I'm looking to upgrade my 40 year old valve springs. I haven't found what stock springs were rated for. Removing the governor but hoping for springs that will keep me in the mid to upper 4000 rpm range. Will 16 pound after market springs do that or am I better just going with stock Raptor springs? Are intake and exhaust springs the same? I see different Pound springs have different heights.
valve spring poundage of 5 HP 1980 flathead
- Thread starter xtratoy
- Start date
I got the motor disassembled. The exhaust valve spring is 1.385" long and the intake is 1.165" long. Both springs are made from .090" wire. If I went with 2 exhaust springs what would be the max rpm with the governor removed? Rest of the motor stock except I will have to add a small mikuni type carb because I found out tonight the gas tank was so corroded it rusted a hole through the part inside the tank that acted like the carburetor bowl.
flattop1
Dawg 89
It should easily make the 4000 rpm . I doubt the springs are going to limit your rpm , if that's a concern . The dyno 1.385 or 1.400 springs are good choices .
What its max rpm is when the rod let's go , I don't know . Ran very few stock rods then switched too billet . My best guess would be around 6200 it's going to be short lived long term .
They raced it for quite a while before the billet rod was legal . It might rpm more .
What its max rpm is when the rod let's go , I don't know . Ran very few stock rods then switched too billet . My best guess would be around 6200 it's going to be short lived long term .
They raced it for quite a while before the billet rod was legal . It might rpm more .
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The old style with the stamped steel dipper held 6000 easy.
Pushing 6200 caused the dipper to become a 2 piece item, followed shortly by the rod seizing to the crankshaft.
Not sure what the rod with the built in dipper would handle.