Well it's been a while on this project, but progress is slowly being made. I purchased a used cylinder head that was found locally and decided to save the shipping to Arizona. Instead on the recommendation of another sixer here on the forums, I sent it to Portland Engine Rebuilders and they are doing all the porting work, valve jobs, 2V conversion, etc... I am told it is nearly completed.
My idea had been to buy the RAS rockers but as you probably know Mike is replacing those with Classic Inlines rockers, and he's told me I'll be getting a set soon, or whenever they come in. They will be 1.65 ratio. Once I have those and the cylinder head I can begin the transformation!
Ok, I do have one question though, and that concerns the new carb. I'll be going with an Autolite 2100 from Pony Carbs. I'm just wondering about the CFM needs for this application, and I don't want to make a mistake here.
In the "Selecting the Right Carburetor" section of the Classic Inlines tech pages, it lists anywhere from 295-420 CFM on a 250 ci for a modified log head, depending on type. He says large valves would be 345 on up. My log head will be highly modified and have large valves. Final compression ratio hasn't yet been measured but indications are it will be close to 9:1.
Likewise, on the CFM Calculation page, it indicates a 250 ci should get 347 CFM even at only 80% volumetric efficiency. Probably my modified head will have at least 80% VE, and likely more. So, from these two sources I'd say I should get an Autolite 1.21 which has a flow of 351 CFM.
However, the only thing making me think twice about this is this comment from the Classic Inlines shop, on the Autolite page:
Well good heavens, that's quite a difference! Surely this description must have been directed at the 200ci engine and not the 250?
I don't want to go overboard on the carb but then again I also don't want to limit performance on the induction side after having done all this other work on the engine. What do folks say, is 350 CFM going to be too radical for this application, or just right?
Luke
My idea had been to buy the RAS rockers but as you probably know Mike is replacing those with Classic Inlines rockers, and he's told me I'll be getting a set soon, or whenever they come in. They will be 1.65 ratio. Once I have those and the cylinder head I can begin the transformation!
Ok, I do have one question though, and that concerns the new carb. I'll be going with an Autolite 2100 from Pony Carbs. I'm just wondering about the CFM needs for this application, and I don't want to make a mistake here.
In the "Selecting the Right Carburetor" section of the Classic Inlines tech pages, it lists anywhere from 295-420 CFM on a 250 ci for a modified log head, depending on type. He says large valves would be 345 on up. My log head will be highly modified and have large valves. Final compression ratio hasn't yet been measured but indications are it will be close to 9:1.
Likewise, on the CFM Calculation page, it indicates a 250 ci should get 347 CFM even at only 80% volumetric efficiency. Probably my modified head will have at least 80% VE, and likely more. So, from these two sources I'd say I should get an Autolite 1.21 which has a flow of 351 CFM.
However, the only thing making me think twice about this is this comment from the Classic Inlines shop, on the Autolite page:
While 287cfm may work on a modified log head, it is well suited for use with our new aluminum cylinder head, along with our 2V intake manifold, a performance cam, headers, and a 9-9.5 compression ratio. However we recommend the 240cfm or 245cfm carbs for most street applications where bottom end power and good throttle response are desired.
Well good heavens, that's quite a difference! Surely this description must have been directed at the 200ci engine and not the 250?
I don't want to go overboard on the carb but then again I also don't want to limit performance on the induction side after having done all this other work on the engine. What do folks say, is 350 CFM going to be too radical for this application, or just right?
Luke