HackTheBox

Need advice here. I'm working to convert my C3 from Carb to EFI and E85. I've found several Fuel Tanks from Zip Corvette, Tanks Inc and Top Flight Automotive. They all seem to be the same except for years they support.

For Example from Zip Corvette Lists this tank (https://www.zip-corvette.com/68-77-efi-gas-tank.html) and from the pics looks like it's from Tanks Inc. however, I cannot find a tank on Tanks Inc site for specifically 1975. Top Flight has this kit (https://www.topflightautomotive.com/...fuel-tank-kit/) which is better priced than trying to piece meal it together from Tanks, Zip, Top Flight and Summit. But Top Flight only Lists 68-74.

So my question is, are the fuel tanks the same size/shape from 68 to 77 with the exception of 75-77 using the non-standard filler neck/sending unit? Will the Top Flight Automotive Kit for the '74 fit in the '75?

Thank you!

60 SHARK

I have a '75 with EFI. I'm compelled to ask why do you think you need a new tank?

4-vettes

Best suggestion I can give you is read my thread. 77 EFI Conversion.

HackTheBox

oh yeah, I read your thread a few week ago but was looking for some that can use standard parts.

I'll keep this in mind. Thank you!

4-vettes

Exactly. My car uses standard parts. No new fuel tank needed. 75-77 use the same tank. Fuel pump is readily available from Summit as well as other's.
https://www.corvetteforum.com/forums...onversion.html

4-vettes

However, if your made of money and really wish to purchase a entire new tank. Then yes. The 74 tank will fit in your car just fine. 78 and up will not.

HackTheBox

Well, I'm just not sure the amount of time and effort I would have to put the fab work and the risk of making a mistake is worth the $329 difference for an EFI ready tank. My sending unit is shot so I would need a new one to start with. Then there's the 50yo tank, my luck would have it that it would spring a leak and I'd need a new one anyway.

Holley makes a sending unit with fuel pump but has a fixed 58 psi regulator, thats probably fine and all but just another thing to break in the future. Besides if i stick with the TPI it has a bypass regulator already.

Thanks for letting me know the tanks are the same as 74.

4-vettes

There's certainly more than one way to skin a cat as they say. It's your car. So you should do it your way.
My 50 year old tank looks like new inside, and not bad on the outside as well. So I thought fabing up a mount was a very simple and inexpensive solution.
A EFI ready tank with a pump and sending unit for that price? OK.

theandies

I putting a Sniper 2 in my '71 now and I'm going to use Holleys in-tank pump/sending unit replacement. No new tank needed.

carriljc

HackTheBox
I recommend getting a 1982 sending unit and modifying it to fit your 1975 tank; that way you can pull it out of the top and don't have worry about draining the tank, or dropping the tank, or any of that struggle. The 1982 aftermarket sending units are Stainless Steel and relatively inexpensive. When modifying you can use a Cannister Pump Assembly (lots of different options there) or one of those Hydramat expensive things.
If you can fabricate a little it's not even difficult.
Here is my story. I don't remember if the 75 has a big hole or a tiny hole.... but, nevertheless, you can see how I made it fit in my 68 relatively small hole. One of my goals was being able to pull the pump via the top.
PS- if I was doing it again I would relocate the electrical connector penetration --- would be overall easier and less gouging on the fuel tank.
https://www.corvetteforum.com/forums...surements.html

carriljc

HackTheBox
I got curious and looked up the sending units for both the 75 and the 82.
Methinks the easiest thing to do would be to get a 1982 sending unit and use it by mounting it on top of your 1975 thing. You could probably do it without dropping the tank (like I did with my 69) but may be easier to drop the tank ---- in the future you would just be able to pull the EFI pump straight up the top.
It would be super easy for you since all you need is to make a bigger hole and bolt the thing on. The tubing and electrical leads would be easy anywhichway.
I would probably keep the stock gas tank level sender (as long as it's not in the way).
Looks easier than my 68 exercise since you can put your hole exactly where you want and make it as large as necessary.

HackTheBox

That 8s interesting. What size outlet line amd return line does the '82 have? Im shooting for 3/8 for both outlet and return.

HackTheBox

I looked at that unit but don't like the fixed 58psi regulator built in. Just one more thing to go wrong inside the tank.

I also peeled back the lining on my tank to f8ne lots of rust. At this point i really dont want to risk a leak after all the other work ive done.

doorgunner

That was my thinking, too. I had to go over the river & thru the woods to make it happen.
I installed an OEM replacement external 45 psi electric fuel pump (I couldn't find a 5-7 psi pump. The original Ford pump lasted 200,000/20 years, so I said "why not".
I did have to install a Holley adjustable 4psi-10 psi regulator w/bypass




Temp. installed to test for leaks....

4-vettes

Yes you want 3/8th's in and out. The 82 sending unit won't do that. The set-up in my how to thread would be far easier to install. And have the correct sized lines. Your liner holds the fuel in your stock tank. A aftermarket tank has no liner.
best of luck.

HackTheBox

There's lots of rust between the bladder and tank. Also I'm not sure if the bladder is ok with E85.

carriljc

HackTheBox
The 1982 sending unit I got was 3/8" Supply and 5/16" Return.....
but it would be pretty much irrelevant in your situation since you are making mods.
You could either replumb the 82 return, or plug the 82 return and use the original return, or plug the 82 return and use the 75 supply as a return.....it all would depend on the way the tubing is arranged under there. Really not a big deal and you'd still have the big benefit of Removing and Installing the sender & pump via the top.......

I really recommend coming in from the top. It will save you heartache later if you ever have to do repairs or maintenance.....even if you have to drop the tank this first time, but I really think you could do it from the top as I did..... It would be better to drop it this time (after you take you placement measurements) because you could then braze, or weld/ some nuts on the underside of the removable 75 plate to bolt on the 82 filler neck..... not absolutely necessary and you could use some stainless screws --- just depends how you want to go about it.

It sounds like you need to inspect the tank anyway so you could just drop it
Can you remove the bladder and use one of those tank sealing kits? .... rumor has it that they are wonderful..... From your comment about corrosion I would drop the tank to take a look and do the 82 mod....whether on this old tank or a new one.... that big removable plate on that 75 makes everything doable on a workbench (but I'd measure and mark at the fuel access door before dropping the tank).

HackTheBox

@carriljc you make a very good point about future access. That is one drawback with the tanks in tank.

I've already got the tank out. I can do a more thorough inspection later this week.

I'll look at the 82 tanks and your thread again to see what all will be involved if i go that route.

c3_dk

My fuel tank was fine, so I did this.

60 SHARK

.
I used the origonal tank in my '75 as it was in great shape. I also did not want to put any 'new' holes in the tank. I Modified the original 75 sending unit and intake siphon to attach my new in tank fuel pump and Holley Hydramat.. i used the origonal 3/8 feed for the new return. I ran new feed line to the EFI unit. The charcoal can is still working and in use also. Ill try to link my post with some pictures if i can figure how to attach it.
.https://www.corvetteforum.com/forums...l#&gid=1&pid=2
Hope this helps. Its been in service for going on five yrs i think....👈👍😁