I have a couple of the older Carter small block mechanical fuel pumps, M6902. One is currently installed on my 360 motor, the other one is in the box...LOL, you know, just in case the 1st one gives up the "ghost"...

OK, so out of curiousity I went looking for the replacement kit...I figured if anything the rubber diaphram would be the first to go, especially given the gas mix these days. No surprise I suppose, but I did not find any genuine Carter parts.

So that begs the question, other then Mancini selling some generic stuff (claims to work with M6902, etc, but on-line feedback is "so so" at best), what are the other alterantives?

Off I went to Summit Racing, but as it turns out the M6902 is no longer available, and it seems the only like part is the M6270.

Therfore, I am curious: what is the difference between the old M6902 and the new M6270 pumps?

Their specs read pretty similar, the only difference actually seems to be:

M6902
Free Flow Rate: 120 gph
Maximum Pressure (psi): 6 to 7,5 psi

M6270
Free Flow Rate: 120 gph
Maximum Pressure (psi): 6.9 to 8.1 psi

So is it really just a matter of a NEW replacement part for the old pump?

I have one of the older pumps and the Mancini kit won't work. There is place back east that makes a kit for it. I can't think of the name right now but I'll pull the file and look at the receipt.

I also don't recall what the difference is between the pumps but they are different. I know the kit I bought had valves that flowed more than what Carter sent them out with.

Thank you for your inquiry .
The cost of the kit is $47.50 plus shipping .


Lisa Pawlik
Then And Now Automotive
447 Washington St.
Weymouth, Ma. 02188
781-335-8860

M6270 is the "strip" pump, for whatever that's worth. I had one on my Duster, went low 12s @ 110 with it. Good pump, never any issues with it.

It does put out a little higher pressure than a 'normal' mech. fuel pump so if you use the 6270, might just want to verify what kind of pressure you're getting at the carb inlet.

That's the place. Nice people and easy to work with. I knew it was east somewhere. Getting old sucks. When I was younger I'd have remembered it.

Good to know. Thanks for sharing.

Differences:
Based on the info from the late 80s and early 90s, I believe the difference is the return spring. Here's what was published at the time.
Super Street M6902 Presure Limit 6 psi, Adv Free Flow 120 gph
Competition M6720 Pressure Limit 7.5 psi, Adv Free Flow 80 gph
M6270 was also sold by Mopar Performance under p/n p4007040 so I thought it must be the hot ticket.

As I learned the hard way, 7.5 psi is really too high for unregulated use.

One thing I did know from lab classes was that the pump performance curves can not be described with just those two points. So I sent a used M6270 to Ryan Brown for testing.
1. The Pressure Limit was accurate. 7.5 psi against a dead head (zero flow).
2. Holding outlet pressure at 4.5 psi, flow at 2000 rpm was 45 gph, it dropped a little and then climbed to almost 50 gph at 3000 rpm. From there up it was pretty flat until 4500 rpm when flow increased steadily to 70 gph at 6000 rpm.
Graphed results posted at Fuel Delivery, Pump Performance

A good explanation of how the spring regulates the flow is in this RFS thread http://racingfuelsystems.myfunforum.org/viewtopic.php?f=28&t=1032#p9568

For some reason I can't open the link. I'd like to read it.

Yea I just tried it too. Try it again in a few minutes. The server that hosts the forum is returning a "too many connections page" Hopefully it clears up soon. The guy who made the post I thought was helpful used the screen name Catherder. I *think* there were also some pictures borrowed from a Packard Studabaker website.

edit. OK. Fixed the link to my page. Also the link to the RFS is working again. And yes I borrowed a picture as well posted some graphs there.

Thanks

Mattax,

Good info. Should "gpm" be "gph"?

Yes. absolutely!

I'll edit that.

Thanks guys...that is plenty enough, more than I had actually hoped for!!!

Help me out with something else though: I ran into some problems last year regarding low fuel pressure, see my two separate threads:

1) fuel pressure cut-out during 1/4 mile run

2) street filter, which one to use?

So long story short, I removed the pop-can filter from BEFORE the fuel pump and placed a Powerflow stainless screen filter between the pump and the pressure regulator (FILTER, Fuel filter, in-line, 3/8 NPT in/out, aluminum, 10 micron, 160 GPH @ 7 psi).

I re-started the car with this setup and noted a low fuel pressure at the adjuster...it literally was dropping as low as 3-4 psi @ idle. Between the time I posted this thread and now I figured I would take a stab at the original M6902 pump gone bad possibility and replaced it with my spare M6902 unit. Results though show a slightly improved pressure reading (5 psi) but it is still nowhere near the 7psi the pump is supposed to produce.

Then as I read through the linkes provided in this thread I noted the following:

"...The Flow Rating is the maximum freeflow output. Since all mechanical pumps see some resistance to flow both in and out, the free flow potential is of limited use. Around 2003, Holley came out with a new line of mechanical pumps and actually provided pump output curves. Below is one from their '110 gph' series. It shows both free flow and the much more useful flow against a restriction developing 4.5 psi. 3-5 psi is ballpark pressure going down the track for a lot of us..."

So I am curious here, is the pressure reading I am currently seeing consistent with the true flow of the pump against a restriction, as opposed to a true "free flow" situation?

I left the NEW pump on the motor. I will try to make a couple of safe WOT passes to see if I still experience any sort of that WOT fuel cut-out I originally ran into during my 1/4 mile pass. Will post an update once I have the results...

Yes. 3-4 psi at idle is OK.
Hitting 7.5 psi should only happen when the bowl is full (inlet shut) and the rpms are up a bit (and no regulator). I found this would most likely happen in situations such as when cruising on a highway at 60-65 mph and then letting off the throttle. Then the bowl would get overfilled (needle forced open) and I'd have to pull off and dump some fuel from the bowls.

A pressure gage reading of 4psi in the feed lines into the carb during your 1/4 mile run is fine. If it goes to zero, that's an indication there is not enough fuel flowing even though the bowl inlets are wide open.