Originally Posted by Keita
How could I tell if its a 351 with 302 heads? and if so what advantiges are there of having 2v 302 heads on a 351 block.
Basically, more compression = more power. The compression your motor requires will depend upon cam shaft size. One limitation with more CR or increases pressures = possibility of pinging. This can be minimised with good fuel, correct timing and advance curve.
With 302 heads on a 351 you'll pick up roughly another "point" of compression.
eg: 10:1 with 351 open chamber heads versus 11:1 with 302 closed chambers.
A 302 crank has a 3 inch stroke and a 351 is 3.5 inches (1/2" or 12.7mm difference). ie: how far the crank pulls the piston down the cylinder bore. The only way to tell with the heads on is to pull your #1 spark plug and measure the distance when the #1 piston is a BDC - bottom dead centre. Put a LONG piece of wire or plastic down the hole and mark it with a texta. DON'T scratch your bore, and don't drop anything short inside
This won't be a true measurement of the stroke as it will include spark plug thread hole, combustion chamber and head gaskit and possibly a slight angle measurement not parallel to the cylinder which will increase the distance.
To get the stroke by itself, hand wind the motor back to TDC on the #1 cylinder and then measure it again.....mark with texta and then measure between the 2 marks. ~3.5" (89mm) = 351 and 3" (76mm) = 302.
Let's hope its a 351