8 second OEM 4 link drag race chassis setup

[Dusty Bradford]

From what I understand, the amount of front suspension travel and the rate of travel has much to do with the available torque the particular setup has. I'm beginning to think that it can also be a way to fine tune an IC that may not be exactly perfectly placed.
I would think in your case, Dusty, tying down the front suspension alltogether might be an option, also. But, if I remember right, back in this thread, you did mention that you found that you needed a certain amount of travel. Have you changed your setup? Have you found that the car is now needing something different than what you were posting earlier in the thread?

Front travel will depend on track conditions and how hard I can hit the car at launch so it's constantly changing from track to track, or changing from a 100 degree track vs a 130 degree track. A very good track I may only need 1.5" of travel and the shock full tight. This keeps the weight further forward to avoid wheelstands and allows me to bring in the boost very quickly. Adding weight to the nose is also something that has to be done if the track is great.

On a very loose track I need more front travel to move the weight further back so I can apply more power to the tires. The shocks on the car are a little on the loose side, even at full stiff. So if the track is bad I put more travel in it but leave the shocks at full tight.

A shock that's too loose will allow the front end to smack against the travel limiter and then it will rebound, unloading the rear tires. This is what your saying about the rubber isolater dampening this smack.....but if you have a shock sensor you'd see the rubber isolater isn't helping with the rebound effect. If the car tops out the travel and then rebounds, it needs a tighter shock.

 

[Alky V6]

Good stuff, Dusty.
I know as I start getting the chassis more finely tuned, I'll need to figure out a way to be able to change the amount of front end travel in a quick manner. Welding in a stop bolt would most likely be the easiest way.

 

[Alky V6]

What do you think of this situation.
A car that is trying to control front end rise, has the travel set minimal, the shocks set at tight. The performance isn't such that the car is at 100-105 AS% with the front end completely tied down.
But, let say the AS% is above 105 AS%. Let's say it's 115-120 AS%. Would it be reasonable to try a lower AS% and maybe end up getting some front end travel or lighter shock rebound adjustment from the AS% change?
I'm just trying to get a feel for the dynamics in this.

I guess what I'm trying to say is, does the AS% and IC location have an inter-relationship with the spring rates, suspension travel and shock settings? The AS% and IC location being the more rough adjustment, and the spring rates, suspension travel and shock absorber settings being the narrower fine tuning range?

 

[Dusty Bradford]

Good stuff, Dusty.
I know as I start getting the chassis more finely tuned, I'll need to figure out a way to be able to change the amount of front end travel in a quick manner. Welding in a stop bolt would most likely be the easiest way.

When I had the stock control arms, I welded a nut to the control arms where the rubber isolater was at and used 5/8 all thread with a jam nut to limit travel.

Another thing with the stock control arms and rubber bushings. When I replaced them with the TRZ arms which have heim ends, the shock really needed to be even tighter. The stock rubber bushings have a lot of travel resistance. The TRZ arms free that up, requiring a tighter shock setting.

 

[Alky V6]

When I had the stock control arms, I welded a nut to the control arms where the rubber isolater was at and used 5/8 all thread with a jam nut to limit travel.

Another thing with the stock control arms and rubber bushings. When I replaced them with the TRZ arms which have heim ends, the shock really needed to be even tighter. The stock rubber bushings have a lot of travel resistance. The TRZ arms free that up, requiring a tighter shock setting.

Yeah. That's close to the same idea I had with the bolt thing.
That's very interesting with the different control arms.

 

[Dusty Bradford]

What do you think of this situation.
A car that is trying to control front end rise, has the travel set minimal, the shocks set at tight. The performance isn't such that the car is at 100-105 AS% with the front end completely tied down.
But, let say the AS% is above 105 AS%. Let's say it's 115-120 AS%. Would it be reasonable to try a lower AS% and maybe end up getting some front end travel or lighter shock rebound adjustment from the AS% change?
I'm just trying to get a feel for the dynamics in this.

I guess what I'm trying to say is, does the AS% and IC location have an inter-relationship with the spring rates, suspension travel and shock settings? The AS% and IC location being the more rough adjustment, and the spring rates, suspension travel and shock absorber settings being the narrower fine tuning range?

