(FUEL) Interchangeability of Fuel tanks- The facts.
 

I've noticed a few questions and misconceptions about the 84-85 S3 fuel tanks lately.

This thread will address the myths and facts between the FI and Carb, (13b/12a) tanks for the S3 only.

MYTHS:

1. The SE has baffles, the others don't.

2. You can't interchange the tanks.
a. Can't use an SE tank with a 12a.
b. Can't use a 12a tank with a 13b.

Facts:

1. Both tanks have baffles. The 13b/SE tank has a 'cup' that the fuel supply and return tubes sit in.

2. Yes you can.
a. No problems or risks with this swap. It is a direct fit.
b. You can, but since the 12a has no 'cup' to maintain a constant fuel supply for the pickup, a surge tank is recommended. This becomes especially critical if you are boosting!

Both tanks are identical in construction and configuration, with the exception of the 'cup' in the SE tank.

Both tanks have the same bolt pattern for the pickup and return assembly, they ARE interchangeable.

Note the pics below. I have yet to figure out how to include them in the body of a thread, so bear with me. (But Jon has... so here I come to edit!)

Pic 1. 12a tank on the left, 13b on the right.
https://www.rx7club.com/attachment.p...hmentid=107639
Pic 2. 12a pickup assembly on the left, 13b on the right. Note difference in the filters and the size of the hard lines.
https://www.rx7club.com/attachment.p...hmentid=107640
Pic 3. The 'cup' in a 13b tank. Not a good pic, but you get the idea.
https://www.rx7club.com/attachment.p...hmentid=107641


For those of you who are doing 13b swaps, in a non-SE, I recommend the SE tank, and the SE hard fuel lines. If you cannot find a good SE tank and lines, then add a supply line the next size larger, use the existing supply as a return line, remove the original return and add a surge tank. The easiest way to do this is source an SE pickup, otherwise you will need to have a larger pickup tube added into the assembly.

I hope this clears a few things up.

Scott.

The cup is very similar to the one in the FC tanks.Many people call that cup a slosh baffle (thats what it does) so that may contribute to the,"12A tanks have no baffles" myth.Just a misunderstanding caused by different terminology.Both tanks have bulkhead baffles going from top to bottom,but only the SE has the pickup baffle around the intake/return pipes.Good pics!

You might want to note that when swapping an FB (SE or non) tank into an SA car, you need to cut the spare tire well and raise it up about 2" for the tank to sit flush.

The SA spare tire well is deeper then FB (SE for sure)

That was the main reason for this thread, thanks clarifying my 'cup'

That is why I limited this post to be S3 specific. I have no experience with tank swaps into the earlier Series, therefore I posted no information about them.

I would rather post no information, than information that is questionable or in doubt.

I've owned 1 S2, and it met the sawzall quickly, it was really that badly rusted. Most of my experience is with S3's and S4's. The S4 tank is a definite no for a swap. The S2's, I do not know if they are interchangeable or not.

S2 gas tanks are the same as S3 12a 84/85 tanks but the fuel sender has only two wires.

All will interchange on 81-85 models. If you have the 84-85 model use your sending unit. If you have the 81-83 model then use your sending unit when interchanging between the years.

79-80 tanks will not fit in the later years.

thanks, Trochoid. :)

+1

I wish someone had a pic of a S2 tank and a S3 Tank next to each other like that

The S2 tanks also have the fittings welded to the tank (making it a real pain in the ass to seal the inside of the tank without clogging them), whereas the S3 tanks have them on a seperate plate that is attached to the tank as shown in the original post.

Hmmm you are correct I forgot that, I am running a 83 tank in my 84 with no issues though, of course it was a sealed tank with a clean inside....

Yea they will fit right in, any 81-85 tank will interchange with each other. Mine luckily was pretty clean so I didn't use the tank sealer I got, but if one needed to it would be a pain in the ass to keep the lines from clogging. Oh well...