FuryRebuild
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| posted on 4/12/12 at 04:25 PM |
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Hi Jim
The tank gives about 30L of fuel, and I have an ATL probe fuel level sender and matched gauge to measure the levels. I'm going to do some
track-days and some long-distance cruising but probably not compete now. However, that doesn't mean the right things shouldn't be done -
scrutineering has rules for a reason. I found that with my pinto engine, i would get about 13mpg on a cruise, and am going for a 215bhp duratec this
time, so again I expect heroic fuel economy 
I did lose it at the raggedy limit at harewood and span it into the armco, probably not going much quicker than I did on the previous lap. What I
remember is that first circuit it was quick but I had all the traction I needed. Second circuit I was in the armco. It put the car out of action for a
whilse.
In this incarnation I'm looking to reduce mass and move what I can lower down. Hence rewiring the car as well. I'm going to modern
projector headlights and led rear lights, solid-state relays, a power distribution module (making my own) and mil-spec connectors and high quality
wire.
When all you have is a hammer, everything around you is a nail.
www.furyrebuild.co.uk
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scudderfish
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| posted on 4/12/12 at 06:01 PM |
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Shifting weight closer to the centre will make it less likely to break away, but when it does you'll get less warning and it will rotate faster.
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JimSpencer
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| posted on 4/12/12 at 06:08 PM |
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Hi
Where it was really noticable was on a S bend, like the ones at Loton for example
When you wanted to switch from a quick left to a quick right, very quickly, you would get it trying to wag it's ar5e as about 10kgs of fuel -
that had been at the very left hand end of a long thin horizontal tank right across the very back of the car - suddenly all moved to the other end!
Could have probably improved it with lots of baffles or lots of foam - but it also made one worry less about going off backwards when the first thing
into the scenery after a layer of fibreglass wasn't an old mini van tank 
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Andredp
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| posted on 5/12/12 at 06:31 PM |
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Hi
I fitted a smallish 17L tank behind the passenger seat in my Locost and tried it out in a 2 hour endurance race at Kyalami raceway here in SA this
past weekend. My best lap was almost a second faster than my previous best at Kyalami, so an "inboard" tank do seem to make a good
difference.
Andre'
Luego Locost SA
Locost IRS Racecar: www.locostformula.co.za
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sebastiaan
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| posted on 5/12/12 at 06:57 PM |
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quote:
Originally posted by scudderfish
Shifting weight closer to the centre will make it less likely to break away, but when it does you'll get less warning and it will rotate faster.
Exactly! a lower polar moment of interia will help the car to turn easier, but it will be much harder to correct when it all stsrts to go wrong...
I'd go for a properly baffled (non-sloshing...) rear and low mounted tank if I were you.
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FuryRebuild
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| posted on 5/12/12 at 07:37 PM |
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I disagree.
When the car starts to go with a high polar moment of inertia (think of a 1kg weight on the end of a 1m stick, and you're holding the
non-weighted end and waggling it) once you have that weight moving, you have high inertia and stopping it moving (as in correcting it when it starts
to go wrong) is more difficult. What's more, you're correcting it with inputs from the front, trying to affect strange forces acting at
the back. This again fiddles with chassis dynamics.
Reducing the polar moment of inertia means turning in is easier, the car is more stable and if it goes, it requires less energy to correct it.
What's more, your rear tyres don't have the lateral forces pushing them out which means you reach the same limit of friction at a higher
speed.
I would argue that if you're losing it at higher speed, you're going to have more of a controlled drift rather than a whip. One of the
nicest cars I ever drove for this was an original wedge-shaped MR2 - you could drive it on your right foot as well as the steering wheel.
If you take a look at how race cars are packaged, lots and lots of effort goes in getting the mass down, the centre of gravity low and the polar
moment of inertia down. There's never a massive weight hanging out behind the rear wheels. The most rearward part is the last bit of the
transaxle and the wing pushing down on the chassis.
I was at a practice session at Harewood and a chap with a very successful sevenesque kept losing it (he was regularly placed in the top 5, so somewhat
good a driver). He took off his rear mounted spare wheel and was suddenly right back on the pace. that wheel and tire would weigh more or less the
same as a tank and some fuel. It's an extreme example (as in well back) but illustrates the point.
So, still doing the tank. Thinking of using the tank as a mold and making a carbon fibre jobby instead - less mass again.
quote:
Originally posted by sebastiaan
quote:
Originally posted by scudderfish
Shifting weight closer to the centre will make it less likely to break away, but when it does you'll get less warning and it will rotate faster.
Exactly! a lower polar moment of interia will help the car to turn easier, but it will be much harder to correct when it all stsrts to go wrong...
