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DRR Pro |
Reading Morgan's book and was looking to see if anyone had any experience finding the center of gravity as outlined. I would have to do it by myself and the thought of balancing a RTR car on a pair of jack stands is a bit daunting. Also I have a few old batteries and paint cans that I can put in the drivers area but not much else as substitute weight - any other ideas? | ||
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| DRR S/Pro |
Use the height of the camshaft. close enough. | |||
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| DRR Elite |
Been a long time, but I have done it. Start with four stands and move them in as close as you are comfortable. If you put the rear ones a smidge higher, you can use a jack on the rear end. when you go forward with those rear stands far enough that it teeters and starts to come off the fronts, you are close. Mission accomplished IMO at that point. I never found it a particularly fruitful exercise. You have to assume where the vertical cg is. so even if you have the horizontal, you are still kinda guessing with the crankshaft height. These guesses kinda add up to making a big difference when you are plotting your IC. And that's the end goal right? Figuring out where your IC is in relation to the CG. I put a lot of effort into it, and in the end it was experimenting with different bar angles to find shock travel that made sense for my combo. The shock travel data is probably the most useful thing, with the driveshaft data and g meter data being next in line. Foxtrot Juliet Bravo | |||
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| DRR Elite |
I think he is looking for the horizontal cg. Foxtrot Juliet Bravo | |||
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| DRR Trophy |
Never tried Morgans balance deal but have weighted car with driver weight by using sand tubes from Menards. They weight 70lbs. each. Three is just right for my fat azz.  This message has been edited. Last edited by: vetman, The difference between ignorance and stupidity. Ignorance is lack of knowledge. Stupidity is the inability to learn. Don't be stupid | |||
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| DRR Pro |
He actually mentions that in the book and indicates that you are fooling yourself, so while it might end up being the same I would like to find out what it actually happens to be. | |||
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| DRR Elite |
What is your ultimate goal with this and how precise do you want to be? Foxtrot Juliet Bravo | |||
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| DRR Pro |
Bucky - my thoughts right now are that I have never been totally sold on the way this car -- does anything. I took it over from my son late last year and sorta of worked with what I had, I am just not totally sure of what that is so I thought lets just go to a beginning and work from there. I have had Morgan's book longer than I can remember and for the most part I have used it as reference book for fixing (or trying to fix an issue). So yes I would like to be accurate but I don't know that dead-nuts is going to make a huge difference. I made some changes in the car in the late fall but we got rained out around here so I have no testing on them yet. I have a few things I want to clean up and figured it would be good to really get a grip on this chassis. Besides getting the brake issue squared away I felt that the convertor was too tight, so I bumped up on that and I also feel that there is some ET in the chassis. My best in the car last year was a 5.71 at 121. About 75F, 50% humidity, decent air. The car weighs about 2000-2100 (will verify that this weekend) and packs a 434 SBC with a Glide and 4.86 9" on a 31" tire. Engine was dyno'd at 750 on gas, I run alcohol. I think the combo should be in the 5.40's. | |||
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DRR Trophy |
I wonder if a guy could scale each wheel, and figure it out mathematically somehow? I realize that the scales are likely not readily available. | |||
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DRR Trophy |
Yes, it's a relatively simple tilt test with 4 corner scales and a bit of math to find the longitudinal and vertical position of the car's CG. Lateral CG position can be done the same way just tilting and weighing side to side instead of front to rear. The toughest part is making and installing "solid" links in place of the shocks to keep the car at ride height during the testing. | |||
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| DRR Sportsman |
While this is intriguing and I have sought after this in the past - at the end of the day even if you had it there is no magic formula that will tell you where to put the IC for a particular car. The car leaving is not static and other factors start playing into it - hence the need to experiment with on the track results. At best it might reduce or tie together results you obtain. No substitute for real-world testing to get it right. I will throw out there with all that...change tracks that have a different slope/crown to the track - the car is sitting totally different than your perfect flat garage floor- and again you might have to make adjustments. The most useful thing I did years ago was to find the true centerline of the car and permanently mark the car for easy reference. This saves TONS of setup time and is a great way to see if its the car or something else happening if the car starts leaving off straight. Again sometimes it is the track.  Configuration: 3350#, 582 C.I., 60 - 1.24 1/8 - 5.53@ 126MPH 1/4 - 8.73@ 159MPH  3700#+210lb driver, FULL interior, through mufflers, 10.5 tire. 60'-1.333 (IN 4000ft DA! Joisy Math excluded; 1.25sec using JOISY MATH.)  1/4 - 9.60@144MPH | |||
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| DRR S/Pro |
So your missing ET is not in the chassis, at least 95% of it anyway. If your making 750 HP then your 5.40 number is more in line with speeds in the low 130 MPH so both your ET and MPH aren't even close to those which means you got issues or the motor is not making that power. So the first question is why did you switch from gas on the dyno to alky in the car? I'd get the gas carb you dyno'ed it and try it in the car and see what that tells you first. The converter being tight will hurt ET but not MPH anywhere near as much, your missing both. Nothing wrong with laying out your chassis setup. CG height IMO is far less important than CG location front to back. Have you weighed your car separately so you have both the front and rear weights? If you have that and your wheel base then you have your CG front to back location. But as I stated above, you need to figure out the power issue before you deal with fine tuning the chassis setup. Your current numbers only show that your getting 570 HP from the motor. | |||
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| DRR Elite |
And of course, information is usually a good thing. I wouldn't discourage you from the exercise. Foxtrot Juliet Bravo | |||
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| DRR Pro |
Bucky - I'll just say good points. The engine was dyno tested on gas because that's what the engine builder did. And the gas carb that was used is now gone. It was switched to alky as the rest of cars run that and it just makes management of fuel and cooling easier. Mid-Va in the summer is not exactly sweet and cool. I have a lot of stuff to look at for both engine and chassis. And again the 5.40 number is where "I think" it should be - running calculators which are certainly perfect world the car is supposed to be quicker and faster. | |||
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