Might be moving forward with V8 conversion of the '72 Chalon-bodied race car and was hoping not to have to lay out $3K for a custom fit fuel cell that goes in where the stock tank originally resided. I currently have a 12 gal rectangular fuel cell that takes up most of the room in the frunk, and doesn't leave enough room for a radiator. I was thinking of raising the height of the fuel cell so it won't interfere with my front sway bar and cutting an opening in the forward "firewall" to allow me to slide the fuel cell rearward to butt up against the rear true firewall. I haven't seen anyone else do this, so I'm wondering if it can't be done for structural or other reasons. Any insights on this?

Current placement of fuel cell.
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It has been done both race production wise and after-market wise. You have to brace the top across the shocks and other stressing to the front (torsion bars), lateral support, etc.

Original fuel tanks from factory or race teams put in a 100liter tank which was also done on the 911 racing versions. Several were done by hobbyists.

It would change the weight distribution along center of gravity moving everything back toward the middle of the car.

I do not know what is here on this site; check via search.. Also, check with Pelican Parts both 914 and 911

Do a search for the GT 100L tank on Google, there are several writeups that show how they cut that wall and reinforced the area.

Quick note: once you move the fuel cell back, you will need to weld/semi-permanently close all heater hose and other holes in the drivers firewall. Any good tech inspector will stop the car in it's tracks if that isn't accomplished

Just curious, George ...

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I doesn't sound like the OP is planning to cut into the firewall between the passenger compartment and the fuel tank bay, just the bulkhead at the front of the fuel tank bay.

SInce the original tank already shares the same bay with the fresh-air ducting, why would a different (better/safer) tank be cause for concern?

If all the fresh-air ducting is/has been removed, yes, sealing the openings sounds sane, regardless of the type of fuel tank ... even if not a track car.

Mark, good point. I guess I'm so used to my own car that I didn't think about it. What I should have said is that anyone serious about tracking their car should seal up those access holes, regardless. Mostly, it's a hazard and an open avenue for gas, fire, etc to make it's way straight into the driver compartment, particularly in a rollover. Simply leaving the heater controls in place isn't a big help either, obviously because Bakelite is flammable. I know SCCA doesn't like to see any holes over a pencil-width in the firewall for sure. Some folks might let it slide, but I dunno.

Regardless of where the fuel will go, I agree that any openings in the real firewall need to be closed off/welded shut for safety. My car was issued a SCCA logbook with the fuel cell in front of the forward bulkhead, which has no penetrations in it. Moving it back by cutting the forward bulkhead would require all openings in the real firewall to be closed off, which I will be doing shortly. Wires coming through grommets should be OK shouldn't they?

Engman used to make block-off plates for the fresh-air vent openings. ... not sure if Mad Dog is making them now?

It should be OK to cut through the metal in the bulkhead between the shock towers. As mentioned elsewhere, you might consider reinforcing that area if you wind up cutting a lot of it out since it's important for maintaining front suspension geometry.

I put the fuel cell for my 914 in the forward portion of the passenger footwell. It leaves lots of room up front for oil cooler ducting, and keeps the weight from fuel low and on the right side of the car to offset driver weight. I guess one could argue that corner weights will change as the tank empties, but car balance will change as the tank empties no matter where you put it. I'm not a fan of putting the fuel tank up high if it can be avoided, since a full tank is a lot of weight.

Scott

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Heres some thoughts...
All fuel cells expire in 5 years. I assume that since your posting here, you race. My thought is that you could find a different sized fuel cell that would fit in front in the fire wall with a radiator.
With that said I had no problem cutting mine. Look before you cut. There's some structure in the top part I left attached in my pictures. I wouldn't cut any higher then I did.
Not sure about capping the holes under the dash or not. I've heard of people putting fuel cells where the passenger seat goes and have no problems with the tech guys. I think that since the tank is in that box it counts as a layer of protection. I'd definitely check with your club. NASA and Chumpcar never gave me any crap except the expiration date and the huge size!
Good luck.

I shoulda mentioned in my earlier post that I extended the firewall backward into the passenger area to cover the fuel cell (which already is in a metal case like most). I agree it could be an issue with tech if I didn't have that.

Motorvated, how about just a new tank/cell that is more vertical and keep the wall intact and still leaves room for oil cooler ducting. Best, Mark

I need quite a bit of space for engine coolant radiator with fans and inlet ducting, as I'm installing a 0.030 over 215 Buick V8 motor. More space than needed for just a forward oil cooler. I'd rather not cut the forward metal bulkhead between the strut towers. I have since located and purchased a used cell with bladder that fits in the stock tank location from another world member, just waiting for it to be shipped. I checked SCCA rules, and they specifically say that there is no time limit on fuel cells, so a good used one should be OK.

I'm sure you know this, but check the bladder carefully, esp. if it's more than 5 yrs old. There are a few vendors that can repair bladders if they're not in too bad condition.

This is the way I added the fuel cell and radiator for the Subaru. I am going to part this car out as I have built a Cayman for SCCA racing

Current placement of fuel cell.
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This is the engine bay with the Subaru and the new Cayman.Click to view attachment Click to view attachmentClick to view attachment