Questions about drag car launch.

Tech questions that don't fit above forums

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ou812
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Questions about drag car launch.

Post by ou812 » Sat Dec 17, 2005 8:58 pm

Hi all. Got a 3100lb duster, W2 360 running 6.70 in the 1/8 with a 1.43 best 60ft.
Question...I went from 2 degrees down to level (bottom ladder bar) with ground and # 8 setting on my Strange shocks (Rebound adj. 1-12 ) and it hits alot harder, but traction was hit and miss, any thoughts?
10.5x28 Mickey slicks, started at 18lbs and ended at 15.5 with my best 60 ever, and track was not sprayed much. I foot brake it about 3000rpm. Cant get anymore than that with current converter which is an 8" 5000 stall.
Forgot to mention that last pass, I went from #8 on shock to #5 which sped up the rebound. So it liked less rebound and less air than normal with the bar moved up on marginal track and air was good. D.A. was around 2000ft.
Before that at another track with not so good air and bar at 2 degree down and shock at #8 car hooked consistent as hell and only began to spin the last 2 passes when they quit spraying the track...and that was with 18lbs. of air.
Thanks
Brian
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Post by LilRacr » Tue Dec 20, 2005 10:24 pm

What gearing are you using? Rear and 1st trans gear?
From what I have seen and played with over the years when using high numerical gearing is that the car will shock the tire to hook but then release some pressure alowing tire spin. I have dropped gearing from 4:88 to 4:10 with a 30" tire and it loves it. I would struggle with low 1.40 60' times, now with the 4.10 gearing I have been 1.34 consistantly.
I am footbraking the car, with a 3500 flash converter, 30 X 10 goodyears.

I have also found with limited front end travel the car with spin the tires.
How long are the bars? I am running factory G-Metric chassis (GM 4 link) with the bars modified to about 50" intersect point.
-Bobby-

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Post by ou812 » Wed Dec 21, 2005 1:27 am

4.56 gears, low first gear. Have thought about going to the std first gear setup to see how it responds. Converter is kinda tight 8" so I dont want to take too much hit out. Infact, I want to leave as hard as I can. Was you car a small block car?
Brian

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Post by LilRacr » Wed Dec 21, 2005 7:46 am

Was you car a small block car?
Yeah, it's a small block... but 434 cubes. I have taken away everything to make it launch soft and the more I take away the more it likes it. The motor does have good torque numbers to keep the tires planted.
-Bobby-

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Post by T RICK » Wed Dec 21, 2005 9:05 pm

What I remember helping a freind years ago. The car left about the way your picture shows. The front end would fully extend but it did not have enough motor to hold it up. It would drop like a rock and unload the rear as the weight would transfer back on the front wheels. We ended up tying the front end so the long travel was less and this cured it. The old mopar tuning book back in about 1969 said to do a stock alignment then drop the torsion bars an inch and a half. I had leaf springs (69 dart 340 auto) which they recomended removeing the rear clamps on the leaf springs so the would seperate and leave the clamps on the front of the leaf springs. This worked good enough to run 12.70's at OCIR on 9 inch slicks. No 60 foot or 1/8 mile numbers in those days. Hope this helps. Where is Barona?

Rick

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Post by ou812 » Wed Dec 21, 2005 11:02 pm

Barona is the indian name where the track is located. Its right outside of Ramona, near san diego. My car is ladder bar coil over. Thanks for the replies...going to try some new things the 14th.
Brian

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Post by LilRacr » Thu Dec 22, 2005 9:45 am

Have you found center of gravity of the car?

What is the ladder bar lenght and height compared to center of gravity? Are you on the plus or minus of the anti squat line?
-Bobby-

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Post by ou812 » Fri Dec 23, 2005 12:01 am

Dont know where gravity center is. Bar is 32" length. If center is in drivers hip then the bar is below gravity c/l and from the mopar chassis book it says center of gravity in most mopars is located at the drivers hip. I am going to try moving the bar back down on hole, cause I think when the front end comes down and unloads the rear, the bar's leverage in the top hole is less than in the middle hole. I ran it 1 time in the middle hole in AZ and the car was BRUTALLY consistent. And had good 60ft.s (1.44-1.46) considering the air was bad and temps were low 90's. I would have to weld on the car to limit front suspension travel and I dont want to do that. I do think a looser converter would help "power" out on launch which will be my next upgrade.
Thanks for all the help, much appreciated!!
Brian

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Post by T RICK » Fri Dec 23, 2005 7:04 am