I do all the rear ic changes by watching video to see if the car is squatting or seperating. (Rough adjustment as you called it) I've always tried to get the lower CA as close to parrallel with the ground as I can to avoid alot of tire seperation at launch. But I have found the lower powered cars (low to mid 5's) can have some seperation without it causing issues and may help limit tire shake.

Once I get the car where it's obviously planting the tire without to much squat or seperation I move to the shock settings in the rear and travel/shock settings in the front.

 

[Alky V6]

Thanks, Dusty. That helps a lot.

My latest IC target puts the IC location throughout the range of rear axle travel very close to parallel with the 100% AS line. The IC reaching close to the 106% AS line by 2 inches of front and rear tire separation. I have no idea how much AS% will yield how much tire separation. I suppose that's where the video taping comes in. After watching the video, you can start relating the AS% to the actual amount of anti-squat you're getting from your particular chassis.

In any instance, I think by me moving the IC from 93-98% AS, and up front, to 115-120% AS, and a little more rearward, is going to take care of my top end traction issue. I hope, anyways. Then, we'll just have to see what we have at the launch.

 

[Dusty Bradford]

Thanks, Dusty. That helps a lot.

My latest IC target puts the IC location throughout the range of rear axle travel very close to parallel with the 100% AS line. The IC reaching close to the 106% AS line by 2 inches of front and rear tire separation. I have no idea how much AS% will yield how much tire separation. I suppose that's where the video taping comes in. After watching the video, you can start relating the AS% to the actual amount of anti-squat you're getting from your particular chassis.

In any instance, I think by me moving the IC from 93-98% AS, and up front, to 115-120% AS, and a little more rearward, is going to take care of my top end traction issue. I hope, anyways. Then, we'll just have to see what we have at the launch.

The car having alot of squat or seperation on launch will effect the ic and as% but from what I've seen it takes ALOT of movement to cause traction issues. The control arms are long enough that it takes a good bit of ride height change to upset the chassis. Now if the upper control arms were very short, it wouldn't take as much of a height change during the trip down the track to upset the chassis.

 

[Alky V6]

The car having alot of squat or seperation on launch will effect the ic and as% but from what I've seen it takes ALOT of movement to cause traction issues. The control arms are long enough that it takes a good bit of ride height change to upset the chassis. Now if the upper control arms were very short, it wouldn't take as much of a height change during the trip down the track to upset the chassis.

I understand. Good to know.

 

[Alky V6]

Here's an idea. What if you could have a shock absorber that started out relatively firm for the first quarter inch and then progressively got firmer before it topped out?
That's kinda what the rubber bumpers are providing. Is there an obvious disadvantage to this strategy that I'm missing?

 

[Alky V6]

If anyone has an opinion on my IC selection, nows the time to speak up. I've fabbed the bracket extension pieces but haven't drilled any holes yet.
I've made the extensions long enough so that I can actually space in two lower hole options.

 

[Alky V6]

I figured out a great solution. There's enough room with the extensions to fit in 3 extra lower holes if I stagger them. This will give me these IC choices for each hole.

95.2 This is the current AS% with a 63.4 IC length, 13.3" ht.
107.4 AS%, 58.6" IC length, 13.9" ht.
118.7 AS%, 54.8" IC length, 14.3" ht.
129.1 AS%, 51.7" IC length, 14.7" ht.

The holes are spaced every .400" vertically, 21/32" horizontally.

If I can't get something going with one of these choices, then I'm in some deep trouble.

 

[Alky V6]

I'm wondering if I should spread the holes out to give me more anti-squat on the last hole. I understand that drag radials need more anti-squat and a shorter IC length than slicks. Drag radials need to be planted harder to keep the tire from slipping. Unlike slicks, where a little bit of slippage is desireable, you don't want drag radials slipping at all. They have to hook hard.
DRs do not recover like a slick does once they begin to slip.

 

[Dusty Bradford]

Here's an idea. What if you could have a shock absorber that started out relatively firm for the first quarter inch and then progressively got firmer before it topped out?
That's kinda what the rubber bumpers are providing. Is there an obvious disadvantage to this strategy that I'm missing?

