[glhs#116]

1971 Trans Am

I know there's all sorts of better options for when you need more fuel. I know I'd be better off with an in-tank electric, full size return and so on. I know RobbMc makes these big mechanical pumps.

My particular deal is I'm trying to go faster without a bunch of unsightly "race" looking stuff and get good bang for buck. I've got the factory hard fuel line to a factory Q-Jet and so I like to keep the factory "big can" style fuel pump.

Now I did find an interesting post on the inlet and outlet hose locations. Basically, that’s the difference between the M6122 and M6405 and neither of them match factory for my 71 F body.

On Summit the price difference is pretty big between the two and the M6405 is sold as a “Muscle Car Series” pump and the spec shows 120gph vs the 40gph of the M6122 and all the other “OEM” spec pumps. That would be really cool if true. And the price is indeed almost 3x higher for the M6405. However, if one visits the Carter spec page or, for example, the RockAuto info page one sees both listed as 40gph (although the price difference remains).

So, anyone know what the deal is? Are Summit smoking something? Are Carter themselves confused? Are there “two” M6405s?

https://www.summitracing.com/parts/c...2/make/pontiac
https://www.summitracing.com/parts/c...5/make/pontiac

Sam

[P@blo]

Rockauto shows the Carter M6405 as a 40 GPH (minimum flow) pump and so does Jegs. Wondering if the 120 GPH rating is maximum flow?

It would be nice to see a fuel pump in this configuration that flows 120 GPH minimum flow.

https://carterengineered.com/mechanical-fuel-pump-m6405

[glhs#116]

If you look at the Summit listings they are 40 for the one and 120 for the other so whether it is minimum or maximum or whatever the implication is that one flows 3x the other. However, as you say, if you look at Carter or RockAuto you
• Don't see the "Muscle Car Series" branding
• Do see them both rated the same at 40gph
Weirdly, the M6405 costs considerably more than the M6122 even on other sites. That would normally imply to me there's more difference between them than just which way the hose inlet and outlet point...

Sam

[JLMounce]

What about running an in-tank fuel pump and modifying the factory pump so that you're sending the fuel through it and the factory hard line? You state you know that's really what you need, but you don't want a bunch of race looking stuff. You'd have a stock look with enough fuel for what you're trying to accomplish.

Hide the bypass regulator up near the tank and the pump power with your fuel line. You could effectively hide everything.

[Cliff R]

Regardless of the pump rating the problem with trying to use a mechanical pump to feed a big CID powerful engine in a pretty fast car is delivery to the pump.

I can tell you from actually doing it that 40gph or 120gph isn't going to much matter trying to feed it with 14' or so of 5/16" fuel line (the inside diameter of 3/8" line BEFORE you bend it). It is ALWAYS better to push the fuel vs pull on it. This certainly makes modern in-tank pump systems the way to go if and when the goals for your vehicle include a powerful engine and steps for the car to make HARD runs with good traction.......FWIW.....

[ta man]

Originally Posted by Cliff R

Regardless of the pump rating the problem with trying to use a mechanical pump to feed a big CID powerful engine in a pretty fast car is delivery to the pump.

I can tell you from actually doing it that 40gph or 120gph isn't going to much matter trying to feed it with 14' or so of 5/16" fuel line (the inside diameter of 3/8" line BEFORE you bend it). It is ALWAYS better to push the fuel vs pull on it. This certainly makes modern in-tank pump systems the way to go if and when the goals for your vehicle include a powerful engine and steps for the car to make HARD runs with good traction.......FWIW.....

x2 if I was at the starting stage with my build I would go in tank pump 8an or half inch lines and all connections and don't look back. I've seen so many big cubic inch builds at the track fall short on mph and et because of the fuel system...running lean is not good. Build it once and forget about it.

[NeighborsComplaint]

The higher rating is at free-flow, the lower at 6-7psi.

[AG]

I've run 11.8 in the 1/4 with stock fuel line in a '65 LeMans with the Carter 120 gph pump for a basis of comparison.

[glhs#116]

Originally Posted by AG

I've run 11.8 in the 1/4 with stock fuel line in a '65 LeMans with the Carter 120 gph pump for a basis of comparison.

Was that the M6405 then?

Sam

[glhs#116]

Full disclosure: I am working this winter on a supplemental system with a one-way valve and a pusher electric triggered by the WOT switch on the throttle. I'm a regular guy with a mortgage who could never afford to buy my car if I had to do it again. I have a lot of financial and time commitments which means that there are a lot of "dreams" I have for the car that will have to remain dreams. But I am trying to keep it in good running order, have fun racing it in the summer, and if possible go just a little faster each year. Full fuel system replacement sounds great. But it's on the list with the Vintage Air system, the engine rebuild, the TKX, the uprated suspension, the resealing of the leaking front and rear window (which will have to go in conjunction with the rust mitigation and repaint).... It's a long list of things I know I don't have time and money for. So I like to find little things I CAN do that won't take a huge amount of either but might make a difference.

