Fuel System

This was one of the easier parts.  But it did require some specialized parts to make it all work together.  This is a stock’ish  5.7L LS1.   Shouldn’t make more than about 400hp or so.  Even with E-85, the fuel requirements are not that high.

Goals – again – are inexpensive, light weight, easy maintenance, and durable.  For this car, small is also a bonus.

I couldn’t think of any reason not to use stock 10mm nylon fuel lines.  They’re in millions of cars, with decades of use and gazillions of miles.  Most of the cars that come out for any track week end have them .  So, why not?   AN lines are nice, but certainly not necessary here.

Fuel line assembly
Fuel line assembly

Dorman Products  makes both the lines and connectors.  Available pretty cheap from pretty much any parts store.   It’s recommended to use a special tool set to put the ends on the hose.  But that’s not really needed.  I warmed them up in hot water, lubed them, and then assembled with a calking gun and a flaring tool.

Running the lines down through the transmission tunnel was also pretty easy.  The fuel lines are about the same size as the battery cable.

The LS1 is designed for a returnless fuel line.   But an electric pump needs a constant flow, so there has to be some kind of return to the tank.  And there needs to be a pressure regulator.  The Corvette uses a combination fuel filter and pressure regulator.  Makes life pretty easy and – again – inexpensive.   All the Corvettes on the track with me are using, why shouldn’t I?  Feed is 3/8″, and return is 5/16″.

Fuel filter and pressure regulator
Fuel filter and pressure regulator

The trick is finding a good place for it.   I made this little bracket for it, and attached it to an existing hole in the fuel tank flange.  This is a good spot, because it matches the natural curvature of the fuel line.  Parts literally fall in to place.  The bent tubing is another Dorman part.

Fuel tank stands
Fuel tank stands

 

The fuel tank will not sit down where it’s supposed to.  The sump hits the differential cradle.  This is a well known issue.   I made these stands out of tubing and large washers.

 

Drain plug for fuel tank
Drain plug for fuel tank

Speaking of the fuel tank, some tanks have a drain in the bottom of the sump.  A handy feature.  If you need the plug for that hole, I got mine from the dealer.   When I went there, the parts guy said Miata tanks don’t have a drain.   He was surprised to find that some do.  🙂  I’d like to replace it with a ball valve and hose some day.

Of course, I replaced the Miata fuel pump with something bigger.  Lots of good choices available.  Just make sure your pick up goes to the bottom of the sump.

Connecting the pump to the fuel lines was a conundrum.  My parts came from a ’92.  They used simple hose clamps and rubber hose.  Probably just fine, especially for the return line.  But I like the security of the nylon connectors.   I didn’t have any way to make the proper flare in a steel line.   Even if I did have the right tool, I didn’t think it would fit in there.

Lots of people use connectors from Russel and Aeroquip.  But, if you read the specs, they’re only rated for aluminum line and 50psi.   Stock LS1 fuel pressure is 52psi.  Apparently, people are not having any trouble, and I haven’t seen any reported failures.  But I still didn’t like that.  There’s that OCD thing again.

Fuel tank connections
Fuel tank connections
Yor-Lock tubing connector
Yor-Lock tubing connector

After some research, I purchased these Yor-Lock  connectors from McMaster-Carr.  Stainless steel, straight and reducing, rated at 2,600 psi, but not exactly cheap.   Shouldn’t be a problem.  I connected with sections of tubing from Dorman’s with the proper flare for the nylon lines.

Fuel tank installed
Fuel tank installed

P1010255

 

The next big trick is the filler neck and vent.   Not a whole lot of options here.  There doesn’t seem to be any off the shelf options here.

But, I already owned the stock Miata parts.  So I spent a few hours making them work.   I forgot to take pictures of that, though.  But this is what the stock filler neck and hose look like.  There’s a ball valve in there to prevent leakage in case of a roll over.   If was to big/long for me to use.   Maybe I’ll switch to a fuel cell some day.

Fuel filler neck
Fuel filler neck
Check valve inside the stock filler neck
Check valve inside the stock filler neck
Stock Miata gas cap
Stock Miata gas cap

So I cut, welded, bent, and trimmed until it all fit.   Didn’t come out too bad.   Seems to work just fine.  I also used the stock Miata filler cap.  Why not?  I already owned it.   There are some much better looking options available; but they will be somewhat more difficult to fit.