From carb. to injection, what to do to fuel system?

[Eric]

i am swapping an sr20 engine to my '79 620. Is there anything i should change to the fuel system other than installing an electric fuel pump, inline or in tank?

[datzenmike]

Does it have a return line? It should have an aluminum vent line to a charcoal canister mounted to the rad support so don't mistake this for the return and don't use it for that. Forgive me I don't remember what year or engine is in your 620. Our later 620s with L20Bs had a return line already and your might. An EFI engine will definitely need one. Any hoses and hose clamps should be EFI rated as the 620 ones only have gas pulled through them. EFI is under at least 45 PSI so get something rated for much higher.

[Eric]

Mine is a 79 and had an L20B, and the fuel tank has a return line.

 

 

Here is the tank, according to my workshop manual it has a return

 

 

So that won't be a problem, i will replace all flue lines just to be sure. The charcoal canister is present in the car, i know these from my s13 and s14.

[Spiff]

I used an inline pump on my 720, I also had to plumb a return line since it didn't have any. 

In tank is definitely the quietest choice but it is a bit more complicated than just plumbing in an external in line type. 

[datzenmike]

We all had return lines on our 720s. It was for extremely hot weather that causes vapor lock. After shut off, the under hood temperatures get so high the gas boils in the line and/or the carburetor. The return line allows cooler fuel to circulate past the carburetor. It also keeps the tank cleaner as slowly all the gas in the take is circulated through the in line filter.

[thisismatt]

Make sure the return line is large enough (check the size of return line from the vehicle the motor is from).  The return line shouldn't add more restriction past the fuel pressure regulator.  You'll also need an EFI pressure rated fuel filter.  Wiring will include the applicable pump wiring, fusing, and relay triggered by the ECU.

[Spiff]

On 1/19/2020 at 12:13 AM, datzenmike said:

We all had return lines on our 720s. It was for extremely hot weather that causes vapor lock. After shut off, the under hood temperatures get so high the gas boils in the line and/or the carburetor. The return line allows cooler fuel to circulate past the carburetor. It also keeps the tank cleaner as slowly all the gas in the take is circulated through the in line filter.

 

I should have noted that mine was a J16 equipped 720. The L and Z engined trucks probably had the return line but mine didn't.

[Stoffregen Motorsports]

So many benefits to an in-tank pump. They run quieter and cooler (which makes them last longer) and it's easier to avoid starvation problems with a submerged pump.

 

A generic pump, like one from https://www.tanksinc.com/ would be pretty easy to plumb into a stock fuel tank. You just need to double check the pressure requirements before you buy. These are the pumps I use - https://www.tanksinc.com/index.cfm/page/ptype=product/product_id=84/category_id=61/mode=prod/prd84.htm

 

Also, a three-way fuel filter/regulator means you don't need a return line all the way to the engine bay. https://www.tanksinc.com/index.cfm/page/ptype=product/product_id=425/category_id=172/mode=prod/prd425.htm

Edited January 21, 2020 by Stoffregen Motorsports

[Unfamilia]

I have been looking at those LS corvette filter regulators for my set up. We didnt get those here in Australia so a bit more expensive to source. 

Anyway, Is there any issue of running these as they are set at 58psi when the injectors from the car i plan on using are usualy run at 42psi? 

 

Also how often do they need changing? 

Would be worthwhile if its only every 50000miles or so. 

Dont want to modify the tank if possible

[Stoffregen Motorsports]

 

On 2/3/2020 at 12:39 PM, Unfamilia said:

I have been looking at those LS corvette filter regulators for my set up. We didnt get those here in Australia so a bit more expensive to source. 

Anyway, Is there any issue of running these as they are set at 58psi when the injectors from the car i plan on using are usualy run at 42psi? 

 

Also how often do they need changing? 

Would be worthwhile if its only every 50000miles or so. 

Dont want to modify the tank if possible

The only way to not modify the tank is to use an inline fuel pump, and I believe we've discussed the pitfalls of those.

