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head mod questions

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Ive been "lurking" this board for a few weeks now and have learned a lot in that time, but now I have some unanswered questions.

Im trying to get a better grasp on what 4 stroke head mods consist of. first off, when a head is modified when or why are the valve seats cut ? does a different angle produce different power ? I am wondering because I have heard a few shops talk about how their head mods consist of the valve seats being cut on a SERDI valve cutting machine, as if that alone is amazing. Pro Circuit and Eric Gorr specificly and I question anything PC does.

correct me if Im wrong, but aren't the valve seats removeable and dont they sit within the head a little bit ? I know these questions seem elementary but I just want to get my facts straight.

Next, valve springs, how are aftermarket springs different from stock ? Are they just a heavier rate ? are they dual rate ? can they be longer ? and why are some kits dual springs ?

Can you run larger radius valves in a stock head ? I know using a larger exhaust valve would remove exhaust gas faster, but do you have to make anything else larger in order to use one ?

Finally, WHY is stainless better then Ti valves ? Alot of race cars use Ti valves with hollow stems and dont seem to have a problem (maybe they change them every race though? :thumbsup:)

Any help answering these questions would be greatly appreciated. :devil:

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proper valve seat angles leading up to the valve can produce changes in the the amount of air flowing into the head .increased valve diameters alow a head porter to get a better throat to valve dia. relationship for a better transition from the port past the valve.most after market springs offer increased forces to control the valve at higher rpms or for a more violent lobe profile they also offer more movement before coilbind so that higher lift cams can be used this also decreses the amount of coils that a spring can have and reduces the life of the spring and requires that the springs are made from higher quality wire than the oem part.very surious race teams replace the titanium valves every race for that mater there isnt much of any thing that a stock car team will reuse after a 500 mile race . except the engine block

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