I am getting some parts and pieces together for my autocross only car. One thing I bought is a fuel cell that I was thinking was small enough to fit in the bottom of the trunk. Well I was wrong and at a very minimum I will need to do some cutting. Not a big deal but I was thinking it might just be easier to cut the trunk floor out between the frame rails. There is no stress behind the spring mounting points so I shouldn't have any problems there and the chances of getting rearended on an autocross course is also pretty minimal so I am leaning towards cutting the complete trunk floor out. It will allow me to move the fuel cell about 8 inches forward from where it would have been if I just put it on the trunk floor and I would have to make some way to mount it and seal it off from the passenger compartment either way. The other thing is the battery is in the trunk so that would also need to be moved. It would just be easier to cut the trunk out and kinda start from scratch but would like some opinions. Remember this is an autocross car that will never see street duty. All Of the suspension mounting points have been tied into the cage so the chances of anything flexing if I cut out the trunk floor will be pretty much none. I am still going to keep the unibody frame rails intact so it's not like anything will be loose.

 

We build race cars in our shop all the time. On dirt track cars we don't have a trunk area installed since aero does not come into play on those cars. When you mount the tank, use a 2x2 square tube welded between the frame. You'll need two. One in front and one behind the cell.

Weld them in so the cell fits within a couple inches of the rear axle or as close as possible. Also keep it as low as possible in the car. The closer the cell is to the rear bumper the more fuel slosh will cause handling problems.

You can use smaller 1x1 tubes to weld down in front and back of the cell and under it as a support. Use a 2" flat strap on top of it top bolt it in place. Of course the size of your cell will determine if you can use these sizes I mentioned. We use larger cells in our circle track cars, so keep that in mind.

As fuel burns off if it will pick up a push so keep it full as well. Fuel is just over 6 lbs a gallon so keep that in mind in picking the size cell you need. I like taller cells over wider ones of the same capacity. I feel there is less room for fuel slosh on a taller cell.

 

https://www.thirdgen.org/forums/atta...p-104_4135.jpg
This is how I did my fuel cell

 

I ended up cutting out the trunk between the frame up to the back of the rear axle. Welded some tubing between the frame rails so I could mount the fuel cell as low as possable and only about an inch behind the panhard bar. I also built a bracket to mount the battery behind the fuel cell and to the right to offset the drivers weight. Then I sheet metaled it all in. Looks pretty good but my sheet metal skills are definatly lacking. I only need to add fuel before an event so I just cut an access hole above the cap and used push rivets to hold a cover over it.

 

Sounds like you did it the right way and did a good job of it. Post up some pics of the cell and your car if you will. I'd like to see it.

I'm building an IROC race car version, well as close as I can get it to the real thing at least. I have not got into the math yet, but the front struts will be leaving and I'll replace that with a suitable spindle and tube upper A arms. everything in the front and rear suspension will be running on rod ends as well and fully adjustable. Should handle really well. Hope I can get it past tech and run it at Road Atlanta in some nostalgia events when it's done.

 

Mine is mounted at about the same place as 500+hpta is but much lower. Both the fuelcell and Battery are hanging a few inches lower then the rear bumper but there is still plenty of ground clearance so that shouldn't be a problem. I am actually embarased to show pictures of my welding to the world. I was useing a friends welder and just haveing a hard time with it so my welds are what I call "bird ****" welds because that is what they look like, I should have loaded up my welder and brought it to the shop. It's funny how 2 different welders can weld so differently. All in all I am pretty pleased with how it came out.

 

I know what you mean about welders. Mine is picky as all get out. It's a mig/tig combo. It refuses to work unless the liner is very clean and it's kept as straight as possible. It likes to kink wire on occasions. More than I like it to. I find that if I take it and spray WD40 down the liner and stick a length of wire through it and pull it back and forth like a saw it cleans out the liner and it works great for a while. And the settings have to be perfect or it will burn a hole through armor plating ... lol. When it works, it's great, but when it throws a fit I go ballistic. Plus I like to do double pass welds on my roll cages and like and then I hate to go back and grind it down to make it look pretty.

 

Well mine is just a 140 amp flux cored mig. I can convert it to gas but really like the convienience of not needing to haul a tank around everywhere I go. I have been impressed at how well this little machine welds. Flux cored welds are never pretty but I can get decent looking results with it, at least not embarased if they are seen. I built a rockcrawler Jeep from the ground up with this little welder and never broke a weld. I know with a little practice I could have got good looking welds with my friends welder but these welds are just plain ugly.