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Drag Racing Discussions => Front Engine Dragsters => Topic started by: Curly1 on June 20, 2020, 07:15:28 AM

Title: FED bounce problem.
Post by: Curly1 on June 20, 2020, 07:15:28 AM
I have a 225 inch FED runs 4.90-5.0X and I am having a problem with it. Data logger is showing some bounce / tire spin down rack. Last race I took the wheelie bar off and weight out of nose to be able to run index in high altitude bad air.  I THINK I know what the problem is but want some input on how to resolve it. Mind you it is not bad but I want this car to get down any track under all conditions as close to perfect as possible.
Last week in final round saw a video that kind of affirms my thoughts. The car took off at the hit and pulled front wheels up about 8 inches and carried them out about 60 foot and then set them down nice and smooth. That is more than normal but no big deal. What I saw that was interesting is a lot of chassis flex in the middle and what I think is happening is with the long car it is flexing and causing bounce down track.  I understand some of that flex helps it hook but I think it is too much here.

I THINK stiffening up the chassis will help it hook better and smoother in the shut down area to. Several tracks we run at is rough in the shut down and it will get my car bouncing. I have also done a lot with tires and tire pressure but this is more than tires now.

My question is how can I test and verify my thinking on stiffening the chassis? Was thinking about tying the chassis with cable under tension to see if it helps and verify it is right direction to go. Something where it attaches in the front and back and goes over middle bar on top to limit downward flex. Then if it works could go in and add more bars to stiffen chassis. I want to do it right but want to verify it is heading in right direction and not making it worse before I do a bunch of major chassis changes.
Title: Re: FED bounce problem.
Post by: wideopen231 on June 20, 2020, 08:37:58 AM
probably off wall idea. Maybe identify where flex is. Either video of chassis.maybe go pro mounted front facing back where you think it is. Maybe something as stupid as piece of good tape around area.If broken you know its flexing. there. Heck use small cable if any real bounce it might show it. Again off the wall ideas

I don't think you will get it all out of a FED. I noticed mine getting good bounce last weekend when entering bleach box. Also noticed I may be doing some rework during extreme heat part of summer,Motor plate seemed to hit with bounce. Might be raising chassis or lowering rear end inch or so. Bigger tires are next option,taller that is. 

After years watching FEDs get real bounce in shut down I have my chute handle setup manual or air for oh shyt moment.Now to get fast enough shot to see how it works.Only 125 so far and was still in throttle thru light. Also applying brakes some while baking off throttle. Man these things do require a driver.Got to love it!
Title: Re: FED bounce problem.
Post by: dusterdave173 on June 21, 2020, 01:42:06 PM
Our car would bounce if you got on brakes too hard--Ease down GENTLY on the brakes and ours was minimal--I had a 200 in car with torsion bar front--if we ran it out the back door or hit brakes hard and or rough track she would really scare you but we learned if bad get on power start all over again on slowdown and if we did run out of room just ride it out and pray--I had one run my dad was watching and it was a even match so I ran it out the back door to hard then ran out of room and Had to brake hard --it bounced so hard I smacked a place on my helmet--got lucky and did not wreck but taught us a lesson----You can practice like when you run 1/8th on a quarter length track --Brake hard get her to bouncing--get on power --start over--it is a good lesson to learn you car
Title: Re: FED bounce problem.
Post by: Curly1 on June 21, 2020, 05:11:00 PM
It is bouncing some during the RUN under power! And you could see the flex in the chassis when front wheels are in the air. Now the shut down area is a different issue and yes easing into the brakes or throwing parachute out helps.

I can deal with the shut down area but I want it to hook good on any track any time and right now it is not. I suspect it is too much flex in the chassis allowing it to bounce under power. I want this car to be best performing car out there to carry me when driver is not on top of his game. Lol.

Another thing I do not mind adding more bars to stiffen chassis thing is I want to find a way to verify that it will help it before I do it.
Title: Re: FED bounce problem.
Post by: wideopen231 on June 22, 2020, 05:08:04 AM
MAybe some chassis pics would help those who know what they are looking at to see something. By the way I am not one of those folks Roo man or Bruce might see it.

