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Drag Racing Discussions => Front Engine Dragsters => Topic started by: Mister_Fitz on June 01, 2014, 11:30:49 AM
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What is the best way to launch a FED?
I have an FED, old 60s Jr Fuel, that I'm racing with just for fun. My problem is that the FED tends to pull to the right (most of the times) when I let it go from the transbrake. I have tried some different launch rpms and different tire pressues with out finding something that I think works good enough.
I have a long distance to the nearest dragway so I get perhaps 10-15 passes a year. So it takes time to figure it all out by my self. So if any of you have any ideas I would really appreciate it.
The FED has 150" WB.
350" SBC, alcy injected
PG with transbrake
Chrysler 8-3/4" - 4.11 rear ratio
M&H Racemaster 12" x 33" x 15"
Once I get up to speed the car is stable.
Am I perhaps launching it to "gentle" so that the slicks hock up to soon/hard? Can I get this problem then?
How do you launch your FEDs?
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The first thing you should do is check the circumference of the tire . Inflate the tire to the pressure you want and take a tape measure and measure both tires it should be within a 1/4 inch . If one is too small you can sometimes stretch the small one a little by inflating it to around 20 lbs and then let the air back out and check it again . If the tire is old this may not work .You may not want to hear this but with a car that short you really need a wheelie bar . With the tracks the way they are today and using an auto trans it just makes good sense to use one . I am not a big fan of changing tire pressure to make a car go straight but I know that some people do it . Could you borrow a smaller set of tires from someone to try I think it might help give you a little wheel speed and that will help a lot . When we ran the short wheelbase cars years ago we ran a 10 inch tire and a clutch .I hope this helps you . Bill
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This is a great topic, thanks for posting it Mr. Fitz .
I have done only three test passes so far in a dragster, my old FED (173", SBC 400, PG, transbrake, MT 3068W 31.0/10.5-15W M5, unknown rear axle ratio). They were all incomplete passes due to scary moments at launch (the local track is very narrow!). On my second pass I tried to 'tame' the launch by launching on 2nd (top) gear. It shot straight to the right side guard rail (didn't hit) and I aborted it. I realized that, because most of the cars at this track are door cars, with a wider tire tracks, I had mistakenly placed one tire on a stickier path than the other. Not sure if this could relate to your problem but thought about mentioning it anyway.
Does your car wheel stand? Do you have a wheelie bar? If so, the older 2-wheel style or the newer mono-wheel design?
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The rear tires are brand new and are within 1/4".
I allready have a wheelie bar. It has a singel wheel. According to my measurements the wheelie bar wheel is of center with about 1". I'm not sure how this affects the launch but I will make i adjustable and center it.
I also have a hard time knowing if the wheelie bar hits the track or not.
What is a good starting point for wheelie bar height?
What is the best way to get a good amount of wheel speed with the setup I have now?
Skickat från min GT-I9505 via Tapatalk
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Mr Fitz, I had the same problem with my car when I first started running it. I tried lots of things, but the bigest thing I found that helped my car was lowering the wheelie bar. I run mine set at about 2 1/2" . You can also try differant tire pressures from side to side after you know your tire rollout. I run mine at the same pressures now, but running the right tire a 1/2 pound lower than the left also helped.
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To easily verify what the wheelie bar is doing is by painting the wheel with shoe polish and to have someone on the crew veryfi the marks left on the track. you can pick up notes on ---
when the bar hit at launch and for how long, is the wheel steering the car?
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Mr Fitz, I agree with Bruce, shoe polish on the wheelie bar wheel, and look at marks on the track after you take off. You can also use VHT wheelie bar spray, or I use kids side walk chauk. Also if you have a crew member video your runs have them shoot your wheelie bar tracks so you can watch.
I have run into a FED pulling to the right when I had one of my motors in a B/ND running in NHRA Comp, we fixed it for that event until we got the slick company to give us another pair, by running 1/2 pound more in the right slick.
Another good idea is to check rear end location by measuring wheel base on both sides, keeping in mind if your chassis has an offset front axle [ NHRA allows 2" offset]. I know a famous JrFuel driver that always commented on how much he had to "drive" the dragster that was built in the 80's, but when they had the car "front halfed " the chassis guy found the rear end was not square in the frame, so Don was very happy afterward that the car went straight. The very best thing to do if you think your race car is not plum is get it on a chassis jig.
The reason the wheelie bar height is important is if your bar is too high, and you have a tight converter, at launch you could be jerking you front end up hitting the wheelie bar hard thus unloading your slicks and maybe unloading your right slick more. Bruce is right about 2 1/2" height. It could also add to your problem if your wheelie bar is too stiff, thus adding to the unloading of your slicks. We use a 3 bar CM 5 feet long with no supports between the 3 tubes so it works like a spring and more gently pushes the front end down.
