Greetings all…
I just tore the engine down out of my '67 Cougar (base) 390 GT. The crank is stamped 3U. No other discernibIe markings. I know it has been rebuilt at least once (.060 stamp on each piston). From what I have researched, this stamp indicates a TRUCK crank…a bit disappointing from a (near) rookie’s stance. Is my disappointment warranted? Any thoughts from those out there wiser than I…?
Thanks,
Dennis
My concern would be the .060 overbore, i may be wrong but .060 is the max overbore safely without having the block sonic tested.
Understood…I don’t believe the block will have to be bored again. The condition of the cylinder walls and crank journals appear to be quite excellent. No copper lines visible on any rod bearings and connecting rod side clearances all within spec. Short of having a proper measurement of the walls done, I don’t think this engine has seen very many miles at all since the .060 over job. Not even a ridge to be seen or felt at the top of any cylinder. I’m just wondering if this 3U crank was “misplaced” or not…?
Follow up question…I will be replacing the cam (and flat tappet hydraulic lifters) due to one badly worn lobe. I am keen on the 270H Magnum grind. Does anyone think that it might be too much for the 390? Keep in mind…10.5:1 compression (factory anyway…perhaps less with the overbore), and I am prepared to upgrade the converter as needed. 3 speed auto C6, and 3.00 gears in the 9" rear end.
Thoughts please…
The 270M cam is listed as Comp’s largest cam you can still use a stock converter with. That being said something in the 2000-2200 would net you a little more holeshot. With 10-10.5:1 that cam would work well. Did a similar build on a sbc back when that cam first hit the market (327 double hump heads, 10:1 compression, four speed 3.42:1 gearset in a '79 camaro). That car ran really well, so I would imagen your 390 would run all the better. Have you put any thought on an something like an XE268 or XE274? Would probably net you more power, but the idle would be a little different than the straight grind. Not as choppy. Any of the 3 would run pretty well with your compression, but off the top of my head both xe cams would need a little more stall. I could be wrong on that one. That 270 does run well. I had good luck with it.
Thanks for that feedback guitar74. I have considered the XE grinds, but I really like the lope of the 270H and all indications are that it will work well with the Super Comp headers I plan to install as well. Happy to give a little HP for the sound I really want…I’m not a racer. I’d rather turn heads than snap them back.
Thanks,
More information here:
http://www.network54.com/Forum/74182/thread/1331580986/3U+crank--
,
With the compression ratio, boring an engine out actually increases the compression ratio. It displaces more air, but the combustion chamber volume is still the same. Being +.060, it raised the compression ratio by about .2 if everything else stayed the same relative to the stock configuration.
Thank you for that clarification Steve68Cougar. I stand quite corrected…and further educated.
Correcto, Steve. Your swept volume increases with an overbore so your static compression is higher. And yes, Anthem, that 270 has a nice nasty sound to it.
Here is the answer to your 3U question.
http://www.fordification.com/tech/castingnumbers-FEcrank.htm