Doe it have diagonals  in front section of frame? Is frame wider style or narrow like older cars? 
Title: Re: FED bounce problem.
Post by: Curly1 on June 22, 2020, 02:47:23 PM
Frame is wider style with diagonals so it should be relatively stiff chassis. That is part of reason I am reluctant to just start adding more bars.
Title: Re: FED bounce problem.
Post by: xlr8 on June 23, 2020, 12:40:02 PM
I would check the chassis for cracks first. Sounds like a lot of flex.
Title: Re: FED bounce problem.
Post by: BK on June 23, 2020, 07:27:14 PM
I just let air out of slicks until it stopped bouncing.
Title: Re: FED bounce problem.
Post by: Curly1 on June 24, 2020, 05:21:42 PM
I have tried 4 different tire combinations at all different air pressure. Will try another tire combination soon but I know the chassis is flexing and I know the tire is bouncing until I drop it down and then it wads up and chatters and all over track at the top end.

My thoughts are tire change will help some at the hit and in the shut down. Parachute will help in the shut down but I THINK the bouncing in the middle of the track is chassis flex and that is what I am trying to eliminate here.

This car is not bad and it is very competitive but it is not perfect yet.
Title: Re: FED bounce problem.
Post by: wideopen231 on June 25, 2020, 01:17:10 PM
 Question and not being smartazz this time.  Are you sure its because of flex? I have had cars act stupid because too rigid or where in bind from chassis work that had been done. If memory serves  you had a bunch of chassis work done. Has cart had this problem  ever since? You stated it rigid chassis now.  Do you have daat recorder on car? If so it would dang sure show any bounce in driveshaft  graph.
Title: Re: FED bounce problem.
Post by: Curly1 on June 25, 2020, 02:35:32 PM
Data logger driveshaft sensor is showing bounce and tire spin. I also feel it and others have seen it. Could chassis be too Rigid? I guess it is possible but I can see flex and feel it flexing so my thinking is it is probably too much.
When the car pulls a wheelie you can see the flex in the chassis. You can also see evidence of chassis flex on the body panels.  It pulls wheels up nicely and carries them out a way then sets them down pretty soft. But I think after that it is still flexing some and causing the bounce in low gear and after the shift.

Title: Re: FED bounce problem.
Post by: gregm784 on July 07, 2020, 11:45:19 AM
Silly question,  is the car or the track?

mine bounces good on some tracks.  driveshaft speed looks like a sewing machine needle.
Title: Re: FED bounce problem.
Post by: BK on July 09, 2020, 06:18:26 AM
I've heard of adjustable cables in rear engine cars.
What are they for and is it anything that might help your problem?
Title: Re: FED bounce problem.
Post by: wideopen231 on July 09, 2020, 07:11:20 AM
normally. Cables in rear engine cars are right in front of drivers compartment. They are adjustable tension wise and allow car to arch more while limiting travel in opposite direction. If car flex is from downward motion and reactions.Then  I guess they could help Curly there.  Now that is my understanding.Not chassis expert like Roo man and Bruce,but I have slept in holiday inn(or what motel in commercial). 
Title: Re: FED bounce problem.
Post by: Curly1 on July 10, 2020, 09:04:18 PM
I simply do not know just looking for a way to verify it is right direction before I do something more permanent like welding more diagonals.
Title: Re: FED bounce problem.
Post by: Scott Krieger on July 23, 2020, 10:43:15 AM
Your trying to use her as a rifle and not a hand gun, using only one hand to hold the gun to hit the target

Flex fades away over time. eliminate any flex from front motor mount to rearend.

Top rail in front of motor likes a slip joint to plant the rear tire, while forcing the fronts to stay planted in the beams every pass never lifting out.

Slipping the top front rail allows the car to eat up the track and hard top end breaking.

A lot of arch makes the front tires pull to the right on the launch. no give in the steering rod. we use clamps on the chassis to control movement.

She will be happy

Enjoy
Title: Re: FED bounce problem.
Post by: Curly1 on July 30, 2020, 08:09:43 PM
New Tires are in going to try that and see if helps before I start welding in more bars. Right now I think tires are only a small part of the problem but anything helps and I think chassis needs to be stiffer. I am trying to get this car to where it will go down any track under any conditions and be competitive all the time.

