Author Topic: shut downn bounce  (Read 5862 times)

Offline wideopen231

  • Hero Member
  • *****
  • Posts: 1458
    • View Profile
  • Your Best Time: 1/8 3.70@ 198 1/4 5.78@245
  • Your Engine: Hemi 526 ci alcohol
  • Your Track: Piedmont
  • Your Vehicle: 225 CMC FED
  • General Location: NORTH CAROLINA
shut downn bounce
« 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.
Relecting obama is like shooting right foot because it did not hurt enough when you shot left foot

Offline rooman

  • Moderator
  • Hero Member
  • *****
  • Posts: 541
    • View Profile
  • Your Best Time: 6.200/222.05 (1/4 mile--NT/F)
Re: shut downn bounce
« Reply #1 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
Yeah, I am from the south--any further south and I would have been a bloody penguin.

Offline dreracecar

  • Hero Member
  • *****
  • Posts: 1650
    • View Profile
  • Your Track: Bakersfield
  • Your Vehicle: 7-0 pro dragster
Re: shut downn bounce
« Reply #2 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

Offline digster

  • Jr. Member
  • **
  • Posts: 86
    • View Profile
  • Your Best Time: 8.01 1/4
  • Your Engine: Hilborn Injected 427 SBC (Methanol)
  • Your Track: Top End Raceways, Sabin Mn
  • Your Vehicle: 1970 190 inch FED
Re: shut downn bounce
« Reply #3 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.

Offline dreracecar

  • Hero Member
  • *****
  • Posts: 1650
    • View Profile
  • Your Track: Bakersfield
  • Your Vehicle: 7-0 pro dragster
Re: shut downn bounce
« Reply #4 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.

Offline Rusty Kramer

  • Newbie
  • *
  • Posts: 25
    • View Profile
  • Your Best Time: 3.90 @ 185mph 1/8 Mile
  • Your Engine: 472CID KB Olds Blown alky 14-71 HH
  • Your Track: Eddyville Raceway Park Eddyville, Iowa
  • Your Vehicle: Self Build Rear Engine BA/D
  • General Location: Midwest
Re: shut downn bounce
« Reply #5 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.

Offline aafa760

  • Jr. Member
  • **
  • Posts: 83
    • View Profile
  • Your Best Time: 7:02 @ 196
  • Your Engine: Blown BBC 450 BAE 496
  • Your Track: Wild Horse Pass
  • Your Vehicle: 225 Frameworks 7.0 Pro
  • General Location: PHX AZ
Re: shut downn bounce
« Reply #6 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.
« Last Edit: May 09, 2016, 06:59:40 PM by aafa760 »

Offline longm1958

  • Newbie
  • *
  • Posts: 49
  • Couldn't have done anything without my wife,Becca
    • View Profile
  • Your Best Time: still building so nothing to report
  • Your Engine: Injected 410" SBF on alky
  • Your Track: Silver Dollar when car is complete
  • Your Vehicle: -----
Re: shut downn bounce
« Reply #7 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.
Mike L in Ga.

Offline wideopen231

  • Hero Member
  • *****
  • Posts: 1458
    • View Profile
  • Your Best Time: 1/8 3.70@ 198 1/4 5.78@245
  • Your Engine: Hemi 526 ci alcohol
  • Your Track: Piedmont
  • Your Vehicle: 225 CMC FED
  • General Location: NORTH CAROLINA
Re: shut downn bounce
« Reply #8 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.
Relecting obama is like shooting right foot because it did not hurt enough when you shot left foot

Offline masracingtd1167

  • Hero Member
  • *****
  • Posts: 1068
  • bill masiello Shelton Ct.
    • View Profile
  • Your Best Time: 7.40's at 181 on motor 6.94 at 192 nitrous
  • Your Engine: 394 chevy
  • Your Track: Lebanon Valley Dragway
  • Your Vehicle: 2003 Neil and Parks
Re: shut downn bounce
« Reply #9 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 !!!

Offline aafa760

  • Jr. Member
  • **
  • Posts: 83
    • View Profile
  • Your Best Time: 7:02 @ 196
  • Your Engine: Blown BBC 450 BAE 496
  • Your Track: Wild Horse Pass
  • Your Vehicle: 225 Frameworks 7.0 Pro
  • General Location: PHX AZ
Re: shut downn bounce
« Reply #10 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.

Offline masracingtd1167

  • Hero Member
  • *****
  • Posts: 1068
  • bill masiello Shelton Ct.
    • View Profile
  • Your Best Time: 7.40's at 181 on motor 6.94 at 192 nitrous
  • Your Engine: 394 chevy
  • Your Track: Lebanon Valley Dragway
  • Your Vehicle: 2003 Neil and Parks
Re: shut downn bounce
« Reply #11 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 !

Offline wideopen231

  • Hero Member
  • *****
  • Posts: 1458
    • View Profile
  • Your Best Time: 1/8 3.70@ 198 1/4 5.78@245
  • Your Engine: Hemi 526 ci alcohol
  • Your Track: Piedmont
  • Your Vehicle: 225 CMC FED
  • General Location: NORTH CAROLINA
Re: shut downn bounce
« Reply #12 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.
« Last Edit: May 11, 2016, 03:50:55 PM by wideopen231 »
Relecting obama is like shooting right foot because it did not hurt enough when you shot left foot

Offline BK

  • Sr. Member
  • ****
  • Posts: 250
    • View Profile
  • Your Best Time: 8.45 / 5.30
  • Your Track: Empire Dagway
  • Your Vehicle: Late 70's FED
Re: shut downn bounce
« Reply #13 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.

Offline dusterdave173

  • Hero Member
  • *****
  • Posts: 579
    • View Profile
  • Your Best Time: 5.38in 1/8th
  • Your Engine: 355 CI SBC
  • Your Track: Mooresville, NC
  • Your Vehicle: CenPen 200 inch FED
Re: shut downn bounce
« Reply #14 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
I have always had a fascination with fast cars at the expense of more normal character development