unshrouding intake valve near cylinder

[twl]

I run small motorcycle hemi heads, and a large percentage of your low lift flow on a hemi is going right out the exhaust valve.
If you still have overlap at the .100" lift points, then any flow you have below that is useless for anything but getting the flow signal started in the inlet. You aren't capturing any of it.
Most people work very hard to cut their low lift flow in hemi heads as much as possible. We use 50 degree seat angles to help reduce low lift flow, and get better high lift flow. If you are lifting to .900", you might want to think about 55 degree seat angles, if you aren't already doing that.

[wideopen231]

HAve not looked at that.Good point on both. How much flow change in low lift do you see with 55* seats? If your working on cutting low lift flow then from what we have found so far the opening of eyebrow may be less than I was thinking it would.It might flow more,but is it really helping? Don't you love this what if stuff? I do makes it a always learning thing.

[twl]

We haven't done 55 degree seats because our engines don't lift high enough for that. But we have gotten up to 15% more flow at lifts higher than .300" with 50 degree seats. On the other hand, the lower lift flow below .300" is reduced probably 15%. On balance, it works out better if you have enough lift. Also, the flow starts a little bit later because the valve unshrouds the seat a few thousandths higher in lift, due to the geometry of the steeper seat angle.

I think from our experience, you would benefit from steeper seat angles on both ends of the lift cycle if you have high lift. I personally would not worry about that eyebrow cut and its 6cfm effects at very low lifts.

[wideopen231]

well not only cfm also slight cleaRANCE ISSUE. You can actually see where valve has rubbed eyebrow. Some opening is a must even .020 would help. Will look into the 50* seat. Lift is .850 on int. and .825 exhaust with 282*@.050 or in area of still working with cam grinder to get what I want and what he can deliver. You stated 15% increase in upper lifts based on what cfm range? Afterall 15% of 400 and 15% of 540 is good ways apart in cfm.Not that it matters its still huge gain. Since I have enough knowledge to get me in trouble. I will have few more questions after this weekend.Even if not going to worry with getting everything from eyebrow work I still would like to know.

A day without learning something new is a day waisted,or so Mr Alan Starr always told me. I figure not bad rule to live by.

[twl]

well not only cfm also slight cleaRANCE ISSUE. You can actually see where valve has rubbed eyebrow. Some opening is a must even .020 would help. Will look into the 50* seat. Lift is .850 on int. and .825 exhaust with 282*@.050 or in area of still working with cam grinder to get what I want and what he can deliver. You stated 15% increase in upper lifts based on what cfm range? Afterall 15% of 400 and 15% of 540 is good ways apart in cfm.Not that it matters its still huge gain. Since I have enough knowledge to get me in trouble. I will have few more questions after this weekend.Even if not going to worry with getting everything from eyebrow work I still would like to know.

A day without learning something new is a day waisted,or so Mr Alan Starr always told me. I figure not bad rule to live by.

We went from 260cfm to 300 cfm @.600" lift with the 50° seats, and the appropriate other adjustments to the other flow angles and bowl.
The whole matter is useful on nearly any engine which has enough lift to take advantage of it. If I had .850" lift, I would try 55° seats.