Video:

unfortunately the time-tree didn´t work that run so we don't know what 60ft time we got.
But from what we could se from the racepak it was the best launch ever. I´d guess around 1.10-1.13 60ft.

The run after we had a 1.13 60ft.

 

I found this article helpful.

http://www.dragstuff.com/techarticles/PB-4linktuning.html

A lot of downward rake of the lower bar will tend to dead hook the tire vs. help get wheel speed up.

How much power are you making? Where is the top bar attached on the housing end?

 

Hello.
I´ve read that article many times and that´s why i don´t want any more rake of the bottom bar.
The top bar is in the lowest hole on rear axle and the bottom bar is on the lowest hole too.
The engine is not dynoed yet but best pass so far is 7.74 @172mph. 2500 lbs.
You do the math.

Fore more pictures, videos and info please check out our facebook page:
www.facebook.com/tianmotorsport

 

My top bar is in the lowest hole and my bottom bar is in the lowest hole far away from the axle. I run 57.7 out and 7.1 up, have good wheelspeed and in the 1.04 to 07s 60. AS is around 76 at rest. If you want more wheelspeed, I would either raise AS a bit, or lower tire pressure. Once I get everything totally lined out, I should be .980.

I am no expert, but I have been told what works in a high powered car when I went past the 1,500 horsepower mark and couldn't get the car away from the left wall on launch.

 

the first link didn't work for some reason so here we go again:

www.facebook.com/tianmotorsport

 

Re: Too much bottom bar angle? Video.

If i raise the IC (higher AS%) it dead hook. Been there, done that.
We don't have the torque at the starting line. Remember, it´s just an old BMW 6 cyl.

 

Re: Too much bottom bar angle? Video.

If i raise the IC (higher AS%) it dead hook. Been there, done that.
We don't have the torque at the starting line. Remember, it´s just an old BMW 6 cyl.

Maybe a little less tire pressure will get your wheelspeed up.

129% C screw Hemi here

 

There's no "right" lower bar angle...you have to give it what the car wants to be quick. As a "general rule" starting with ¼" downhill is a good start. Raising the IC should not make it dead hook. I run ours at 8¼" high with the lower bar angle with 1/8" uphill. The more you run your bar downhill the harder it's going to give it more bite. The higher you run your IC, the more anti-squat it will have so it won't mash the tire. The lower your air pressure, the less bite you will have.

Where is your pinion angle set? The wider your 4 link bars are spread, the more leverage it's going to have on the rearend. What kind of shocks/struts are you running in the front & rear. Most people underestimate the importance of getting the front end set up correctly as it will affect the launch characteristics a lot.

 

I know how you are thinking, but we need initial wheel speed or it won´t have the power to keep it going.
It helped a lot when we switched from 4.10 to 4.56 in the rear axle.

Higher IC or more anti-squat = body separation / more initial hit = less initial wheel speed.

when we raised the IC, it didn't have any initial wheel speed at all and it dead hooked.

-1 degree pinion angle.
Strange shocks in the rear, in the front i don´t really know.
Maybe we could get away with higher IC with some better shocks!??

But in the end i guess i just have to give it what it wants, with the things i have.
For this coming season we will have a new converter, which maybe change it all anyway.:lol:

 

I went and watched your video closer........... focusing on the front tire separation. When I first got into this, I had Strange struts with tired valving, it would let the front raise pretty quickly and really let the rears hook. A friend and chassis guy came and jumped on the front frame rails. He said to send those shocks back for the "Pro Mod valving" that did help.