Stock TBI Fuel Pressure Reglator Springs Measured

[dave w]

I had a chance to get some very precise measurements on a couple of Stock TBI Fuel Pressure Regulator Springs. The spring force was measured at 15mm compressed height, which is about the maximum compressed height a stock TBI pressure regulator will allow. I don't have a clue, or even a wild guess as to what kind of fuel pressure the stock springs are capable of providing when compressed to 15 mm! The conclusion I get: more Newtons = more fuel PSI.

dave w

[1project2many]

Multiply Newtons by .2248 and divide it by the area of the regulator piston in square inches and you'll arrive at the PSI reading those springs can achieve.

[dave w]

Multiply Newtons by .2248 and divide it by the area of the regulator piston in square inches and you'll arrive at the PSI reading those springs can achieve.

That's excellent information!:thumbsup:

My thinking was to second source TBI fuel pressure regulator springs:
http://www.leespring.com/compression_spec.asp?springType=C&forWhat=Search

Here are more TBI fuel pressure regulator springs I measured today:

30 PSI (454 Late) = 217.1 Newton @ 15mm compressed height
22 PSI (Ebay Parts supplier) = 114.3 Newton @ 15mm compressed height
15 PSI (Ebay Parts supplier) = 87.63 Newton @ 15mm compressed height

[EagleMark]

Nice! :thumbsup:

[dave w]

Multiply Newtons by .2248 and divide it by the area of the regulator piston in square inches and you'll arrive at the PSI reading those springs can achieve.

Here's what I measured for the piston diameter (6.26mm +/- 0.03mm)? I'll need to do some math / conversion for area / square inches.



dave w

[1project2many]

Calculated pressure provided at that much force produces values in the 300 to 500 psi range. The math is right, and I agree with the piston diameter measurement. The spring compression stock must not be anywhere near that. It should be possible to work out the stock spring compressed length in a non-adjustable regulator very easily. Measure the free standing length of a known spring, say the 30 psi spring, and enter it into the spreadsheet free length. I'll use the result in another spreadsheet I've made for a handy TBI spring helper.

[dave w]

I have input the 454 30 PSI free height into the attached spreadsheet. I added a few addtional measurements. I've been wondering, if maybe the spring O.D. is the pistion diameter?

dave w

[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