Another crazy thing that might be going on is since you are new to this FED deal is right after launch you may be looking for your shifter [ on the right ?] thus going to the right. After all you will go to where you are looking.
Have Fun with your new project !
Jon Hansen, Hayden Wheels, and Hammer-Hansen-Hook JrFuel
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A simple way of a quick check on the chassie is to string it
Both tires equal air pressure
String/cord from Home Depot/hardware store
Tie lenght to 2 heavy jackstands per side(3-4 feet longer than WB)
place 1 JS behind rear slick and adjust front JS so that the string "JUST TOUCHES" the front/rear sidewall,
Do that on both sides
Stand back to see what you have
Is 1 wheel towed in more? is the whole RE cocked? at this point you can check the front end toe by measureing each rim to the string. Front ends can be off , the import measurment is the difference between the front and rear of the rim be the same for both sides. 4 7/16 & 4 1/2 and 5 7/16 & 5 1/2 is still 1/8 toe and not dealing with 2" offset or the front axle off to one side
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All great input here, I'm following this thread very close.
I think one way to eliminate any chance of being tires' at fault is swapping their positions in the rear axle. Agree?
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All great input here, I'm following this thread very close.
I think one way to eliminate any chance of being tires' at fault is swapping their positions in the rear axle. Agree?
Very good idea !!
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Thanks for all the good and helpful answers!
I had a small impact with the track wall about a year ago, very narrow track. Then I built a chassis jig and straightened the chassis. After the repairs the wheelbase and the cross measurement of the wheelbase differed around 2mm, that's around 1/16". So I think that the chassis is as square as it can get.
I'm currently running about 1/4" - 1/2" of toe in. I know it is a bit much, but I thought I rather have to much then to little, the car would be more stable at high speed? Are there any down sides except the increased roll resistance?
I will try to get hold of some shoe polish to paint on the wheelie bar wheel. It is a very good idea.
How do I tell if the wheelie bar wheel is steering the car, or if the car is steering to the right for some other reason and the wheelie bar just follows?
I do not think that I'm steering the car to the right by mistake. I don't shift to 2nd until about 100-150 m out, so during the launch and the following seconds both hands are on the steering wheel.
I was just in my garage and I measured the roll out of the tires and I noticed that the left tire have changed allot since before the race previous weekend!
The tires are brand new and this weekend I put one burnout and one pass in them, both the pass and the burn out were actually quite gentle...
I have measured the roll out of the tires during 1-2 weeks in the garage, tires mounted to the rims, and they were within 1/8".
Now how ever has one of the tires expanded and the roll out differs a little more than 1"!! How is that even possible??
I have completely deflated the big tire and put about 21 PSI in the small one. I will try to inflate the small one even more and put it out in the sun for a while. Is it possible to get them back with in 1/8" again? Have some one heard of anything like this?
I do not think this sudden tire expansion completely explains the launch problem. Last 2-3 seasons I have had the same problem with my old set of tires.
My Race master tires have arrows on then so they are direction sensitive. Is it possible to swap them anyway? Or will the tires be damaged?
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1/8" is nothing, air pressure set at the last moment before you bring the car up into the fireup zone is the best. Direct sun on one tire will raise presssure on that one tire and not the other. Goodyear tires are only directional for the first strong hit to set the tire-after that they can be switched--dont know about M&H. Raise the bar and add more weight to the front and try again, if it does not turn its the bar
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I try and have someone video each run. After the video, i make sure they video the wheelie bar mark on the ground. Pick a goofy color of chalk or shoe polish, so you know what mark is yours.
Tire speed is easy, start dropping tire pressure in 1/2# increments. It'll eventually give you tire speed. If i dead hook my tires on my 200" car, it'll drive the car in a random direction.
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I had similar problem with my car. I ended up steering the car with the wheelie bar. When I had two wheels I would set the left wheel about an inch lower than the right. It would stop the left side letting more weight transfer to the right. With the single wheel I would have the wheel 11/2 to 2 inches off to the left. I also ran a 1/4Lb more air on the right. Mine would dead hook and then unload the tires on the bar. To take some hit out I put a pneumatic cylinder with a needle valve on the throttle. Slowed the 60 foot a little but the car was deadly consistent. I was running Super Pro brackets so ET didn't mater that much.
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1.) Is the car lifting the front end and then making a move? If so, look at wheelie bar alignment. We had a bar that was bent and it actually drove the car to the side.
2.) If it is not on the bar and going to the side, then all the above will effect it.
