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DRR Trophy
posted
https://youtu.be/-cYE7WdQPB0

Hi, Above is a video of my cars launch , its 2600 lb with driver , 375ci sbc ,methanol carby making approx 600hp , 6000 rpm convertor , powerglide 1.80 gear and transbrake , ladder bar with koni double adjustable coil overs with 100lb springs, 4.30 gears , 29.5 x 13.5 MT with 8.25 psi. I leave at 4500 rpm chip, flashes to 6100 rpm , change at 7000 rpm falls back to 6000rpm and goes thru the traps at 7350rpm, current shock setting EXT 8 clicks from soft (14 clicks total), COMP 4 clicks from soft ( 12 clicks total), ladder bar is in middle of three holes which is a 2.5 degrees down at front. Car runs 1.36 60s ,high 9.30's to 9.40s at 143 -144 mph.

I'am no expert but it looks like to me it hits the tire too hard but also it has a bounce while it's hitting it , what would you change first to sort this out ? Also it has lost consistency in the 60'.
 
Posts: 26 | Location: sydney | Registered: September 13, 2006Reply With QuoteReport This Post
DRR Pro
Picture of Footloose
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I am in know way the chassis professional but if it was my car I would lower the launch rpm to 4k and try the rear tires at 9 lbs. maybe more. It looks decent on your video. Just the tire is getting hit too hard or wadding up on launch. There is some killer suspension guys on here that build there own cars. Like to see how you end up. Oh how hot is it there this time of year? 94 degrees in Alabama today. Super Angry Good luck you will get it figured out. Smile
 
Posts: 1455 | Location: in a van down buy the river | Registered: September 07, 2002Reply With QuoteReport This Post
DRR Sportsman
Picture of BLIND MULE 2217
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We usually run 9.5-10 psi on a 29.5w tire. It looks like the side wall is bouncing not the car. Also 100lb spring is pretty light for a 2600lb car.
 
Posts: 307 | Location: Opelika AL, | Registered: January 02, 2002Reply With QuoteReport This Post
DRR Sportsman
Picture of 57 Vette
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You need to take some hit out of the car on the starting line. Ladder bars are notorious for hitting the tire too hard. Lower the bar to the lower hole.Should be closer to 5* down at the front.Also tighten up the shock compression.
Also try lowering launch RPM to soften the hit.
I would increase the rear coil over spring rating to at least 125>130 lbs.

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Posts: 226 | Location: Toronto Ont/Surprise AZ | Registered: August 18, 2003Reply With QuoteReport This Post
DRR Pro
Picture of Rob7181
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I think the problem is your trying to launch the car from the passenger side (right side). Move over and sit in the drivers seat and you should be fine Laughing Hard

In all seriousness, I think you need to increase the pressure in the slicks 1/2 a pound per pass, until it spins and then drop down 1/4 pound and do another video.

Thanks,


Rob Robertson
 
Posts: 870 | Location: Laplata, MD | Registered: December 06, 1999Reply With QuoteReport This Post
DRR Pro
Picture of Mike Beck
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Ok, not an apples to apples comparison, but my car comes in at 3200lbs with me in it, ladder bars, double adjustables set dead-middle, never touched them, runs 9.6's full out whether footbrake or trans brake, quicker in awesome air.

I run a 29.5x10 Hoosier Bias Ply slick, 18 psi, have been up to 20psi, 10" wheel. Have been 8.8 with this same setup, just add wheelie bars for safety! No rim screws, no tubes, after 10 passes the tires stop moving on the rims, until then I swap them side to side every weekend so I don't lose the balance job.

Have never touched the ladder bars, they point downwards a bit at the front, close to level, maybe 4 to 6* down, never measured them, have always worked.

My 60's are in the mid 1.3x range when not restricted and going shallow, typically 1.4x deep staged and footbraked.

I say add more air. Not sure of my rear spring rate, I do have an old set I can check, but they are a lot more than 100lbs.
 
Posts: 1672 | Location: South River, NJ | Registered: June 19, 2007Reply With QuoteReport This Post
DRR Trophy
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Needs more front travel
 
Posts: 33 | Location: indianapolis in | Registered: July 12, 2006Reply With QuoteReport This Post
DRR Trophy
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Hitting the tire a little too hard and needs more separation

Loosening the rebound (some call it extension) can help increase chassis separation

I also agree the front suspension needs to be looser as well and I also agree the tire pressure needs to increase
 
Posts: 397 | Location: Georgia | Registered: May 09, 2008Reply With QuoteReport This Post
DRR Trophy
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Thanks for the replies ,

Rob, I fixed the problem of launching from the wrong side.

https://youtu.be/fJc2NiLOhfM

Keen to try everything suggested , we don't have any test n tunes at the moment , Next meet was going to try lowering launch rpm and go up in tire air pressure first .
The front suspension is an old style koni coil over strut don't know what spring rate or even how to adjust the shock the part number on them is 0866-34-900 which i can't find any infomation on.
 
Posts: 26 | Location: sydney | Registered: September 13, 2006Reply With QuoteReport This Post
DRR Pro
Picture of Brktracer
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Lower front of ladder bars first. Tighten rear shocks next. IC is too short/high and not lifting and carrying front end. IC is too short/high relative to CG.


