Needing help choosing a mechanical fuel pump for a mild 440/727 under 500 HP mostly street driven.
I see some stock style pumps ranging in price from $20 to $250. Some say rebuildable but the rebuild kits cost as much as the replacement pump.
What fuel psi is normal/ideal for a 750 vacuum secondary carburetor?
If I were to go with an electric fuel pump, how to choose the right one that's not overkill or junk? Thanks
Copper

I've been a fan of the Carter style pumps. BIggest issue I've had in recent years is actually with the push rods going soft and wearing out (specifically the Comp units). I think Mancini or someone sells a hardened one that I've yet to seen fail.

Carter street/strip pump.

I'm happy with my Clay Smith. Not happy with all the grinding I had to do to make it fit.

Summit offers several different part numbers for them, I like and use the older take apart bolt together NASCAR racing type expensive pumps for my Hi Po street cars with no electric pump on them

That is what I have used and never a problem with them. Plus they come apart if need be.
Nice to have something you can fix.

Yep. The Carter M6903 mechanical has been the go-to pump for big block mopars for a LONG time!

i use carter 6903's. i do take them apart and modify them to some extent. i do run return lines. the carter 4862 pump will have too much pressure for normal operations and will have to be regulated.

They work great.

I read several guys modify the M6903 to fit the larger 3/8" fittings. I suspect this mod isn't necessary for my use/application.
No one chimed in about simple electric fuel pump options that would substitute for a stock pump pressure and volume. Thanks
Copper

converting to 3/8" pipe thread is irrelevant unless your using AN fittings. the issue is 1/4"I.D. internal passages which are ok for 5/16" line but are small for 3/8" fuel lines. the edelbrock pumps are carters and have these mods done to them. the issue i've had with edelbrocks is pressure and i can do the internal mods myself and save the extra cost.

I've had 2 Edelbrock pumps literally fall apart on me in the car.

could you explain this ? TIA !

Had to grind the pump and the block to get clearance. They mention this on the web site but I had to go way beyond what they pictured. Still, no problems since installation and no sign of leaks. 1/2" ports, too.

It is like the nascar pump and much larger diamter so it needs to be ground to fit against block.

That has to be for the "Thirsty Engine" option?
Where on the broadcast sheet does does that option appear?
Copper

CV products r5 pump fits 440

I am not sure how much difference that is going to make for moderate applications such as yours.

3/8" tube has a .297" ID. The 1/4" NPT fitting is about .250" ID going into the suction side of the pump. Output is a 5/16" fuel line with .256" ID. The needle and seat are the smaller restrictions. Even the hemi runs a dual off the 4024 which is very similiar except a scalloped chamber with slightly more volume than the 6903/4862. All three use a 3/8" tube input (1/4" NPT fitting) and 5/16" tube output.

The 6903/4862 are the same pump major parts, except the diaphragm spring is stiffer on the 4862 and a slightly different diaphgram disk. What fuel pump pressure is right is really based on your carb spec. Old carter had smaller needle and large float and were rate at a higher psi like Chrysler asked for. Helps with preventing vapor lock. Also helps ensure full pump stroke at high rpm. Edelbrock seem to like a lower pressure, they use the smaller float and larger needle seat which means more force on needle, less force countering from float.

But I have seen both used fine with no issues on moderate hp cars. Even in combo with low pressure electric fuel pump.

The pump is a positive displacement diaphram pump and works fine as designed. Now I can't say if the modern version have strayed from the design criteria and the chinese or who ever have not messed up creating some pumps with much higher pressure. But the original Carter design worked fine.

the 1/4" pipe fittings i have measure around .290+", still bigger than .250" . the 3/8" tube i have measures .300+". if a 3/8" supply line is used with a 1/4" pipe fitting wouldn't opening up the supply port to .31" be an advantage; i think so. if a 3/8" tube is used to supply a carb then wouldn't a .31 pump pressure side passage be more compatible, i think so. now if 5/16" tube is used on the supply and pressure side then the mods are a mute point.

the smaller edelbrock carbs use a .093" seat with the small float and seem to work ok. the 800's i've messed with use a .110 with a small float. i know from experience the small float isn't ideal with the larger needle and seat. the larger needle and seat seem to work better with the larger float which edelbrock doesn't supply. i am picky on tune up so maybe i notice something some folks may ignore. i've seen mopar use the larger float with both small and large needle and seats. all the 340/383 factory avs's i've messed with had small floats and small needle and seats, while the bigger avs's i've had had large needle and seats with large floats. i think the smaller float provides less pressure to the needle and seat and doesn't provide the control that the big float does.

