big port heads

[chocolatelab]

Silly question, start the flame thrower

What exactly does "big port heads" mean?

Thanks in advance

[RWebb]

the air-fuel mix and the burned up waste gases enter and exit the combustion chamber thru the ports

flowing more stuff makes more hp

one way to flow more stuff is to make the ports bigger

[Won]

Also in the 911 context:

For US market cars the 78-79 911SC had "big port" heads with 39mm intake port. Then Porsche went back to 34mm intake port for 80-83 cars, i.e. "small port". For ROW cars I think they stayed with 39mm port throughout the model run.

The general consensus is that the smaller port produced more torque earlier in the RPM range for increased driveability while the larger port favored high RPM output.

[Bill Verburg]

Originally Posted by chocolatelab

Silly question, start the flame thrower

What exactly does "big port heads" mean?

Thanks in advance

Usually in referece to he varaitaions used on the n/a 3.0 liter engines
'76/77 930/02 used in Carrera 3.0 had 39/35mm ports
as did the 930/03, 04, 05, 06 used in SCs '78/79

for '80-83 all the SC's, 930/07, 08, 09, 10, 12, 13, 14, 15, 16, 17, 19 used 34/35mm ports

then there were the really big ports used in 930/18 3.0 SC/RS @43/43

all of the above used the same valve sizes @ 49/41.5mm

[dcriss]

Why did Porsche go back to the smaller ports for '80-83?

[chocolatelab]

Thank you all for the info.