Fuel Feed Line Size

[kryptik]

Hello,

I have a GM zz383 crate motor with a 680 cfm Quickfuel Vacuum Secondary Carb, being fed by a Carter Super Street mechanical pump, non-regulated. The motor puts out an advertised horsepower of 425@6000 at the crank.

Recently I replaced all of the lines on my '70 Camaro with OEM 3/8" hardline, as well as a new sender/sock filter (also 3/8").

I was told today that 3/8" hardline may be too small for this combination. I was wondering if I should go ahead right now and swap the lines to 1/2" hard-line, with a 1/2" RobbMC sender, or just stick with what I have. This is a street car at the moment, but I do not want to lean the motor out on those occasional track-days. So stick with the 3/8"? Or ditch it for some over-size line?

Also, would -8AN lines from the hardline to the pump, and from the pump to the carb, be ok?

Thank you for your help guys,
Matt

[68Formula]

A 3/8" hardline should be adequate. Since you already replaced it, do ahead and run it. Add a temporary fuel pressure gage and see if you get a pressure loss at the high end. As long as the pump is doing it's job, you shouldn't see a loss.

[wmhjr]

If you're in there anyway, 1/2"/-8AN certainly wouldn't hurt. The RobbMC sending unit is a REAL nice piece. My only issue at the moment is that my fuel gauge isn't terribly accurate between it and the Autometer gauge, but it's not a big deal and I've done nothing to diagnose it yet.

[CarlC]

-6 / 3/8" is more than adequate for your setup. The previous engine in the Camaro was a 406 making more power and there were zero problems on-track.

Don't forget, GM used much larger engines than yours as factory builds with a 3/8" fuel line.

The main thing to be careful of is to use fittings that do not restrict the flow too much. Many -6AN fittings neck down to 1/4".

[kryptik]

Alright sounds good I'll save myself the time and money...

I already have a -8 fitting brazed onto the hardline before the pump, would it hurt to use -8 everywhere to avoid any restrictions like you mentioned?

[Roadbuster]

-6 / 3/8" is more than adequate for your setup. The previous engine in the Camaro was a 406 making more power and there were zero problems on-track.

Don't forget, GM used much larger engines than yours as factory builds with a 3/8" fuel line.

The main thing to be careful of is to use fittings that do not restrict the flow too much. Many -6AN fittings neck down to 1/4".

Thanks Carl! I was just looking up what was the inner diameter of AN fittings and you answered one of my questions.

[My427stang]

I went to 1/2 inch on my 489 with the EFI for a later 505 S/C engine planned, but ran 3/8 on a 1000 cfm Holley on a 489 inch FE Ford for years, no issues and never leaned out on top. 3/8 is plenty for you

[wmhjr]

Thanks Carl! I was just looking up what was the inner diameter of AN fittings and you answered one of my questions.

The fittings vary. You can do -6AN with fittings that don't neck down.

In general, if it looks like this it maintains full bore:
http://www.summitracing.com/parts/FRA-118006-BL/

If it looks like this it probably necks down.
http://www.summitracing.com/parts/FRA-482268-BL/

[CarlC]

What I've found is the opposite.

The hose ends have to reduce their diameter to fit into the hose bore. So, if the hose is 3/8" the bore size of the fitting is going to start at under 0.300" (usually closer to 0.250") at best and smaller on many fittings.

On the forged fittings often the drilled bore is larger than hose end (0.300"). However, due to the square inside corner of the the intersecting holes they are not good for high-flow applications.

[wmhjr]

What I've found is the opposite.

The hose ends have to reduce their diameter to fit into the hose bore. So, if the hose is 3/8" the bore size of the fitting is going to start at under 0.300" (usually closer to 0.250") at best and smaller on many fittings.

On the forged fittings often the drilled bore is larger than hose end (0.300"). However, due to the square inside corner of the the intersecting holes they are not good for high-flow applications.

Actually according to the manufacturers, the hose ends expand the inside diameter of the hose and is the very closest to maintaining full bore. At least that's what Fragola told me. Now you've made me curious, though. I'm going to mic the ID of some of those hose ends just to be sure.

I can say from my own experience that the hose ends have definitely expanded the inside of the hose, which is why installing them on lesser quality (ie, thinner and less flexible) braided line is far easier than on higher quality stronger line. Sometimes when working with -8 or larger, I've found it tough to get the hose end in the hose.

I know there's a joke there somewhere :)