3.) Look at your driving techniques. I have seen people that actually turn the wheel without knowing it on the launch. Sounds weird, but sometimes when accelerating, the drive may use the steering wheel to support the hand and it will rotate unintentionally.
4.) Try to get the car to slightly spin the tire.
5.) I have been up to one PSI different between the two tires. Don't be afraid to do it!
Good luck...
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Years ago when cars had torsion suspension, the front axle would drop thus moving the spindle pivot and turning the wheel all while the driver had the steering straight. Driver would look at the turned front wheels and would correct the situation by turning the steering wheel- but when the car came back down the front would correct itself and head towards the wall. Look at some old dragster wheelstand pics. The Good drivers would turn the front wheels even further for the reverse action when the car would come down and the wheels would go the other way.
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My car has a torsion suspension at front, I will have to check for any "bump steer" effect when the axle unloads/loads.
I made some measurements on my wheelie bar today. It seams like it is about 2" off to the left. I guess it is to the right direction, to help unload the left wheel since the right one will be unloaded by the engine applying torque on the rear axle?
I will make the wheelie bar adjustable side ways asap. Is it a good idea to decrease the offset a bit since the car is pulling to the right?
One other thing I saw was that when the single wheelie bar is offset the wheelie bar wheel is no longer parallel to the car. Is this a problem? I have not seen any wheelie bars that is adjustable to compensate for this.
Tire speed is easy, start dropping tire pressure in 1/2# increments. It'll eventually give you tire speed. If i dead hook my tires on my 200" car, it'll drive the car in a random direction.
I do not really follow you on this one. Shouldn't I be adding pressure to eventually loose some traction with the harder tires and then get some tire speed?
How big is the window from starting to get tire speed to smoking the tires?
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Or...
Am I doing it the hard way now... Is it better to just leave the wheelie bar as it is, since it probably is fairly right. Pick a fixed launch rpm and only experiment with the tire pressure until I get some tire speed at the launch and see if the problem is gone?
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If it were mine before I did anything else I would pull the axles and look at the splines. Even a fairly bad alignment should not cause a side launch because in the car has any suds at all it is basically on the rear wheels at that moment. Only other possibility is you are correcting the steering during wheels up instead of letting it do its thing. Wheels flop to one side on most conventional steered cars. When I have a guest shoe in the car I always tell them Do Not correct steering on the launch. car will run straight on its own. Any back talk and their ride is cancelled. on mine when the front wheels come up the wheels flop left however when the car settles they are perfectly straight again with no correction.
Have a video of it that shows it very well.
don
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I am assuming you have been over the whole car and looked for craked welds? Spool are all spline in good shape? About everytime I have had a car launch to one side or other more than once I found something broken Or had let someone work on chassis that caused it to bind up and act stupid,long story lots of cussing.
]Went from DNQ to number 2 (4th qualify round)on early shutoff after cutting 2 bars that we had been told was new rule.Before cutting the car acted like it was on crack,jumping all over the place. Just throwing thoughts out there since most other have been hit upon.
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Mr. Fitz. When you do your burnout and then back up how far do you go behind the starting line? The reason I ask is that "MANY" people back up to short and make track alignment corrections in a very short/too short a distance as they stage.
We back our 200" up to a crew member standing on the track side of the waterbox. We then make any alignment corrections in the first few feet as we pull forward, rolling as straight as possible for as long as possible to center the tires and chassis to the track.
When you make a moderate to strong correction durring final staging you put a twist or side load in the tires, lift the front and the car will center to the last big correction.
I too am chasing a wheel speed issue now but that should be corrected on the next time out. If the new convertor gets here in time. We launch at about 2500 rpm which is just too low for our combo.
Have fun and let us know what you find.
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My car has a torsion suspension at front, I will have to check for any "bump steer" effect when the axle unloads/loads.
I made some measurements on my wheelie bar today. It seams like it is about 2" off to the left. I guess it is to the right direction, to help unload the left wheel since the right one will be unloaded by the engine applying torque on the rear axle?
I will make the wheelie bar adjustable side ways asap. Is it a good idea to decrease the offset a bit since the car is pulling to the right?
One other thing I saw was that when the single wheelie bar is offset the wheelie bar wheel is no longer parallel to the car. Is this a problem? I have not seen any wheelie bars that is adjustable to compensate for this.
Tire speed is easy, start dropping tire pressure in 1/2# increments. It'll eventually give you tire speed. If i dead hook my tires on my 200" car, it'll drive the car in a random direction.
I do not really follow you on this one. Shouldn't I be adding pressure to eventually loose some traction with the harder tires and then get some tire speed?
How big is the window from starting to get tire speed to smoking the tires?