i don't think mechanical pumps are as straight forward to get ideal performance as some electrics are. i've found messing with mechanical pumps that the proof in the pudding is a road or track test with a pressure gauge. this has been an eye opener for me. i used to mock pumps up on a block with a camshaft and push rod installed and spin it all with an electrical motor and do pressure/volume tests. that was a good learning experience.

i've looked into the clay smith pump and do believe for the average guy they could be a can of worms. think they're 12-14psi so they need control, physically don't fit with some folks actually grinding holes in the blocks water passage trying to get them to fit. they were designed specifically for oval track were electric pumps were forbidden. i have to wonder if mopar did some minor casting changes to get them to fit nascar/usac blocks. it's all interesting stuff if one likes the details.

Maybe. What is the BSFC requirement of the motor. The pump as is, can pump the normal motor requirement and beyond. As long as the input chamber fills on a stroke, there is no difference regardless of the hole size. The pump isn't starving for fuel at the inlet. All those smaller oriffices upstream limit the volumetric flow. If the pump was oversize you would spend much of the time with the diaphragm hung in the up position because of the needles being shut. You do want the pump to draw a vacuum on the tank if it needs to pull fuel. My point is it is not too small on the suction side for the design output.

If you look at the hemi inlet it is actually larger, but the bottom design is slightly different. Inlet is at the port, while the 6903/4862 has the actual pump inlet on the opposite side of the bottom with that 1/4" port transfering fuel to the other side. Does beg the question why the carter engineers did that.

Regardless still a 3 valve small chamber pump. The Nascar/Smith type is a 6 valve large chamber. Fuel pressure can still be controlled by spring tension. Just large volume to meet needs of the higher horsepower high speed endurance running.

Some of this got my curiousity and I took a measurement of the 6903 input. Here is a 6903 at the top and a hemi 4024 at bottom. These are period parts. 70s maybe early 80s, carter parts. Again, the 4862 and 6903 share all the same casting part numbers so the bodies are the same. The hemi is on the bottom, the parts are aligned with the smile matched. Bottom and middle only go together one way.
Notice the increased volume of the hemi body because of the gear shaped cavity. That is the output chamber that fuel is drawn into via the diaphragm. 2 valve for inlet, and single valve for outlet. Also notice how small the volume is on the outlet check valve slots.

On the bottom piece you can see how the hemi has an open inlet chamber immediately at the 1/4" NPT threaded hole. The 6903/4862 have a reduced transfer port that moves the inlet fuel to the opposite side. I measure this, and it is not 1/4". It actually is a 5/16" hole. So the 1/4" NPT input goes down to a .3125" hole, still larger than the 3/8" pipe ID even if slightly greater than .300".

Now maybe the newest stuff has smaller holes and such, but still the smallest restrictions are on the output side anyway.

So personnaly I would not be opening a new pump to modify it for a mild car; and if you had a more radical car and need more volume I would look for a 4024, or even some of the older Marine RB pumps that used the same chamber as the hemi. The few holley and such that I have opened still had this smaller chamber. Which is a reduction in volume per stroke, but also generates a slightly higher pressure at shut off to hold the spring compressed. But still plenty of fuel for most needs.

Thank You sir !
i kind of expected this was what was needed, and what was done to remedy the problem, but wanted confirmation of such.
Thank You again for your reply !

if the pumps share the same casting numbers, would it be possible the gear shaped cavity be in the newer pumps ?
the only way to know would be to open them up.
just asking in order to gain knowledge of the 6903 and 4024 pumps.
sorry if i sound so dumm................

6903 and 4862 share same casting. The 4024 is different, but some older style 60 pumps did share casting numbers with 4024. Yes casting numbers are inside. Only outside casting number is on the top arm assembly. Which despite different casting numbers I have not really found any significant difference. Same lever # and assembly. Vent varied some, but.....

I have ran Carters, Edelbrocks, Clay Smith, a Race Pump and a few other auto parts brands. You have to be careful with the PSI ratings they are all over the place.

IMO an Aeromotive Stealth tank is the hot setup for anything that need more than a stock style mechanical pump. There are very few applications I could see the Clay Smith or Race Pump being logical.

Hence why the Race Pump is on the sheld and nobody will buy it LOL.