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 Post Posted: Mon Aug 02, 2010 2:50 am 
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Timeslip?? All I can tell you is when I first came to the car it ran 8.65 average time with the engine it had then. It raced for years with that engine and did those times so its was stable test bed. I altered it, i lowered it, re sprung it and re shocked it and reset the 4link over some time and then it went 8.42 average on same engine. That engine was very consistent in its power. In fact it always went the fastest when the engine was worn out slightly at the end of the season, it didn't have enough traction to hold the torque off the line. The engine would drop approx 25hp through the year of running. Every year it was freshened and it went a little slower at the start of the season, it was all down to the first 7 feet of track. Thats what made it ET fast or not. Just slightly too much power and it would turn the tire and go slow. Most people claim that turning the tires is faster, but thats definately not the case when you dont have enough weight to start with on the rear. You have to generate enough effort from the snap at the start to get it up and transferring weight. If you cant snap it right at the start because youve blown the tires off, it wont go forward fast enough. The car takes 14" of track movement to reach its peak G force and when its turning the tire too much in that 14" it doesnt get to peak G. By running a short IC with hard springs and soft shocks I can use the inertia of the turning wheel to push the body up enough to create that temporary down force I need for the first 14".
The reason why the car is so low is if you run a short IC (to snap the diff down) with the CG high you get airborne too easily and it heals back on the wheelie bars and looses traction. It doesnt break loose at the start but it does it 10 feet out. So Its set low so that the wheelie bars are basically not needed and they only just touch the ground for about 14" of track. That youtube video is a bit over the top because its the first run with a 3 speed box but its setup for the 2 speed. So it planted the wheelie bars a bit harder than what we like. We didnt care at the time as it was a 'one off slap together run' just for the funeral ashes thing. The engine was disassembled and everything on the car was apart just before that run so it was slapped together to do that.

I ran into an issue with the chassis torsional rigidity. Everytime it ran faster than an 8.40 I would have to reset the preload, it didnt scale exactly right, something was yielding. It was moving the chassis with the loads of just a little faster run. So we added frame bars in the rear and some in the front and a larger antiroll bar to the rear. Now its really good. It can run down to 8.17 (and probably faster) and not a tiny bit of movement. it scales exact year after year now.

Eventually the engine was sold and it was going to be supercharged. So the block and crank and rods and glide were setup for blown (434 cubes, splayed valve heads, 14-71 it would have been fun). But midway through the driver got cold feet and the idea got scrapped and changed to 406 cubes NA. So now we had all this heavy stuff we didnt need. ](*,) The car gained 180lbs over the front and it has been a handful ever since. I don't complain about it because Ive figured out how to deal with it, thats why when you watch the youtube in slow motion you see the body rotate about the rear axle then launch upward and forward at the same time. Its like a cat pouncing from a crouch position. I have had to adopt this approach in order to sustain downward force on the rear tires for a longer time period than simple torque reaction only could provide.
Its all interesting stuff isnt it.


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 Post Posted: Mon Aug 02, 2010 5:08 am 
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Bubstr wrote:
like slapping a cannon ball coming out to speed it up.
Oh by the way, thats the funniest thing Ive read for a while I laughed a lot at that one. =; =D>


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 Post Posted: Mon Aug 02, 2010 5:58 am 
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shrinker wrote:
I have an Excel program I use to do it, it uses circular referencing to arrive at the balance of forces related to engine output.

Then, it should be a simple matter to find and correct the errors in the free body diagrams I posted (and which are available, with further explanation, at Page 49 of my site). Otherwise, your Excel sheet is GIGO.

Basically, this is a relatively simple dynamics problem which any second year engineering student should understand. But, problems arise when the basics are misunderstood and further analysis is attempted. If you can't understand and use a free body diagram, further conclusions are questionable.
http://www.racetec.cc/shope


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 Post Posted: Mon Aug 02, 2010 10:54 am 
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shrinker wrote:
Timeslip??

