Howdy Claymore and All:
I'm somewhat stymed by your lack of willingness to start with the head. If I may be a little preachy the head is where the greatest potential lies. If I were in your shoes and building a 250 for a dual purpose 4 wheeler, I'd start with a '78 and later head (D7 and later) for the larger valves, hardened seats and bigger intake tract volume. I'd do a three angle valve job, milling to increase CR to a true 9:1, and backcutting the valves with a 30 degree cut. I'd also have a center exhaust port divider welded in while the head was being machined. I'd also spend some time polishing the chambers and cleaning up the ports- nothing too extreme.
While the head is in the machine shop I'd have it machined to be able to direct mount a wide base two barrel carb- either a Holley 350 or Autolite 1.21.
These two processes, along with a good, well tuned DuraSpark ignition, either 1st (a '75 could have either a DuraSpark with the small distributor cap, or the large cap DS II) or second generation, should get you real close to your goal of a good mid-range powerhouse. Talking HP for a situation like your's is a bit of a smoke-and-mirrors myth. Low and midrange torque and driveability will be what makes it a success or not.
Headers are very cool, but very expensive and help most at higher rpms, not what you need. A properly modified exhaust manifold and 2" exhaust system with a turbo type muffler will be more appropriate for your criteria.
Short of a convincing you to start with the head off, I'd rebuild an RBS, maximize the timing advance, improve the stock exhaust and enjoy. You'll be surprized what a torquey 250 can do.
Thanks for the ? on the NAPA number. We'll be double checking tomorrow.
Changing cam and/or timing gears really should be part of a Short block rebuild. It is not cost effective to just change to the earlier gears for a performance increase. In fact the reason Ford made the timing gear change was to improve low end performance, with too tall gearing and mileage in mind. Low end is only slightly improved but anything above 4,000 rpm is snoozers. Still not out of line for want you want.
Keep us posted on your plan and your progress.
Adios, David
I'm somewhat stymed by your lack of willingness to start with the head. If I may be a little preachy the head is where the greatest potential lies. If I were in your shoes and building a 250 for a dual purpose 4 wheeler, I'd start with a '78 and later head (D7 and later) for the larger valves, hardened seats and bigger intake tract volume. I'd do a three angle valve job, milling to increase CR to a true 9:1, and backcutting the valves with a 30 degree cut. I'd also have a center exhaust port divider welded in while the head was being machined. I'd also spend some time polishing the chambers and cleaning up the ports- nothing too extreme.
While the head is in the machine shop I'd have it machined to be able to direct mount a wide base two barrel carb- either a Holley 350 or Autolite 1.21.
These two processes, along with a good, well tuned DuraSpark ignition, either 1st (a '75 could have either a DuraSpark with the small distributor cap, or the large cap DS II) or second generation, should get you real close to your goal of a good mid-range powerhouse. Talking HP for a situation like your's is a bit of a smoke-and-mirrors myth. Low and midrange torque and driveability will be what makes it a success or not.
Headers are very cool, but very expensive and help most at higher rpms, not what you need. A properly modified exhaust manifold and 2" exhaust system with a turbo type muffler will be more appropriate for your criteria.
Short of a convincing you to start with the head off, I'd rebuild an RBS, maximize the timing advance, improve the stock exhaust and enjoy. You'll be surprized what a torquey 250 can do.
Thanks for the ? on the NAPA number. We'll be double checking tomorrow.
Changing cam and/or timing gears really should be part of a Short block rebuild. It is not cost effective to just change to the earlier gears for a performance increase. In fact the reason Ford made the timing gear change was to improve low end performance, with too tall gearing and mileage in mind. Low end is only slightly improved but anything above 4,000 rpm is snoozers. Still not out of line for want you want.
Keep us posted on your plan and your progress.
Adios, David
