Questions about drag car launch.

Tech questions that don't fit above forums

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T RICK
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Post by T RICK » Sat Dec 24, 2005 10:14 pm

Brian,

convertors have a lot to do with where the motor power band is and how wide it is. If a motor makes power from 6000-8000 rpm then you basicly have a band of maximum excelleration in this range. You want the convertor to slip and lock up around the bottom of this range. If you get a chance to listen to a comp eliminator dragster with a 5 speed you will notice the engine revs high the whole lenght of the track and the trans shifts with the engine staying at the same pitch. The clutch is set to slip just as the convertor does. The cam, carb, heads, manifold, all determine where in the RPM range this band takes place and how wide it is. Your cam manufacturer may be able to some what tell you where this band is and how wide. The idea of the lower tire pressure (to a point ) allows the side wall to colapse increaseing the contact patch of the tire to the pavement resulting in positive traction and less chance of slipping in poor track conditions. While the tire side wall wraps up when the tire is shocked is also softening the way the car leaves. you may loose a little reaction time. Some of our best runs were when the car leaves smooth. Runnig the comp car we got away running 3 highaltude convetoers and 3 low altitude convertors and many racers had a lot more. So to say changing from one convertor to another really depends on you power band and car combination also your need for maximum performance on any given condition.

Rick

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Post by Speedy Goomba » Sun Dec 25, 2005 9:29 am

ou812 wrote:I think that might be causing at least 50% of my front end pop up to unload the rear tires.
Brian
Brian,
When i have this problem, tightening the rear shocks is the first solution i look to. If tightening them is unsuccessful, only then do you loosen them.
If the rear shock extension is too stiff, it will yank the sidewall of the tire up and spin.
If the rear shock extension is too light then it will allow the front to drop to quickly, and spin.

Similar results to both, but you will notice that if the rear shocks are too stiff it wont seperate.

if they are too light it will seperate almost to full extension.


You might decide to cut to the chase, and buy Afco double adjustable "bolt-on" rear shocks. They were one of the best investments i've spent my money on. Worth every penny.
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 Speedy Goomba » Sun Dec 25, 2005 9:35 am

http://www.davemilcarek.com/110605/page ... %20016.htm

This shot shows optimal rear seperation with my suspesion, its a pretty good amount.


The next pass i tightened it slightly (my goal was tuning the rear shocks)

http://www.davemilcarek.com/110605/page ... %20016.htm

Still leaving nice but not wheelying as high.

both passes were identical 60fts 1.501
11.15
117.42MPH
1.46 60 foot(footbrake)
7.03 @ 94.65
3215 lb. '67 Camaro

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

T RICK
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Post by T RICK » Sun Dec 25, 2005 11:25 am

Speedy- can you show us a picture of the car staged with out being on the convertor and also up on the convertor before launch? Want to see the body in nuetral state. Body lift loaded. Thanks

Rick

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Post by STK 758 » Sun Dec 25, 2005 3:43 pm

OU812 , On my stocker with radial Hoosiers 9 in and Caltracs , if I let them down below 18 lbs the center of the tire picks up and promotes spin . I run them now @ 21 lbs and the shocks set at 8 from a max of 9 . This also takes away the body separation like Speedy has said and 60 ft's better. The car is a 69 Camaro 427 at 3610 just for info and the min is 3570. This is the same with bias tires , below 14-15 they spin so I keep them at 16-17. The car picks up 9-11 hundredths depending on the track of course with radials . I also have 53-54 % on the nose and adjust for conditions with weight at the rear panel. All of this depends on how high I leave . With a 57-5800 conv I leave @ 22-3000 depending on the track...... On a good track I leave @ 2600 and have a rear wheel 60 ft of 1.45-50 and if the front end comes down like it should and trip the lights it has a 1.35-1.37 = 10.40 @ 124-125 . MSD 2 step on the mat ! This is in go round mode for consistency and all bets are off with a heads up run against a same class car. Just for info if you get down to 60 deg track temps the radials are not as consistant like the bias . I hope this helps .

