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post #1 of 4 (permalink) Old 07-10-2007, 03:27 PM Thread Starter
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question for D.I.L.L.G.A.S

I WAS FOLLOWING YOUR RESPONSES TO THE GUY WHO WAS TRYING TO CALM HIS CAR DOWN ON THE LEAVE. I HAVE A CLOSE FRIEND THAT I HELP OUT IN A PRO-STICKSHIFT CLASS AND HE IS HAVING THE SAME PROBLEM, THE CAR IS ON THE BUMPER INTO SECOND GEAR AND ONCE THE SECOND GEAR SHIFT OCCURS THE CAR DOES NOT HAVE ENOUGH POWER TO DRIVE OUT OF IT AND DROPS OUT OF THE AIR PRETTY QUICKLY. AFTER SITTING BACK AND READING ABOUT THE EXTENSION VALVING AND TIGHTENING IT UP WE TRIED IT AND THE CAR GOT WORSE. WE WENT UP 2 CLICKS TO TIGHT AND IT TRIED TO RUN OVER THE WHEELIE BARS WHICH ARE THE OLDER LEAF STYLE. THE CAR ACTUALLY WAS ON THE LEAF ITSELF ABOUT 12" IN AND BENT THEM ENOUGH WHEN IT LEFT THAT THE WHEELS ON THE BARS ENDED UP ABOVE THE GROUND. HERE IS SOME DEATILS ABOUT THE CAR;


66-67 CHEVY II WITH A 406 SMALL BLOCK / NA ON ALCOHOL WITH HAT INJECTION. 2900LB WITH DRIVER / 14 x 32 M/T STIFF SIDE WALL TIRE / LADDER BARS WITH STRANGE DOUBLE ADJUSTABLE COIL OVERS IN REAR AND 115 LB SPRINGS / ALSTON FRONT CLIP WITH TUBULAR A ARMS AND COIL OVERS IN THE FRONT 550ISH LB SPRINGS. LITTLE TO NO FRONT SUSPENSION TRAVEL. TRANS IS A JERICO DR-4 4 SPEED AND THE CAR RUNS 9.50-9.60 REPEATEDLY IN THE 1/4 AT AROUND 136-138 MPH. THE CAR SIXTY FOOTS IN THE 1.26 TO 1.30 RANGE ALMOST ALWAYS . THE CAR DRIVES AS STRAIGHT AS AN ARROW NO MATTER WHAT. THE LAUNCH RPM VARIRES FROM 6000 TO 6800 DEPENDING HOW WELL THE TRACK IS PREPPED ALSO WE HAVE ONE SET OF HOLES LEFT IN THE FRONT LADDER BAR ADJUSTMENT TO MOVE DOWNWARD AND THIS IS OUR NEXT MOVE.

JUST THOUGHT I COULD PICK YOUR BRAIN A LITTLE / PERSONALLY I THINK THIS CAR WOULD HOOK IN WET GRASS AND TRACTION IS NEVER A PROBLEM NO MATTER HOW BAD THE TRACK GETS

THANKS TRAVIS
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post #2 of 4 (permalink) Old 07-11-2007, 04:03 AM
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Sounds like your buddy has his hands full. A clutch/ladder bar car can make for a violent setup. And if it also dead-hooks that can (at times) add to the problems. You can't always use the same tuning ideas that you would for an automatic car because a clutch car doesn't benefit form a stall converters torque multiplication effect. That's why you see some clutch cars need some amount of wheel spin/rotation at the launch to work right. I'm not saying it's impossible to dead-hook a clutch car, but doing so might work better with an adjustable slider type clutch. He might just have a combo that needs to wheel stand to work (like a number of super stock cars do), and it might never be able to leave like a calmer 4-link car. But there are a few things to try because there is so many different ways to adjust a car.

If he wasn't actually dead-hooking before, and was really spinning the tire a few rotations at the launch, this could explain why the tighter extension (rebound) shock settings made the problem worse. The tighter shock setting could have slowed/calmed the initial suspension hit/smack just enough that the tire/sidewall had a fighting chance & hooked with less launch spin/rotation, and the car came up higher/faster/harder.

