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Author Topic:   FUEL CELL LOCATION ???
155fan
Member
posted May 19, 2002 09:32 PM
I like it to the left side because it will add cross as fuel burns off.


CUSTOMPERFORMANCE
Member
posted May 20, 2002 10:33 AM
I have tryed mine in different plaxces and like it centered with the engine and up high.


#28
Member
posted May 20, 2002 01:51 PM
You're right, 155. You put the cell on the right to add cross as fuel load decreases. This is the way I set up my cars and I add all weight to the left. This way, as I burn off the fuel, I lose rear percentage, but I gain cross and left side. I'd rather have the rear percent, though.

Me.

155fan
Member
posted May 23, 2002 09:02 PM
Greggie, you got it backwards, with a left hand mounted cell, as fuel burns off you gain cross.


olexiewicz
Member
posted May 24, 2002 04:42 PM
quote:
Originally posted by wfoondirt:
Greggie, you got it backwards, with a left hand mounted cell, as fuel burns off you gain cross.

No way!! as fuel burns off you take weight
off of the left rear, which takes cross
OUT of the car. put the car on the scales and
try it for yourself.


Mod6M
Member
posted May 24, 2002 07:06 PM
Wfoondirt is right. I like a car to gain LR as it burns fuel myself.


Fourty8
Member
posted May 27, 2002 04:01 AM
I just couldn't resist adding my 2 cents worth here.

Wfoondirt is exactly right in that, mounting the fuel cell to the left side of the chassis, the cross weight of the car will INCREASE as fuel burns off. Just think about it.

Mounting the fuel cell on the left adds PHYSICAL WEIGHT to the left side of the chassis, not crossweight. You can only change the crossweight by raising or lowering the corners of the chassis.

By all means put it on the scales and check it out. Mount the fuel cell as far to the left as possible and put say 20 gal. of fuel in it. Set the ride heights of the car on all four coners to what you normally run. Set the car on the scales. Set whatever crossweight you normally use. Write it down. Now fill the fuel cell up and read the cross weight. It DECREASED. Granted, you have added left side weight and total weight to the chassis, PHYSICALLY, but in doing so you have also lowered the left rear corner, thereby DECREASING the crossweight.

Now, get in the car. The left side weight and total weight increased. But, what happened to the crossweight? It decreased further, because the left side has lost even more ride height. When you get out of car, the left side weight DECREASES and the crossweight INCREASES due to the increase in ride height. Fuel burn works exactly the same way.

If the cell is mounted on the right side it works just opposite. As the fuel burns off, the right side physical weight decreases, the RR ride height increases, increasing RR to LF crossweight and REDUCING the LR to RF cross weight. Although you have decreased right side physical weight, you have raised the ride heights due to decreased weight on that side.

The only way to keep the cross weight consistant, or at least close to what you started with, is to mount the fuel cell in the middle. That will have the least effect on cross weight change. Rear percentage will be affected the most and but cross weight affected the least.

Wfoondirt, you are exactly correct. This must be the biggest misunderstanding in racing. Phisical weight vs. cross weight. It should always be remembered that you cannot change the physical weight of a chassis with jack bolts. You can only redistribute that weight to a limited degree.

If you add 5 lbs to the RF with the jack bolt, it also increases the LR 5 lbs. Where does that weight come from? It comes from the LF and RR. Each of those will LOSE a proportional amount of weight resulting in a total of 20lb redistribution of weight. But the physical weight has not changed.

This subject can certainly be confusing at times.

Fourty8


dirttrackracer
Member
posted May 27, 2002 06:57 PM
Fourty8 is exactly right on,simply put,raise left rear corner 1/4-1/2 inch and re-check cross.It will always raise cross.Greggie was on here not too long ago wondering why he was blistering right rear tire,now we know why,I bet he is a rocket in the heat,and goes back in the features.


155fan
Member
posted May 28, 2002 05:54 AM
Here again, we are dealing with weight re-distribution, due to changing percentages. Whether it becomes loose or tight, late in a race would depend on several factors. The primary balance of the car, being the most significant.

It should be remembered that physical weight gain or loss affects all four corners of a race car, thus affecting crossweight as well.

Let's assume that these are the percentages of a race car. 60% rear, 53% left and 51% cross (LR/RF). That would leave 40% front, 47% right and 49% (RR/LF). Weight would be gained or lost at each corner proportional to the percentages of that corner. A 100# reduction in rear weight would be distributed as such: -60# rear/-40# front, -53# left/-47#right, LR -31.8# (.53 X 60) LF -21.2# (.53 X 40), RR -28.2# (.47 X 60), RF - 18.8#.(.47 X 40) This is PHYSICAL re-distribution of the weight. This is also the BALANCE of the car.

Now we get into spring rate. The springs we use on a race car are linear rated. Meaning that spring height is directly proportional to weight. (It takes 200# to compress a 200# rate spring 1 inch.) Each corner normally has a diffrent spring rate. ie: 650 LF, 750 RF, 200 LR, 175 RR. As weight is reduced at each corner, the spring will gain height proportional with the weight reduced at that corner. The lighter the spring, the more height you will gain.

To answer your question of whether it will be loose as fuel burns off, if the RR spring is too soft, yes. If it is too stiff, again the answer will be, yes. Adjust the spring rates to compromise and keep the ride heights as close to the original height as possible.

Everyone should remember that we are talking STATIC percentages here. DYNAMICS are a whole new ball game. Add body roll, track banking, surface conditions, caster, etc., etc., etc......... and everything changes.


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