FrontEngineDragsters.Org Forum

Technical => Roo Man's Room => Topic started by: wideopen231 on May 03, 2016, 08:02:27 PM

Title: shut downn bounce
Post by: wideopen231 on May 03, 2016, 08:02:27 PM
 so as not to highjack Dave thread on wheelie bars I figured maybe better section for question.

Mainly asking Roo Man and Bruce.What are yout thoughts as to main contributing factors that cause bounce in shut down.Obvious are of coarse lifting quick and braking hard w/o chutes.Anything in chassis setup that can help or hurt is main thing I would like to hear thoughts  on.
Title: Re: shut downn bounce
Post by: rooman on May 04, 2016, 04:35:17 AM
If the car has a flexible frame and arches quite a bit or has a torsion bar etc, snapping the throttle shut and getting on the brakes at the same time can cause the frame to whip down to the limit of its travel and then bounce upward setting up an oscillation that quite often magnifies itself. Unless the track is exceptionally short it is better to let the car come down off the tire a little before getting on the brakes.
  On my last run in Horan's NT/F (which had a push brake) I must have clipped the brake handle when I hit the chutes and it slowed the wheel speed while the tires were still 220+ mph tall, putting some daylight under them. In that case the bouncing was lateral but it was still a rough ride for a while.

Roo
Title: Re: shut downn bounce
Post by: dreracecar on May 04, 2016, 08:44:20 AM
If you get on the brakes too hard it winds up the tire, when the spring effect overcome the winding, it launches the car in the air, comes down and starts over again
Title: Re: shut downn bounce
Post by: digster on May 04, 2016, 04:32:16 PM
Roo and dre. Have you seen the bounce problem worsen when chute tow line was not mounted at the correct height? I'd imagine pulling the hind end of the car up at deployment wouldn't help.
Title: Re: shut downn bounce
Post by: dreracecar on May 05, 2016, 08:52:53 AM
I also have seen it pull the front end up. The problem is that its not consitent, most of the time not , but then it does it. Some tracks have a horrible shutdown surface which only adds more to the problem
  Because what we do is not NHRA S/C where all the cars are the same, To really find out where the tow line should be mounted for any particular car or chute design(YES that does affect it) a 3/8" cable should be mounted to the top of the cage and lower frame rail, the tow line should be on a pulley that rides the cable. at the end of the run with the chute deployed a video would show the optimum mounting posistion by drawing a straight line down the tow line to the back of the chassis.
Title: Re: shut downn bounce
Post by: Rusty Kramer on May 05, 2016, 10:01:42 AM
I think all the above is very good information. I really feel that in any kind of car in any class,  that you should have someone video and or watch,  your runs at the finish and try to determine based on your car, speed, chute type etc. how soon or how many feet before the finish you can deploy the chutes and have them hit very shortly after the strip while you are still on the throttle so you "drive into the chutes." .. I am going to try to do exactly that this summer to see how soon after I shift into 3rd gear I can hit the lever instead of trying to judge the finish line.
Title: Re: shut downn bounce
Post by: aafa760 on May 09, 2016, 06:38:25 PM
Being very new to the FED world I have been finding that I hit the chutes,clutch in ,fuel shut off and brakes at same time as I have shutoff on brake Handle.
SO FAR NO BOUNCE
I am guess because chutes hit before I get on the brakes
   Chutes are air set off.
Title: Re: shut downn bounce
Post by: longm1958 on May 11, 2016, 06:35:04 AM
Does this info apply to only an fed or also to a rear engin car as well? I have a hardtail red.
Title: Re: shut downn bounce
Post by: wideopen231 on May 11, 2016, 07:19:33 AM
Would think most would apply to hardtail RED also.Fed's are just better at bounce.LOL With hardtail its the deceleration of tire and shrinking in hieght that cause bounce and from my experiance its when getting on to brake as soon as lifting. On fed I have zero experiance and could bypass getting any.Thats not all that likely,especailly in bracket racing and driving the stripe.
Title: Re: shut downn bounce
Post by: masracingtd1167 on May 11, 2016, 12:23:10 PM
Chris They all bounce and skip at one point or another . I think the biggest cause is hitting the brakes a little too hard . Some of the brake pads out there are more aggressive than others . Carbon brakes are real touchy . I can make 20 runs at Lebanon Valley and not have any problems but there is a bump in the shut down . If I hit it with the brakes on it will skip like crazy ! easy dose it ! Oh Chris ! Get that car finished !!!
Title: Re: shut downn bounce
Post by: aafa760 on May 11, 2016, 01:17:06 PM
Also the short cars can ping pong from side to side and bounce.
The FA with 36" tire really can get going before we added front brakes.

I have seen 2' under the tires at old Tucson Dragway as it bounced before chutes blossomed.
Title: Re: shut downn bounce
Post by: masracingtd1167 on May 11, 2016, 02:14:10 PM
Also the short cars can ping pong from side to side and bounce.
The FA with 36" tire really can get going before we added front brakes.

I have seen 2' under the tires at old Tucson Dragway as it bounced before chutes blossomed.
  I drove a short wheelbase blown altered 2 times and it tried to kill me both times !
Title: Re: shut downn bounce
Post by: wideopen231 on May 11, 2016, 03:48:07 PM
Thought I was ready to pull trigger on laST 3 BIG ITEMS ,new tires,delay box and input shaft,Then work truck when and kncked cpl rod bearings out.2800 bucks later about twice what car needed. Just ordered ringless input for it 2 days ago.

