I bought an older Rigid Frame Altered. I just completed the car with a .030 over 700 HP 454. The car weighs approximately 1800 lbs. The chassis is a tube chassis with rigid (unsprung) suspension (Front and back). I launch at 3200 RPM for tuning purposes instead of 4200+. Front is a king pin set up. 116 inch wheel base. The car weighs approximately 1800 lbs. I have Good Year Front Runners (23x5-15) and 33x16-15 rears. When launched, the car wants to go right. Subsequently, it never gets good traction going down the track. The rear end is all over the place. Rear air pressure is set at 8.5 lbs. I am currently checking rollout and front end alignment. I have heard the car should be launching off the wheelie bars? Is this correct? Can anybody help me with any other tuning tips that will correct the launch and traction problem? Thank you in advance.
Are you running an open rear end or a posi? I was told by old altered drivers that posi=wall, always run open unless the car is set up perfect.
Not being sarcastic, but is 8.5 PSI too much? Have you tried to lower it on the right side to 'compensate' for the pull to the right? Have you had someone video tape MULTIPLE launches, then go through them frame by frame to see if the car is reacting the same way every time? Have you tried swapping slicks with someone else to see if it's the tires (brand, etc.) I'm only asking because I've contemplated building a rigid frame, short wheelbase, big block (Ford) powered car myself, but since I've never been down a drag strip and only read about chassis tuning, these are questions I want to ask myself... Any other info about the track surface, consistency, etc would be awesome too. Thanks! JK
Put 10 in the right and leave the left at 8.5 . Do an absolutley violent burnout then see what happens. I run a solid rear with a posi I leave wheels up and can drive no hands if necessary. Car goes absolutley straight. I also would weigh the car (four scale) or move one scale around with fake scales under the others (aka blocks of similar thckness wood.) The car should not be heavy one side to the other. Mine is within 4 lbs. If there is a variation moving the battery to the light side will often fix the problem. When the front wheels are in the air alignment is irrelavent. if you are using an old school steering with a long steering link to one side mke sure you are not correcting in the wheelie. It will correct itself when it settles. I have some video that will show that happening. Sometimes drivers try to steer when the wheels are up. Not required. My wheel flops left on a wheelie on every pass. i do not adjust for it at all. It goes straight on its own perfectly when the suspension is reloaded on touchdown. Watch here http://www.youtube.com/watch?v=-RrGDPXOQtI&feature=mfu_in_order&list=UL Don
Are you running a single or duel wheelie bar? A single wheelie bar will not steer the car but duel wheel set tends to steer the car.
Switch slicks as suggested. Check the rollout with a tape measure. I would try 6 PSI. Use a spool in the diff.
have you had it on the scales, to check wieght bias and such? is it moving right on the wheelie bars or is it all the way down teh track? when are you checking tire pressure? in the pits under the shade? or at the end of the staging lanes right before the run? How much nose wieght are you running? need a lot more info before we can tell you anything. and not to step on anyones toes, raising one side tire pressure isnt the best way to get it straight.
How old are the slicks if they are old they may have internal problems from sitting around possibly on the ground , not on jack stands. Rob
"raising one side tire pressure isnt the best way to get it straight." Ouch! True but it will help you in a flog. When I am tryng to find out what is wrong I will try this. I spend most of my efforts working on the 60 footers and the launch because I dont have 700 HP to pull me top end. A crooked launch costs time as we all know. One pass with a altered tire pressure will often help quickly find what the problem is or what it is not which frees you up to look elsewhere. You dont even have to make a full pass. Just launch and see if it is any better.Costs nothing. You will know in less than ten seconds. Also something else worth checking. Are both tires the same diameter (WHEN MEASURED) or rollout? I have had mismatches before even on new tires. Sometimes over an inch. Is the diff centered in relation to the front axle? Is the chassis twisted from years of racing? Don<!-- / message --><!-- sig -->
Simple things first ... is the chassis square/true. If the rearend is "cocked" in the chassis it won't go straight. It may have been built correctly BUT if this is an old chassis it could be "tweaked" from previous use/hitting the wall. As I recall "posi" is NOT the way to go, nor is an "open rearend" ... you need a totally locked rear as in "spool". An "open" rear will generally only spin one wheel. The problem with a "posi" is the power can shift from one wheel to the other causing all kinds of handleing issues. A spool totally locks the axles together so when power is applied it is ALWAYS applied to both axles/wheels equally. If this chassis in ancient, you might want to open up the rear and visually verify what you have (the reason I suggest this is some people used to replicate a spool by simply welding the spider gears together and that is NOT acceptable today).
