1975 F250 390 V8 Camper Special 2wd C6 Dana 60
My grandfather originally bought this truck. With the exception of the cam (specifics unknown), Ignition (Mallory HyFire VI-A multi-spark and Promaster coil), Accel spiral core plug wires, The air filter and housing (big old K&N with substack), and Carburetor (Carter AFB) it is stock.
I rebuilt the engine about ten years ago. I did it because leaded gas was going or had gone away and wanted heads that would be reliable with that fuel. I had the head rebuilt with hardened seats and new valves (I think). That is when I put in the different cam (at the machinist's suggestion, he was a pretty big Ford fan and was building some pretty high dollar motors). I cannot find the card anywhere. It was supposed to be a good cam for towing, which is what this truck does. The engine had good compression before and the cylinder walls looked good so the machinist honed the cylinders and I put new rings on the old pistons.
The reason I'm writing is that the truck never felt as strong after the rebuild as before and it seemed to be more sensitive to spark advance. It is getting about 6.3 MPG and I think I can do better. It should at least feel strong at 6.3 MPG!
I have a Zeitronix wide band O2 sensor and have tuned the carb for WOT, Part Throttle, Off Idle, and Idle. The problem is that vacuum drops significantly under much of a load. I put a fuel pressure regulator in front of the carb to make sure it was getting fed consistently.
My current plan is to:
- Replace the stock manifolds and single exhaust with headers (http://www.sandersonheaders.com/product_info.php?products_id=88
)and dual exhaust with 2.5" Aero Chambers.
- Get with a cam manufacturer and figure out what cam is in there (degree wheel and dial indicator). I'm wondering if the new timing chain I put on there messed with the cam timing. I read on ford-truck forum that there were timing sets with retarded cam timing for emissions purposes. This truck has ZERO emissions equipment. I think its GVWR made it exempt. (Do you recommend a magnetic base or a bolt down base for a dial indicator on cam work?)
- Ask you guys here for guidance.
There are some leaks that need to be fixed so I may be pulling the engine. I was thinking of pulling the heads off and radiusing the combustion chambers a bit to prevent pre-ignition. I want to be able to maximize the spark timing.
How good are the heads and the stock intake manifold? I figure they are at least good enough to deliver the previous performance but I'd like to know if they are a big weak point. (where do I find the casting number that would tell you guys which heads these are?)
I don't have unlimited funds but as far as labor goes, I'm willing to go all the way.
I'm hoping to maximize mileage. I'm shooting for 12 MPG with an empty truck (more is always welcome) but if it is going to suck fuel it at least needs to do it with some POWER!
I've heard you guys here are real sharp engine folks who specialize in FE motors. I hope you can help me.