Just messing with the rear shock's valving probably isn't going to be enough. And since the ladder bars only have one lower hole left, that might not be much help, but if that's all you have left it's worth a try. On the other hand he might also try moving the bar to a higher hole. Yes this might sound wrong but sometimes hitting the over-worked sidewall harder could induce more launch wheel spin/rotation which can throw away enough inital "hook" to slow the front from rising as much or as fast.

He can try a taller slick which would give him more sidewall to wind-up. This could calm the car down a little as it spends more energy/time winding up the extra sidewall instead of climbing the ring gear. He can also try a different rear gear ratio to change how hard the motor's low end power hits the slicks to help make their job easier. Longer wheelie bars are another idea to look at.

Even though the front suspension travel is currently limited, that might not be enough. If it's front shock extension valving is set real loose there might not be enough lift resistance, even with limiters. Yes, limiters do control a cars front suspension travel, but not the inertia the chassis builds/stores up during the amount of travel that is allowed. At times being able to adjust the speed of the front suspension's travel with valving is more important than limiting the total amount of said travel.

Just remember if you try all of the so called "right" chassis tuning ideas with no luck, don't be afraid to try something that "theoretically" shouldn't work. Even if 10 other people say it won't work, you just never know when an off the wall idea might just be what is needed.

D.I.L.L.I.G.A.S. Dave::
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post #3 of 4 (permalink) Old 07-11-2007, 12:41 PM Thread Starter
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Dave, thanks again for the tech help here on chassis's. I think what most people don't understand is that making a car more efficient is probably one of the most looked over aspects of a racecar.

On another note, we constantly check the scaling of the car with 4 wheel scales. A national record holder showed me how to scale the cars to his liking and so far each and everycar we have done this way reacts nicely .He showed us how to adjust on the front of the car with the rear ladder bar unhooked on the driver side until the car came within reason to being close to equal weight across the rear tires and keeping the car level with the driver in the seat. Then we adjust the driver side rear ladder bar until the bolt falls in and then make the weight dead on across the back. His theory was that when the car is up on the back tires the weight needs to be equal on both tires to get the car to drive straight with little to no preload in the car. Of coarse tire roll out and air pressures will affect the straigthness of the wheelie too. So far it has seemed to work on most all of the ladder bar cars we have done and the one 4 link car that I have fooled with. Of course these are fairly mild combo cars as far as ET and MPH compared to pro-stock and Pro-mods which I think everything I have picked up on would be thrown right out the window.

Thanks again,
Travis
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post #4 of 4 (permalink) Old 07-12-2007, 07:15 AM
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Quote:
Originally Posted by TravisRice
His theory was that when the car is up on the back tires the weight needs to be equal on both tires to get the car to drive straight with little to no preload in the car....Of course these are fairly mild combo cars as far as ET and MPH compared to pro-stock and Pro-mods which I think everything I have picked up on would be thrown right out the window.
That's true, static slick weight is only part of the picture. You can't forget that that engine torque & body roll can also play a part in shifting weight around at the launch effecting preload needed.

Depending of course on the type car and chassis (especially ladder bar & 4-link with anti-roll), there will usually be a horsepower/torque range at which setting the static side-to-side slick weight (with driver) at an "even" or "equal" setting (zero preload) cant be used.

This is because as a given engine's power & rotational torque loads increase, it causes an increasing amount of body roll. Because of this effect it's common for high powered/big slick cars with ladder bars or a 4-link with an anti-roll that is set to "zero/neutral" preload to launch to the left. Because the ladder bar (or anti-roll) is fighting this increased amount of body roll additional weight gets applied to the right slick increasing it's weight & traction under launch load which launches/drives the car to the left.

To offset this effect you might find you have to shift more & more static weight to the driver side slick as the power levels (& amount of body roll) increase. On the other hand a 4-link without an anti-roll can (at times) deal with big power levels and still be set around the "equal/zero/neutral" preload area because the body roll is free to go where it want's to. That is of course if you don't mind a butt load of body roll over.

D.I.L.L.I.G.A.S. Dave::
460 street '66 Ranchero.......................finished someday.
460 race '70 Maverick..........................finished someday.
All 'glass Top Sportsman '69 Mustang......ummm, check back when I win big playing the Texas Lotto, or online poker.
My youtube page. Some ancient & newer local race video.

Join the Poker Players Alliance (theppa.org). US online poker should NOT be turned into a crime.
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