The Ford Barn - View Single Post - here we go again... does anyone make 3 7/8

scooder · 11-19-2015, 02:16 PM

Chuck,
If you do a search on here the 3 7/8 piston question has come up before. I stated in that thread that using stock Ford 3 3/4 pistons and stock Ford uncut heads, as in OEM, will work. From the combinations I've measured, it'll just bolt together. I've dry assembled a 99A block, 8CM crank (4"), OEM 3 3/4 pistons, stock head gasket and uncut 81A heads. The pistons literally just kissed the heads. Now remove the 4" crank, swap in a 3 7/8" crank now you've got 1/16" clearance over the pistons.
The dome on the pistons I had and the dome in the 81A heads matched perfectly. These heads could also stand cutting 0.010" to give 0.050" clearance without cutting into the dome. The dome on these here heads is kinds counter bored into the head, so a 0.010" cut won't actually contact the dome.This would give you a nice uniform quench area, nice. This combination obviously ups the compression ratio aswell, as the combustion chamber now has another 1/16" of piston Sat in it. I think this would be a lovely combination. Higher compression with stock heads with there relatively deep transfer area.
Martin.

11-19-2015, 02:16 PM	#36
scooder Senior Member Join Date: Jul 2010 Posts: 2,593	Re: here we go again... does anyone make 3 7/8 Chuck, If you do a search on here the 3 7/8 piston question has come up before. I stated in that thread that using stock Ford 3 3/4 pistons and stock Ford uncut heads, as in OEM, will work. From the combinations I've measured, it'll just bolt together. I've dry assembled a 99A block, 8CM crank (4"), OEM 3 3/4 pistons, stock head gasket and uncut 81A heads. The pistons literally just kissed the heads. Now remove the 4" crank, swap in a 3 7/8" crank now you've got 1/16" clearance over the pistons. The dome on the pistons I had and the dome in the 81A heads matched perfectly. These heads could also stand cutting 0.010" to give 0.050" clearance without cutting into the dome. The dome on these here heads is kinds counter bored into the head, so a 0.010" cut won't actually contact the dome.This would give you a nice uniform quench area, nice. This combination obviously ups the compression ratio aswell, as the combustion chamber now has another 1/16" of piston Sat in it. I think this would be a lovely combination. Higher compression with stock heads with there relatively deep transfer area. Martin.