Stock fuel pump limits

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mopowers

mopowers

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What are the limits of a stock 340 fuel pump? Trying to decide if upgrading pumps will be necessary for the occasional trip to the drag strip.

Combo is as follow: stock stroke .030" over 9.7:1 340, RHS heads, 231*/.562" hyd flat camshaft, airgap intake, Dougs headers, 727, 3.91s.

I've got a 670 Holley Street Avenger carb on it now, but I'll soon be swapping in a 750DP Holley and taking it out to the drag strip. Just wondering if the stock fuel pump will suffice. What do you guys think?
 
Carter makes a nice higher performance mechancical that looks factory that I use on most builds. A stock pump will move enough fuel for 3-400hp.
 
If the car leaves hard off the line it will run out of gas with mech stock pump.
 
If you dig into the specs for the current replacement Carter pumps (that are priced at $25-30), the spec is 25 GPH max at rated output pressure, which is not good enough for 350-400 HP. But I suspect many will do 30-35 GPH; 35 GPH is good for 400 HP. The higher performance Carter pumps like M6270 (and M6902 if you can find one) are good for the 50-60 GPH range at rated pressure. With these Carters, watch out for the pressure of the M6270; it is above the pressure range for a lot of carbs, so a regulator is needed.

BTW, the Summit descriptions of these Carter carbs that they will flow 120 GPH at rated pressure are wrong. 120 GPH flow is the free flow rating.
 
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I think you are pushing it with a stock fuel pump. I'm running the carter high volume mechanical with no trouble into the low 12s soon to be high 11s.
 
moper said:
Carter makes a nice higher performance mechancical that looks factory that I use on most builds. A stock pump will move enough fuel for 3-400hp.
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Carter mechanical fuel pump on my 400 horse 340. Nice because its already rated at 6 or 7 psi which is the limit of the eddy carb. On the dyno the engine builder said after about 7 seconds at wot it would just start to lean. But as we know there are shifts in between so although you may be wot there is a rom change in between gears unless your power shifting which i wont ever do. I probably could use a little bit better volume pump but it seems to work fine and the engine builder didn't recommend it. Its a street car after all. May be needed if the car will see multiple track visits a year
 
Thanks for the input guys. If I need to upgrade, I'm hoping to find a pump that I don't have to use a regulator with. It's too bad Carter doesn't make their M6902 anymore.
 
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Yeah, I think my son got one of the last M6902's from Mancini....but adding a regulator should not be a show stopper, IMHO. I would upgrade so as to never worry about running a bit lean when I wrung it out.
 
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Trying to decide if upgrading pumps will be necessary for the occasional trip to the drag strip.
Combo is as follow: stock stroke . Just wondering if the stock fuel pump will suffice. What do you guys think?
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I would put a known accurate gauge plumbed to the carb inlet & see what the current pump delivers then go from there
 
I ran the carter HV pump for many year, had many times of starvation, but in the end. It was never the pumps fault.
Fixed cracked rubber vent hose(metal line plugged full of bugs)
Installed headers, clip cam off of fuel line next to header. Fuel line to close to header (vaper lock)
insulated fuel line in that area.
built a shield to block radiator heat from fuel pump (made it worries)
added a little electric fan to blow on fuel pump it self.
added insulated spacers on carb.
even tried the wooden clothes pins on the fuel line.

some of these things help but none of them fix my problem. The fix?
A cheap autozone inline fuel pump(yeah that little cheesy on with the look like a filter with two wire on it)
As long as i turned it on, i never ran out of fuel in the 1/4 mile on a hot summer day.

I think that carter mechanical fuel pump will supply all the fuel that most will need. As long as you can keep it away from the hot spots.
That's why a electric pump works so well, they don't boil the fuel, the push it thru.
A return fuel line would have fix all my problem as well.:BangHead:
 
Ive run the heat sheath on my fuel line from the torsion bar up and it seems to help most noticeably in the summer months
 
stock 1971 340 4 speed Duster with 750 Holley, ld340 intake, 1.5" Tubular Automotive headers, 4.56 gears, slicks. runnin 13.1 at 102 mph. add fuel pressure gauge-at top end 1 psi. add electric pump-12.8 at 105
 
Ya know.... just for grins, I computed about how much fuel is used by a 12 or 13 sec drag run with a rather mundane BFSC of 0.5. It comes out that at WOT, you're gonna use a whole whopping 1 pint (or a bit less) of fuel in that 12 or 13 seconds! No wonder that a stock fuel pump will cut it at 25 gph for the 1/4 mile.... the fuel in the bowls will drop a bit but not by much. It may be that Marcohotrod's experience with adding the electric pump and lowering ET may be showing that the fuel is juuuust starting to drop in the carb.

Now take that same pump and HP and car and run it on the open road at 100-110 MPH, and it's gonna run the fuel low in the carbs.
 
25 gph will give you 10.6 ounces in 12 seconds, quite short of a 16 ounce pint. and 25 gph is in a perfect world, add a filter and some 90 degree fittings and some G forces, and my results are real world facts
 
Marcohotrod said:
25 gph will give you 10.6 ounces in 12 seconds, quite short of a 16 ounce pint. and 25 gph is in a perfect world, add a filter and some 90 degree fittings and some G forces, and my results are real world facts
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Roger.... the total consumption is lessened a bit by the fact that you are not running full fuel consumption through the whole RPM range, so that is a bit of a break to the pump.

The point is that 25 gph (stock type pump) is on the margin of running out in the 1/4 mile with over 300-325 HP. You have to wonder how many are leaning out on the top end. I just don't see any sense in putting something as simple as a fuel pump at the margin of working.
 
Thanks for the input guys. Seems like a stocker would be close to it's limit at the track. Especially when you do the math.
 
mopowers said:
Thanks for the input guys. Seems like a stocker would be close to it's limit at the track. Especially when you do the math.
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Just saw this, a lot of good input!
My own experience with top end on a 1972 Challenger 340 4 speed, saw 125mph and 5500 rpms, don't ask where!
Added Holley red pump, saw 138mph and over 6000rpms, still had pedal left!
So yeah, even a stock 340 can use more pump.
 
I can't believe nobody mentioned the limiting factor of the factory 5/16ths inlet fuel line. The pump can only push along what is available to it. Stepping up to a 3/8 line will make a significant difference in the amount of fuel the stock pump can pass along under load.
 
sccachallenger said:
Just saw this, a lot of good input!
My own experience with top end on a 1972 Challenger 340 4 speed, saw 125mph and 5500 rpms, don't ask where!
Added Holley red pump, saw 138mph and over 6000rpms, still had pedal left!
So yeah, even a stock 340 can use more pump.
Click to expand...
Hmmm, that is very telling. Thanks for the info!
 
sccachallenger said:
Just saw this, a lot of good input!
My own experience with top end on a 1972 Challenger 340 4 speed, saw 125mph and 5500 rpms, don't ask where!
Added Holley red pump, saw 138mph and over 6000rpms, still had pedal left!
So yeah, even a stock 340 can use more pump.
Click to expand...
Who aims to hit speeds that high only halfway into the pedal. Bullshit.
A 410 cid engine has run with a stock pump into 130 + mph .
 
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