Rate my launch

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molevolent
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Rate my launch

Post by molevolent » Fri Jun 30, 2017 7:33 am

Hey guys been awhile

So car is finally coming around.
Car is 2650 race weight
427 sb2
4 link double adj shocks front and rear
Best pass has been 8.79 @158 wit a big tailwind
Average is 8.81 @155 60 fts 1.27

Question is do I start playing with shock settings?
Car doesn't really react off the line. Almost stays neutral
It is a bracket car. And when we're in Brainerd and the track heats up and gets bit greasy my 60s fall off fast.

Here's a video of what the car looks like on a regular 60 ft
Launching at 4250 rpm and converter flashes to 6200
(Any higher than 4300 I notice 60fts are not consistent )

https://youtu.be/nbAauk9IGWs

Thanks guys
sbc 388 n/a
1969 nova
9.001 @ 149.5 mph

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John Wallace
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Re: Rate my launch

Post by John Wallace » Fri Jun 30, 2017 7:56 pm

To me it doesn't look like it does much on the launch?

Also, maybe around 1st gear change it looks like it stumbles or something?
(front dropped or something)

Have you done any chassis/4 link measuring?
(roll center etc)

What kind of spring/shock travel do you have?
(didn't look like it had much)

I'd look at this site and see if it might give you some ideas?

Shope Chassis Calculators

:?:
John Wallace
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molevolent
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Re: Rate my launch

Post by molevolent » Fri Jun 30, 2017 10:04 pm

Yeah I was on his site last year and picked a 4 link setup that was close to 100 % anti squat

I have all the measurements written down in the trailer

Has afco double adjustabe shocks in rear
And strange double in the front.(full loose on extension)


That's one thing I've noticed is it does a little bounce off line and then again further out.

I feel like I need to loosen my compression and tighten my rebound so it can squat a bit more and hold longer?

But maybe this is where I would do a 4 link change to make it hit harder?

Mostly wanted to know if I should try and make it launch different. I feel like it works. But it looks soft and I think I might be leaving some e.t on the table
sbc 388 n/a
1969 nova
9.001 @ 149.5 mph

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John Wallace
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Re: Rate my launch

Post by John Wallace » Sat Jul 01, 2017 8:07 am

I would think that you don't want any squat in the rear?
(if the body is going down, that means the rear end is going up, less traction)

I forgot about the Four Link program that was on SpeedTalk awhile back in the group buy.

That program would help quite a bit also.

:)
John Wallace
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fastblackracing
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Re: Rate my launch

Post by fastblackracing » Sat Jul 01, 2017 8:00 pm

A couple of things I see are The rear is squatting at the hit when you leave and you can see the back of the car bounce slightly...it could be the tire sidewall compressing once weight is planted after the initial hit/squat.

Then 150 foot out it looks like there is a dip or bump in the track that upsets the car a little bit...I do not see much movement in the suspension...if you bounce the corners of the car while sitting still does everything move freely? or is it bound up?

It almost looks like the way you typically set up a car to race on radials with very stiff shock settings and the rear set neutral to neither squat or separate.

I think you can work on the rear a bit to get rid of the squat that is there and go from that point...try to get it neutral or just a bit of separation...

I know on my car with radials and some of my friends that due to the fact we end up with
very little suspension movement the shocks become even more critical...point is since there is very little shock movement the shock valving has to do its work over a much smaller stroke
and the less expensive DA shocks may not cut it at this level as they are too slow to react and get the job done as well as more high end shocks can do that will react faster....

on a good track my car would just get it done with radials and QA1 DA shocks but on a marginal track not so much...next time it goes out I will probably step up on shocks.

molevolent
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Re: Rate my launch

Post by molevolent » Sun Jul 02, 2017 3:09 pm

So have I been thinking about this all wrong?
Should I be tightening my compression and loosening the extension? To help let it separate

In my mind I wanted to loosen compression tighten ext

But thinking about it kinda makes sense that your pulling tire away from the track
sbc 388 n/a
1969 nova
9.001 @ 149.5 mph

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Re: Rate my launch

Post by John Wallace » Sun Jul 02, 2017 3:26 pm

That's the way I would do it, at least see what it does.

A lot depends on the way the bars are setup and the spring weights, etc.
The suspension needs to work to get it to plant.

:)
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molevolent
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Re: Rate my launch

Post by molevolent » Tue Jul 11, 2017 8:48 am

So went to the track this weekend. Tried loosening the extension about 6 clicks over 3 passes and the spread is smaller now. Was 1.26 in morning and 1.31 by end of hot day.

But car looks the same coming off the line
Only so many passes cause of rain Sunday and eliminations on Sat.

One thing I wanted to do on Sunday was raise the launch rpm to see if it would help hit it harder.

Plan is to do a 4 link change and try to hit up a test day

Right now the ic is 47 out 12 up and anti is like 180 % acording to some software.
I'm limited on moves cause I need weld the brackets lower on the frame side.

But I could do a bar change and get it to
Ic 53 out ic 10 up and anti at 121
sbc 388 n/a
1969 nova
9.001 @ 149.5 mph

statsystems
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Re: Rate my launch

Post by statsystems » Wed Jul 12, 2017 5:00 pm

molevolent wrote:So went to the track this weekend. Tried loosening the extension about 6 clicks over 3 passes and the spread is smaller now. Was 1.26 in morning and 1.31 by end of hot day.

But car looks the same coming off the line
Only so many passes cause of rain Sunday and eliminations on Sat.

One thing I wanted to do on Sunday was raise the launch rpm to see if it would help hit it harder.

Plan is to do a 4 link change and try to hit up a test day

Right now the ic is 47 out 12 up and anti is like 180 % acording to some software.
I'm limited on moves cause I need weld the brackets lower on the frame side.

But I could do a bar change and get it to
Ic 53 out ic 10 up and anti at 121
The bottom bar should run down hill and intersect a line through the lower ball joint. That is the first place to start. Next, why so short on the IC? Used to be everyone said start at 1/2 the wheel base and cam high. The higher HP cars would just beat the shit out of the tire.

I think you need to be 90-95 out and 7-8 up. If you need to control the hit, do it with shocks.

I always consider a ladder bar when I start. They are too short for almost everything and too high, so the beat the tire into the ground. Lower the bar...less hit. A 4 link is just an adjustable ladder bar. Personally I never got caught up it the squat/anti-squat/neutral deal. That's engineering stuff for long hairs. You have to keep the IC where it moves the car but doesn't kill the tire.

As a general (very general) rule the higher the HP and the higher the launch RPM, the longer and lower the IC will want to be. I had stick cars that were 109-110 out and at the ground to keep them from pounding the tire into the ground.


Edit: your IC is just a bit longer than a 32 inch ladder bar. And, depending on where the bar was installed, is about where an average install in the center hole. That's a bunch of hit. Also, if your car likes higher tire pressures compared to what "normal" is, you are hitting the tire too hard. If you are under "normal" tire pressure it wants more hit.

molevolent
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Re: Rate my launch

Post by molevolent » Wed Jul 26, 2017 12:29 pm

Went back to the track. With a bar change. 98% anti squat 60 out 8 up (still need to move my brackets)

Think it looks better but it's no faster

Might try more tire pressure and tighten the compression
Thoughts

https://youtu.be/kPj4EIY8OY0
sbc 388 n/a
1969 nova
9.001 @ 149.5 mph

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