As for bounce in the shut down I find on this car it stops best if I just let off on the gas and then let it slow a little before I ease into the brakes. When I do that it stops faster and smoother. Sometimes that is hard to do on short tracks with rough shut down areas. If I try to hit brakes hard same time I kill gas it does not like it at all. Also I have been using the parachute more and it helps. For stopping once again I think it would stop better if chassis was stiffer.

Problem here is not many people have a combination like mine so what works on your car may not work on mine. A typical Rear Engine Four link dragster has a much stiffer chassis and suspension to make it work. FED are more flexible and no suspension so we have to work with weight, tires, chassis flex, engine angle etc.
Title: Re: FED bounce problem.
Post by: Scott Krieger on July 31, 2020, 08:43:38 AM
Curly,
My daughters car is a 174" fed, triple slip joint top rail, BBC 600 HP, turbo 400. Runs 5.60 at 124 & 8.75 at 150 mph 3000 rpm launch in 2nd gear nice and calm bracket mode 4000 D.A. Chassis has 6.00 cert

I will try to get my daughter to post a run or two, watch over the tops of valve covers & see how much the of front tires come & go from sight under launch, settling down and hard braking on the top end, all controlled by amount of slippage at each joint to let car run free & easy. I do not like chassis flex as it goes away, I have some that will show itself over time and I readjust the slip joints to raise her back up.

Enjoy
Title: Re: FED bounce problem.
Post by: Curly1 on August 01, 2020, 05:43:55 PM
My new tires are here will mount them tomorrow and then try to test soon. Still considering a way to "Tie" the chassis down to make it stiffer to test before I start welding in more diagonals. I do feel part of the problem is this chassis is too flexible but hard to prove with out taking a chance and welding in more bars.
Title: Re: FED bounce problem.
Post by: jeff/21 on August 02, 2020, 01:55:20 PM
If really think that just make some bars that will clamp-on, make collars and weld or bolt bars to them( bolted you could move them up and down the frame)
Title: Re: FED bounce problem.
Post by: afaulk on August 04, 2020, 12:46:43 PM
You beat me to it...I was going to suggest the same thing.
Title: Re: FED bounce problem.
Post by: BK on August 04, 2020, 06:39:29 PM
To expand on Jeff/21s idea.
Clamshells on the end of a tube and hose clamp them on.
Should be good enough for a test.
Especially if you could come up with aircraft style clamps.
Title: Re: FED bounce problem.
Post by: jeff/21 on August 05, 2020, 05:38:04 PM
clamps could be  simple tubing that is cut length wise, into two halves  before cutting you weld pieces of tubing across so you could insert small  bolts to clamp  i would use 4 bolts for better clamping and they could be smaller, there are so many ways you could do it keep it simple
Title: Re: FED bounce problem.
Post by: Curly1 on August 05, 2020, 07:39:57 PM
I will try to pull the body off soon and see if there is a way I can do that.
Title: Re: FED bounce problem.
Post by: Curly1 on October 19, 2020, 06:40:00 PM
Okay for an update. I changed rear tires to the MT 10.5Wx33 and they seem a little better but did not completely resolve the issues. So I took car to my chassis guy and added in some braces in two compartments in front of motor. Car works pretty good now and Won me my 4 th NE2 Championship. Car works good now and is fun to drive. By just moving a little weight I can do huge wheelies or barely any wheelies. As much fun as it is to drive I am going to sell it soon, prefer driving Altereds and bought me a nice 4 link Altered with Strut Front and four wheel brakes. Much easier to load and unload and can go back to shorter trailer with bathroom package so I can make some long distance races.

Title: Re: FED bounce problem.
Post by: THE FRENCHTOWN FLYER on October 20, 2020, 05:36:11 AM
Congratulations on your championship season. I too prefer an altered as you describe (except I do not use front brakes so I can still burn out across the starting line and get a "read" on the track) for the reasons you mention. Altereds have a reputation of being squirrelly and hard to drive, but with the application of modern Pro-Stock-like suspensions the chassis are easy to tune. Good luck with your new car.
Title: Re: FED bounce problem.
Post by: Curly1 on October 23, 2020, 06:16:54 PM
My new Altered handles really well and is easy to drive. I am going to make a bunch of changes in the off season and will run her next year.  The "Long Shot" has been good to me and is fun to drive but the "Short Fuse" is the new ride.