Slowing a shock down progressively through a long stroke would work. I'm not sure how much that rubber compresses before it rebounds but I can't see it being more than 1/4" at the most. I'd bet you could replace that rubber piece with a piece of all thread and not notice any difference.

 

[Alky V6]

Slowing a shock down progressively through a long stroke would work. I'm not sure how much that rubber compresses before it rebounds but I can't see it being more than 1/4" at the most. I'd bet you could replace that rubber piece with a piece of all thread and not notice any difference.

You'd be very surprised how much that bumper actually compresses. I think I might have 1/4 to 1/2" clearance between the bumper and the block I bolted to the frame, with the car at rest. It must be closer to 1/4" because I can't fit my finger into the clearance. If I remember right, I have over 2.5 inches of suspension drop.

 

[Dusty Bradford]

You'd be very surprised how much that bumper actually compresses. I think I might have 1/4 to 1/2" clearance between the bumper and the block I bolted to the frame, with the car at rest. It must be closer to 1/4" because I can't fit my finger into the clearance. If I remember right, I have over 2.5 inches of suspension drop.

It must not be doing much of anything. I don't remember it being much more than 2.5 inches thick:biggrin: It must squash like a pancake.

 

[Alky V6]

It must not be doing much of anything. I don't remember it being much more than 2.5 inches thick:biggrin: It must squash like a pancake.

Yeah, it does flatten out pretty good.

What you need to realize, and I didn't realize this myself until I started playing with the size of the block to get a low target amount of suspension drop, that the position where the bumper is located in the arc of the upper control arm means that for every 1/4" that the bumper is crushed, that distance translates to over double that at the tire end of the control arm.

Add to that, you are stopping the control arm travel where the spring is compressed that much more than it would be if the suspension was allowed to fully extend. That much more spring pressure at this earlier stopping point is really doing a job at crushing the bumper a lot more than would be the case where the spring were allowed to extend further before coming to a stop.

As an example, a 350 lb/inch spring forced to stop 2 inches sooner as its being extended means there is 700 more lbs on that rubber bumper. Flat as a pancake is about right. In fact, I was thinking of making something to jam the suspenion when the car is on the ground so that when I store the car on the lift that rubber bumper doesn't have to sit there for weeks being crushed to death.

 

[Alky V6]

The position of the bumper in the travel arc of the control arm also means that for every inch of travel at the tire means less than half that much travel at the bumper. So the progressive rate of added firmness that is helping out the dampener is even slower, or more gradual per inch of tire travel than you would first think. It's a pretty neat deal when you sit back and really think about it.

 

[Alky V6]

I added one hole .688" forward and .400" lower than the original hole in the axle housing for the LCA. This will give me a 109 AS%, up 13% from the original mounting hole.
I was able to make this change without having to weld on the extensions. We'll try this out and see how it works. If I have to go lower, I'll have to weld the extensions on.
It will be interesting to see what this 13% change will do, going from a little under 100 AS% to over 100 AS%.

With this hole change, I had to shorten the LCAs 20 flats.

 

[Alky V6]

I just finished tuning up the front suspension travel limiters. My aluminum blocks. They were still in a prototype stage and were moving around a bit due to the stresses.
In the process of finishing the limiter block design, I incorporated a feature that will have the UCA contact the block when full extension travel has occurred. This will have the block supporting the weight of the suspension at full extended travel instead of the rubber bumper having to deal with the full weight when the car sits on a rack. The bumper will still do its job to help progressively ramp in more damping as the suspension extends to the travel stop.

I took some measurements when I finished.
The clearance between the rubber bumper and the limiter block is lucky to be an 1/8" on both sides with the car resting on the ground.
Full extension travel from when resting on the ground is:
2.00" left side.
1.875" right side.
Considering chassis twist during the launch, the left side should still leave the ground before the right side. And should land last.
To adjust this extension travel limit would be a simple matter of milling a little bit off the top of the limiter block. By design, this would also change the point where the block contacts the UCA at full extension.
I'm also going to set the front shocks to full stiff on the rebound as a starting point. They are presently at full loose.