Six Pak Fuel Pump

Building a standard stroke 440 six pack 440. I’ve read several six pack tuning articles where the fuel pressure is critical when tuning six pack carbs. The suggested mechanical fuel pump was a carter M4845. According to that pump specs it is rated at 8 psi fuel pressure and 33 GPH. The 8 psi seems too high. Six pack engines did not come with pressure regulators. Seems that high of psi would blow the needle off the seat. Would the 1/4 return line from the fuel filter located down stream from the pump bleed off the pressure to an acceptable level? What pump are you all using on a stock 440 six pack? Also what temp thermostat (160, 180, 195)? Thanks.

I've drag raced Mopars with Holley carbs including six pack since the early 1970, the bigger the needle and seat I.D. the less pressure it will take to hold it open.
The .090,.100 and .110 with the Viton tips will seal well at or above 9.0 lbs. up to 11.0 lbs.
The .120 and .130 will seal well at 7.5 or lower
You do need to know and remember that not all gauges read EXACTLY the same, I had one Autometer race fuel pressure gauge that read 8.0 lbs. when several other gauges with the same part number read 11.5 lbs.
I was wondering why that carb. wouldn't seal up at 8.0 lbs.

I replaced a carter m6903 with an m4845 and had to set the float level down with .110 holley brand needles. I am down as far as the nut can go and still be on the needle. I did not test the pressure. I did not have the return hooked up as the tank was dirty and was running it on a gas can. I can' t say if the
060 bleed hole would be enough to fix it, or if you need the
097 needles also. I am going back to the 6903 5.5-6.5 lower pressure, higher output pump, they did not have one when I needed it. It also does not look stock if that matters to you.

Mr. Sixpack (Bob K.) wrote in an article that Six Pack setups can only use a maximum pressure of 6 psi. That is a Carter 6903.

6paks used the same pump as the hipo 440 which is an 8+ pound pump, but the vapor seperator return orifice regulated the pressure.

Thanks for the information. Anyone use a 195 degree thermostat on a six pack big block?

Cabs comment are correct but fuel pressure not used to open valve since gravity will open it when level in bowl drops. Rather the size of needle and seat beside controlling fuel volume it, does affect how much force the float has to supply to CLOSE the valve against a set pressure. Larger the surface area of the needle the more force applied by fuel pressure against the float. All else being equal. So if you went to a bigger needle, you would find your fuel level rise in the bowl until you lowered fuel pressure or adjusted the float level.

If you look at the service manual, pressure was checked at the carburetor with a T fitting. So the pressure spec included the separator as part of the system. Hemi was 7 to 8.5 psi. The 440HP was 6 to 7 1/2. This from the 1970 SVM.

i have and won't again. the real issue with a 6pak is getting the intake too hot and boiling the fuel in the carbs. regulate the heat to the intake if you're using the factory cross over and try a 180 thermostat, unless you're driving in Minnesota winters.

If you go here there is a decent write up on tuning six paks, there is an even better write up but that is not being published
six pak tuning
use the carter street pump....

if you follow that guide you have a very good chance of your car running right
If you follow some of the advice in here...well good luck esp the 195 thermostat is too hot bs....no in reality a car like that is not tuned up properly so i am calling bs on the play

@sogtx is one very accomplished six pak tuner and we happen to be friends but don't let that fool you. He will tell you the same that i am telling you...use the guide- it works and run a 195 thermostat-explanation is in the guide

six pak tuning

have you ever owned or tuned a 6pak?

440-6, stealth heads, Lunati 60303, 10CR, iron intake, stock exhaust manifolds, M4845 and 180 thermostat. Starts right up, idles with slight attitude, runs good.

Suggestion: try to find OE/NOS fuel pump pushrod; some aftermarkets will wear prematurely...DAMHIK...

Good advice and don't bother with a comp cams version as I've had 3 go south within 20 miles in customers cars and my own