how much NET valve lift to employ ?

[swampbuggy]

S.B.C. Gen. 1 Max. effort deal. , 4.185" X 3.375" = 371 C.I. , we will flow the heads WITH intake and carb. in place. These parts should flow 400 cfm at appx. .800 lift. Now lets just say the test shows the max. flow is actually (factually) at .800" lift. My question is to you folks who have actually TESTED and KNOW, how much extra net lift do you add to the peak flow lift number Please answer honestly from your personal way of doing this, because it will be interesting to see any differences from one engine builder to another. Thanks Mark H. Oh BTW i certainly do not want to employ any MORE lift than i need to, and also this engine SHOULD make peak H.P. in the area of 8500 to 9000 R.P.M. if that makes any difference. Mark H.

[Warp Speed]

S.B.C. Gen. 1 Max. effort deal. , 4.185" X 3.375" = 371 C.I. , we will flow the heads WITH intake and carb. in place. These parts should flow 400 cfm at appx. .800 lift. Now lets just say the test shows the max. flow is actually (factually) at .800" lift. My question is to you folks who have actually TESTED and KNOW, how much extra net lift do you add to the peak flow lift number Please answer honestly from your personal way of doing this, because it will be interesting to see any differences from one engine builder to another. Thanks Mark H. Oh BTW i certainly do not want to employ any MORE lift than i need to, and also this engine SHOULD make peak H.P. in the area of 8500 to 9000 R.P.M. if that makes any difference. Mark H.

As much as you can afford without further compromising the open and closing events.

[andyf]

It may not matter, just depends on the combination. I've had a fair amount of experience with engines that do not respond to additional valve lift. If you engine doesn't need more lift then you're just wasting energy.

[NormS]

I think it is the mid lift flows that are more important to cylinder filling, because those are encountered twice in the intake cycle. I would look at the flows at the higher valve lifts to see at what lift the flow is starting to taper off. If the flow is barely bigger at .750" compared to .700" flow, and .800" flow is barely bigger than .750" flow, I would say max valve lift of around .750" would work well. Instead, I suggest concentrating on maximizing mid lift flows, say from .300"-.600" lift.
I had an engine some time ago that had really good mid lift flow numbers, and disappointing high lift flow. It was cammed taking into account where the flow tapered off at the high lifts, and it ran really well. Even though your intake system combo has the highest flow at .800" lift, that doesn't necessarily mean that the mixture velocity into the cylinder at that lift is going to be beneficial to cylinder filling.

[Stan Weiss]

This graph shows the cylinder head flow mapped onto the cam. The upper set of lines is is using 2.0:1 rocker arm ratio and the bottom set of lines is using 1.6:1 rocker arm ratio.

Stan

ab-cfm-2-1-6rar.gif

[user-30257]

Who cares what the heads flow. Max effort is max lift you can attain.FACT

[MadBill]

I'm with Warp. re targeting 'affordable' intake lift, since diminishing returns and escalating build and maintenance costs loom when (depending on head specs and application) it gets much over 0.800", especially for a single carb, modest displacement SBC.
With correct inputs I've found Dynomation to be an accurate predictor of engine characteristics and with a port flow that pretty much flattens out~ 0.800", it shows ever-smaller gains as the lift is increased beyond that range, e.g. if going from 0.650" to 0.700" adds 25 HP, stepping up to 0.750" might be good for 15 HP more, 0.800" adds 10 more, 0.850" gains maybe 6, etc...

[swampbuggy]

Would somebody, or can somebody explain ( WHY ) in words understandable that adding more valve lift past a point ADDS more power Mark H.

[Rick360]

Would somebody, or can somebody explain ( WHY ) in words understandable that adding more valve lift past a point ADDS more power Mark H.

Time above the lift of peak flow.

Rick

[andyf]

Would somebody, or can somebody explain ( WHY ) in words understandable that adding more valve lift past a point ADDS more power Mark H.

It only adds power if the engine needs more air. The cam is not always the limiting factor. If the cam isn't the limiting factor then adding more lift just beats up the valvetrain and the engine doesn't make more power.

[swampbuggy]

Thx. To all who made replays, Mark H.

[hoffman900]

Dynamically, it allows for more lift area where you need it (which isn't necessarily peak).

[gmrocket]

its never enough.

[swampbuggy]

I think we'll put them out 900 it.

[swampbuggy]

Correction I think we'll put about 900 lift in it