There is some good and bad info here so use some common sense. As mentioned check squareness of the rear and tire rollout first then weight.Tires have to be the same size and rear square or it will never go straight.
oj is partially wrong all slicks are not directional as he said the motor and diff has to be squared and the frame not tweaked and when you stage you have to be straight because the car will go in the direction it's pointed and the circumference of both tires should be the same too much tire pressure will make it bounce but will not make it pull did you change lanes at the strip at one strip we go to the right lane pull right and the left lane pulls left maybe you are trying to overdrive the car and correct every movement or the steering is too fast without seeing the car run or the track it's hard to make a call
Most drag slicks are non-directional, to find out for sure would be to contact the manufacturer of the tire you are running. 8 1/2 psi is too much, 6 psi would work a lot better. Sounds like you could have too much rollout on the left rear tire than the right rear tire. Scale the car first to make sure the chassis isn't tweeked.
should be running no more than 5-6 psi in slicks - if it's leaving on the wheelie bars, that's the problem - something on your wheelie bars is out of line with rear end - you can change the wheelie bars left to right to get the car to go straight - ask me how i know - just went thru this a few months ago with a friend's car
You are on the right track to start with. First thing to do is check the rollout on the slicks. Make sure that they are at the same pressure and measure the circumference. If there is a variation you may be able to correct it by putting more pressure in the short one and leaving it out in the sun for a while to stretch it. Next is the chassis. The front end alignment should not have much effect unless you are tending to steer the car at the launch. Set the toe in at 1/16" to 1/8". It is a little hard to check the rear end for squareness without pulling the car apart and using a line-up bar but try to measure from the outside of the slicks (at the vertical centerline--rear axle height) to the center of the front cross member if you can get a straight shot between the two points. If you can get access to a set of scales (try the local circle track guys) that would help. The right rear should be not more than about 50 lbs heavier than the left at worst. If the car does not have a spool put one in (along with good axles if they are not already there). Leave the tire pressure at 8.5 unless wheelspin is a problem. If you go too low you may wad the tire up at the hit and make things worse. Check the wheelie bar height- with a rigid chassis I would start out with the wheels at the same height. Use white shoe polish on the wheels and have your crew check the tracks--they should be about the same length and not too long--the car should get up on the tire as soon as possible and lift the wheelie bar wheels. Video the launch and see if the car is carrying the front wheels for a long time, if at all. If not try raising the wheelie bar until it does pick the wheels up. Then the rear tires will be working as hard as possible. If the front end is up too high or too long drop the wheelie bar until the front end stays closer to the track or wheelspin is a problem. Shoe polish a whitewall around the outside of the slick and video the launch so that you can see if it is wadding the tire up. Also put a "slip stripe" from the rim the the tread on the tire so that you can see if the tire is slipping excessively. The shoe polish deal just makes it easier to see on the video what the tire is doing. Roo ps My ride is quicker and faster than the one Jay plays with
Yeah but my driver is better looking.... Thas all I got as I am somewhat retired from drag racing LOL!
Hey ROOMAN is right on. My car is a hardtail with torsion front. Air pressure was 8 lbs. this past weekend and went 5.67 to the 1/8 fastest ever. How old are the tires They might look ok but the sidewalls might be wore out. good luck
I want to thank everybody for the great input. Based on the input and research I received; I will check the rear, and chassis for square. I will allign the front suspension since I do suspect an allignment problem. I will also track down some scales and check weight distribution. I'll check wheel roll out this weekend. Dont expect a problem here since they are new tires. The rear is a Dana 60 w/ spool. Wheelie bars are 2 wheeled and springloaded. I'm told the springs need to go away. Recommendations? Car is not currently leaving off the bars. We are only launching at 3200 to ensure everything is working first. S&W recommends I check the chassis preload. They indicated that the car should be lifted at center of the front crossmember. The right front tire should come off the ground 1/2 inch prior to the left. If not, preload is not correct. How would you correct this? Ballast? Movement of engine/drivetrain?. I'll keep everybody posted as I work this out. Once again, thank you!
When I worked on fuel cars for a living and wanted to check things at the track we used to jack the chassis under the center of the rear end with a large deep well socket on the jack pad aligned with the longitudinal axis of the car. That will allow the car to roll freely as you raise it. The left rear should come off the ground first. ie the right side should have some pre-load. Fixing the pre-load is a little difficult on a rigid chassis if you don't have the adjustable height spindles. If you have adjustable A-arms you can fix it by lowering or raising the appropriate wheel. The preload is more important than the camber. Even if the tires are new you must check the roll out unless the dealer made sure that they were a matched set before selling them, and probably even if he did because they can change after a heat cycle or two. Definitely make the wheelie bars rigid rather than sprung. Replacing the springs with a sleeve is probably the quickest way. A low priority item until you are leaving on the bars. Again, some pix of the car would help so that we know the basic configuration. Roo
Rooman, check my public profile. I have some before and after pics. I will provide more detailed photos of the chassis in the next few days.
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