[Mattndew76]

You would have to make a custom Pump and Float bracket to avoid modding the fuel tank.

 

That is one filthy tank

[thisismatt]

On my 521 I've been thinking of doing a low pressure inline pump into a secondary "surge" tank housing the factory 350z in-tank pump.  The low pressure pump just has to keep the surge tank topped off, with a return to the main tank, and the in-tank pump (now in surge tank) feeds the motor and the motor return line goes back to the main tank also (or none at all in the case of the return-less 350z stock setup).  This seems overly complicated, but I could retain the stock fuel sender & tank pickup location, and reduce the need for any  major tank modifications (eg baffling for the in-tank pump).

[datsunrides]

Here is what I did to my 521 tank when I swapped a KA-E.

 

 

 

 

I have have also done a setup with a surge tank and also used the tanks inc. module. The surge tank is probably easiest but it’s kind of messy plumbing wise. Tanks inc. setup is nice because no welding. Back when I did the 521 the Tanks inc. setup was not around or that would be the way to go.

Edited February 12, 2020 by datsunrides

[Eric]

i think i will use the surge tank option. all can be fitted under the bed so nobody can see the messy plumbing. External fuel pump bolted the the frame and thats it.

[Stoffregen Motorsports]

Lots of problems with surge tanks. The major aftermarket EFI companies have been working through those problems now and offer some aftermarket surge tanks, but there still is the potential for fuel starvation and burning your motor down.

 

The Tanks Inc setup has a baffle as part of the assembly and it works well.

 

Why are you so opposed to modifying the tank?  All the work you will have into the surge tank, the in tank option will be easier and look a lot cleaner without all that crap under the hood.

[thisismatt]

What crap under the hood?  And how are the surge tanks ending up with starvation?

[datzenmike]

Over thinking this. Do all Nissans with EFI have 'surge tanks'?????  It's a 620 truck so I doubt much auto cross. Get a simple but good inline pump that is mounted lower than the tank or as low as possible. It's never going to run dry down there. Keep the fucking tank at least 1/4 full

[thisismatt]

2 hours ago, datzenmike said:

Over thinking this. Do all Nissans with EFI have 'surge tanks'?????  It's a 620 truck so I doubt much auto cross. Get a simple but good inline pump that is mounted lower than the tank or as low as possible. It's never going to run dry down there. Keep the fucking tank at least 1/4 full

 

Except their are advantages to stock in-tank pumps. My point was not to make a surge tank for the sake of a surge tank, but to possibly avoid the difficulties of  retrofitting a stock bottom feed tank  with a stock efi pump. Depending on the tank height and efi pump height, the pickup may be quite far from the bottom of the tank without recessing the pump, there's no baffling, you'd likely have to put/drain/dry the tank, etc. 

[Stoffregen Motorsports]

 

16 hours ago, thisismatt said:

What crap under the hood?  And how are the surge tanks ending up with starvation?

 

 

13 hours ago, thisismatt said:

 

Except their are advantages to stock in-tank pumps. My point was not to make a surge tank for the sake of a surge tank, but to possibly avoid the difficulties of  retrofitting a stock bottom feed tank  with a stock efi pump. Depending on the tank height and efi pump height, the pickup may be quite far from the bottom of the tank without recessing the pump, there's no baffling, you'd likely have to put/drain/dry the tank, etc. 

 

The surge tank is under the hood, unless you hide it somewhere else.

 

All of these problems have been addressed by Tanks Inc. The height is adjustable, it comes with a baffle/box at the bottom of the pump. And it's only about $220.

[thisismatt]

I never suggested putting a surge tank under the hood. I was thinking by the stock tank.

[datsunrides]

On the car I used a surge tank setup on, I repurposed a evap can to use as the surge tank as it had enough nipples and in good spots to perform the function. As a benefit, it fit behind the rear panel cover in the back of the wagon.

 

[5t341tH]

I did a SR20 swap as well. I used an in-tank fuel setup so it is much quieter. Mine was a retrofit kit so it was a drop in. Just drill holes and bolt on. Uses -6an fittings