Quote: brian, do you really think that the engine see's a depression representative of 36" when the valve is at .500 lift or higher? i know alot of that stuff is guessing unless youre privilage to pressure sensor info from intake ports and combustion chambers, though that data would be respective to that particular combo. do you try for different air speeds if the same head was being used on a 408 or a 340, since the depressions that both those engines will run at with the same head are so different? do you ever try to influence the intake port when flowing backwards to compensate for inertia like when the engine is running, and how easy or not so easy it is to counteract the pressure you have in the intake port?
ive worked on super stock 318/340/360 combos with moving the pushrod pinch over,, i dont remember exact cross sections but i think we went from .950 across to 1.200 and the motor peaked the same within 100 rpm or so, but past peak made more power. if i remember a 9/1 360 thermoquad made 565 with the .950 pinch and then 570 with the moved pushrod wall both at about 6800rpm, but at 7400 was 40 hp better than with the .950 dimension. you can have too much air speed where fuel will fall out of the air stream but i think thats very uncommon,, or using the wrong parts for a particular combo like a 318 head on a 408 or something like that.
jeff
When I flow backwards I have played with both air speed and flowing it with the intake on. I haven't been doing it enough to have a strong data base for what I find, but I do refer to guy I trust that does great work. I do change air speed for different applications, but I think on a fast port that might see 7000 rpm it's likeley it will see in excess of 28" of depression, however not steady that's for sure. I do it basicly to see how the port reacts to higher air speed. I do it to everything just to see how it reacts. Looking at your example, it would seem that if you took that engine and raised the compression and rpm point that the pushrod work would be worth alot more because of the demand on the intake tract. Infact, I bet it would double the power output that you gave. Jeff...I'm not the best head porter out there, so not to worry! Just wondering why you would care about a little guy like me??
