Valve spring ?
 

What problems can happen with valve springs that has lost 100 pounds of seat presure? car was going low tens now hi tens lost 5 mph and 5 tenths. anything else?

You'll get valve float which would rob some power, not to mention the possibility that valve and piston may collide from the valve not retracting fast enough.

Here's the specs for spring pressure from the Ford manual:

Compression Pressure (Lb @ Length)
Intake 74-82 @ 1.78 to 211-230 @ 1.33
Exhaust 77-85@1.60 to 200-226 (doesn't say at what length, so maybe fully compressed? Non HO specifies 192-210 @ 1.05, maybe HO is at same length)

Free Length
Intake 2.02
Exhaust 1.79

Ah, I see that it says service limit is 10% pressure loss @ length. 100 lbs is close to 50% at short length.

Hope this helps,

Rich D.

weak valve springs
 

Thanks for the reply have you ever heard of weak springs killing your 60 ft.? Lets say you have cam that needs 330 seat pressure and it only has 180 but the car goes a 133 in the 1/4. then backs up to 128 after 6 passes. What do you think the perf. would be like with the right spring pressure? Just curious becuse i got screwed on a set of weak *** springs.

my slipping clutch is hurting my 60's....