I have some new info for the gear heads
I've become further compelled to learn everything I can about 4 stroke engines for what ever reason. I'm not even really sure why anymore.
I just bought a new book. "Performance Automotive Engine Math" by John Baechtel. The title pretty much gets me out of describing it any further.
In the book, there is a formula for figuring out port velocity. I also taught myself how to run Microsoft Excel today
and I made a calculator for this. I will post it if I can figure out how. (Maybe someone can help me with that)
I started crunching numbers based on my 470 build which I dynoed last year, the numbers I was coming up with was suggesting that I was way too small on my porting and carb size. So I called suzukiray to discuss this with him, and he confirmed it and made a few suggestions.
12.5:1 470 (94mm x 67.6mm) +1 (37mm) intake valves +1 (30mm) exhaust valves, web 539+6/539 cams, 40FCR (which I knew was too small), custom header, and dyna for relevant mods. Here's the chart.
We have come to the realization on this board that these big bore strokers are needing quite large cams to breathe, and they are not giving up low end to get it. Mine certainly follows that trait. The porting is responsible for this. Information I have been finding has suggested that ideal peak port speed falls somewhere between 300-360 feet per second. With my setup as dynoed, it was beyond that by 7000rpm. (This is with a 90% volumetric efficiency correction factor also which should be generous for this type of engine) You can see it on the torque curve. With cams this size, it should be pulling hard beyond 10k, and it's not. The induction just can't handle as much air as this thing is trying to move. By 10k, it's trying to move the air at 521ft/sec.
I'm absolutely certain there is more power in this thing by porting it bigger. I'm going to see if I can find a HSR 45mm carb for it too. I will most likely lose some low end doing this, but I have smaller cams sitting around if I need them too, and if nothing else, for the sake of learning, I'm all about doing this! I can always go back to what I had
Now for the sake of discussion, I also believe I could also taper bore the FCR to 43mm and port to that size, and not lose a bit of useable power. Just pure gain on the high end.
I will try to find a way to post that calculator, but this is completely open for discussion if anyone has any questions, comments, or just wants to tell me I'm wrong, or an idiot.