What is the difference between the stock fuel pump found on 302/351W engines for 68 to 79 and the pumps used on ford trucks 80-87?

First one is Carter M6962 fuel pump listed as being 30 gph free flow with the hose inlet on the forward most tube and the outlet on the rear most tube. Then the other one is for the 80-87 trucks same style pump but the Carter is a M60318 rated at 25 gph free flow and the hose inlet is on the rear most tube and the outlet on the forward most tube.

Im curious how did they get 5 more gph free flow out of basically the same pump body?

Im trying to figure out which pump I need to run on my 306 build. I keep leaning towards the 25 GPH one as I do not believe a 306 could ever burn through an entire fuel tank in less than an hour, but I am curious how they got that extra 5 gph and if there is a difference as I might consider running the older style fuel pump.

 

Tolerances?

That GPH rating is "free flow". Do they have a flow rate spec at 5 psig? A little bit of flow resistance will drop the flow rate on any pump, and a lousy pump will drop a lot.

 

Nope just free flow. I am trying to select a mechanical fuel pump that wont be over kill for my truck. Fuel lines are all stock so I know I cant go with a insane flow rate as it will be hindered by the stock fuel line.

 

Maybe the later versions had a return line? The psi number is just a measurement indication of the flow, that's what counts, the internal pump spring against the diaphragm is what determines the pressure, each cycle of the arm moves a certain amount of fuel, the flow is greatest as the pressure approaches zero. The old rule of thumb going back forever was a mechanical fuel pump should flow at least 1 pint of fuel in 30 seconds or less, something like that, which is at minimum over 15 gallons per hour. The engine doesn't burn anywhere near that much! Hopefully.

 

See that's my thing the newer pump is just rated at 25 GPU free flow with the older pump being 30 gph.

But I keep thinking at 25 GPH that means my stock 15 gallon fuel tank would be ran dry. I dont see a 306 build drinking that much fuel. So part of me is like the stock pump should be adequate but I am also second guessing myself if I should just upgrade the pump to a 80 GPH free flow pump.

 

No no no .... That's not how it works, that's what I was trying to explain. The pump needs the ability to supply a lot of fuel under certain conditions. Like wide open throttle. Let's say for the sake of argument your fuel pump produces 20 gph free flow and engine nets 15 mpg. That obviously isn't going to happen in practice, because it pencils out to 300 miles per hour, or some really fouled plugs. Fuel line diameter and restrictions, the float needle, etc, reduces this considerably. When the float needle closes, the pump isn't moving any fuel.

 

And the stock fuel line on a 80s truck is 5/16" so that's why I am not sure as I dont think if I got the Holley 80 GPU fuel pump and reduce the 1/4 NPT to a 5/16" barbell would not me more than the stock pump.

Carb is a dual fill summit 600cfm and I saw some people state stock pump will be fine with a 4v with a transfer fill but with dual fill you need more than stock.

 

I've read 5/16" fuel line is adequate to around 300 horsepower.

 

Which would be bad for me cause DD2000 is estimating 380HP and I figured 306 with 9.5:1 compression with afr heads would be around 340hp.

I take that back I guess the fuel line is 3/8" on my truck. Wonder why the OEM replacement fuel pump uses a 5/16" hose.

Looked up 80-86 fuel lines all tank to pump lines I found were listed as 3/8.

 

I think at least one constant is that the "free flow" rate is supposed to be spec'd at 1000 rpm. At higher engine speeds, it should pump more. But in all cases, if the pump builds fuel pressure up to its designed working pressure, it will simply stop pushing more fuel through (unless it has a return line, in which case it will just bypass the additional fuel to that, back to the tank).

The lines before the fuel pump back to the tank are indeed 3/8", and the fuel in there will be at atmospheric pressure so a bigger line helps flow rate. The pressure side can usually be made smaller because the pressurized fuel can flow faster in a smaller line.

 

I've been running my 400+hp 331 with three two bbl carbs with an electric 30-35 gal/hr pump for 15 years. This is enough volume to supply all three at WOT for 3-4 minutes (don't ask why I know this ) The only time it runs short is when the inline filter needs changing. Stock fuel lines in my 77 Comet and with it in my 89 Ranger with a 3/8 fuel hose run from the stock tank to the carbs through two filters. I used a Purolator electric 30 gal/hr pump on the Ranger and a Mr Gasket 35 gal/hr in the Comet.

 

I found most of those electric fuel pumps to be incredibly noisy. Are there any that are like the high pressure gearotor type pumps for EFI, but produce low pressure for carbs?

 

Neither I ran are noisy at all. You can barely hear either with the key on and the engine off.

 

OK, what brand/types of electric pumps did you run?

 

I think I will just run a 5/16" line from the pump to the carb since I have the line as well as 3/8" line but I don't think 3/8" line would be worth it considering the pick up on the sending unit is 5/16" would be sucking through a straw.

Plus I don't think this 306 is going to make over 350 hp. DD2000 seems to think it will make 370 hp but I think it will make over 300hp but under 350hp.

Should be enough even with a stock fuel pump as ford seemed to have used this style of fuel pump back to 1967 the only thing different it looks like is the inlet and outlet are reversed and the inlet is a straight 5/16" barb while the newer 80-87 pump has a curved barb. Difference cited by carter is 5 gph freeflow between the two. I keep seeing it said now that carter is contradicting themselves on flow rates.

None the less I need to do research on which brand of pump, Summit pump I can get with 80 gph free flow for less money than the Holley pump but the Summit pump has lower rating review wise than the holley. I also don't like the chrome pump look either, Summit has a black pump and I also saw Carter has a plain finish one as well but that one was over $100 for the pump. Even the holley pump was under $90.

In any case looks like I will just be going with 80 gph free flow even though I could probably get by with a 30 gph free flow. But later tonight I might take a gander at the lower gph free flow pumps and see what pricing and what options are out there. I really don't want chrome or a shiny finish pump considering this is a driver and its a freaking truck. I got enough chrome on the outside of the truck don't need to chrome the engine out I want it very stock looking minus the valve covers and the polished stainless steel flanged headed bolts for the valve covers.



As far as the noise on electric fuel pumps goes, you have to mount them in rubber isolators. Ive had some pumps mounted firm and they would make noise like crazy, such as the Holley Red/Blue Electric, even the rubber isolator on the strap around the pump wasn't enough to stop the noise. Took some rubber feet and mounted the mount bracket with a rubber isolator and it was quiet as could be just a slight hum you could hear but not over the exhaust.