I'd go for a properly baffled (non-sloshing...) rear and low mounted tank if I were you.
When all you have is a hammer, everything around you is a nail.
www.furyrebuild.co.uk
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sebastiaan
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| posted on 5/12/12 at 08:05 PM |
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One last note: making the car easier to turn means the initial oversteer will develop easier as well. In a way, you are removing interia from the
system, making everything happen quicker. Good for ultimate laptimes (hence the racecar packaging) IF you can handle it. I for one cannot ;-)
On the CF tank, remember that steel / Ali yields before rupturing and CF will not. Sorry to be a bit negative about this, but I would not make the
tank out of CF for that simple reason. CF with a fuel bag, maybe.
But, in the end, it is your car of course. And I admire the amount of thought and fabrication skill that is going into your (re)build.
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FuryRebuild
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| posted on 5/12/12 at 08:34 PM |
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Hi Sebastian
Firstly I'm enjoying this debate; it's good that topics can be challenged and kicked about and I do value everyone's input and
thanks for your measured and patient explanation. I'd sooner put an idea out there and either get it confirmed, refined or culled.
that is a point you have about over-rotating it, and I expect it's going to be a major effort to learn to drive the car again, especially with
all the suspension changes I'm making - part of the setup will be the measured circle g-force tests.
When hill-climbing I used to run a setup designed for chuckability - some of the 12ft 90 degree corners are like slotting it into a back-lane, and I
used to get entry speeds into the first corner at harewood of 60mph. I have seen the evo boys go in way quicker than that
I've also gone for a good anti-roll bar setup so I can soften my springs (and changing from spax to gaz dampers) so it should now manage roll
the correct way and will be less twitchy on the larger circuits.
On the subject of tanks that is a great observation, and not one that had crossed my mind. I will have to go away and think about that very carefully.
I may just go for metal. Ali would be good for weight, but I can't weld that at home - I'd have to offset the price of someone tigging it
for me vs tigging the steel myself. Saying that I've been rigorous with removing weight, so may have to part with a few sheckels more to get the
weight. Once the ali has oxidized then I won't need to worry about any further corrosion.
When all you have is a hammer, everything around you is a nail.
www.furyrebuild.co.uk
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britishtrident
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| posted on 5/12/12 at 09:38 PM |
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What everybody tends to forget with fuel tanks is fatigue, mass X of fuel sloshing around in the tank causes the surfaces of the tank to flex
and it is not unknown for the seams to crack. Years ago an after market tank supplier ran into big trouble with a replacement tank for FX4 taxis
which split along the seam, many members who have been around here for a while will also remember the sad saga of the plastic tank man.
A fuel tank should have as few seams as possible and the folds should have very generous corner radi.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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FuryRebuild
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| posted on 5/12/12 at 10:02 PM |
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Thanks BritishTrident.
Bend-radii are at 3mm - I spoke with my cutter/press-brake people and this is the minimum radius they've recommended for stainless. it's
less for mild and i don't know what it is for aluminum.
I can push a different global bend radius through the cad to change this; it may mean the odd alignment needs resetting but the s/w will let me set
alignment per bend for this (as in radius starts at the material edge, or finishes at the edge).
I have tried as much as possible to reduce the number of welds, and have measured all the folding options to keep the welding down but at the same
time needed to be sure it was theoretically buildable.
what happened with the plastic tanks? i've not heard of that.
When all you have is a hammer, everything around you is a nail.
www.furyrebuild.co.uk
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britishtrident
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| posted on 5/12/12 at 10:58 PM |
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I would use at least 13mm radius as an absolute minimum , most commercially tanks you will find have radi > 20mm.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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mcerd1
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| posted on 6/12/12 at 08:58 AM |
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^^ flex in the tank was one of my concerns about your 'T' shaped tank idea
depending on how it was mounted to the chassis there could be quite alot of stress on the inside corners of the T.
the chassis might be alot stffer than the tank, but that doesn't mean it won't flex at all...
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procomp
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| posted on 6/12/12 at 12:12 PM |
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Hi
Don't concentrate to hard on getting the mass too low and forward in the car. Remember that you need weight transfer to add front end grip
during cornering. The lower you place all the weight and further forwards it is the less weight transfer you will have. Also it will exaggerate the
fact that the one mass you can not move your body which is offset to one side, this will only add to more unevenness weight transfer. Personally from
dealing with a few Furys and strikers i would concentrate on getting the loading more even across the rear axle and then play with weight transfer
control to the front during cornering IE Damper control in compression and rebound in particular.
My 2p
Cheers Matt
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