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cam and heads

 
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johnnyjaws
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Joined: 06 Jun 2013
Posts: 1
Location: usa
140.26 points



PostPosted: Thu Jun 06, 2013 10:36 am    Post subject: cam and heads Reply with quote

could some one tell me what heads to get for a comp cams xe262h cam it has a spring pressure of 370lbs eldebrock heads like the e street head only has 320lbs same is the e 2120 head maybe the performer don't know the spring pressure on that head don't say
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Big Dave
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Joined: 04 Dec 2005
Posts: 2644
Location: Tampa Florida
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PostPosted: Thu Jun 06, 2013 12:04 pm    Post subject: Reply with quote

You buy heads to meet your motors expected usage. If it is going to be a no holes bared race engine you optimize for high end use by choosing a high flow rate with an equally high port velocity.

Flow rate is advertised everywhere, but beware of the size of fixture they tested the flow rate with (unless your engine bore is the same size or larger than the fixture size). The head manufactures rarely tell you the velocity of the their heads ports. But professional head porters talk to each other on the web, and thanks to Goggle, you can listen in as they discus the flow rates of various heads; and what they did to improve above the as cast figures.

If you are building a motor for the street then you want smaller ports that build a high port velocity at lower RPMs such as the e-Tec heads from Edelbrock. You do not want a mammoth port that is going to be lazy at your driving RPM. Nor do you want that becomes the bottle neck in getting air into the motor. You are looking for the "Goldilocks of heads" not too big and not too small.

Finally you buy valve springs to match the cams requirements. Best bet is to buy a cam kit with cam, lifters and the premium springs all in one kit. You want the premium springs to be safe in case you over rev the motor (it is cheap insurance). If the springs they recommend do not fit your head you (or your machinist) cut the spring pockets to fit the springs only if the head manufacture says there is enough metal to do so (you don't want to hit water). It is best to buy the same outside diameter valve spring that you have now, to avoid the headaches of a larger diameter spring.

Just be aware that a larger diameter spring has more spring mass to control; which requires a bigger, stronger spring to account for the added spring mass. Also a bigger spring means there is less room for the head bolts and the washers under the head bolts to fit without touching a spring (the after market sells head bolt washers with circular notches in them to clear a hardened spring seat that has to be under all valve springs. So buy a bigger valve spring seat as well when you buy your larger springs. Larger stiffer springs can also overwhelm a 5/16th inch diameter push rod so if you buy the bigger 3/8th inch diameter chromemoly push rod you have to also buy the push rod guide plates to fit the bigger pushrod or machine the heads if they use self guided rocker arms.

I compliment you on your cam choice and I think the E-Tec head with a set of matching Beehive valve springs from Comp will be a perfect street motor that should net you one horse per cubic inch, with good engine vacuum and throttle response with a 650 cfm carb.

Big Dave
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