Why did I do this?

Mitch Krause

Silver Supporter
I recall seeing a bunch of pictures at different times of uses for the compartment immediately behind the driver in the "sponsom" (if the is the correct word). And some discussions on what was done with that space. I had made some notes, and found a cover and cut a hole and having some time before hockey the other night tapped 24 holes and installed the cover. (See pictures). Then the wife asked "what have you been working on?". Good thing I had some other progress to answer with, since if this had been the only thing, I think my reply might have been "I cut a hole and then took a slightly bigger piece of the same material and drilled and tapped 24 holes and patched the hole".

I don't yet have a particular plan. So what have you found most useful to utilize this space for and why?


Mitch Krause

Silver Supporter
Oh, one other addition to that. I got the cover from Mayhem MetalWorks. Cost was $50. I did have a little trouble sourcing it, as that size of cover seems to be hard to find, in particular in the blank. A few places on the web had it on their site, two of them I actually ordered it from (who both had the same part number on it), and they were both out of stock. Did find a couple of other places where the cover was $85 or more for just the blank. Was happy with what I found, so thought to mention where I found it.
The empty sponson room is good storage for tools, flat tire kit or anything else. You can put the bottle for a fire system in there as well. If you use it for storage you may want to make some of the fasteners "dummys" so you don't need to remove 20 bolts to access the spot!

I would suggest an ignition module should go where there is some potential airflow for cooling. Especially with an MSD unit as the failure rate on those is rather high!
I used mine for the main Power Distribution point at the lower level, and tools/parts/compressor storage for the remaining 2/3 rds of volume space. BTW, the OEM Corvette compressor is integrated with a built-in Fix-A-Flat "Goop" container and selector switch. I believe Honda has them in some of their models, too. Good quality and compact.

If I was to do it again, I would have made mine into a surge tank, but the holes were already drilled by the previous owner.

The MSD box can be hidden and mounted upside down at the battery box cover. There's enough room between it and the battery and you can ventilate that area through the sponson with or without a small computer fan.

Mitch Krause

Silver Supporter
A Surge tank for what purpose?

The ignition box in the battery area is interesting. Not sure how much top clearance I have, but have a fiberglass battery cover that provides some additional room above a line that would be flat to the sponson. Gives an idea for sure.

That also brings up another question in my mind. I did get an Optima battery. Is the battery area normally vented somehow, or can it be closed off? How bad does the heat get in that area, would it be better to figure on something like a computer fan, or make a small vent out the side of the sponson (which would be behind the fiberglass skirt?
Mitch, if your car is EFI and will see track use or extended downhill drives your in-tank pumps will starve out based on fuel level, side accel and deceleration. Mine would starve at half tank and below on the track or prolonged descents in the mountains. One tank has the pickup at the rear, the other at mid tank. I also have the tanks stuffed with foam.

The solution is a surge/hopper tank and/or Holley Hydramat. If your car is just a Cars n Coffee car then don't worry about it...

MSD 6AL2 mounted upside down fits under the cover with plenty of room for it and the wires, and the Optima below. Trim the wires you don't need...

Wouldn't advise venting the fiberglass battery cover since it can easily ingest water from the topside which is why I have mine sealed with weatherstripping and secured with 4 Dzus fasteners. Vent at the inner sponson side (Less likely to see moisture), however, the main positive/negative wires pass thru, if made large enough, should be all the venting you need. The outer sponson and lower sill area can see moisture when driven in the rain so avoid drill holes there. I used the 1" plastic threaded conduit fittings to protect your wires from chafing at the pass thru. Rubber grommets will just dry out...
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Mitch Krause

Silver Supporter

Thank you, that is interesting. No mountains here, so I presume I won't be doing any prolonged descents that would cause fuel starvation. It is not EFI, so not sure if that totally eliminates my concern or not.

Not sure if I will have what you call "in-tank" pumps. I had seen an update where I think Holley 125's were used, gear rotor that can pull the fuel even when mounted above the tank with success. I think I am coming close to remembering that correctly. So my plan was to follow that, not sure if that fits the definition. I was imagining both pickups being in the rear, as the would fit under the clip. You mentioned a mid pickup, how did you do that? (is your passenger door welded shut because you do that track), or did you put the pickup in the cab?
Hi Mitch,
I use Bosch 044 EFI pumps so everything is inside the tank and accessible by a 4x6 inch oval cover plate. The "duck foot" pickups are just different lengths for left and right (rear or mid-tank). The positive wire for the pump, pressure and return AN hoses pass-thru, and the cover plate also serves as a mounting point for the capacitance fuel level sender. This is all mounted and accessible behind the B-pillar and near flush to the rear cockpit/firewall (engine side). It's all hidden by the "wings" that were offered (or requested?) on some kits by RCR Fran.

If you're going with a carb, then your pickups at the rear with no other sump solution, may work fine, unless the car will be seeing some track time...

Hope this helps....feel free to PM me with questions.
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Hi Mitch,

I have EFI and use the space as a swirl pot as described. Mine looks like this:

The three ports side-by-side are the feeds from each and sponson and one return line which splits to each. The one with the stainless flange is the pick up to feed the motor and the brass fitting furthest aft is the return. I have a ~3# pump from each sponson feeding the swirl pot and the EFI hi-press pump draws out the pick up, through a filter, and into the fuel rails. All told, the space holds ~2.5 gallons and is a necessity to keep the hi press pump primed under all driving conditions.

When the sponson tanks are low, the low pressure pumps will lose prime very quickly due to the tanks' layout. It's very obvious to hear when they do. I am glad that I set the system up the way I have, although I need to add in a dedicated selector switch to positively control the fuel return. The path of least resistance brings most of the returning fuel to the driver side sponson, so I end up running that pump the most. When that side gets low, I will add the pass side and excess fuel will return to the driver side. A valve to direct the return flow will address this, just haven't gotten to it.

The hoses in the photo are all hooked up to each other as the photo was taken before I had things fully plumbed and I was pressure checking the cavity before committing fuel to it.

.....A valve to direct the return flow will address this, just haven't gotten to it.
Hey Chris,
I used the 3-way Enderle AN6 fuel shut-off selector valve for a dragster on mine. You'll need to swap the firewall mount female ORB fitting with another male AN6 ORB and you're good to go. You can use a solenoid to bump the selector arm left or right, or just use a "choke cable" that runs into the cockpit to select left/right tank return with the available over-center spring. The arm has just under a 1" throw at the outer hole. Works great!


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Mitch, if you've ever tried to go on an overnight road trip with your GT40 then you're familiar with the total lack of storage for even just the essentials - underwear and a wash kit along with perhaps a change of clothes and a sandwich. Any little bit of add'l storage in a GT40 makes it infinitely more usuable..... Just my $.02.
Wouldn't advise venting the fiberglass battery cover since it can easily ingest water from the topside...

I hear you can drill a hole (or two I think) in the bottom corners of the cavity to allow the water to drain.

Don't ask me how I know this...

And thanks for the valve link Tom!