That's how it was explained to me. Engine torque unloading the right rear tire. My experience was bar to left, moves weight to right, car goes straight. Also I agree more air more wheel speed. But more air raises the wheelie bar. My guess is you weren't on the wheelie bar. 2" offset on bar sounds like plenty but not too much.
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A softer (lower rpm) launch will make it easier to climb the ring gear. You want to launch at 600 - 400 rpm under the converters stall speed. And yes, it raise slicks air pressure @ 5 psi. increments until you start slipping the tire. You really need somebody watching the car to help with that, shorter wheelie bar contact with pavement, less than 4 wrinkles of the slick at launch movement. Those wrinkles are important clues also, they need to be in the lower front of the tire, and not behind axle centerline.
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Take a look, remember I am a low HP dragster only running 8.00
Comments
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Glen, your car looked good at Gateway, and that picture has the crush right where it's supposed to be low and in front of axle centerline.
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Who are you and will you be at the HRR next week?
As of right now we will be going.
I'm not preregistered, but called NHRA and was told I can do that at the gate.
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A softer (lower rpm) launch will make it easier to climb the ring gear. You want to launch at 600 - 400 rpm under the converters stall speed. And yes, it raise slicks air pressure @ 5 psi. increments until you start slipping the tire. You really need somebody watching the car to help with that, shorter wheelie bar contact with pavement, less than 4 wrinkles of the slick at launch movement. Those wrinkles are important clues also, they need to be in the lower front of the tire, and not behind axle centerline.
I will try to launch 600 - 400 rpm bellow the converter stall speed next time I'm on the track.
In what range will a "normal" tire pressure be? I know it will depend on a lots of things, but it would be good to just have an idea. I have been running around 10-12PSI before. Wouldn't the tire pressure be very high if I increase with 5PSI a couple of times until I get some tire speed?
Take a look, remember I am a low HP dragster only running 8.00
GlennLever, what is the size of your tires? How much pressure do you run in them?
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My injected combo liked 6-7 psi with the Goodyear 8525. It was a SBC 640hp and weighed about 1500# wet with driver.
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George, what ET / MPH did that set up run? How high on the two-step?
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Best Time: 5.08 ET. 1.06 60' . 138.mph. 1/8 mile Engine: SBC 23 degree. 100% Alky. 355CID. Cast Iron.
Track: Central Illinois Dragway. Havana , Illinois
Vehicle: FED 223" 6.00 Cert. (owner)
5500-5800 launch rpm
Short block and Convertor are for sale. We built a blown combo. George
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I have been following this thread. Hoping to see few comments that said as hard as you can. I have always been aggressive type racer.Don't like to leave anything on the table performance wise and always attack the first half of track extra hard. Gee wonder why I choose SN WIDEOPEN? I have always likesd to see a good rotation and not deadhook on the tire. With blower cars we would be a hair short of smoking the tire,but also had best 60' times and real strong half track and I figure last half is al about power and first half moslty power management.
With less motor it may not workout as well to be as agressive.I will keep checking to see what the guys with FED running experiance have to say.
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When I had the ZZ-4 pump gas engine in the dragster it picked the front wheels up about 3 in. and moved them over to the right just a little, maybe 3-4 in. (still easily driveable) E.T. 5.90 @117. With 2 1/2 times the HP, the problem is much worse :o. We only made one very tentative hit before raining out. Checking the tire diameter, I found almost 1/2 in difference in circumference, which equalized by dropping the pressure by 1 psi. Looking forward to this weekend, hoping for more tuning opportunities. Also lowered the wheelie bar (92" long from axle centerline) to 3". Getting the launch dialed in seems like a common thing with these traction monsters. Next time out, it's spin or bleed.
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A softer (lower rpm) launch will make it easier to climb the ring gear. You want to launch at 600 - 400 rpm under the converters stall speed. And yes, it raise slicks air pressure @ 5 psi. increments until you start slipping the tire. You really need somebody watching the car to help with that, shorter wheelie bar contact with pavement, less than 4 wrinkles of the slick at launch movement. Those wrinkles are important clues also, they need to be in the lower front of the tire, and not behind axle centerline.
I will try to launch 600 - 400 rpm bellow the converter stall speed next time I'm on the track.
In what range will a "normal" tire pressure be? I know it will depend on a lots of things, but it would be good to just have an idea. I have been running around 10-12PSI before. Wouldn't the tire pressure be very high if I increase with 5PSI a couple of times until I get some tire speed?
Take a look, remember I am a low HP dragster only running 8.00
GlennLever, what is the size of your tires? How much pressure do you run in them?
Sorry it took so long, rear tires are 31/12/15
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Thanks!
How much pressure do you run i them?
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Thanks!
How much pressure do you run i them?
7 3/4 pounds