Happy Holidays,
BP

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Post by ou812 » Sun Dec 25, 2005 3:57 pm

Wow!! You guys are great! Thanks for all the replies, I just want the car to 60ft as hard as it can with what I have for now. So...you run a 427 and 5700 stall...This makes me think I could use at least 5700 in my 360!
I'm sure that more converter, trans brake, 2 step (which I have), and a little more tire would help put me in the 1.3's but funds right now are tight, so I'm trying things and learning from them...kinda like learning the basics you know cutting my teeth on this suspension stuff (engine guy).
So I either need to :
A: Lower my ladder bar one hole and try it at Barona with the shock on #8, or
B: Leave the bar and shock alone, and try just tire pressure and more shock settings, or
C: Remove the A-arm bumpers on the front and assemble stops to limit front travel and leave the ladder bars alone.
So lets hear the opinions...and please no arguing...I will take all thoughts into account and then apply what "I" think will help most. If I'm wrong, well no sweat off my you know!!
Brian

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Post by STK 758 » Sun Dec 25, 2005 4:35 pm

I have destroyed the front end with big wheelies being hard headed ! $$$$ Your front end needs FREE travel up but you also can limit it depending on how good or bad the 60 ft is and how high the front end goes depends on the travel limit . I have been taught that if you move the bar down the IC moves forward and down and takes more power to keep the tire planted . Like all the guys on the forum will tell you , go test and tune and find out what it wants . One change at a time !!! Too many changes will discourage you fast . I would guess you currently know where the pinion angle is ? On my car it is down 3 deg and no preload. I also plant the brake hard trying not to preload the car . There are a ton of guys sharper than I on this subject . I don't not pretend to be an expert but I know what works for my car . Speedy's coments on the shocks will help you .

Barry

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Post by ou812 » Sun Dec 25, 2005 4:56 pm

Yeah one change at a time... :lol:
Well then I think I will leave the bar alone and test tire pressure and shock settings. My pinion is 3.5-4 degrees down. I was thinking of moving it down to 5 down...anyone agree/disagree?
The rear of my car on launch tilts down, but the distance between the rim and the wheel opening stays the same, so very little action there. The rear only pitches down because the front rises and gets about 3" of air under the tires. The shot of my car at Barona is before I was getting air under the fronts. I dont have a still shot of it now, but I have mucho video thanks to my wonderful and beautiful wife :D
Brian

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Post by T RICK » Sun Dec 25, 2005 5:23 pm

Brian,

Looking at the launch picture of speedys car and my way of thinking is there should be a rise of 3-4" between the rear tire and the fender opening from the nuetral posistion. This is showing me that the suspension is transfering energy by pushing the rear axle housing down on the tires by the body lift. I still have difficulity with the big wheelstand if you don't have a lot of HP and a narrow tire. Seems like alot of lost motion that could be used to move foward. Then again what works is right. My idea is to get the front end up but not off the ground, then it stays there and comes down in a smooth manner. On our dragster when it pulls the front end you can see the tire wad excessively and the 60 ft slows down. It triggers the clock going up and not moving foward. I can see a door car on a full tree rolling out of the light and then pull the front end off the ground so watch (camera) in slow motion. As far as the pinion angle I don't know if it does much except the load on the u-joints, not a problem with dragsters. Do you log all of the info at the races?

Rick

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Post by STK 758 » Sun Dec 25, 2005 7:07 pm

Rick , We run a B/ED also or at least we did ..... The hp vs tire control thing is the same except with the stocker it has to transfer everything as in wheels up . The differance with the B/ED 60ft is pulling the front end too much and hitting the tire too hard is a typical 102-04 60 ft and a great pass is a.995 60 ft. This is where the wheelie bar ,tire press and start launch come into play. Comp cars need wheel speed, if you hook and wheelie a C/ED it kills it just like the B/ED . 2500 drive shaft rpm say .250 sec into the run ? My stocker does exactly what you stated , it drives out , no spin and lifts it smooth . If the front end does not stay up I am toast . Too much at times but thats my fault. Like the dragster, it becomes a balancing act . We had a doo doo year in comp after we figured out and fixed our motor issues and then had to work on the new tire and launch issues. The friggin B/ED is an ANIMAL at 4 lbs pre inch and on the launch and it has humbled me more than enough. Besides having an index challenged class due to one off cyl heads........ :roll: ... We are switching to door car E/AA.

