Working the Angles


If you have a drill press, you can cut some angles in your stock valves. Right in the privacy of your own garage!

While this is far from the prefered method of cutting angles in your valves, it is an easy way to experiment with angles when you are flow testing. Or, if you are one of those "if it runs, race it" kind of guys like I am, it is a good budget method of getting a little extra flow out of those old stock valves. Watch as I put my $89.00 drill press, "Mr. Buzzy", into action to cut my favorite angles into an E7TE intake valve.

Commonly known as backcuts, or backcutting valves, the object of cutting more angles into a valve is to form a more curved radius from the valve face to valve seat angle while also creating a thinner valve head. Backcut valves will usually increase low lift flow, and often increase mid and high lift flow too. But discretion must be used because backcuts can also reduce mid and high lift flow in some cases.

Please keep in mind that this is a good way to wreck an otherwise perfectly good valve. This procedure is mostly for experimenting with angles during flow testing, and for improving performance on old or stock valves. Do not attempt to modify race or aftermarket valves. The chances of your improving on them are slim to none. And your chances of ruining them run from good to gauranteed.

When working with a drill press, please follow the saftey procedures in your drill press manual, or warnings printed on the drill press. Wear your saftey googles and appropriate protective clothing. Do not wear loose or baggy clothing, or a neck tie while operating a drill press. Bowties are acceptable, but not recommended.

Do not attempt to dress or cut seating surfaces with your drill press. A drill press doesn't have anywhere near the precision to do that type of work.

The photo of the Ford E7TE intake valve, above, shows the 19 degree backcut that is cast into the face of the valve. The perimeter of this backcut can be seen by the light thin line just inside the 45 degree seat angle.

The 19 degree backcut is further illustrated in the center drawing above.

I have found that cutting a second angle, at 25 degrees, between the as-cast 19 degree backcut and the seat, and recutting the 19 degree as-cast backcut as shown on the drawing at the left, works pretty well on the E7TE intake port.

To prepare your drill press to cut valve angles, invert the drill press table so that the working surface is upside down.

Place a straight piece of rod or tubing into the chuck and set your table to the proper angles using an adjustable protractor. The rod is your reference. I have to use "line-of-sight" with this protractor, but it still works well.

Above, I have set the table for a 25 degree back cut, so the protractor is set at 65 degrees because the table needs to be 65 degrees in relation to the rod, for a 25 degree backcut. (90 degrees minus your desired angle = 65 degrees). Once you get your angle, tighten the table angle clamp.

Once you have your table set at the proper angle, chuck the valve, hand tight (Make sure your chuck does not scratch the valve stem), and bring the table down close to the face of the valve . Place a C clamp under the table to hold the height. You don't want to tighten the built-in table hieght clamp. You want the C clamp to hold the table height, because you want the table to be able to swing toward and away from the valve.

Apply some cutting oil to the valve face (I didn't use any here for clarity in the photos). Set the drill press for low speed and start the drill. Holding a mill file against the table, I carefully swing the table toward the valve until the file is just touching the valve face. A mill file has blades that run the full width of the file. A rasp has teeth. You must use a mill file, not a rasp.

You have to be very patient and use very little pressure. You don't want the valve to deflect, and the valve will have a tendancy to grab the file and pull the file and table into the valve. So use both hands, very little pressure, and take your time. Viewed from above, make sure the file cutting teeth are in the proper direction for cutting. Remember, the valve will have a tendancy to grab the file and pull everything toward it. Try this on a throw away valve first.

You want to watch your angle widths. I have found that the 25 degree back cut should not exceed .040" width. And watch that you don't cut into the valve seating area.

My favorite angles for the E7TE. The as-cast 19 degree angle recut to sharpen the edges with a .035" wide 25 degree cut between it and the seat.

Too much of a good thing?
While this 30 degree, .070" wide backcut in this GT40P intake valve helped the low lift numbers, it was a disaster at .5" lift. The average flow with this valve was less than stock. If you don't have a flow device to test your angles, or known examples to work by, keep your backcuts narrow.

Let's Review:

We wear googles and appropriate protective clothing while operating the drill.

We do not attempt to modify good, race or aftermarket valves.

We hand tighten the drill chuck on the valve. We use low speed and cutting oil. We work very slowly so that the valve doesn't deflect or grab the file.

We watch our angle widths so that they do not become too wide, or cut into the seating surface.

We do not try to cut seat surfaces with "Mr Buzzy". Have your machinest do that.


You will find many stock valves are not always quite round.

Some valves are very hard, and other quite soft. The soft ones tend to grab the file the most.

The valve will dull the file where it is cutting the valve very quickly. You have to keep moving the file to other cutting areas.

Do not be tempted to polish off the cast surface on the face of the valve. That ugly cast surface flows quite well as-is.

Do not be tempted to round off, or blend the edges of the angles. I have found that sharp, defined edges on the valve angles flow much better than dull, blended or rounded edges.

While the angles used above work well for my ported E7TE ports, they may not work well on other size valves or port configurations. For instance, these angles do not work well on GT40P intake valves.

More good stuff!