Stock TBI Fuel Pressure Reglator Springs Measured

[1project2many]

The piston is not completely simple. I treated it as if it's a single diameter, which it is when considering pressure applied by the fuel pump. But because some fuel is trapped above the diaphragm even when the pump is off there is a slight amount of force due to gravity acting on a much larger area. I don't expect it to be significant though.

I haven't looked at a regulator in years and I couldn't easily find one in the barn to look at. I think I've got inlet and outlet swapped in my head. If the inlet is the small hole at 3:00 in the previous photo, then the diameter of the disk in the diaphragm is the major piston diameter. Do you have a diaphragm available still to check that measurement?

(Edit: I did have inlet and outlet swapped).

[dave w]

The piston is not completely simple. I treated it as if it's a single diameter, which it is when considering pressure applied by the fuel pump. But because some fuel is trapped above the diaphragm even when the pump is off there is a slight amount of force due to gravity acting on a much larger area. I don't expect it to be significant though.

I haven't looked at a regulator in years and I couldn't easily find one in the barn to look at. I think I've got inlet and outlet swapped in my head. If the inlet is the small hole at 3:00 in the previous photo, then the diameter of the disk in the diaphragm is the major piston diameter. Do you have a diaphragm available still to check that measurement?

(Edit: I did have inlet and outlet swapped).

Here is what I have.

dave w

[1project2many]

Thanks. It looks like the piston diameter is roughly equal to the canister inside diameter. I subtracted the diameter of the outlet port to come up with an area of 1.58 square inches. At that value the 30 psi big block spring returned a calculated pressure of about 26.4 at the installed height you measured. Did you ever measure pressure with that spring installed?

This helper sheet could be made into a spring database of sorts by measuring data such as number of coils and wire diameter. Maximum compressed height before coil bind could be determined along with max pressure for a given spring. That's probably more data than most people need to have though. The "pressure change per 1/4 turn" is based on the internet instructions which install a 24 thread per inch screw in the bottom of the regulator. Using a metric bolt or a machine screw with different thread pitch would alter that calculation.

At least this will give an idea how much pressure can be obtained from various springs.

[dave w]

Thanks. It looks like the piston diameter is roughly equal to the canister inside diameter. I subtracted the diameter of the outlet port to come up with an area of 1.58 square inches. At that value the 30 psi big block spring returned a calculated pressure of about 26.4 at the installed height you measured. Did you ever measure pressure with that spring installed?

This helper sheet could be made into a spring database of sorts by measuring data such as number of coils and wire diameter. Maximum compressed height before coil bind could be determined along with max pressure for a given spring. That's probably more data than most people need to have though. The "pressure change per 1/4 turn" is based on the internet instructions which install a 24 thread per inch screw in the bottom of the regulator. Using a metric bolt or a machine screw with different thread pitch

I measured the fuel pressure. Not sure how accurate the gauge is? Seems to me the gauge accuracy vs. calculated pressure are within the margin of error.

dave w

[dave w]

Thanks. It looks like the piston diameter is roughly equal to the canister inside diameter. I subtracted the diameter of the outlet port to come up with an area of 1.58 square inches. At that value the 30 psi big block spring returned a calculated pressure of about 26.4 at the installed height you measured. Did you ever measure pressure with that spring installed?

This helper sheet could be made into a spring database of sorts by measuring data such as number of coils and wire diameter. Maximum compressed height before coil bind could be determined along with max pressure for a given spring. That's probably more data than most people need to have though. The "pressure change per 1/4 turn" is based on the internet instructions which install a 24 thread per inch screw in the bottom of the regulator. Using a metric bolt or a machine screw with different thread pitch would alter that calculation.

At least this will give an idea how much pressure can be obtained from various springs.

I updated the excel spreadsheet with the free length measurements for the stock springs pictured in the first post.

dave w