Trinik, I'm not talking about my build. It was another guy's build who is building an 8,000 RPM machine. We also talked about how the big block carb run much better on alky.
I didn't explain well. I wasn't asking about my build, but the thoughts on 270 carbs in general just for conversation purposes. I have no plan to use it on my build.
To clarify: The question stemmed from a conversation on the MudmotorKits forums about using 270 carbs on a 8,000+ RPM mud motor screamer build where the head is a 14cc high compression build with a .308 cam, and the guy had only bored the carburetor out to .641 or so. I figured such a build would be better off with a .650, .670 or straight up Mikuni. Given that the venturi on the 270 is like .669, we were wondering if it'd be a better deal just to go for a 270 carb and the adapter. Again nothing to do with my build, but just kicking around ideas about possible comobs. His build is on the other end of the spectrum in that he is focusing on RPM not torque. Just a different conversation altogether.
NOTE: What you suggest is exactly what I'm doing with my build. I'm not using anything but a Box Stock motor as that combo works well: Race Ready Carb, basic JT Box Stock head, and I plan on using a 230-0221 NR Cam that will get all the power down at 5500 RPM. In addition I plan on running a GX160 flat top piston with an extra long rod for more compression and to make it easier on the crank for a longer lasting motor. Nothing more than a Box Stock build with a bump in compression and a better cam for the application.
So given the cost of a 270 with their adapter is it real a better deal than just buying a .670 stock appearing carburetor? My guess just like most is that the bigger carb would be better if he were running alky, but for gas then .650/.670 would be better.
The other this is to spin 8,000 RPM on a mud motor you have to use stinking small prop, 5.5 inches or less. In the marine environment smaller props are less efficient, but there have been people successfully building 8,000 RPM mud motors. I have no idea why, but it is being done.
With my build I would likely gain more speed because I'll have more power and torque at lower RPM, thus letting my use a bigger prop, perhaps even a 7.5 inch prop. In other word use all that power and torque to spin a bigger prop. The oter guy's build is just purely an RPM beast just for the sake of turning RPM.