Sam

[Half-Inch Stud]

Originally Posted by AG

I've run 11.8 in the 1/4 with stock fuel line in a '65 LeMans with the Carter 120 gph pump for a basis of comparison.

Run about 12.0 ( Firebird and GTO) with Carter Pusher, soft-bended 3/8" steel line, Factory Mech Pump, bypass plugged and either Q-JET or 1050.

The GTO struggled with fuel deliveries on the highway sometimes and never got that sorted to a cause.

[P@blo]

Originally Posted by AG

I've run 11.8 in the 1/4 with stock fuel line in a '65 LeMans with the Carter 120 gph pump for a basis of comparison.

No listings of the M6405 being a 120 GPH pump and shows 40 GPH minimum flow on the Carter website. Must be a typo on the summit site. Stock pumps are also rated at the same 40 GPM for scope.

[78w72]

maybe call carter tech line to ask what the difference is for the 2 pumps? Has to be a pretty big difference if one costs almost 3x as much as the other.

Another option is the edelbrock pump, comparable or better specs that the lower price carter and it has a clockable housing that might work for a factory line? I ran that pump for a year or so and it supported ~520hp on a strict engine dyno, did 12.0-12.2 at the track with crappy old/hard tires on the cars first shake down runs.

[NeighborsComplaint]

Free flow vs actual use flow ... using Holley's description of flow on their Red Pump as an example, actual fuel delivery drops for each Lb. of line pressure.


Detailed Description

"... Designed For Enhanced Fuel Flow. Maximum Pressure Is 7 psi ... Motor Flows 97 GPH (Free Flow). Flows 71 GPH At 4 psi."

Similarly, the Carter 120 GPH is the Free flow and the 40 GPH is the flow at 5 psi working pressure. The mechanical pump is just less efficient than the electric so it's actual flow drops more quickly as working pressure increases.

[Kenth]

Looks like there will be challenging to connect the fuel hoses on the Carter M6405?
https://www.rockauto.com/en/moreinfo...t=6256&jsn=435

I guess Delphi got it right.
https://www.rockauto.com/en/moreinfo...t=6256&jsn=426

And Carter M6122, if you can live with 9 psi minimum pressure?
https://www.rockauto.com/en/moreinfo...t=6256&jsn=425

[NeighborsComplaint]

Originally Posted by Kenth

Looks like there will be challenging to connect the fuel hoses on the Carter M6405?

Correct, they do not match factory lines. I tried both '71 HO and earlier RAIV lines. The outlet is clocked differently and neither line would clear the pulley on the balancer. It interferes right at the sweep of the 90 off the pump so you can't really bend an offset there.

I tried a 90 fitting on the pump thinking I could shorten and flare the stock line to drop straight down to the fitting but my flare tool (Harbor) couldn't compress the steel line. I wound up using two different 3/8 power steering return elbows at the carb and pump with a short 2" length of hose as a coupler right behind the alternator (out of view). At some point I will bend a new continuous line from NiCop.

[mgarblik]

Not to hijack, but if your going to bend your own tubes. I purchased a bender dedicated to 3/8" line from Inline Tube at the PRI show this year. It was $35.00. That tool will make incredibly tight bends on hard steel lines, smooth as silk, not a trace of any type of kinks. I also have the Harbor Freight black bender. This new one will bend circles around the Harbor Freight junk.

[Formulajones]

Carter pumps likely aren't going to get you there and depending on which you choose, You're going to be bending new fuel line anyway if you want a stock appearance. My experience with them anyway has been hit and miss on reliability

Since you're worried about cost doing it the right way with an in tank pump is out of the question. Your best bet cost wise and still better than these store bought pumps is a Robbmc. You can bend a new steel line up to the carb to keep stock appearances, which is what you'll have to do with some of those carter choices anyway. As far as the pumps appearance goes, you can't see the darn things on a Pontiac burried under a power steering pump so no one will even notice let alone care.

The Robbmc stands a much better chance of accomplishing your goal than any of the Carter offerings while still maintaining a mechanical pump in the stock location and not killing the wallet.

[grivera]

How about an M6907 - Too much fora QJET?
https://www.summitracing.com/parts/crt-m6907

[grivera]

How about an M6907 - Too much fora QJET? $115 at Summit
https://www.summitracing.com/parts/crt-m6907