| Going to a 1mm oversized valve is going to give you gains. With the stock valve we are at 30% valve area to bore size. That is a very low figure. For a DOHC engine the sweet spot is percentaged at 54%-55%. IDRL uses a massive 64% valve area to their bore size. Thats considerable considering the airflow you are trying to utilize. With a 1mm oversized valve we go from a 30% from a stock valve area to a 32% to the 1mm oversized varient. A .5mm valve came in at 30.7%. But think about it for a second. at .5mm you are only increasing valve area by .010" per side of the valve. Take a dial caliper and measure .010". Its a very small increment. So total over a whole valve you've increased the valve only .020" seems a lot when looking at numbers but in physical area its very small in relation to physical size. Go to a 1mm valve you are enlarging the valve .020" per side (radius) which puts your diameter at .040" larger. .020" compared to .010" is a big step when you consider doubling the figure and showing it over a sized area. The valve itself comes no where near interfering with the cylinder bores. The lift of the cams we use (majority of users here run an R5 cam) is .395" lift. This puts the valve no where past the deck of the head and certainly has more than generous P to V figures. Obviously this is statement is made being that your timing is set correctly etc etc. The biggest thing is opening the valve curtain to enable the valve area to be effectively and efficiently utilized. This is the big thing that should always be done. By enabling the use of the larger valve curtain and valve aera you remove the restriction and provide airflow the full area to flow through and to the cylinder. Percentage wise we can go even bigger in valve area and size. Based on this alone you could run up to a 1.5-2mm valve and still be well under the sweet spot (54-55%). The situation then would be overlap which wouldn't be too much of a hassle considering most everyone now a days is switching to adjustable cam gears so phasing the cams will help in that area. Overall, 1mm oversized valve will give excellent gains over the RPM range. Just remember, bigger ports doesn't mean better so be sure to proportion your intake ports accordingly based on valve area and throw dimensions. You can kill airspeed in a heart beat by enlarging the throat too big which creates a low pressure area and hurt airflow. Valve angles on the valve job as well are very key too. Based on port angle and entry, looking at the floor and roof lines and path certain angles on the valve job will increase airspeed and airflow so don't think cutting the factory angles is the be all for the valve job. You'd be amazed at how a valve job can improve an engines ability to continue further in the rev band in making power. Hope that helps.
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