I have an individual 60 deg cutter that I can use to reduce the width of the 45.
SM Head Modifications on a budget
- Thread starter Earlie A
- Start date
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That’s how I had to do it with my Neway cutters. For years I couldn’t cut 70 degree angles.
ValiantRacing
Well-Known Member
You guys that would like to see these or other mods done to possibly stock or Speedmaster heads should speak up. Maybe we can make a small donation to fund some tests. It could get interesting.
Cut the new 2.055 valve job this morning. It's 70-60-45-30-15 with the 60 deg cut around 0.120" wide, the 45 degree cut around 0.055" and the 30 degree cut around 0.060". The 15 deg cut width varies with the chamber, but it's around 0.050"-0.080" in most places. The 70 deg cut is around 0.080" in most places. Throat size still at 1.823 avg, so 88.7% with the new valve size. No hand blending at all yet.
The 45 degree seat is a little wide and the 30 and 60 degree cuts may be a little wide as well. I don't mind recutting to see what change it makes.
Here are pics of the valve job, one showing the valve after lapping. Contact patch looked good to me, right at the edge of the valve and fully contacting the seat.
Flow data for the 1 angle and 30 degree back cut valves also shown below.
The 45 degree seat is a little wide and the 30 and 60 degree cuts may be a little wide as well. I don't mind recutting to see what change it makes.
Here are pics of the valve job, one showing the valve after lapping. Contact patch looked good to me, right at the edge of the valve and fully contacting the seat.
Flow data for the 1 angle and 30 degree back cut valves also shown below.
Your .300-.350 flow numbers are starting to raise pretty nice in row 5 for a simple amount of work. Great job. Thanks.
gzig5
Well-Known Member
I may have missed it, but what machine/equipment did you use to cut the seats?
Multiple angle seats are ground with stones. Radiused seats are machined with a machining center like a Serdi. Here is a diagram of a Serdi carbide cutter.
Here's a little exercise I often do with a new valve job that helps me see the relationship between the valve angles and the seat angles. If you zoom in close you can really see the venturi that is being formed. This drawing is very close to the valve job I cut this morning - as close as I can measure.
On the computer I can move the valve to any lift and look at the actual curtain area. In this case the lift is 0.050" which forms an actual opening of 0.035" wide for the air to pass through. If we know the curtain size and the diameter of the curtain, the curtain area can be calculated. Bernoulli says 350 fps is the maximum theoretical velocity (it really isn't since this is a venturi), so multiplying the curtain area by the maximum velocity gives us CFM.
This drawing also demonstrates the complexity of defining curtain area with a simple equation. As the valve lifts higher, the point on the valve and the point on the head that define the curtain width (the two points closest to each other) change. I'm sure the math can be done, but most discharge coefficient numbers are based on a curtain area estimate that is not real accurate.
In this case the math says 31.7 cfm and the flow bench says 32.5 cfm. Pretty good correlation.
@273 this is especially for you since you like the math and have talked about the fact that flow at low lifts is always about the same on any head. Since the velocity is limited to 350 fps (or slightly higher due to the venturi effect) then cfm is totally dependent on curtain area. Curtain area is a function of valve seat angle(s) and valve diameter.
On the computer I can move the valve to any lift and look at the actual curtain area. In this case the lift is 0.050" which forms an actual opening of 0.035" wide for the air to pass through. If we know the curtain size and the diameter of the curtain, the curtain area can be calculated. Bernoulli says 350 fps is the maximum theoretical velocity (it really isn't since this is a venturi), so multiplying the curtain area by the maximum velocity gives us CFM.
This drawing also demonstrates the complexity of defining curtain area with a simple equation. As the valve lifts higher, the point on the valve and the point on the head that define the curtain width (the two points closest to each other) change. I'm sure the math can be done, but most discharge coefficient numbers are based on a curtain area estimate that is not real accurate.
In this case the math says 31.7 cfm and the flow bench says 32.5 cfm. Pretty good correlation.
@273 this is especially for you since you like the math and have talked about the fact that flow at low lifts is always about the same on any head. Since the velocity is limited to 350 fps (or slightly higher due to the venturi effect) then cfm is totally dependent on curtain area. Curtain area is a function of valve seat angle(s) and valve diameter.
Peterson TCM-25 Seat & Guide machine with Goodson 3-D cutter system.
gzig5
Well-Known Member
Yup, I’m aware of the options but am curious what was used. I’ve heard that the shallower angles can be difficult with stones. I’ve got a nice Sioux valve and seat setup but haven’t played with it yet.
Do you think play with valve seat angles a little more then blend, or blend then play with the angles? What's next?
I would personally blend and get rid of any casting faults on the shorturn. Then set you pinch to .950 then flow it again. I automatically do my pinch to the tube and then I push my common wall over to my head bolt tube but this exercise is to see what someone could gain easily and on a budget to possibly see 500 plus horsepower. Most guys aren’t going to go over a .570 lift cam so those numbers you gained from .250 up are golden. You can check airspeed right??? After those mods I would check your speed at the pinch and short turn.
I guesstimated what a larger 2.14" valve's average curtain diameter would be and plugged it in but it only had a slight changed in the square foot curtain area was 0.00157 (from what I guesstimated) vs 2.055" 0.00151.
Had a pretty good feeling this was why but now I get it for sure even though a 2.055" vs 2.14" seems like a big change to us, at low lifts the curtain area has only slightly changed.
I should have mentioned this but I’m sure you know. The wall past the pushrod pinch continues to slant in. Make sure you have at least .950 well past the pinch.
I'm embarrassed to say I have never noticed the slight slope on the wall. I have noticed the floor and roof converging, but that's easy to see. Thanks.
Without drawing it I wouldn't know for sure, but with some quick math I believe you are thinking correctly. I'll try to draw a few more valve and seat combinations some time. It helps me see things better.
Now think about this. It is common for the discharge coefficient (efficiency of the venturi formed by the valve and seat) to increase from 0.050" to about 0.150" lift, then rapidly decrease after that. The decrease is easily explained by the loss of a good venturi shape as the valve opens, and by the rest of the port starting to affect flow. But why the increase from 0.050" to 0.150" (or maybe 0.200")?
This increase in Cd (or DC as sometimes noted) does mean that the average velocity through the venturi at the valve will exceed 350 fps when the Cd is highest.
Here's some before and after pictures of the bowl blend. This took about 2 minutes using a 60 grit 1" diameter cartridge roll. In the before pictures, the black ring is the 45 degree seat, the red is the 60 degree bottom cut and the purple lines are the blend zone which includes the 70 degree bottom cut. The 2 blue rings perpendicular to the purple lines are the ridges to be removed. A couple of casting lines down the sides of the bowl were also smoothed out.
Now on to the pushrod pinch @pittsburghracer?
Newbomb Turk
Well-Known Member
Mostly A
Not the craziest of gains but if you buying bare heads, and planned on getting a valve job anyways this mod will get you what like 20 hp ? On a decent engine, what extra cost would be over buying 2.02" and getting a decent VJ ?
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