The larger valves may increase volumetric efficiency (VE in Panic's post 9). He estimated 95 percent VE. Really difficult to get above 90 percent in a street normally aspirated stovebolt engine.
Note at 95 % the engine could use 441 CFM at 5500 RPM.
So at 90 % - 418
And 100 % - 464
Where is your absolute redline, and where is your practical (street) redline?
Jon
Jon and Panic, thanks for all the information and sorry for not being able to respond sooner but I don't get much time lately. I do have to say it is a lot digest considering I have never worked on a carb and only limited amount on a couple engine rebuilds with my dad many years ago. I think a major point that was made and finally sunk in on me was the amount of time just driving normally 95% vs amount of time wanting it to perform. That being said I know this engine won't sip gas and am willing to suffer some for fun every now and then. Although filling up at the pump today for my daily took a chunk out of my wallet! I think what got me considering larger carbs were first the Holley site where you punch in the size of your engine size and if it is stock, mildly modified or highly modified and it would consisently spit out 470- 650? when I put in mildly modified. Then there were videos of folk doing dyno runs on 250s and 292 saying 500 was insufficient for the 250 (first video) and I think they used a 750 on a 292 that was somewhat modified being built for turbo (second video). I really wish Richard Holdener would have finished his series on a 292. He did compare a two barrel vs a very large 4 barrel at the time and I think the 4 barrel was almost equivalent with the two barrel but the engine and head were stock if I recall correctly. Unfortunately the video series was never completed. I would have been great see how it performed with multiple carbs and intake manifolds.
Richard Holdener 292 Series
I am not going to argue the math or physics and the excellent explanations provided for a smaller carburetor in this forum but you can see where this confusion stems from when watching these builds. I mean based on everyones calculations on this page anything over 450-500 is a waist. I understand that there are a lot of variables but other than the video of the 250 the other two builds had less done my build.
So is there anyone that makes a decent Q jet carb that you might recommend in the size Im looking for? I would prefer one that is easier for the newbie to work with if that is at all possible.
