62Ranchero200
Famous Member
Greetings Ford Six Fans,
As a reminder, I'm building a '74 250 for my '62 Ranchero / C4. It's going to be .020 over, with stock stroke, the CI aluminum head, the CI intake manifold with a large 2 BBL or small 4 BBL carb, long tube headers, a streetable CI cam, and a DUI (I already have the DUI, so I'm definitely going to use it).
Heard from Mike today that the current batch of CI aluminum heads have 55 cc combustion chambers, +- 1 cc. I should receive my aluminum head within a couple of weeks.
With this information, I can update my CR calculations. Please check my arithmetic.
With stock, 6.5 cc dished pistons:
With stock type, flattop pistons:
With 255 pistons:
While I admire the courage of people who run their engines on the cutting edge of detonation, I think 10.77 is a bit too much compression for 87 octane street gas (which I might be forced to use on occasion) with a streetable cam.
I had once hoped to use Jeep 255 pistons with a .070 overbore, but sonic testing revealed that my block wasn't safe for that option.
There's still a slim chance I may be able to use 300 rods and custom pistons, but if not I'll probably fall back to the stock type, flattop pistons.
Bob the Builder
As a reminder, I'm building a '74 250 for my '62 Ranchero / C4. It's going to be .020 over, with stock stroke, the CI aluminum head, the CI intake manifold with a large 2 BBL or small 4 BBL carb, long tube headers, a streetable CI cam, and a DUI (I already have the DUI, so I'm definitely going to use it).
Heard from Mike today that the current batch of CI aluminum heads have 55 cc combustion chambers, +- 1 cc. I should receive my aluminum head within a couple of weeks.
With this information, I can update my CR calculations. Please check my arithmetic.
With stock, 6.5 cc dished pistons:
With stock type, flattop pistons:
With 255 pistons:
While I admire the courage of people who run their engines on the cutting edge of detonation, I think 10.77 is a bit too much compression for 87 octane street gas (which I might be forced to use on occasion) with a streetable cam.
I had once hoped to use Jeep 255 pistons with a .070 overbore, but sonic testing revealed that my block wasn't safe for that option.
There's still a slim chance I may be able to use 300 rods and custom pistons, but if not I'll probably fall back to the stock type, flattop pistons.
Bob the Builder
