I am thinking of re-doing the port once again. I am thinking that I can gain some more efficiency with a slightly different design. I am not sure that I am in the sweet spot for this engine configuration and my specific needs yet. There might be something left on the table.
To get a pretty accurate idea of possible HP output by taking into consideration max CFM flow at Delta P 28"h2o:
Max flow × .25714 × # of cylinders.
At the current state that would approximate hp around 11.46hp. These numbers are a good estimate if your engine is built well and tuned well. I have used this formula before and it was just slightly conservative on other builds, meaning I made slightly more power than the formula suggested. Others have used it and the formula is pretty spot on.
I am not sure if this combination can actually meet the qualifications to actually make 11.5hp. I would guess the actual hp number would be less. The formula points to a max hp if the engine criteria is well suited for the flow and engine specs are designed well. The current engine specs are probably a little too conservative to reach the peak hp number and still have good guts below the curve. I'm more interested in the guts below the curve supporting enough oomph to get it to the upper range where the peak hp numbers live.
I would rather have a very stout mid-range that peaks at 9.5hp than a lazy mid-range that wakes up only to pull strong in the last 1,500rpm to peak at 10.75hp. Currently it seems pretty balanced. Good usable hp lives in the mid-lift range, especially with a conservative cam and lower compression ratio. I have pretty good flow between .100" and .200" and then it drops off slightly but I lost low-lift flow. I won't gain a ton with overlap because there is very little overlap with this cam but with the current flow numbers I doubt that I would have any benefit from scavenging at all. I got caught up in searching for peak flow at .175"-.200" and lost low-lift flow. Now I have to try to decide whether going back in search for the low-lift flow I had would be worth the compromise of time and possible loss of peak flow at .200".
Just to give others a little bit of an idea of what you can look for when searching for the right balance and a good design I will share a few things that I am focusing on to zero in on what I want. Like anything else that envolves many different physics certain things can work well in one specific design but not so well on another design. Proper research and a solid scientific method should be incorporated into your efforts. I am only sharing my own data, observations and opinions in an attempt to help others. I am not suggesting the following in absolutely correct.
A couple of things that I have noticed with all of the data that I have collected is that if I push the choke point closer to the valve bowl it bumps low-lift flow with a compromise to stability in the flow between .175" and .200". Also, the stall ramp on the low-flow side of the valve bowl greatly effects flow numbers. If the ramp is at a sharper angle it improves low-lift flow but can kill flow at .175"- .200". You can move the ramp closer to the port to improve this some, however. A more gradual ramp helps peak flow, especially at .175" on up but degrades low-lift flow from .100" on down. A tighter choke area improves low-lift flow dramatically but can produce turbulence at .150" on up as well as limits peak flow.
As you can see there are a number of ways to affect flow and it's through trial and error where you can learn what works best and how to target your specific goals. This only works for sure with dry air at a constant Delta P... It's guesswork on whether it will provide satisfactory atomization and balance in a running engine. I am searching for a safe design that would lend itself to allow forgiveness. The more you get to the edge of optimization on the flowbench the more dramatic the changes can be when you include fuel and a real-world running environment. It can greatly help or hurt overall engine characteristics.
For instance, if your port/valve bowl/valve curtain design does not atomize fuel properly (not enough or too much) it is greatly enhanced in the very hostile and dynamic engine that is cycling hundreds and up to many thousands of times per minute. Also, if you design an intake that seems stable when you run it at a constant 28"h2o pressure drop it can become very unstable and turbulent when it is encountering very fast and dramatic pressure cycles. This is why I chart out the flow from 10" to dynamic (wide open vacuum) to see if I can detect any hiccups that might show a dramatic difference in flow. I have noticed several times where the design became turbulent and caused less flow with more lift under the same Delta P than it should have and then less flow than it should at a higher Delta P at the same valve lift. If I just flowed at the constant 28" it would appear that the flow just maxed out because of the port. But I adjusted a few areas in the valve bowl and gained flow at the valve range and above where it started to show the hiccup before and I gained 3.8cfm. Thats a lot on a little port like this, especially since I did not open the cross-sectional area at all, I only adjusted the way the valve bowl interacted with the air.
Some other things that can have an effect is the size of the valve bowl, valve bowl wall slope, valve bowl wall length, short turn radius slope/height/radius/placement, valve throat area/radius/length/angles, etc. Tons of things, obviously, effect the flow but I would argue that it's just as important to understand how each area relate to one another than it is to search for a certain "go-to" design or set of parameters. You can really dial in certain characteristics of how the air flows by understanding the relationships of the different areas. Not all engines are used in the same way. If you are looking for more torque at the low end for an engine that will be used for grunt work you can dial that in. If you want decent grunt but also decent mid-range and high rpm you can focus on that. If you want a race engine that will have a high-rpm engagement and you want to stay in the high rpm range then you can dial that in. The intake and exhaust system should be designed around the specific goals as well as proper cam specs, stroke, compression, fuel, valve, valve seats, etc. It's all about knowing what compromises to make and knowing the relationships between the components and putting them together to harmonize the entire engine as a whole for your specific goals. A huge part of that is getting the proper intake flow. The valve bowl and seat area are crucial and the port is very important as well.
Once you know what you want your engine to do and get the right components picked out the first place you should focus on is the intake system and port to provide the right amount of air at the right velocity, then the valve bowl and seat area to be as efficient at getting the air/fuel into the combustion chamber as efficiently as possible with the best atomization as possible targeted towards your rpm goals. Then harmonize everything to be as efficient as possible to burn and evacuate the burned fuel as efficiently as possible.