Believe me I do not need to be reminded its play time.If these guys would quit bringing up the blower idea.Its like waving kilo of cocaine in front of drug addict.
Title: Re: shut downn bounce
Post by: BK on October 09, 2018, 02:28:51 AM
We have a track with a short bumpy shutdown near us. I found that low tire pressure let me get on the brakes as hard and as soon as I wanted without bouncing. Low being around 4.5#s.
Title: Re: shut downn bounce
Post by: dusterdave173 on October 09, 2018, 10:47:14 AM
my experience points to getting on brakes too hard causing the most issue with mine--If I let it settle down and ease on the brakes never an issue--If I run out the back door in close race at short track then clamp them hard it is like the NBA
I have had some luck in severe bounce getting back on throttle then starting over if room enough
Title: Re: shut downn bounce
Post by: wideopen231 on October 09, 2018, 12:54:07 PM
Thought thread looked familiar ,only 2 1/2 years old. Seems everyone's repl mainly breaks,which just so happens to have been main reason for OP. Bracket racing and breaking at finishline go hand and hand. Sometimes too much breaks is going to happen. Rereading replie's  I am thinking of adding the solenoid activated chute deal I had on old TA/D i ran. Was more of ol crap button,but a pre ol crap button might be ticket here. If lloks like going to be hitting breaks just dump laundry early so as to keep her straight if starts bouncing .Beside little excitement keeps it interesting and while straight is quick its also boring. LOL
Title: Re: shut downn bounce
Post by: rooman on October 09, 2018, 02:17:10 PM
If you have to hit the brakes hard before the finish line you missed the dial badly and need to work on getting your car consistent (or guessing better on the dial) rather than jumping on the brakes and upsetting the car.

Roo
Title: Re: shut downn bounce
Post by: wideopen231 on October 09, 2018, 06:38:47 PM
Well when you are holding 2 or 3 hundred and its close you have to run it to your drop point and drivers do get aggressive at times in heat of battle. Not saying its advisable but it does happen. Know my driver,he is not much on loosing and can get aggressive.LOL
Title: Re: shut downn bounce
Post by: rooman on October 10, 2018, 04:20:56 AM
This link will take you to a video showing the extreme consequences of trying to "dump" the opposition. It also illustrates the folly of wearing your shoulder belts loose so that you can look back. Mark Rebilas posted a motor drive sequence which shows why the driver of the left lane car was so badly injured.
  Here is the video link: https://www.youtube.com/watch?v=y2wpdJWOXo8

And this is the Rebilas sequence: markjrebilas.com/blog/top-dragsters-take-twin-tumbles-at-nhra-brainerd/

You can clearly see a haze off the rear tires on Kritzky's car as he brakes right before the lights. Some have argued that he was trying to avoid Monte Green but at that point he was ahead and his best course of action (if he saw Green getting into trouble) would have been to stay on the gas and get out of the way. The later photos after the impact with the wall show just how loose the shoulder belts were and why his injuries were so severe.
  Any braking before the finish line that induces tire smoke or gets the car bouncing should result in an automatic DQ. It amazes me that at one time an NHRA promo video showed Dan Fletcher's kid spinning out at the finish line in his stock elim Camaro, just missing the car in the other lane. I guess that it was intended to show how exciting the sport is but to me it was just an illustration of stupid driving.

Roo
Title: Re: shut downn bounce
Post by: wideopen231 on October 10, 2018, 08:52:27 AM
I  agree 1000% on seat belt deal.I know a huge percentage of drivers at this weeks 100k super bowl of bracket racing had seat belt loose enough they could probably have climbed out w/o unbuckling. Not to mention not wearing gloves so you can feel the trans breake button,BS. Also agree on smoking tires.Not as much on bounce,as few here have said letting butterflies shut too quick can cause it especially in FED as they have lot more issue than the cadillac  four link standard issue bracket dragster. Maybe because odds are hugely in favor of me being only guy crazy(according to most) enough to build a FED to bracket race.  Repeated times with bounce I can see as problem and reason for action.

I do not plan on getting into situation,but at same time taking steps to help reduce chances if driver(me) gets brain fart and can only see WIN lights.
Title: Re: shut downn bounce
Post by: masracingtd1167 on October 13, 2018, 07:54:35 AM
I work part time for NHRA div 1 and we have people in the tower that watch for things like that ! If we see a driver with loose belts he gets warned or excessive braking ! Some times you just cant save people from them selves !
Title: Re: shut downn bounce
Post by: wideopen231 on October 13, 2018, 09:00:25 AM
Sometimes you wonder if you should save them.LMAO
Title: Re: shut downn bounce
Post by: coupemerc on October 13, 2018, 09:59:14 AM
I like being in there so tight that I can barely breathe! On the bouncing thing...just don't touch the brake handle until you need to turn off
Title: Re: shut downn bounce
Post by: jeff/21 on October 13, 2018, 01:55:45 PM
I've bounced off the end of an outlaw track, started put it in neutral as I let off the gas after stopped before the end with out bouncing
Title: Re: shut downn bounce
Post by: im6under on October 17, 2018, 12:27:41 AM
1994 we didnt have the (personal) rule, i know you armed the chute, baby, but show me the flag in my face before i stage.  :o

So after ripping the chute lever off the car i went for the brakes. And bounced and chirped all the way out into the sand pit at about 125.

Had roll cage blue smeared all over my brand new white simpson helmet. That pretty much ended that weekend.

Definitely was hard on the brake that got it going.