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Author Topic:   cast heads
I-B-RACIN
Member
posted November 22, 2004 04:18 PM
What does a person all have to do to a set of heads to make them good. Dumb ? but I mean like valve guides,seats valve job is 3 angle enough ? most performance reman heads only have a 3 but is a 5 or seven angle worth the effort on a 2 barrel 9,5 to 1 motor..


beachracing
Member
posted November 22, 2004 09:34 PM
If you are stuck with using stock production heads, a good valve job(3 angle will be fine), opening the short side radius behind the intake valve. Run 2.02/1.60 valves, and unshroud the intake side in the chambers. The more you port,the bigger the intake runner, but you have to be careful not to run in to water passages, etc. Open the exhaust port, especially in long track situations. If at all possible use undercut valves, they will help with flow. If you use .100 length valves, pushrods should be same,etc. Get some one to shim, and set your spring pressures on each valve, to little pressure can be bad. I have to run a 2 barrel application. Now if rules allow for aftermarket, then spend your money on those, because when you finish all the work on a set of production heads, the cost will have been enough for a set of aftermarket peices.


engineman
Member
posted November 23, 2004 03:21 AM
quote:
Originally posted by I-B-RACIN:
What does a person all have to do to a set of heads to make them good. Dumb ? but I mean like valve guides,seats valve job is 3 angle enough ? most performance reman heads only have a 3 but is a 5 or seven angle worth the effort on a 2 barrel 9,5 to 1 motor..


certainly not a dumb question, it's a really good question. a 2 barrel engine needs all the help it can get! That being said...you arenít going to like the answer.

First of all, without flow testing any head, it is hard to give a hard core answer to what angles to use. we all know that the "good old 3-angle valve job" works, a 30deg top, and a 60deg bottom on a 45 deg seat, and a back cut valve almost always improves airflow.
However. Including another couple of angles on the top & bottom, or changing the seat angle itself (like to a 30 or 60) can throw things off. Depending on all of the variables involved like intake or exhaust seat, valve lift, valve size, valve depth in head, short side radius, port bias, seat width, approach to the back of the intake valve, approach to the face of the exhaust valve, ect...ect...ect... you wont know without flow testing.

The point is this....unless you are prepared to spend a bunch of money to get the heads flow tested only to get a couple of cfm out of them....stick with the tried and true good ole' 3 angle valve job.

I will say this, cutting the "throat" with a 78 to 80deg cut, and toping off the intake 30 with a 15 deg cut ALMOST always helps a little too, but leave at least .060 of the 60deg cut on the intake side.

another thing that is "tried and true" is unshrouding the intake valve by chamber cutting the intake side of the chamber, this almost always improves airflow when a bigger valve is installed....in fact you can loose airflow if you install a bigger valve and donít cut the chambers to unschroud the valve.

But I'm telling you if cost is a factor (and it always is) donít get carried away with strange valve seat angles.

------------------
Mark's Racing Engines

(903)883-0196

www.northtexasracing.com

engineman@northtexasracing.com


I-B-RACIN
Member
posted November 23, 2004 03:35 PM
thanks for your thoughts I am stuck using cast production head and as much as I would like to no porting, releif cuts or any work to the cumbution chamber or machineing more than 1/4 inch below seats but I can run any valve I choose so undercut is a must..
THANKS AGAIN