[Jimbobeast]

Originally Posted by P@blo

The seat pressure was not the problem in wiping your previous cam. If you used a high rate spring on a short IH, your spring pressure over the nose increased by a large factor. Unless your cam wiped the base circle?

Over the nose pressure on a HFT should be kept in check. Well, the ones you want to last anyhow...

I beg to differ. The aftermarket springs were installed without machining the valve stem "boss". The inner spring sat 1/4" above the seat (and the outer spring), giving an effective seat pressure of 160. The springs were OK for the application but were installed incorrectly (and assembled by a previously very competent Pontiac loving machine shop).
The boss is now machined and the inner springs are flat on the seat along with the outers. All is in harmony.

[P@blo]

Originally Posted by Jimbobeast

I beg to differ. The aftermarket springs were installed without machining the valve stem "boss". The inner spring sat 1/4" above the seat (and the outer spring), giving an effective seat pressure of 160. The springs were OK for the application but were installed incorrectly (and assembled by a previously very competent Pontiac loving machine shop).
The boss is now machined and the inner springs are flat on the seat along with the outers. All is in harmony.

A 322psi rate spring with a 110psi seat pressure will put you at 271psi open pressure at 0.50" which is perfect. I had a set of 670s done and used the 995 402psi spring and have 292psi open which is perfect. Not sure the focus on closed pressure but I would keep open pressure to 300psi or less.

Also, I would not trust anyone, Pontiac friendly or not, who did not verify a spring fits before installing. Not by a country mile. The issue should have been caught when checking the spring pressures before sending the heads out the door too. Two strikes right there. The third would be them willing to fix it for free. I'd run the other way with the heads you have. Scary really.

[PAUL K]

Originally Posted by P@blo

A 322psi rate spring with a 110psi seat pressure will put you at 271psi open pressure at 0.50" which is perfect. I had a set of 670s done and used the 995 402psi spring and have 292psi open which is perfect. Not sure the focus on closed pressure but I would keep open pressure to 300psi or less.

Also, I would not trust anyone, Pontiac friendly or not, who did not verify a spring fits before installing. Not by a country mile. The issue should have been caught when checking the spring pressures before sending the heads out the door too. Two strikes right there. The third would be them willing to fix it for free. I'd run the other way with the heads you have. Scary really.

How do you take into account the pressures lost during the first couple heat cycles?

[P@blo]

My 995 springs were broken in prior (used) but to answer your question, I would say the pressures would drop after break in as expected. Just like the factory spring would and specs Kenth posted. The factory probably understood the initial pressure loss and springs are spec't accordingly.

I have a question for you too Paul. After initial break-in and loss of pressure, is it assumed that valve springs are stable and will last forever? Or will they wear based on cycles that decline over time with use? My thinking here is the decline after breakin might be slow but still there and wanted to get your thoghts.

[PAUL K]

Originally Posted by P@blo

My 995 springs were broken in prior (used) but to answer your question, I would say the pressures would drop after break in as expected. Just like the factory spring would and specs Kenth posted. The factory probably understood the initial pressure loss and springs are spec't accordingly.

I have a question for you too Paul. After initial break-in and loss of pressure, is it assumed that valve springs are stable and will last forever? Or will they wear based on cycles that decline over time with use? My thinking here is the decline after breakin might be slow but still there and wanted to get your thoghts.

After the initial break-in the pressures stabilize and stay like that for a long time. Sometimes we'll shim up expensive roller springs depending on the application. But for the most part once the springs start to loose pressure after the initial break-in they're replaced.

[Jimbobeast]

Originally Posted by P@blo

A 322psi rate spring with a 110psi seat pressure will put you at 271psi open pressure at 0.50" which is perfect. I had a set of 670s done and used the 995 402psi spring and have 292psi open which is perfect. Not sure the focus on closed pressure but I would keep open pressure to 300psi or less.

Also, I would not trust anyone, Pontiac friendly or not, who did not verify a spring fits before installing. Not by a country mile. The issue should have been caught when checking the spring pressures before sending the heads out the door too. Two strikes right there. The third would be them willing to fix it for free. I'd run the other way with the heads you have. Scary really.

Unfortunately Yow's Machine shop closed their doors 12 years ago and Roy, Johnny and Dave Yow have long since "shuffled off this mortal coil". That's from Hamlet. It's a play. By Shakespeare. It means they're dead. In their defense they did the machine work on 5 other GTO engines for me, including a RAIV, without problems.
I do love the looks of an Orbit Orange/Black Top '70 Judge convertible, even in the garage. Always have.

[P@blo]

Originally Posted by Jimbobeast

Unfortunately Yow's Machine shop closed their doors 12 years ago and Roy, Johnny and Dave Yow have long since "shuffled off this mortal coil". That's from Hamlet. It's a play. By Shakespeare. It means they're dead. In their defense they did the machine work on 5 other GTO engines for me, including a RAIV, without problems.
I do love the looks of an Orbit Orange/Black Top '70 Judge convertible, even in the garage. Always have.

Hamlet reminds me of grade 10 or 11. I can't remember now. Nice car there!