This is for a 1968 Malibu with a small block quadrajet. Just your basic car. What determined whether the factory used 3/8" or 5/16" size tubing? On one of my Chevelles, years ago I replaced the tubing the full length of the car with steel braided tubing because it was available to me free. Now I want to put it back to stock, but can't remember what size it was I removed.

Also wondering how hard it is to install the stainless vice the O.M. whether it be the 3/8" or the 5/16". Is it bendable enough to do with the rearend, crossmember, exhaust, suspension and the motor in the car? I've done one before with all those elements out. In other words a bare frame.

In general small block 5/16, big block 3/8's


Rocky

My son brought his 68 Malibu over to the house a few minutes ago. It was originally a small block 327, 4bbl. First thing I did was get under it and measure the outside diameter. It was 3/8". So that kind of kills the small block verus the big block theory. Am I right in measuring the O.D. vice the I.D.????

Paul,usually the lower hp. cars came with 5/16 fuel lines.Such as 6 cylinders and lower hp. V-8's.Higher hp. small blocks and big block cars came with 3/8 fuel lines.Today with the large hp. numbers we see with even the majority of most small blocks ,it's just not feasible to use fuel line smaller than 3/8.It all comes down to Basic Fuel Consuption per hour.

The assembly manual shows that the SS cars & trucks used a different line than the other cars. Because only SS cars had big blocks in 68, I would assume that they had the 3/8" line, and the other cars had a 5/16" line. Did you use calipers to measure the line on your son's car? 5/16"=.312, 3/8"=.375, so it's a small difference. Tubing is measured by the OD, be sure you're measuring the tube and not undercoating or rust on it.
It's going to be very difficult to install the line with the body on the chassis, especially where it goes around the spring pocket on the right side. You'll probably have to lift the body up on the right side to slide the pipe through.

BillL

Both of my coupes were originally 327's, 275 HP. Neither car is an SS. I am the original owner on one and the 2nd owner on my son's. But I've owned it for 20-25 years. I know that the 3/8" tubing in his car is original. They also came with 4 speed saginaw's. I used an outside caliper to measure the tube. It was a clean area.

I don't know myself but just seems like all 68's would have 3/8" od tubing for the simple reason that it would cost GM a bunch just to put a line on some cars that is only a teeny bit smaller.

If I were you, I would put 3/8" on it anyway.

Open end wrenchs work good for checking tubing od size.

I don't know myself but just seems like all 68's would have 3/8" od tubing for the simple reason that it would cost GM a bunch just to put a line on some cars that is only a teeny bit smaller.

If I were you, I would put 3/8" on it anyway.

Open end wrenchs work good for checking tubing od size.
Yeah but they probably made up for using the smaller 5/16 tubing because smaller tubing would cost less.:D

What size is the tubing going from the fuel pump to the carb?? Just wondering if that's where it's different.
BillL

My 70 came with 5/16" - It feeds my 406 SB just fine.

LK