060 seat and a .030 spacer on each exhaust. No valve float to 6800rpm in a pretty aggressive cam package.


985
Seat Load 164 @ 1.750
Open Load 331 @ 1.250
Coil Bind 1.150
Rate(lbs/in) 333#

987
Seat Load: 138 @ 1.750
Open Load: 325 @ 1.250
Coil Bind: 1.150
Rate(Lbs./In.): 344#

Also, think of spring rate as how much pressure springs give as they're compressed. The higher, the more pressure at a lower number. IE: 333# spring rate = 333 pounds of pressure per inch of compression. Higher is not necessarily better, the number is used mostly to figure out the spring pressure at different valve lift heights.