I am putting a 440 six pack engine in my 70 challenger. I know they had a fuel separator when they were new. I now have a 1/2 fuel line from the tank to the fuel pump. If I don't run the separator am I going to have fuel problems on a hot day? This is a mild build street car. Looking for people that have run without it. Thanks Guys.

I’m not sure but I think the the fuel separator was to regulate the high pressure pumps more than anything. I’ve run a 340 six pack for years with no return line and never had a problem.

I ran a six-barrel set-up on my 57 Plymouth for 30 plus years without that fuel separator. I used a 3/8" line from the tank and everything was fine.

My old pump gas Duster (725+ HP) and my 1969 Dart GTS 383 car both have 1/2 gas lines from the tank to the HP Carter mechanical fuel pumps that never had a issue, the Dart was driven on the street and raced in the Mojave Desert Victor Valley in SO CA for years year around with no issues. I added a 3/8 pickup to the stock tank pickup along with using the stock 5/16 fed into a T hooked up to the 1/2 inch line.
The Duster ran a bunch of 10.00 through the 3.0 inch exhaust and muffs with the air cleaner on, that motor was a 517 C.I. pump gas stroker with a single 1050 CFM Dominator. The Dart was a stock stroke stock bore 440 with ported 906 heads and a single Holley 950 CFM carb. Best ET was 11.17 at 122.+ MPH on a set of 28.5x10.5 slicks in Las Vegas at a race in November

the hipo 440's and street hemi's did use higher pressure pumps and the return on a separator does regulate that, but it also eliminates vapor lock plus filtering. to have a return to relieve fuel vapors more fuel pressure at the pump was needed to maintain adequate pressure at the carb for the 440 and hemi performance engines. 383's had a 3-5lb pump and didn't use a separator and were very prone to vapor lock; just plain lousy pumps. i think to not have some sort of control on todays alcohol gas, which flashes faster than the old gas, could be troublesome.

66-67 hemi used the same fuel pump and pressure and they did not have a vapor separator or return line. So the choice of using a vapor separator is purely based on whether you think your set up will vapor lock. Having lower rated fuel pressure pump in a 383 motor would be MORE susceptible to vapor forming in the fuel pump and lines and they don't use one. Even on the HP motor.

i think the mopar vapor separator is a fairly ingenious part. it filtered and eliminated the vapors, but it's at it's best when matched to the proper fuel pump. the 3-5lb big block pumps were miserable pieces. i remember fighting the vapor lock problem with a 383. it seemed the problem really raised it's ugly head at the track when folks were idling in the staging lanes. i did all kinds of silly things to cure the problem. eventually (sometime in 1968) i switched to a street hemi pump and never noticed any more vapor lock problems (i didn't do a return/vapor separator). but, the high pressure street hemi pump by itself set me up for other problems. all this works the best when parts are matched together..

s.

I fully agree. Most folks don't realize the early MOPAR AFB floats where larger, which means they had a greater buoyance force to keep the needle closed also. That is why they can handle a higher fuel pressure. The AVS used 3 different size floats and had different float setting to account for it. The later Federal/Edelbrock use a smaller float with less bouncy force hence the 5-6 psi limit on Edlebrock.

For a mechanical pump that is a constant displacement, you get faster fuel flow with a higher-pressure pump spring, which also helps keep the fuel in a liquid state in the lines. As long as the float system can handle it, and level set correctly your better off with it.

Blocking the heat crossover is a huge help as is running an electric pump out back. Reason being the line from the pump to the tank is under a negative pressure and more prone to V/L. Stay away from Ethanol based fuels if possible. And as stated a higher pressure mechanical will help and the holley's can take ~ 7 psi on the safe side. try to keep the lines away from heat sources. phenolic spacers under the carbs can help as well

Good reading. I'm in the same position as the OP.