Are there rubber snubers under the upper A- frames? If there are look into large bolts with nuts and washers to replace the snubbers. The bolts can be adlusted to limit the A-frame travel. Hopefully the snubbers are round and no drillimg or grinding is needed. I sense from what you are saying is if you lower the bars the front end lifts higher and maybe snaps up faster?
The motor combination won't hold the front end up then drops hard unloading the tires? I would try limiting the front end travel as get the front end to rise a little over level and see if the car stays up longer before dropping, or maybe setteling down becomes smoother. Do the mickeys have a stiff wall and do you use tubes? If so the tire pressure may need to come down, it seems high for my way of thinking. Are these street tires or race slicks? My last racing days were in the late 90's with comp eliminator dragsters. Still crew on a f-16 dragster (west coast it's called Top comp) so I have to admit it has been a long time since dealing with a door car. I would like to hears your results and what you tried. good luck

Rick

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Post by ou812 » Fri Dec 23, 2005 9:47 am

Thanks Rick. Mickey slicks, reg. side wall and yes I run tubes. I've talked to a few stock eliminator guys who have had good results running more tire pressure (18-22psi) so I always try to run as much as possible. I cant complain with my 60ft times I just want to squeeze every bit of 60ft and et out of my car...and I love to learn so that's why I wont quit till I get in the 1.3's...
I will post my results, but were not going till the 14th!
Yeah you know I might be able to use the bump stops like you said...I am going to check into that!! Thanks.
Brian

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Post by Speedy Goomba » Sat Dec 24, 2005 10:58 am

Brian,
Stock eliminator racers can run alot of tire pressure becuase of the slicks they use.

They're using whats called a Radial Slick (not to be confused with a drag radial) its a slick with a radial construction.

The sidewalls dont deflect as much on the starting line, and they can be ran with alot of pressure (18-22 as mentioned).
11.15
117.42MPH
1.46 60 foot(footbrake)
7.03 @ 94.65
3215 lb. '67 Camaro

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Post by ou812 » Sat Dec 24, 2005 11:26 am

This was way before the radial slicks. But I may be trying to run too much air... :oops:

So for a 28x10.5 tire, what do you guys usually see working for tire pressure? If I go below 12lbs. my mph drops noticably, so I hate to go below that. I guess I could try a taller tire and run 10-12 lbs.

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Post by T RICK » Sat Dec 24, 2005 12:38 pm

Brian.

You've got me intrested more in your project. The Mickeys probably evolved a lot since I was around them. There are a couple of ways to launch your car that may prove interesting. This information is from comp racing but may be an interseting approach. If some one has tried this please comment. On a C/ED we played with launch RPM with a MSD 2 step. I realize that you must not have a trans brake but I was thinking if you were able to chip down to a cosistat rpm at stage and controled it like a trans brake this could help the launch in consistancey as well as the convertor flash harder. Look at wiring the 2 step into the brake light switch or add antoher to work off the brake pedal. don't forget to put a master switch for turning on before staging. Also if a lower tire pressure decresed the 60 foot readings I would continue even if the tire shock wads the tire. In my mind the energy spent lifting all the weight of heavy cars is a comprimise for traction and taken away from accelleration. I have never followed stock or SS but remembering somthing about hiding extra weight around the rear bumper to help keep the car up and not drop the front so hard. Inconsistancy in reaction time classes like the super catigories you don't want the front end of the ground as coming up out of the light makes the car inconsistant compared to foward motion. Try one idea or combo at a time or you can get lost real quick. Always be able to back track if ideas don't work. Good luck and I'll keep checking

Rick

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Post by Speedy Goomba » Sat Dec 24, 2005 4:19 pm

ou812 wrote:This was way before the radial slicks. But I may be trying to run too much air... :oops:

So for a 28x10.5 tire, what do you guys usually see working for tire pressure? If I go below 12lbs. my mph drops noticably, so I hate to go below that. I guess I could try a taller tire and run 10-12 lbs.
i used to run 14-15lbs with Bias Ply slicks. Why not try out the radials?
11.15
117.42MPH
1.46 60 foot(footbrake)
7.03 @ 94.65
3215 lb. '67 Camaro

http://i27.photobucket.com/albums/c181/SpeedyGoomba/

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Post by ou812 » Sat Dec 24, 2005 7:52 pm

I may try the radials...
The way it looks on paper, I'm on a fine line of traction-wheelstand-hard launch. My 60fts. are really good, infact better than most cars at the track running faster than me. But I wont be satisfied until I get than magic hardlaunching, wheel standing leave. My converter might be partially to blame. I feel if I left the line at 4000rpm instead of 3000 that I would be in the engines power band vs. now I think I am slightly out of it. I think that might be causing at least 50% of my front end pop up to unload the rear tires.
Question...with a ladder bar car, is it normal to run more or less tire pressure when you hit the tire harder? I assume running more, but my car proved it wanted less...at least on that day at that track. I think I'm going to move the bar back down one hole and move the shock to #8 and go back the 14th and see if there is any change. I will try shock settings and tire pressure too so maybe I can find a pattern until I get another converter.
Question 2: Has anyone gone from say 5000 converter to 5700 with a small engine heavy car and seen a gain?
Brian

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