build diary

March 13, 2006:
A cheap way to clamp off fuel lines.
That's a 99 cent tool!
entry 1141

March 15, 2006:
Lots of destruction last night.
I reinstalled the throttle bodies a couple of days ago after fixing a small amount of play in the synchronising mechanism. It wasn't causing a huge problem but it did mean that I couldn't run an idle switch for the ECU. See, the ECU gets upset if the engine speed hits 2000 rpm and the throttle body is still at idle. I had just enough slop to make this happen when leaving from rest, leading to a bad driveability problem. So I'd been driving around without an idle switch which was fine other than cold start up. After installing the fixed throttle bodies, I adjusted the butterflies by eye and fired up the car. It idled happily even though it was stone cold. Very nice.

I drove the car out the garage, turned it around and then went right back in. Why? Time to work on the gas tank! First the fenders came off (didn't I just put one of those on?), then the rear panel was removed. Now the fun part - the fuel tank. I'd forgotten how much fun that was, having to remove every single fitting on the tank by putting my arm inside. At least it's the last time for this tank! The car now looks truly sad but I'm on a mission to build this tank as quickly as possible.

The new design will sit at the rear of the car behind the differential instead of on top. This is a more traditional Se7en tank. It'll be wider and thus more susceptible to fuel slosh, but I'll address that with internal baffles. The best thing is that the center of gravity in the rear will drop down significantly, cutting down on roll. This is my primary reason for the work. I'll also have a trunk of sorts! Initial calculations tell me that by simply filling the area below where the old tank sat, I'll have a 6-7 gallon capacity. Not bad at all! Tonight I'll make a cardboard version.
entry 1142

Fixing the throttle bodies for better synchronisation.
There was a bit of slop in the mechanism that joined the two halves.
entry 1143
I had a request for a better shot of the exhaust.
I haven't had the car outside in the light for a while so this is the best I can do at the moment...
entry 1144
The rear bodywork is off, now it's time to get that old fuel tank out of there.
entry 1145
The rear end naked and ready for a new tank.
I'm going to put the tank in the deep area at the back and use the small hole in the center (you can see the grey sway bar in it) as a sump. It should work out pretty nicely.
entry 1146
A new project, as if I needed one.
This is going to become a fairly potent naturally aspirated Miata rally car. More details to come!
entry 1147
Maybe I should put one of these cars together so I can drive it!
entry 1148

March 18, 2006:
I was supposed to be on my way to a track day, but a Colorado storm took care of that plan.
So instead I dug into the job of the fuel tank. Step 1 was to spend some time with cardboard. It looked fairly easy, but I had to consider removal as well as fuel flow and capacity. I do not want to end up with a tank that requires much disassembly to remove. After a couple of hours I had the solution and some quick calculations showed the capacity as 7.5 gallons. Excellent!

With a wave of my magic wand I transformed the cardboard models into steel. By "magic wand" I mean bandsaw, belt sander and welder of course. On the first test fit, the tank fit perfectly and I was able to install it without resorting to cheating. Hopefully that will be the case with the final unit! Once four sides were done I decided to weld up my sump. Once that was finished, I took a look and decided there was a better way. 30 seconds later, the plasma cutter had removed a big chunk of what I had. The sump is now complete and ready to be affixed to the bottom of the tank, then it's just a matter of a couple of internal baffles, the top and then sealing. POR-15 makes a gas tank restoration kit that should do the job nicely.
entry 1149

March 19, 2006:
Today was supposed to be a ski day, but, well, it didn't happen.
So I went mountain biking and then attacked the tank again. I'm really enjoying this. The sump was welded on along with a couple of internal baffles and then the back. Now I just have to install the fitting for the return line and weld the top on the tank. Some sealant, paint on the outside and then it's just a bit of plumbing. I'm pretty happy with this upgrade so far. I think it's going to be all good with little or no downside other than a lost weekend spent fabricating. And is that really lost?
entry 1150

The cardboard templates for the new fuel tank.
entry 1151
There are some odd angles in the tank to let it fit into the car.
entry 1152
The first test fit of the new "tank" - sort of.
It fits!
entry 1153
The first sump.
It probably would have worked well, but I thought it could be better.
entry 1154
The reconfigured sump, ready to weld on to the tank.
entry 1155
The sump is in along with a couple of baffles to cut down on sloshing.
I'll have foam in the tank as well. The baffles don't go all the way to the top so I can actually put the foam in the tank.
entry 1156
The back of tank is on.
Only one more panel left. Of course it will probably turn out to be the biggest hassle of the lot.
entry 1157
Before I weld the top on, I think I'll add a couple of straps like this to keep the sump nicely filled.
Of course, in the current state I figure I won't have fuel starvation until I'm down to about a cup of fuel and pulling a high-g corner.
entry 1158

March 21, 2006:
After cutting, sanding and welding all weekend I took the tank home to see how it fit in the car.
It slipped in with millimeters to spare past the roll bar but then wouldn't clear a tube at the bottom. The sump was hanging up. I peered underneath and discovered that a weld bead I'd run around the outside of the joint (it's fully welded inside) was hitting the tube. I ground that flat and the tank popped right in to place. It's as if it were designed for this car! Hang on...

I did a few happy dances as one did not seem to be enough. I could not be more proud of this tank. I've decided to put a couple of zip-tie anchor points on the outside to make it easier to hold hoses in place. I picked the sealant up yesterday as well. On the Locost mailing list, I was asked why not aluminum? Well, after paying for the Kreem sealant it's not cost. I don't know how to weld aluminum and I'm on a bit of a schedule to be ready for the Car and Driver test. But I do have to say that if I did it again, I'd certainly consider alloy. The finished tank is just under 16 lbs compared to about 8 lbs for the previous plastic one. That weight gain is about the difference between my new battery and the old so there's no real change overall. I won't have to run as much fuel to avoid starvation on the track so that's nice. Plus of course the weight distribution is much better.

The preparation for the magazine test continues. I've been told they're going to be doing instrumented testing so I'm nervous about that - what if the car only does a 0-60 run in 10 seconds? Well, a Caterham SV 160 does the sprint in 4.9, but that doesn't reassure me much. I've ordered some new springs, going to 500 lb in the front and 250 in the rear. Heikki thinks the 500 is far too soft but I think I can improve the wheel rate with some shock mount tweaking. He's also driving a pure track car and doesn't have sway bars. I don't feel the front on my car is too soft anyhow, it's the rear that needs beefing up. Will I regret this? Probably. But I'll have to make the mistake first. I can see Heikki shaking his head from here.
entry 1159

We just got a plasma cutter at work.
I can't stop finding reasons to use it. Like this one.
entry 1160
In the car! I could not be happier with the fit.
entry 1161
A shot of the tank from the rear.
The sump is quite obvious here.
entry 1162
The sump from the side.
The fuel line is just hanging off here as I had been checking the clearance for the nuts. The ugly welding along the seams is not needed, it's fully welded inside.
entry 1163
<< | show individual entries | >>