Anybody know of something larger than a Metri-Pack 150 wiring bulkhead that can be fitted to stock TPI fuel tank? This is for a 340 pump install. Trying to avoid touching fuel lines and make this an easy retrofit.

Option 1: I looked at the GT 280 bulkhead used on later model cars (13516627) but it has a significantly larger o-ring diameter than the original pass-thru in the fuel tank.

Option 2: There is another 6-pin 150 connector of sorts that comes up with internet searches but it appears to be even larger diameter yet.

Option 3: Splice together two wires to double Ampacity of the (B+), And then poke a screw with nuts through the top hat for the (B-). I am not real excited about a screw because a loose nut and ring terminal can spark. Seems the Racetronix double pumper kits use a screw though.

Option 4: Aeromotive has a pump assembly with ring terminal connections, but presents new challenges mating to stock fuel lines.

Picture of stock wiring bulkhead (pass thru). The yellow colored thing-a-muh-bob. (This is from my 2.8L car but the wire bulkhead looks same as TPI).

 

I don't have formal electrical training, just trying to do my best to understand this. I would appreciate input from people that are educated about these things.

After shopping around the internet, it seems all the "upgraded" wiring kits and sender modules I can find have one thing in common.... they're not an upgrade. They all have a stock style wiring bulkhead with 14 AWG wire and Metri-Pack 150 unsealed pins inside the tank. Might be a 3-pin style like original, or might be a 4-pin as a retrofit option, but they're all the same specs. So I figured it would be beneficial to get a better understanding of the terminal specs.

Picture below shows continuous current ratings of Unsealed Metri-Pack 150 terminal (from an old Delphi connectors catalog I have squirreled away). The sum of the matter is keep the surface temperature of the terminal below upper spec limit so that it does not overheat.

• The chart on the left shows what is the heating effect of current through the terminal.
• And the chart on the right blends that with the effects of surrounding air temperature.
• Values are shown for 20 AWG (0.5 mm2) ; 18 AWG (0.8 mm2) ; and 16 AWG (1.0 mm2) wire lead crimped to the terminal.

The key thing here is that the wire acts as a heat sink to help cool down the terminal, and larger wire is a better heat sink. I think the GM engineers used this for advantage.

The 3rd gen wire harness use 14 AWG wire which is bigger than any crimp terminal you can buy for Metri-Pack 150 connector systems (16 AWG max). That tells me right there that GM engineers did something special trying to increase the current carrying capability of that bulkhead. And the resulting current rating (for the terminal) would be off the charts shown here. Assuming the interior of the gas tank does not exceed 50°C (122 °F), the approximate values from the chart is,

20 AWG @ 50°C ---> 14 Amp
18 AWG @ 50°C ---> 16 Amp
16 AWG @ 50°C ---> 18 Amp

If the trend continues, then using 14 AWG might allow that terminal to carry somewhere close to 20A. I'm starting to think a person can get away with using the stock bulkhead with a 340 Lph pump (about 14A @ 13.5V, so can be >14A at higher voltage). And the voltage drop through the plug would be <0.14V.

The next question is, how much does it help to upsize wire size after leaving the fuel tank? I'm looking at that next.

 

My Father says this looks excellent thus far!


He wanted to mention that when comparing Terminals of similar size, the Surface Area of a given Terminal will be a more significant factor than the Mass of said Terminal in regard to the maximum continuous Ampacity attainable.

This is why a Metri-Pack 280 Terminal (with More Surface Area and Less Mass) can support a maximum continuous Ampacity value of 30 Amperes...
Compared to an Amphenol AT/ Deutsch DT Terminal (with Less Surface Area and More Mass) that can only support a maximum continuous Ampacity value of 15 Amperes.

Thank you for the PM!


-Marcello III

 

Seems the two subjects of interest are,

(1) Is the existing 14 AWG wire enough to run the pump?
(2) And how much benefit is there to upsizing wire size?

The 340 Lph pump will be pushing right up on top of the continuous current rating of 14 AWG wire. General rule of thumb is 14 AWG can carry 15A continuous. This is a bit of a soft number though, not a hard rule.

Without going into details, the current rating of the wire is based on an allowable temperature rise (and those targets can vary too), and then another correction factor is applied for use in environments with elevated ambient temperature. A conservative result is about 15A. I think what it really comes down to is life of the wire insulation. The higher the temperature of the wire, the shorter the life.

Probably of more concern is the voltage drop thru the wire and its impact on pump performance. Below are resistance values of 20 foot section of wire,

20 foot of 14 AWG: 0.057 Ohm
20 foot of 12 AWG: 0.038 Ohm
20 foot of 10 AWG: 0.023 Ohm

With a pump current draw of 14A, the voltage drop in the section of cable is,

14 AWG @ 14A ---> 0.80 Volt drop
12 AWG @ 14A ---> 0.53 Volt drop
10 AWG @ 14A ---> 0.32 Volt drop

It appears each step up in wire size is worth ~0.25V across the pump.

And the little 2-foot section of 14 AWG pigtail from the fuel tank would be a pretty insignificant thing to worry about. In other words, keep the pigtail if it is in good condition, and work a fresh harness from there.

 

Excellent info, Chello! Thanks!
And I'm glad Sr. is enjoying following this thread.

 

With that established, the next question is, How does the pump respond to this?

Unfortunately Racetronix only publishes one voltage test point (13.5V) for the RXP340 pump, so I can't use that data to evaluate effects of voltage drop. But Walbro does publish two test points (13.5V, 12.0V) for the 350 Lph pump, same pump that Holley uses in the Sniper fuel module. Different pump curve than Racetronix but not wildly different. If anything Racetronix flows more.

Looking at the Walbro @ 60 psi (for LS engine swap) the numbers are,

300L @ 13.5V ---> 800 Hp
245L @ 12.0V ---> 650 Hp
Note: The Horsepower figures are from the rule of thumb that it takes 1 Gal/hr to make 10 Hp.

This next step is a big assumption, but I gotta start somewhere and I don't have a better idea. I'm using 10 AWG as the "baseline design at 13.5V". And then doing linear interpolation between data points to estimate pump flow at reduced voltage with 12 AWG and 14 AWG wire.

10 AWG @ 14A ---> 13.5V (baseline) ---> 800 Hp
12 AWG @ 14A ---> 13.3V (interpolated) ---> 780 Hp
14 AWG @ 14A ---> 13.0V (interpolated) ---> 750 Hp

Each step up in wire size is worth about +25Hp from the fuel pump. I know, this is loosey goosey but I just wanted to get a feel for how much a difference wire size makes.... and it maybe appears to not be as much as people sometimes think....

Walbro 350 Lph pump flow curve

 

The Racetronix in-tank harness addresses this by utilizing 2 of the pins (the original position and the unused pin) for the power supply, running a pair of + wires to the pump. The negative maintains the same original terminal as well as a second in-tank wire to the sending unit itself, which gets an added external ground wire (it’s been several years but I’m pretty sure that’s how it was). All wires are upgraded gauges from stock as well. The Level Sender wire is maintained so the whole thing is as plug-n-play as can be. Hope this helps

 

Thanks! That's where my mind was headed too. Get the 4-pin bulkhead, double up on the (B+) wire, and just accept that the ground will be run out through 1 pin.

And there's no point building it from scratch if Racetronix already makes sub-assemblies.

 

You’re welcome. I had to go back and find my receipt, from 2016 lol, to check the p/n. FL98 / F7 bulkhead connector assembly.

https://www.racetronix.biz/k/fl98-f7...ly/bcwa-fl98hd