air flow ?

[rod]

I have this ? if you had an intake port which flowed 200cfm at .500" lift, is there any good reason to lift the valve to.575"?
thanks
Rod

[Stan Weiss]

Originally Posted by rod

I have this ? if you had an intake port which flowed 200cfm at .500" lift, is there any good reason to lift the valve to.575"?
thanks
Rod

What lift do you plan to use?


What does the port flow @ .550" and .600" lift?


Stan

[Mike Taylor 3601]

with 575 lift you get to use 500 2X...basically take advantage of the peak by keeping valve open .500 a little longer

[Stan Weiss]

Ok lets map the head flow onto the cam lift curve.Flow @ .500" 200, @ .550" 200.5 @ .600 210


The cam is a Lunati that has .507" lift with 1.5:1 rocker arms (green line) and .541 lift with 1.6:1 rocker arms {blue line) and .575" lift with 1.7: rocker arms (magenta line)


Stan


PS - Let me add a little more explanation. I have the ICL set at 110. If the engine is a 350 ci sbc (4 x 3.48 x 5.7) the peak piston velocity will be @ 74.3 ATDC which is also point of peak piston flow demand. Now as RPM goes up there will be a small delay seen at the intake. But you can see how as lift has increased the flow at peak demand has also.

[ss chief]

Yes, lots of good reasons.

[Stan Weiss]

Has the "OP" gone? Still would like to know what the head flows @ .550" and .600". While we have all talked about reasons why you would want to have greater than .500" valve lift. There are reasons based on flow @ .550" and .600" why one would not want valve lift greater than .500".

Stan

[Stan Weiss]

While only a couple of us have posted in this thread I take it there is some interested in this topic based on the number of views. Over on Speed Talk there is a thread where we are talking about some old Cleveland Pro Stock heads. I had graphed 2 them. As can be seen one of the heads would not work well with lifting the valve most past max flow.


Stan

[Stan Weiss]

A number of you have flow benches. I didn't know what manufacture or model. The pages below are from Super Flow. These numbers are calculated for the above plot of head flow on cam lift. Just another way to look at it.


Max Total CFM Sq In Area = Valve Duration @ 0.000 * 146 (Only good if head flow is @ 28" of Water)
Max Total CFM Sq In Area = 42632.00


Rocker Arm Ratio = 1.500
Total CFM Sq In Throat Area = 13624.13
Total CFM Sq In Net Valve Area (Valve Area - Valve Stem Area) = 11213.23
Total CFM Sq In Valve Area = 10892.74

Rocker Arm Ratio = 1.600
Total CFM Sq In Throat Area = 13985.12
Total CFM Sq In Net Valve Area (Valve Area - Valve Stem Area) = 11510.34
Total CFM Sq In Valve Area = 11181.36

Rocker Arm Ratio = 1.700
Total CFM Sq In Throat Area = 14294.91
Total CFM Sq In Net Valve Area (Valve Area - Valve Stem Area) = 11765.31
Total CFM Sq In Valve Area = 11429.05


Stan

[rod]

OK, I didnt think this would be so complicated.
these are actual figures for my SBC 292 [misnamed] turbo heads.
28" H2O @ 70 degrees and at about 575' elevation and almost no humidity.
Intake exhaust

.200 151 136
.300 210 181
.400 246 210
.500 265 223
.510 267 223
no increase, on either side, after.510 lift.


so I understand, that some additional lift could be used, above .510, to make up whatever type of loss. even some extra amount of duration, for the same reason.
however, on my desk top dyno, there is no increase in power output, past about 525" lift.
it appease, on paper at least, that you are just wearing out springs and guides, with additional lift. maybe in the real world, there might be some benefit.



so, new thoughts.
thanks all
Rod in AZ

[Stan Weiss]

Originally Posted by rod

OK, I didnt think this would be so complicated.
these are actual figures for my SBC 292 [misnamed] turbo heads.
28" H2O @ 70 degrees and at about 575' elevation and almost no humidity.
Intake exhaust

.200 151 136
.300 210 181
.400 246 210
.500 265 223
.510 267 223
no increase, on either side, after.510 lift.


so I understand, that some additional lift could be used, above .510, to make up whatever type of loss. even some extra amount of duration, for the same reason.
however, on my desk top dyno, there is no increase in power output, past about 525" lift.
it appease, on paper at least, that you are just wearing out springs and guides, with additional lift. maybe in the real world, there might be some benefit.



so, new thoughts.
thanks all
Rod in AZ

Rod,
While there is no increase, on either side, after.510 lift. The question still stands what is the flow @ .550" and .600" If it basically leveled off is one thing If it drops and or goes turbulent is another thing. In your desk top dyno program have you entered any flow numbers for .550" or .600"?


Stan


PS Let ask what is your combination? Is it possible that your desk top dyno program is not showing and increase in HP with more lift because you already have the needed flow?