Performance fuel pump

[77 K20]

Removed my old engine today and bought a HT383 for a replacement. The GM install manual said they recommended one of their own GM Performance mechanical fuel pumps. So I bought the part # they listed.

My old fuel pump has 3 lines under it. 2 inlets, and 1 outlet.

New fuel pump has only 1 outlet and 1 inlet. Do I just Tee the 2 inlets together? Is it one inlet from each tank (I have dual tanks) Or is one a source and the other a return?

Haven't had time to search here... maybe this has already been covered? I work nights, and for the next few days will be getting up at 8am to work on the engine swap. Then do a full night shift at work also... 4pm- 3am. Not much time for searching or sleep.

 

[77 K20]

So far it looks like the 3rd line is a return line. Performance fuel pumps don't seem to have return lines.

Options are cap it off, and hope it doesn't have vapor lock issues... or somehow plumb up a Tee fitting into it with a restrictor so I don't loose too much pressure and use that Tee fitting as a return.

The GM fuel pump I bought (P/N 12355612) says it has a 7psi fuel shutoff so I shouldn't need a fuel regulator.

 

[MadOgre]

you should trace those lines back and see where they go. you should have one supply and one return. some had one supply and no return. I have not seen 3 lines to the fuel pump before. but if you had a fuel pump with 3 connections maybe you do have 2 supplies and one return.

 

[77 K20]

you should trace those lines back and see where they go. you should have one supply and one return. some had one supply and no return. I have not seen 3 lines to the fuel pump before. but if you had a fuel pump with 3 connections maybe you do have 2 supplies and one return.

Finally pulled the old fuel lines off of the stock pump. The 3rd line is a restricted return. It is now capped off in the truck.

 

[MadOgre]

Finally pulled the old fuel lines off of the stock pump. The 3rd line is a restricted return. It is now capped off in the truck.

Yep you know I changed my fuel pump the other day and it suddenly struck me that you were talking about 3 lines including the supply line to the carb. I thought you meant not including the supply line to the carb LOL

Ya its a return line. I have found that with stock fuel pumps the ones with the return line tend to last much longer than the ones with out. Especially when running a fuel regulator.

 

[Driver4r]

Run an external regulator with a return . And hook up the return to your factory line.

 

[77 K20]

Run an external regulator with a return . And hook up the return to your factory line.

The pump is supposed to have an internal regulator set to 7 psi. I had the truck running for 2 days before my radiator split... but in those 80 miles the truck ran pretty good. Very good throttle response off of idle.

However the was a few times where it would start bogging down when pulling away from a stop. Looked at the engine later and I could see where the carb was flooding out and leaking from the top plate down the front of the carb. Carb was just rebuilt and the float is at the proper level. Maybe the level should be lowered since the fuel pump can pump more?

 

[Driver4r]

The reason I said to run an external regulator/return is cause #1. Unless both fail. You have guaranteed constant pressure. #2. It gives you a return since right now you have NONE.

I wouldn't touch the float height. If the fuel pump is pushing the needle open. Reduce pressure.

 

[77 K20]

The reason I said to run an external regulator/return is cause #1. Unless both fail. You have guaranteed constant pressure. #2. It gives you a return since right now you have NONE.

I wouldn't touch the float height. If the fuel pump is pushing the needle open. Reduce pressure.

So ordered some parts to be able to hook up the fuel return line again. One thing I have been trying to read about is how much to restrict the return line. Having a wide open 5/16" line will drop too much fuel pressure.

The stock pump has a built in restrictor to it. I've been having problems finding a hose fitting with a built in restrictor. Seems a few online have said somewhere around .060-.070 would be good. Some said just smash down the end of the hose fitting.

What did you do on your return?

 

[Driver4r]

Right now I have no return on my monte. They never had them from the factory. But I've read of people putting in pickups with them and running SS all the way. And I plan to run a regulator/return that way I can adjust it on the go if I need.

 

[77 K20]

Right now I have no return on my monte. They never had them from the factory. But I've read of people putting in pickups with them and running SS all the way. And I plan to run a regulator/return that way I can adjust it on the go if I need.

The only restrictors I found so far were AN fittings... for SS lines and whatnot. Better than rubber... but $$$.

 

[chengny]

You know that particular pump you have looks like a well made pump but it really isn't all that much different than a stock Delco pump.

That GM (or Chevrolet) Performance pump - BTW it has nothing to do with GMC, that is just the name of the company that markets it - has a shut-off of 7 psi and a free flow rate of 30 GPH.

The GM spec for their Delco pump called for a shut off head of 6.5 psi and a flow rate of about 25 GPH.

My point is, I am not trying to criticize the pump - it's just that if you didn't require a dump/return line before, you probably don't need one now.

They can call it what they want, but all diaphragm operated positive displacement pumps have a built in shut off pressure.

When the flow out of the pump is reduced to zero or near zero and head pressure is high, the diaphragm can't flex open as far as it can with no/low head pressure. So the discharge rate/pressure is self regulating. The higher the head pressure it is trying to pump against, the shorter the effective stroke and thence the smaller the amount of fuel delivered per pulse.

If you do a flow test of a stock fuel pump it really brings this home. Take a hose attached to the outlet of a Delco pump, put it in a glass container and crank the engine. It is amazing how quickly you can fill pint bottle. It is supposed to take 15 seconds but it fills a lot faster than that.

When the carburetor is full (and the float valve shuts down the flow in to the bowl) the pump just goes into "neutral" and no gas moves until the float drops and opens the valve again. I honestly don't think that the return line serves any purpose - some pumps have that nipple for a return line and some don't. Maybe the designers were afraid of vapor lock if the fuel got too warm by being near the engine too long. A small recirc line back to the tank would help keep a fresh supply of cool gas at the pump suction.

These are just my thoughts on return lines.

 

[77 K20]

Chevrolet Performance makes a few different mechanical fuel pumps.

P/N 6415325 flows 30 GPH and has 1/4" NPT inlet and outlet fittings. This pump would probably work just fine, and would have fit better. For some reason their install manual says they recommend a larger one.

P/N 12355612 flows 110 GPH and has 3/8" NPT inlet and outlet fittings. This was the one I ordered.

They go on to say if the engine will be used for racing or competetion order a even bigger one with 1/2" NPT fittings. Flows even more.

Thanks for the input. The truck is running pretty good without one right now- but it is pretty cool currently. I'm thinking next summer when it is 90+ degrees out and I'm slowly crawling up a hill doing 3 mph the fuel lines will get plenty hot. Having some flow circulating back to the tank might be a good idea. Just trying to figure out how much would be too much and how the best way to limit it would be.

 

[chengny]

Seriously, when was the last time you heard of someone getting "vapor lock"?

I'm pushing 60, and it's never happened to me and I don't know anyone who had it happen to them.

How would you even know if it occurred? Vapor lock is a buzz term for cavitation at the pump inlet. The normally liquid gasoline turns to a vapor (basically it boils) due mainly to low suction pressure and to some degree by high temperature.

The fuel pump cannot pump vapor and so the flow stops. The car stumbles or briefly stalls. And as soon as the engine slows or stops, the pressure on the suction side of the pump rises to atmospheric. This causes the vapor pockets to collapse and the inlet to the pump is again flooded with liquid gasoline.

If it ever happened, you'd probably just turn the key and restart. You might scratch your head for a second, and wonder "what the hell was that" - then drive away and never give it another thought.

 

[Driver4r]

Never vapor lock. But I've been having really bad heat soak into the fuel line and the carb heating up and it boils the fuel faster then i could burn it.