What is good compresion in a 302c - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

Keita · 07-08-2005, 04:11

Just interested as mine is 170 psi I wanted to know if that was good or not?

brenx · 07-08-2005, 06:13

170's good. Stock they are 145->155psi

Keita · 07-08-2005, 06:57

Thanks, any idea why it could be so much higher than stock. I only just bought it as a standard 302.

brenx · 07-08-2005, 07:07

Someone may have given the heads a skim. Maybe the block been squared. Changing valves will also change your compression. Nothing to worry about though.

cedric · 07-09-2005, 05:35

are you sure its not a 351 with 302 heads

Keita · 07-09-2005, 16:43

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.

TruBlu351 · 07-09-2005, 20:54

Quote:

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

RevHeadRon · 07-10-2005, 02:23

it doesn't have to be number one cylinder either as they will all be the same its just the easiest cylinder to access

Keita · 07-10-2005, 23:23

Thanks for all the help. I measured it and it is a 302 it must just have high compresion. Is it possible to put a 351 crank into it and will I get performance that will be worth all the stuffing around.