Originally posted by monza2206: How important is the seat pressure and rate on valve springs. What would be the results of having way more than needed in a mechanical roller setup?
Originally posted by monza2206: How important is the seat pressure and rate on valve springs. What would be the results of having way more than needed in a mechanical roller setup?
My opinion is that more than needed can cause your push rods to pole vault the valve but not always. CAN not will. Most times it is only more wear and tear on rockers and lifters but doesn't show up as a problem. Too far from coil bind is what I believe to cause surge more often than anything. Not enough seat pressure can cause the valve to bounce off the seat and not enough rate can allow loft over the nose.
Non of this is absolute because the lobe has a great deal to do with it also. JMO
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Originally posted by monza2206: How important is the seat pressure and rate on valve springs. What would be the results of having way more than needed in a mechanical roller setup?
An example of what you're speaking of OP, way too much seat pressure and rate, would be if you set these heads on a sbc with say hypothetically a camshaft around 750 lift, when this spring is set up around 450 on the seat and over 1400 open in correspondence with a camshaft approaching 1" of lift .075 to coil bind.
Hypothetically, if you then set this spring up 300 on the seat in the same hypothetical environment, VS surge would intensify, fundamentally speaking.
Originally posted by monza2206: The reason for asking is i have a engine that seems lazy,slow revving and slow to gain rpm.
Monza, does your engine have way too much spring for the cam? Or is it maybe in the "not quite enough spring" category? By far the most common cause I have seen of the symptoms you describe, are timing issues: (Late Ignition mostly, followed by incorrect valve/cam timing). Also, too much cam, or heads/ports that are too big for a given combination, (Not enough compression ratio &/or wrong head for the chosen cam). Carb sizing, (too big for the engine displacement), and wrong jetting/air-fuel mixture can easily cause laziness as well. Plenty of other possibilities, if you want to provide some details on car and engine it may help others to point you in the right direction.
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posted January 02, 2020 10:36 AM Hide Post quote: Originally posted by monza2206: The reason for asking is i have a engine that seems lazy,slow revving and slow to gain rpm.
Monza, does your engine have way too much spring for the cam? Or is it maybe in the "not quite enough spring" category? By far the most common cause I have seen of the symptoms you describe, are timing issues: (Late Ignition mostly, followed by incorrect valve/cam timing). Also, too much cam, or heads/ports that are too big for a given combination, (Not enough compression ratio &/or wrong head for the chosen cam). Carb sizing, (too big for the engine displacement), and wrong jetting/air-fuel mixture can easily cause laziness as well. Plenty of other possibilities, if you want to provide some details on car and engine it may help others to point you in the right direction.
and gear and convertor,i would verify cam timing first
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Posts: 1468 | Location: texas | Registered: February 17, 2006
Valve seat condition will deteriorate with too low of seat pressure. How much is too much? I assembled a 451 BAE hemi with pac1352 springs with 640 on the seat. May seem drastic but the titanium springs that were on it let .100 deep lash caps go loose. That's alot of ill timed terrible play to let that happen. PAC and Manley recommend .xxx from coil bind. Without this the spring wanders and waves. Valvetrain weight, including push rods and lobe profile all have an affect on the minimum. The seats will tell most of the story. Good luck, BW
Posts: 194 | Location: Rock><Hard Place | Registered: February 20, 2010
Originally posted by monza2206: The reason for asking is i have a engine that seems lazy,slow revving and slow to gain rpm.
In addition to the things others have mentioned, a converter that is too tight, possibly with wrong head/cam, etc will make the combination a dog and not want to gain rpm till you get the rpm high enough.
