5/16" Fuel Pump Inlet for 340?

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domdart

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I'm putting a 72 340 in a 68 Dart. I replaced the 5/16" fuel line with a 3/8" line. My engine builder put a stock replacement Carter M6866 fuel pump on the 340. The M6866 has a 5/16" inlet on it. Should i put the 5/16" sender and fuel line back on the car, or do I need a different fuel pump? I noticed this when I tried to connect the fuel line to the pump with a 3/8" rubber fuel line. Thanks.
 
The stock pump definitely has its limits feeding a 340. Is your motor bone stock? If you have any mods at all or are running a Holley carb you need more fuel. If you want to stick with a mechanical pump they do make high volume mechanicals that you can put a 3/8 fitting in. Of course intended use plays a big part also. If its never gonna see over 5 grand your probably fine with the stock pump.
 
Get a pump with 1/4 NPT fittings and adapt accordingly.
 
Thanks 340doc. My motor is 30 over, 10.5 to 1 pistons, 1800 to 6000 cam, 2.02 valves. It has an air gap intake and doug's headers. Edelbrock tech recommended a 650 carb (have not ordered yet). It's intended use is just for weekend fun and cruises. The Comp cams program claims I'll be in the low 400's horsepower range.
 
For weekend fun and cruises, it seems like plenty of carb IMO. I would not worry over the 5/16" in and out of that pump at 400 HP; the main pressure loss in the 3/8" tank line will be under 1/2 psi at that fuel flow rate and the 5/16" fittings won't add much to that. The 5/16" sender and pickup would be more of a concern.

BUT your main issue is that the Carter M6866 pump is rated at 25 GPH and you will exceed that at 400 HP, so IMO your main concern is the pump itself, not the fitting sizes. Time for an HV pump at least; you don't want to burn a piston top at peak HP due to leaning out.

http://carter.opticatonline.com/part/carter-m6866-mechanical-fuel-pump

PS: And thanks for asking this question....I got to thinking after replying and asked my son, and we realized had just thrown a stock pump on our new 340 with the same HP rating... Whooops! LOL
 
Are the more expensive fuel pumps worth the money? I can get a Mopar Performance 80 gph for $45, a Carter M6902 120 gph for $75, or any of the more expensive ones at $150 and up.
 
How much is your car worth to you?
Don't cut corners on the important aspects....
"An ounce of prevention is worth a pound...." someone once said...
 
I was just thinking about the NHRA HP ratings and carb changes in relation to the 340 over those few short years. Ma Mopar seemed to think the larger TQ was a good thing and the numbers also agreed.
 
Just my two cents- I am doing a 360 into a 70 dart, the usual carb/intake/mild cam/headers, 3.55 gears/auto. Use will be car show/cruise stuff. My thinking was as long as I have the entire car disassembled, I would replace the original s6 5/16 fuel line to a 3/8 line (more fuel volume in a 3/8 line) and tank pickup, with a HP Carter mechanical pump. If needed later, an electric pump could be added. More a "want" than a "need" maybe, but I "justified" the expense to myself! "Back in the day" I do remember my mildly modified 340 Duster (stock fuel pump) running out of fuel at higher rpm until I added an electric pump that solved the problem.
 
I run my 360 Magnum with an autozone airtex $20 pump, demon 650dp, 6.5 psi regulator, 5/16" sender/3/8" fuel line/5/16" pump inlet, 3/8" pump to regulator to carb. Your pump should be fine and a properly tuned 650 is plenty for real world and also when you do the math. My 60' time is .15 quicker with a 650 vs 750. Throttle response is also better with the 650.
 
I mentioned this on another post. There is a preformed hose that goes from 3/8" to 5/16". I'm not sure it is long enough to go from your 3/8" main line to the pump inlet. It might be a couple of inches of short, but you could just extend your 3/8" line with a small connector piece. Cost is about $10 on eBay.

Definitely do NOT replace the 3/8" main line that you already installed. That should work fine.
 
I have the 6902. Its 15 plus years old and still going. It's been pumping 87E10 it's whole life.

Cam that goes 1800 to 6000? Ima guessing around 220@.050? With X/J heads and 2.02s, Ima guessing power will not touch 400. But let's say it does;
400hp @ .5 pound/hp/ hour =200 pounds/hr.; 200/6pounds per gallon =33 gph. As a streeter you will not likely need much of a pump, cuz top of second gear is already speeding. So your 340 will only be pulling hard for 2 or 3 seconds at a time, but let's say 5 seconds;.
so if she pulls for 5 seconds; thats [33/(60minutes x 60 seconds) ] x 5seconds = .0458 gallons =5.86 ounces. Now up here in Canada a regular can of Coke is 10 ounces. So your 340 will need about 60% of that. But wait there's probably 3 or 4 ounces in the bowls....See the point? Just about any old pump will work under these parameters.
Having said that; stay off the track!! or buy a pump.
IIRC 340s came with 625ish cfm carbs in 68/69
I put a 600 holley on my 360 (400/430hp) for a couple of long distance tours. It ran fine when jetted right. Sure I could feel the power loss in the upper register. But with a 223 cam, it wasn't that lazy around town.
From 5000 to 7000 it runs better with a 750.
She really likes the big TQ. At around 800 total cfm, the top is good to go. And the much smaller primaries keep things sharp down low.

I'm running Eddies and a 230 cam. 10.7Scr, TTIs and an AG intake. 3.55s and a 3.09low M/T.
The M/T really likes the DP Holley
http://www.hughesengines.com/TechArticles/11360dynotestfeb2000.php
http://www.forabodiesonly.com/mopar/showthread.php?t=333502
 
Are the more expensive fuel pumps worth the money? I can get a Mopar Performance 80 gph for $45, a Carter M6902 120 gph for $75, or any of the more expensive ones at $150 and up.
It's not a matter of 'worth the money'... it is a matter of do you have an impending problem or not. It all depends on if the individual pump you have exceeds the stock published Carter rating of 25 GPH or not....some will but some won't. If you are pulling 400 HP, and the carb is decently tuned, you will be pulling around 35 GPH flow rate, and that pump is rated at 25 GPH. No one here can guarantee if your particular M6866 pump will support that higher rate or not.... If you run the carb lean, things might be OK, but it might not. The risk is a burned piston top....seems unwise to me to not spend up to $100 for a pump upgrade.

From some comments on FABO, I'd avoid the M6702 which puts out a higher pressure level and can overwhelm the needle and seat on the Holley.

The mid priced ones that you mention should do the job... but I can't say anything + or - about $20 Autozone Airtex pumps LOL
 
A true 650 with good metering characteristics and secondary transition is one thing but he did say Edelbrock.... and the RPM potential for a 340 even in stock form begs for more unless you have a tight converter and highway gears or are over cammed for the compression ratio.
 
A true 650 with good metering characteristics and secondary transition is one thing but he did say Edelbrock.... and the RPM potential for a 340 even in stock form begs for more unless you have a tight converter and highway gears or are over cammed for the compression ratio.

True. Edelbrock carbs do suck.
 
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