Barry

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Post by T RICK » Sun Dec 25, 2005 7:54 pm

We also did run C/ED I have since retired and my driver /partener runs F16 in Denver (west coast top comp) this is what I was confusing the issue with. We did control tire spin with the C/ED even more at altitude. I should have stated planting the tire is with the F16 car when it pulls the front end and wads the tire. The F16 is a 401 Buick sbc with a small shot of nitrous. totaly a different animal but it is amasing that it seams like it can hang there for ever before moving foward. Kills the 60ft pretty bad. When it leaves smooth with out pulling the wheels it will 1.05 60ft up there. This is why the air launch doesn't make sense unless you have a tire width restriction. I see from this my thinking is outdated and I assume the change is the radial tire? The head thing in comp would really piss me off. I'm glad I don't have to deal with that. They might as well call econo, dragster with an automatic and for get the rest. They won't take the time and money to tech what they need to to enforce the apparent problem. Anyway still love to learn new stuff, the first car I ran class was OCIR in G/ps the last year of that class.

Rick

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Post by Speedy Goomba » Mon Dec 26, 2005 12:21 am

Here's a shot of the car so that you know where static height is:

Image

I can post another, but i'll have to roll the car out tomorrow and take some shots from the side.
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 T RICK » Mon Dec 26, 2005 11:09 am

Speedy- thanks for the picture it will work great for the disscussion. First I would like to point out to Brian that in a nuetral state that the distance between the rear tire and the top of the fender opening is closer than the launch picture. This is important to me as before stated. It shows the axle pushing down by the body moving up. If you look at the side of the car and look at the body seam that runs from the head light back to the rear fender opening it is level front to rear. Now as the front end comes up the line now goes down hill front to back placing the weight to the rear loading through the tire to the ground. From one of your post I got the idea that the rear fender opening to the tire showed no significant seperation, this is importian that this happens. Picture the arch from the side at the front as the front end lifts. Picture the rear tire as the pivot and the chassis as a lever. We know that the higher the front lifts the more load to the rear takes place. However the with anything to much will become a bad thing. The part that bothers me is with a small block you won't have the torque a big block will, so trying to get air and maintain it smoothly may be to much. Testing will answer this. If you want to get air I think dropping the front end a couple inches (easy on a mopar)from level will increase the travel and increase the effort before the suspension is fully open. This will possibly cause the front end to drop and unload the rear if you dont't have enough motor. The problem with testing is it may take some time to sort out your combination so keep records of everything. Do you guys agree with the basic idea or am I missing somthing?

Rick

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Post by STK 758 » Mon Dec 26, 2005 1:02 pm

Rick , I agree . The body separation is key , too much kills 60 and not enough has the same effect. Lowering the front end will help . Maybe a little more gear or just a low gear set ? Some of the new converter tech can multiply easier and have the same stall . I forgot to mention we do run a 9 x 94 in rollout max tire in stock . I have to go work on the stocker , you guys have me wound up ... must be the coffee.... LOL Later.

Barry

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Post by ou812 » Mon Dec 26, 2005 2:50 pm

My front end is about 1"-1 1/2" lower than stock with me in the car. So if I raise the front end so the car is level, then it will take away from the slight air I'm getting now right? And this could help or hurt me so something I should try? I have not messed around with the front end ride height at all so far. My traction problem really seems to be right at the hit of the gas...not even 4ft out. And its not really a problem so to speak, but I'm curious why moving my ladder bar up to parallel with the ground made it get less traction than before when the bar was down 2 degrees.
It was a different track, so I guess that could explain it but I wont know unless I move the bar back down and try it at Barona.
I am very curious why I dont get any squat or seperation from my rear suspension. I had a 69 charger years ago, and with SS springs it would get about 2-3" of seperation. Not my duster though. My spring rate is 110# and my shocks are right in the middle of the recommended travel set by strange. I think I need to play with it more and see if the shock settings change anything...they have never really shown me much in the past going from 0 to 5. Maybe when the track is not real good, I will have to run less air, like 13 lbs. Or maybe the lower bar hole is just going to be what this current combo likes. We shall see...
Thanks guys!!
Brian

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