Matt



 
Posts: 1195 | Location: South Carolina | Registered: March 20, 2004Reply With QuoteReport This Post



DRR Trophy
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Thanks for the replies,

Finally got to run the car again. Here is some fresh footage after the changes.

https://www.youtube.com/watch?v=gD-HDDOKkSM

I broke the golden rule of one change at a time , so the changes for this meet were ,1} raised tire pressure from 8.25 psi to 9.5 psi , 2} change the rear springs from 100 lbs to 125 lbs , and 3} lowered the front of the ladder bar down from middle hole which was 2.5 degrees down to bottom hole which is 5.5 degrees down and reset pinion angle.

The car felt slow and smooth , but ran quicker every where , the wheel speed line on my data logger is the smoothest it's ever been especially in the first 0.5 second.

Still looks like its bouncing , I am keen to try so more adjustments was thinking of shock settings next , what settings do you recommend trying?

Thanks
Sean
 
Posts: 26 | Location: sydney | Registered: September 13, 2006Reply With QuoteReport This Post
DRR Trophy
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My old style koni shocks were single adjustable and i think you had to fully compress the shock and turn it while compressed. You could feel the clicks, I don't remember how many or which direction was stiffer vs softer.

Koni had info online years ago, but I did a quick search and couldn't find anything.

Hope this helps.
 
Posts: 7 | Location: Blanco Tx | Registered: April 30, 2008Reply With QuoteReport This Post
DRR Trophy
posted Hide Post
two opinions here

1) the front needs more travel, loosen up those front shocks

2) loosen the rebound on the rear shocks
 
Posts: 397 | Location: Georgia | Registered: May 09, 2008Reply With QuoteReport This Post
DRR S/Pro
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Put 35 pounds in the furthest area, in the back. Go up another 1/2 pound of air, and raise your leave chip 200. It should start to leave with the wheels up a bit and weight transfer better.


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Posts: 1632 | Location: Suffern, NY | Registered: November 03, 2001Reply With QuoteReport This Post
DRR Trophy
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quote:
Originally posted by Strange Magic:
Put 35 pounds in the furthest area, in the back. Go up another 1/2 pound of air, and raise your leave chip 200. It should start to leave with the wheels up a bit and weight transfer better.


would you not rather accomplish it by loosening the front suspension to transfer the weight?
 
Posts: 397 | Location: Georgia | Registered: May 09, 2008Reply With QuoteReport This Post
DRR Sportsman
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Racerdude, my car is a good example of a loose front end with decent travel. You know what a handful it can be at times.
 
Posts: 156 | Location: Going to or returning from the chipmine. | Registered: July 01, 2011Reply With QuoteReport This Post
DRR Trophy
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quote:
Originally posted by Wooley:
Racerdude, my car is a good example of a loose front end with decent travel. You know what a handful it can be at times.


his front end is stiff as a board though
 
Posts: 397 | Location: Georgia | Registered: May 09, 2008Reply With QuoteReport This Post
DRR S/Pro
Picture of Curly1
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I am going to go a little different route here. It looks to me like you are not getting much suspension travel on either end. Rear may be binding up and front may be too stiff.

1. First thing I would do is to try more air in the tires as it looks like that is the only suspension you have.

2. Then I would check to see if rear is bound up and moves freely through out the range of travel. Ladder bars usually hit tire pretty hard which pushes tire down and body up. Not seeing that there.

3. Put a GoPro camera on the rear suspension and verify what it is doing but I do not think it is separating much if any at the hit.

4. After you get the rear working properly then you can fine tune it with the front.


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Posts: 1144 | Location: United States of Texas | Registered: April 02, 2011Reply With QuoteReport This Post
DRR Pro
Picture of Brktracer
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I think your rear shocks are set too soft on rebound and compression. I wouldn't be surprised if your car likes them a lot harder than they are now.


Matt



 
Posts: 1195 | Location: South Carolina | Registered: March 20, 2004Reply With QuoteReport This Post
DRR Trophy
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I had a look at the front end today , from the research I done I could not find any info on my exact shock but I found infomation on newer style similar shocks,which was the same as what Slopoke said. Remove spring , push rod down turn until it drops which engages it and there is 4-5 half turns , with full anti clockwise the softest and full clockwise the stiffest. I did this and found that mine has two full turns of adjustment ,first shock didn't know where it started but second shock it was half turn from full clockwise so assuming they still adjust the same it was half turn from full stiff. I have now set them at full adjustment anticlockwise which hopefully is full soft .
While I had the spring out tested it and they are 250 lb springs . Also check front end travel from resting to wheels just off ground and there is 3" off travel.
Curly1 when i first started racing this car i did put a cable tie on one of the shocks rods and it was moving can't remember how much , but will put a go pro camera under it for next meeting.

So for next meeting I going to try 1} the new front shock adjustment which is hopefully full loose . 2} go pro camera 3} 1/2 pound more air and 4} rear shock adjustment , not sure where to start , was thinks of trying going from 8 clicks on rebound (ext) to 6 clicks and on the compression going from 4 click to 6 clicks what do people think of those adjustments?

Thanks
Sean
 
Posts: 26 | Location: sydney | Registered: September 13, 2006Reply With QuoteReport This Post



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