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1951-F1-NC wrote:Buddy, considering the carb looks like it's in a north-south configuration, I'd assume the intake is an Offy "C". DP's want the carb mounted east-west.
Buddy Rawls wrote:Here is a reverse engineered scenario (using very abbreviated hand calc process) that could match the motor build pretty closely. Granted there are some assumptions I made. For instance I assumed the headers used 1 5/8 primaries, which effectively utilizes the 12:1 static compression to an even bigger gain, even if the exhaust lobe was not optimally placed and sized. I also assumed 300 cid. I also assumed the intake manifold was capable of flowing equal to the intake runner in the head casting (or close). Other assumptions too, that I use in valve event calcs.
One end of the scenario places the intake runner flow capability is in the 215 cfm (28") region, with intake duration (.050) in the mid/upper 230's, installed ~110 intake CL or so.
The other end of the scenario places the intake runner flow capability in the 235 cfm (28") region, with intake duration (.050") in the upper 220's/low 230's, installed around ~112 intake CL or so.
The thing that has me really wondering is that with 12: 1 static CR, a motor that makes peak hp in the 5100 region ought to be freakin coming unglued in its good cylinder filling rpms when the required static compression is nowhere near 12:1. Within this, some part of my assumptions are off base. The 1 hp/cid in the low 5000's shows good cylinder fill and appropriate use of port velocities (crossectional parameters) with nominal compression. However, with high compression you will see significant low and mid range that will carry thru into the upper range as well. I am not sure about the intake manifold, its an Offy, but dont know if a C series or Dual Port. the intake could be the real issue with the calcs not mimmicking the output as closely as I would have though. It also could be counterproductive with the high static compression, simply because the chamber has less fillable room. Pair that with a possible restrictive intake manifold, and it can hurt drastically. I have seen restricted motors respond negatively with high compression. though, this gets back to waht the flows and actual cam specs are.
BUT! I am not familiar with the chamber's contribution on these motors, with respect to flow, or cylinder combustion dynamics. So there could be some wide variation from reality to the engine/valve event process (also I did it pretty much by hand calc, as opposed to at home with my normal methods). I am looking at flow in and flow out, and the relationship of cylinder demands at this rpm range.
I enjoy these kinds of threads. It broadens my thoughts on these motors, more and more data points.
I wonder if we can get more cam data, as well as what intake was used, and header diameters. heck flow data too.
This is such a drastic change from the v8 stuff I normally dink with, too funny.
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