I bought a 75 Highboy Frame from a guy and he told me the motor was a 390 and today I took the heads off the motor and I found that it has a 3.92 stroke and its bored 4.03. You can still see the hone marks in the cylinders. Its a 400CI Stroker. YAHOO, I bet this thing is going to flat get up and go... I am going to check the lift on the cam to see what that is tomorrow. WOW!!! Im hoping for a 486/486 cam. This is one clean Engine...

 

352 B&S: 4.00" x 3.50" / 360 B&S: 4.05" x 3.50" / 390 B&S: 4.05" x 3.78."

 

Yeah, not sure what that is. Maybe your measurements are off. How did you measure it?

 

From the Deck to the Lowest point where the piston is in the Cylinder with my Caliper. I checked all the Cylinders and they were consistently 3.92 on the Stroke. 4.03 on the Bores. The 4.03 is probably because of the carbon build up in the top of the cylinders above the rings but I know (think) the Distance of the Stroke is Right. The previous owner ran way to much carb on this engine, It had a 750 Double Pumper and it was way to rich. The Cylinders still show the Hone Marks so I know its a low mileage motor. The Previous owner said it had less than 10K on it and I belive it by what I am seeing internally. I am going to take the crank out and replace the rear seal as he said it leaked, not that it surprises me. I will inspect the Crank when i get it out for numbers and see if I can figure out what Crank it has. I also wonder if someone used a 360 Block and put a 390 Crank in it but that wouldn't explain the Stroke. I wonder if they could have stuck a 410 Mercury Crank in this thing? The stroke on a 410 is 3.98 or it could also be a 428 Crank.

 

Displacement Bore Stroke
332 4.000 in (101.6 mm) 3.300 in (83.8 mm)
352 4.002 in (101.7 mm) 3.500 in (88.9 mm)
360 4.052 in (102.9 mm) 3.500 in (88.9 mm)
361 4.047 in (102.8 mm) 3.500 in (88.9 mm)
390 4.052 in (102.9 mm) 3.784 in (96.1 mm)
391 4.052 in (102.9 mm) 3.784 in (96.1 mm)
406 4.130 in (104.9 mm) 3.784 in (96.1 mm)
410 4.054 in (103.0 mm) 3.98 in (101 mm)
427 4.232 in (107.5 mm) 3.784 in (96.1 mm)
428 4.132 in (105.0 mm) 3.98 in (101 mm)

 

So just to double and triple check myself on my Measurements it has a 3.98 Stoke and a 4.05 Bore. I am guessing that I didn't have it exactly at zero on the Timing Marks when I took my Measurements so I just put it dead on Zero and checked the measurement of the stroke. I think its got a 428 Crank in it cause I cant see someone finding a Mercury Crank to put in this motor unless they had one sitting around. Where do you find the numbers for the Crank on a Ford Crankshaft?

 

 

Yep sounds like they did swap the cranks. Pretty cool find!

 

So the Plot thickens... The Code on the Block is C6ME-A which means its a 1966 Mercury Engine. In the Intake Valley there is a 352 casting with a 29 Just Under it also casted. I am beginning to believe I have a 410 Block. Its externally Balanced or at least I think it is, there are holes In the Pulleys on the Front of the Crank. but I couldn't see any weights on the Flexplate or the Balancer. One other thing I measured was the distance from the deck to the top of the piston when the piston was all the way up in the cylinder, and that measurement was .121. That's almost an 1/8th of an inch down in the cylinder and that seems excessive to me. I wonder if there is a Piston that I could put in this to eat up a little of that 1/8th of an inch to make the Quench a little tighter. I understand that the Quench should be about somewhere between .02 and .05. With a .040 Head Gasket. I sure would like to buy a new set of Pistons and hone this block and put a new set of Main and Rod Bearing in it with a new cam and make this a real runner. The Heads are 210 Intake and 160 Exhaust I think the code on them is C8E Something... The heads look very good and I can see no sign of Warped or Burnt Valves in them. Lots of Carbon though. I really believe the 770 Holley Double Pumper was to much carb for this engine/cam. I am going to replace the front and rear seal in this engine and I have never done the Rope Seals so I hope its not rocket science because I will probably need help. I may just say the heck with it and take the engine to my Local Machinist and let him do all the inspections, machining and build. Maybe with all this info some of you Engine guys can tell me what I have...

 

 

That's why I am thinking about talking to the Professionals... In other words my Machinists..

 

So if you measured the stroke from the top of the deck, but the piston is .121 down in the hole, then the stroke would not be 3.98. Or am I misreading that?

 

I was under the impression that the stroke is from the Deck to the bottom of the Stroke.

 

Maybe someone else can chime in as I am not sure.

 

The stroke is the distance between the lowest point where the piston stops and changes direction, and the highest point where the piston stops and changes direction. Bottom Dead Center and Top Dead Center.

If measuring from the deck to the piston top at BDC, you would need to subtract the distance between the deck and the piston top at TDC, which would be a needless complication.