Eventually the engine was sold and it was going to be supercharged. So the block and crank and rods and glide were setup for blown (434 cubes, splayed valve heads, 14-71 it would have been fun). But midway through the driver got cold feet and the idea got scrapped and changed to 406 cubes NA. So now we had all this heavy stuff we didnt need. ](*,) The car gained 180lbs over the front and it has been a handful ever since. I don't complain about it because Ive figured out how to deal with it, thats why when you watch the youtube in slow motion you see the body rotate about the rear axle then launch upward and forward at the same time. Its like a cat pouncing from a crouch position. I have had to adopt this approach in order to sustain downward force on the rear tires for a longer time period than simple torque reaction only could provide.
Its all interesting stuff isnt it.


A little tidbit of information, that might help here. You gained front weight and changed power, this does mean you need to adjust traction.
We used to run tracks that some would allow aluminum block engines and some would not. This meant lots of changes back and forth, sometimes two times a week. The simple fix was to mount the two different engines in different spots that allowed the COG to remain in the same spot in relationship to power and the gear was changed to compensate for power. The aluminum block was mounted higher to the left than the steel block. This was on a Circle track car.
Anytime we change power, where weight is or traction the balance is thrown off, you have to adjust the other two need adjustments. Ask where the extra 180 pounds are now compared to tho old COG. As far as power difference, Down on power lower gear, up on power higher gear.

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 Post Posted: Tue Aug 03, 2010 8:04 am 
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Yeah I know, it tough keeping up with the changes sometimes. Now its getting better head flow (used to 365cfm now it's 420)a higher RPM range, new converter, different diff gears, and Ive still gotta sort it out with the 3 speeds instead of 2.
Cant fit any wider or bigger tire under it and I'm not allowed to move the engine back, so Ill probably raise it a bit as I know I can get a new longer wheelie bar past the finance department. If I raise it a bit with a longer wheelie bar I'll stop it from unloading just towards the end of the 14" track distance. Doing that I can move the IC out a bit and slow the snap enough that we could use a launch RPM way below the stall and get a smoother transition of power over a bit longer track distance. it might be the way to go.

The trouble is the track is hopeless on the line. It's BALD concrete. When they poured the track at WSID they broomed it with a very course broom. I measured the surface, its 18 to 22 bristles to the inch. The rubber doesn't hold in the gaps, the cars keep ripping it out all the time. The gaps are too large and the tire reaches into the base of the gap and pulls the rubber out in balls. The glue doesnt seem to solve the problem at the start line. Long cars like dragsters are launching in much better track conditions than the sedans.
When we go to Willowbank in Brisbane the track there is broomed with 42 bristles to the inch, the rubber stays put in the gaps and it builds like a conveyor belt from edge to edge and they make the whole length of the track pull your shoes off. Sydney is like walking on the beach sometimes compared to Willowbank.

Heres one for ya, the blocks of concrete at Sydney were broomed by different crews and the brooming intensity differs so much that rubber will build up on one block and then not on the next one etc. Try running down that and smoking the tires from block to block. Then to top it all off, the blocks were uneven in height and there was also reinforcing bar sticking up out the track so they had to grind that off then grind the blocks down level here and there so those bits used to be SMOOTH. Its all bit of a joke really. The state government built the track.


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 Post Posted: Wed Aug 04, 2010 5:00 pm 
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Ok, so I take a bazillion measurments today and in the past week or two, and when I plot the data into Mr. Shope's 4 link A/S chart on pg 48, I get an I/S that is way low and not even close to the A/S line, so, this would not be considered a A/S of 103% correct? I am thinking not and I also think my chassis guy may have welded my axle brackets on upside down :-k

I am going to put a mail into the company who I baught the brackets from to verify this, but something is just not jiiiiving with my setup now. More to follow I'm sure :-

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 Post Posted: Wed Aug 04, 2010 7:21 pm 
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John, nothing wrong with he brackets on the housing! You have a PM!

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