Stock Springs and retainers
10-27-2013, 03:28 PM
#1
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Stock Springs and retainers
How much boost and power can the stock Valve Springs & Retainers hold with H11 head studs.. trying to maybe make 700hp on a 6266 on pfabs log
10-27-2013, 05:48 PM
#2
Boost and power are rather irrelevant, what does matter is rpm. If your planning on keeping the factory rev limit (9k ap1 or ap2) then leave them alone. If you have an ap1 its not a bad idea to replace the retainers and keepers with the ap2 since they are stouter and better withstand the abuse of a mechanical over rev.
10-27-2013, 05:54 PM
#3
If you have an AP2, dont worry about it. If you have an ap1, go ahead and at least replace the intake side. I replaced mine in my N/A s2k (220whp) with 150k miles that had never been over revved (rev limit set to 9.3k, and never misshifted) and this is what I found
10-27-2013, 06:01 PM
#4
I think 9300 rpm would be considered an over rev when factory is 8900 
Clearly not a lot of extra headroom on the ap1 valvetrain
If I recall, "realstreet" found the factory ap2 valvetrain to hold together up to 10,400rpm before the valves began to float. I don't know how long that was sustainable, but its just an example of the differences in factory equipment. Many have reported bending valves on the ap2 in a mechanical over rev situation, rather then cracking retainers and dropping a valve. Bending a valve sucks, but its a hell of a lot better then dropping one. If the factory ap2 equipment can achieve that, then I really see no reason to upgrade it to anything else other then for the sake of lighter weight, for a little extra power.
I have a built/sleeved bottom end, and I just opted to leave the ap2 head alone. Didn't seem worthwhile to me to throw any extra money in that area of the build.
Clearly not a lot of extra headroom on the ap1 valvetrain
If I recall, "realstreet" found the factory ap2 valvetrain to hold together up to 10,400rpm before the valves began to float. I don't know how long that was sustainable, but its just an example of the differences in factory equipment. Many have reported bending valves on the ap2 in a mechanical over rev situation, rather then cracking retainers and dropping a valve. Bending a valve sucks, but its a hell of a lot better then dropping one. If the factory ap2 equipment can achieve that, then I really see no reason to upgrade it to anything else other then for the sake of lighter weight, for a little extra power.
I have a built/sleeved bottom end, and I just opted to leave the ap2 head alone. Didn't seem worthwhile to me to throw any extra money in that area of the build.
10-28-2013, 07:54 AM
#6
Banned
boost does make a difference. Each intake valve has about 2sq in, if your valve spring is 60 on the seat, and you put 15psi on the back of the valve, thats 30ish lbs of force trying to push the valve open. You'll need to add that to your spring to get the same force holding the valve shut.
new ap1 springs are about 60lbs on the seat, at 100k miles they are down to around 55lbs.
If you miss a gear and overrev the motor with stock stuff you probably bent something. Put good springs/retainers in it and you didnt bend anything.
Once you get up over 900ish hp the exhaust valve stems are the weak point, they tend to kink with high cylinder pressure trying to snap the exhaust valve shut.
new ap1 springs are about 60lbs on the seat, at 100k miles they are down to around 55lbs.
If you miss a gear and overrev the motor with stock stuff you probably bent something. Put good springs/retainers in it and you didnt bend anything.
Once you get up over 900ish hp the exhaust valve stems are the weak point, they tend to kink with high cylinder pressure trying to snap the exhaust valve shut.
