Don Terrill’s Speed-Talk

Hey guys
Can someone give me a formula to calculate actual curtain area at different lifts, taking into account seat angle & width ?
Thanks.

Greg,
check your emails.
shawn

shawn wrote:Greg,
check your emails.
shawn

Thanks Shawn - that's a handy spreadsheet, but it calcs curtain area using valve circumference x lift.
I was hoping someone has a way of calculating the actual area available with a 45 degree seat. i.e. at .100" valve lift you get a lot less than .100" of opening at the seat.

Maybe I have to measure it ?

I'd like the same thing. It needs to calculate it in a dynamic value... I'd like the total curtain area, based on the lift/duration events.

If anyone knows of a program that could do this I'd like to know.

-What I did was pretty simple.
-I used my flowbench valve opening tool ands open the valve in .100" increments and then used a pair of dial calipers or a set of pin gages to measure the actual opening and multiplied that by whatever circumference it is that you feel is represents the curtain.
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-An example of a 45 degree seat was:
-.100" = .073" (open gap).
-.200" = .145"
-.300" = .235"
-.400" = .320"
-.500" = .422"
-.600" = .520"
-.700" = .619"
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-I double checked this several times and this is what I got, even tho it doesn't add up right and it wouldn't be what you would calculate if you were an engineeer, it is what I actually measured.
-I'm not saying that it's perfect but when you check a 30 degree or a 55 degree seat you can get the general idea real quick.

Thanks a heap Bill.
That's exactly what I was looking for.

If you will post the dimensions of your valve job, I can probably make a program to calculate it. I think I would need all the angles and some diameters.

If you are considering different valve and seat angles I might be able to make those inputs to the calculation but I will need some numbers to start with.

Try this ...

Curtain Area = Lift * PI * ((Valve Diameter)-((Seat Width)*2*COSINE(SeatAngle)))

If using in Excel the angle needs to be converted to radians by ...
radians = (degrees * PI()/180)

This figures the distance the inner edge of the seat is from the outer valve circumference and calculates the window from that diameter. Should be correct if the seat goes to the edge of the valve and is the same width as the valve face.

An example is 2.15 valve with 55 deg seat .050" wide at .500" lift

COSINE(55 degrees) = .5735764
Curtain Area = .500 * 3.14159 * (2.15-(.050 * 2 * .5735764))
= 3.287115

Watch out for those parenthesis, they will get you every time.

Rick

Nice job!

Thanks Rick.

HHmmmm I'm looking for something that will account for the dynamic area created by the entire valve event.... To me it doesn't matter about the angles and such as I'm looking to have relative information based on different cam events and rocker ratios and such....

ChrisU wrote:HHmmmm I'm looking for something that will account for the dynamic area created by the entire valve event.... To me it doesn't matter about the angles and such as I'm looking to have relative information based on different cam events and rocker ratios and such....

Chris
Have you seen Valve Pro by Audie Technology ? It might do what you are chasing.
http://www.audietech.com

Thanks Rick!

I've been using the Performance Trends software, .. Port flow analyzer, ..
does all these calcs and more, .. ..

Port mach numbers, . . average velocities, .. curtian area velocities, ..
piston speeds, .. etc. It'll map the entire valve event in the pro version.

http://www.performancetrends.com/pfa.htm

Curtis

ozrace wrote:... but it calcs curtain area using valve circumference x lift.
I was hoping someone has a way of calculating the actual area available with a 45 degree seat. i.e. at .100" valve lift you get a lot less than .100" of opening at the seat.

bill jones wrote:-What I did was pretty simple.
-I used my flowbench valve opening tool ands open the valve in .100" increments and then used a pair of dial calipers or a set of pin gages to measure the actual opening and multiplied that by whatever circumference it is that you feel is represents the curtain.
-------------------------------------------
-I double checked this several times and this is what I got, even tho it doesn't add up right and it wouldn't be what you would calculate if you were an engineeer, it is what I actually measured.

Are you not making this more complicated than necessary? Thus, I am questioning the logic used.

I'd look at it as starting with an angled line, that being the seat/valve angle. The actual angle would not be important/critical here. Now extend that line to generate a two dimensional object, IOW, a parallelogram. As the intent is to obtain the 'curtain' area itself (which is not cubic, but 'surface' in nature), the length of that parallelogram, wherever you measure (as long as you are parallel to lift/valve stem axis, will be consistant. So, according to my thinking, the valve/seat angle would not be a factor at all. Unless, you were after an actual area, and not curtain figure. But in that case, the area would be the same as a rectangle. Which is, the parallelogram with it's angled sides straightened (90º). Are we on same page?

Gary