Ported head
- Thread starter AzCoupe
- Start date
If you take a look at all the camshafts offered by ford six you will notice that they all have between 0.425" and 0.500" lift. This cuts down on the benefits of the ported head slightly as demonstrated by the graph.
Then consider that the reason the head promotes better flow at those higher valve lifts is because the head has smaller cross-sectional area runners than the v-8 heads do, of course because of the smaller size of the engine. Smaller runner area increases the gas velocity and thus a longer distance (valve lift) before the gas is decelerated promotes better flow. So what happens if the gas in the intake manifold is not traveling all that fast? Say in an engine designed to make torque between 2500-4500rpm as opposed to an engine that makes torque at 4000-6000rpm or higher. It means that the gas is not going to be moving as quickly through the head and thus reduce the necessity for it to be ported.
:deadhorse:
If you step back and consider the camshafts again, they all run between 0.400" and 0.500" of valve lift, but the length of time each cam stays above 0.400" mark is limited by the duration of the camshaft. Why? Because of ramp rate, the increase in lift per increase in degree. The ramp rate of any camshaft is limited by the circumference of the lobe base and the size and shape of the lifter. Since those parameters are more or less constant, changing the ramp rate is not much of a tool. Something will end up broken or you will decrease the effectiveness of your camshaft. :nono: So what do you do to increase your time above 0.400"? You increase duration. When duration is increased so is the range at which torque is made, and your low end, is not so much low end anymore.
So, is porting the head that much of a benefit for a low end grunt machine? I can't tell you. From my point of view it does not seem to be.
Probably the thing to do, if looking for a low end machine, would be to get a small lift shorter duration cam, with a pretty flat lift curve and large ratio rockers. If you somehow found 2:1 ratio rockers a cam with 0.425" lift would come out to about 0.566" lift. Maybe I'm just dreaming though. :roll:
Just my $0.02. Optimized for low-end torque or not, I still want one.
Allan
Then consider that the reason the head promotes better flow at those higher valve lifts is because the head has smaller cross-sectional area runners than the v-8 heads do, of course because of the smaller size of the engine. Smaller runner area increases the gas velocity and thus a longer distance (valve lift) before the gas is decelerated promotes better flow. So what happens if the gas in the intake manifold is not traveling all that fast? Say in an engine designed to make torque between 2500-4500rpm as opposed to an engine that makes torque at 4000-6000rpm or higher. It means that the gas is not going to be moving as quickly through the head and thus reduce the necessity for it to be ported.
:deadhorse:
If you step back and consider the camshafts again, they all run between 0.400" and 0.500" of valve lift, but the length of time each cam stays above 0.400" mark is limited by the duration of the camshaft. Why? Because of ramp rate, the increase in lift per increase in degree. The ramp rate of any camshaft is limited by the circumference of the lobe base and the size and shape of the lifter. Since those parameters are more or less constant, changing the ramp rate is not much of a tool. Something will end up broken or you will decrease the effectiveness of your camshaft. :nono: So what do you do to increase your time above 0.400"? You increase duration. When duration is increased so is the range at which torque is made, and your low end, is not so much low end anymore.
So, is porting the head that much of a benefit for a low end grunt machine? I can't tell you. From my point of view it does not seem to be.
Probably the thing to do, if looking for a low end machine, would be to get a small lift shorter duration cam, with a pretty flat lift curve and large ratio rockers. If you somehow found 2:1 ratio rockers a cam with 0.425" lift would come out to about 0.566" lift. Maybe I'm just dreaming though. :roll:
Just my $0.02. Optimized for low-end torque or not, I still want one.
Allan
350kmileford
Well-known member
I was going to cut into my head fund to buy air conditioning. Not anymore.
