Slightly different EFI dual tank question
 

So I’m planning on going EFI and keeping dual tanks on my ‘78 K20. My question is, didn’t the fuel neck opening sizes change sometime around 80-81?

Instead of going the typical ‘87 TBI tank and sender route that most do, I’m thinking about buying a new pair of 1978 tanks, and using a pair of Holley drop in EFI modules that utilize the Hydramat system instead of baffles. This would allow me to keep the stock size filler necks and hoses.

Re: Slightly different EFI dual tank question
 

That's a neat setup from Holley, but it's pretty pricey. Wouldn't it be a lot cheaper to buy the 87 tanks and then modify the necks? You could probably use the ones from your old tankc. Just my $.02. Good luck!

Re: Slightly different EFI dual tank question
 

Yes, the fuel neck size changed after 1980. That said, it wasn't that big of a deal. I just brought my old filler neck to the parts store and told them what new size I needed, matched rough sizes. I ended up cutting 3 or so inches off the new one, but it works perfectly fine. I think the new filler neck hose was around $10.

I have a 1980 and am using a 1987 tank.

Re: Slightly different EFI dual tank question
 

I’d like this to be a drop in deal without any modifications to the tanks or necks, was mostly what I was shooting for. Yeah, the Holley units look a bit pricey, but TBI tanks are more expensive than the regular tanks, and by the time I buy sending units, replacement pumps, and void the warranty by modifying them, I’m pretty close to the cost of the Holley units anyway. Plus, they come with the Hydramat and are returnless (internal regulated) and will work great with the newer single feed line rails.

Re: Slightly different EFI dual tank question
 

I didn't have to modify my tank besides the usual folding in the seams on the side to get the straps to reach around it, I did modify my sending unit by cutting off the flare because I used braided PTFE line, and the EP381 pump that I used just wired in. I did choose to use weatherpak connectors so that was a bit pricy. I only had to change out (and trim) the rubber hose that runs from the tank to the filler door. I suspected my old tank was rusty inside, and didn't want to pull my bed to install the rear mount tank.



I'm definitely not saying the Holley units are the wrong choice, if anything I am sure the performance will likely be better with the foam and the Holley units since the foam will be more effective at preventing sloshing than the small box baffle in the 87 TBI tank, just want to give you my experience for you to make your decision.

If I were to do it again I'd convert to a between the frame rails 20+ gallon tank that sits behind the rear axles and gone with an Aeromotive or Walbro 450 in tank pump, but what I did got me going for relatively cheaply.

Re: Slightly different EFI dual tank question
 

Yeah, I see what you’re saying. I want to keep the original dual tank setup as I do pretty long drives with my trucks. I don’t want to mess with modifying tanks, sending units, or filler tubes - I did this on my previous C10 and while it worked well and came out pretty nice, it definitely was a one off setup. I’m liking this plug and play, especially eliminating the return line.

Re: Slightly different EFI dual tank question
 

HOLLEY 1973-87 GM C/K SERIES MUSCLE TRUCK EFI FUEL PUMP MODULE
Attachment 2023375

This looks like what you are looking for. The fuel pump is a bit smaller at 255 lph vs 340 lph, but it has a sending unit that works with factory gauges.