can i use a 5/16 fuel sending unit on my 440 69 charger??

[8WHEELER]

Hi Rene
Check YO, they have the listings right there, 68-69 440 HP & Hemi cars using 3/8 fuel and 5/16 return lines, and
other years with the same combo's. I tried to copy the page as a jpeg but I can't do it.
http://yearone.com/serverfiles/fbshopmain2.asp?cat=1

This is my wifes all stock 68 R/T kind of hard to see it but the vapor seporator is just below the alt.

Dan

[TylerCharger69]

Thanx  Steve P.   I  was kinda worried there for a second...thought I was missing something....lol      Chris....by the way, also.....thanx for the detailed pics of the fuel system!!!   beautiful resto, by the way...looks  really clean!!!        I'd like to see some more pics of that 68  in an e-mail!!!          drummer1@stx.rr.com                        Thanks  for the heads up guys!!!        Ace

[BigBlockSam]

wow look at that. i know none of my cars have that canister and they both have 5/16 line. the 70r/t  could of been changed but the motor in my 68r/t has never been out of the car. intresting . thanks for the info Dan . Rene

[BigBlockSam]

that canister is the fuel filter rite?

[8WHEELER]

that canister is the fuel filter rite?

Correct, its called a Fuel Vapor Separator, it is actual a fuel filter as well, but I like to run a regular fuel filter as
well 4-6in before the pump. Because if that Fuel Vapor Separator gets clogged it will cost you $60.00.

Dan

[Steve P.]

I wish there was an easy way to figure out just how much VAPOR is RETURNING through the separator!!

[TylerCharger69]

I've been researching..and the only thing I can think of is  perhaps, possibly the assembly line ran out of these 3/8 inch system  and to keep production going went ahead and used the 5/16??  Because it states that they were used on 440 HP cars and didnt mention only hemi  and six pack applications....It says  426  commando too!!!    That's my hypothesis...only thing I can come up with...lol

[BigBlockSam]

thanks Dan . now i got it .. plus is kinda in a pain in the ass place to change. i looked again at my 68r/t. it's got a holley mechanical pump with an in line filter up on top. it musta been changed some time through the yrs.

[BigBlockSam]

possibly the assembly line ran out of these 3/8 inch system  and to keep production going went ahead and used the 5/16??   

[TylerCharger69]

So...if one would WANT to change from the single line system to the other.....the sending unit would obviously have to be changed correct??

[Headrope]

Y'all have me confused now. Why does the diameter of the fuel line matter?
Wouldn't both lines flow the same volume of fuel once primed, because the fuel pump - not line diameter - is the determining factor?

[Steve P.]

Size equals volume. The bigger the line the more volume it can flow. Grandma's slant 6 doesn't need much volume of gas. BIG HP needs big volume of gas. BIGGER HP needs BIGGER volume of gas.. If you add N02 you will need even more volume of gas...

[Headrope]

I understand that. But only increasing the size of the fuel line (not the pump) would decrease the rate of flow; decreasing the diameter of the line would speed up fuel flow - like pinching a water hose. EIther way, the same volume of fuel would move through the line because the volume of fuel the pump can process would remain constant. Right?

[Steve P.]

I'm not just talking about the size of the feed line, but also the return line. There are many calculations and every pump company has their own.

From the way I understand it, Ma Mopar installed, (on some cars), a vapor return line that is rather small. Again, as I understand it, it is to carry vapor not fluid.  What I plan to use on my car may be overkill, may not be. I am going to put a 1/2" fuel return line on my 65' Coronet. It is hot and humid here in Florida and I don't want any problems at all.

Check out Berry Grants site for (Plumbing a hot rod). This is similar to what I want to do..

[Headrope]

Ah...misunderstanding.
By both lines I meant 5/16 and 3/8 - the original discussion in the thread, not a duel line system.

[Steve P.]

Yes, you are right. The big deal to me is how hard are you working the pump and are you providing plenty fuel at the fast end of the track?? If you are pushing an electrical pump hard, you are going to burn it up quick and you are eating up power from your battery unnecessarily.

Mechanical pumps are great, but are one more thing taking power from your motor and causing harmonic noise in your motor. It may not be much, but on some motors with knock censors it has been known to retard the timing due to fuel pump rod knock..

Most aftermarket fuel pumps you would buy are going to be matched to your HP range and size of your lines. IN MO the bigger the lines, the better. If they are too small you will starve the system. Too big is really not a problem..