Flow Test Results for 83 GPz11 with 34's

the 80kz flows better than the gpz with bigger ports and valves.whats up?

mark1122 wrote:

the 80kz flows better than the gpz with bigger ports and valves.whats up?

Velocity Profile comparison = .....c'mon now....I
can't give everything away....

In this case, size ain't everything

A smooth flowing port will allow more air through at a higher velocity than a larger more turbulent port, it's no problem to make a port larger and lose airflow, lot's of people do it when they try to port their own heads. I am a very determined do-it-yourself type, but when it comes to porting I'll let the experts do it

Thanks Steell. Hey Larry, how about a kz ported vs. gpz ported?

I remember reading that a slightly rough rather than polished finish to the port walls will create a desireable amount of turbulence to keep the fuel from dropping out of suspension.
On the exhaust ports a bit of carbon buildup will help insulate the head from absorbing heat.

steell wrote:

mark1122 wrote:

the 80kz flows better than the gpz with bigger ports and valves.whats up?

Velocity Profile comparison = .....c'mon now....I
can't give everything away....

In this case, size ain't everything

A smooth flowing port will allow more air through at a higher velocity than a larger more turbulent port, it's no problem to make a port larger and lose airflow, lot's of people do it when they try to port their own heads. I am a very determined do-it-yourself type, but when it comes to porting I'll let the experts do it

where have i heard this before?:whistle:

mark1122 wrote:

Thanks Steell. Hey Larry, how about a kz ported vs. gpz ported?

Stock valve to stock valve, 38mm/36mm the GPz will out flow the KZ.

Where ported versions are concerned, the KZ with 37.5mm intake valves can be made to flow pretty darn close to a GPz with stock 38mm Intakes. It's more work to get there though.

Food For Thought

The charcteristics of the late model GPz 2V head are different than the KZ heads. They don't even sound the same on the flowbench at 28" of test pressure. At 10" however, the differences are not nearly as distinguisable because the port isn't being worked hard enough.

A lot of shops only have at SF110 bench and there's certainly nothing wrong with that. It's far better than having absolutely nothing to measure progress with. Bob Carpenter went pretty darn fast with heads developed on SF100 and 110 benches.

However, air flow characteristics through a live engine experience depressions in excess of 100" of water. As you can well picture in your mind, the dynamic behavior of the air flow is not going to be the same at low pressures as it is at much higher pressures.

Look at it like this. Picture water flowing over a waterfall at a nice lazy pace. A calm stream feeding smoothly over the radius at the top of the falls.

Now take that same waterfall and picture the major rain events we had here in the north east last summer.

What changed? More volume and more velocity. That nice, smooth flowing waterfall, under the the dynamic condisions of turbulent flow has now changed. The water no longer smoothly turns down over the fall but instead shoots over the radius.

The conditions that influence the flow of water also influence the flow of air.

What does a ridge in the bowl area of the port just prior to the valve seat do to the flow?

Picture water flowing over a smooth concrete surface and then place a broom stick handle across the flow.

So what happens to a port that you have made larger but not picked up a proportional amount of CFM from the effort?

Velocity can drop significantly and torqe can go with it.

Now find the problem down stream, correct it and pick up 5CFM without having increased the cross sectional area upstream any further. What happenes?

If it's proportional, the CFM gained translates into a velocity gain behind it as long as the cross sectional area has not changed there. Why?

Because velocity is area and volume dependent.

larrycavan wrote:

mark1122 wrote:

Thanks Steell. Hey Larry, how about a kz ported vs. gpz ported?

Stock valve to stock valve, 38mm/36mm the GPz will out flow the KZ.

Where ported versions are concerned, the KZ with 37.5mm intake valves can be made to flow pretty darn close to a GPz with stock 38mm Intakes. It's more work to get there though.

Food For Thought

The charcteristics of the late model GPz 2V head are different than the KZ heads. They don't even sound the same on the flowbench at 28" of test pressure. At 10" however, the differences are not nearly as distinguisable because the port isn't being worked hard enough.

A lot of shops only have at SF110 bench and there's certainly nothing wrong with that. It's far better than having absolutely nothing to measure progress with. Bob Carpenter went pretty darn fast with heads developed on SF100 and 110 benches.

However, air flow characteristics through a live engine experience depressions in excess of 100" of water. As you can well picture in your mind, the dynamic behavior of the air flow is not going to be the same at low pressures as it is at much higher pressures.

Look at it like this. Picture water flowing over a waterfall at a nice lazy pace. A calm stream feeding smoothly over the radius at the top of the falls.

Now take that same waterfall and picture the major rain events we had here in the north east last summer.

What changed? More volume and more velocity. That nice, smooth flowing waterfall, under the the dynamic condisions of turbulent flow has now changed. The water no longer smoothly turns down over the fall but instead shoots over the radius.

The conditions that influence the flow of water also influence the flow of air.

What does a ridge in the bowl area of the port just prior to the valve seat do to the flow?

Picture water flowing over a smooth concrete surface and then place a broom stick handle across the flow.

So what happens to a port that you have made larger but not picked up a proportional amount of CFM from the effort?

Velocity can drop significantly and torqe can go with it.

Now find the problem down stream, correct it and pick up 5CFM without having increased the cross sectional area upstream any further. What happenes?

If it's proportional, the CFM gained translates into a velocity gain behind it as long as the cross sectional area has not changed there. Why?

Because velocity is area and volume dependent.

i used to have a picture of bob carpenter on his green/white z1 on my bedroom wall when i was a kid,where can i find a picture of his old z1 at??????