8 second OEM 4 link drag race chassis setup

[Alky V6]

What has my little chassis tuning adventure taught me so far?

Up to this point, it sure appears that I had the chassis more finely tuned from the very beginning than some here thought I did. And, I was able to figure out how to accomplish that without having to resort to scaling the car (spring heights).
I'm really not too surprised. With the old chassis setup, the car launched straight, drove straight and braked straight. The only thing I was really after was more traction down track. I don't think that is going to happen,... unless shock settings can help, and I've heard they can.

Spring rates and shock settings are some of the areas left to fully explore. I don't think I need any softer springs in the rear. They're at 125 lbs/in and I can't imagine needing anything softer.

Other areas to explore;
The final drive gear ratio. A higher gear would tame down the torque level at the wheels. Particularly at and/or after the 1-2 shift where I'm having the most trouble. And, the higher gear would help me out in the quarter.

Hitting it harder at the launch. Figuring out a way to launch the car harder so that the 1-2 shift can be done at a higher power level. I've already found out that the harder you launch the car, the more power you can get away with during the 1-2 shift. Maybe figuring out how I can use a small third stage with the n2o system to give the engine a little help with the turbo during the 60 foot. Or, shutting down the primary n2o system, but leaving the afterburner on during the 60 foot. Maybe it's time to experiment with running the afterburner by itself?

 

[KEVINS]

I'm glad you didn't get hurt trying the Asymetrical crap! Shoppe has been telling people that for years and no matter how much I tried nobody would listen. He has NO experiece in drag racing and all he does is sit on his computer making formulas telling everyone what they should do based on his "calculations". Thats all his website is, formulas.

When you think about it, the LCA's are pushing the car (pulling under braking) and if one is angled differently than the other, then each arm will be pushing the car in a different direction so of course it's going to act differently and the more power the more it's going to affect it. What he's been proposing is dangerous and what would happen if the car really got out of the groove, how predictable will the car be trying to get it back under control?

I love the fact that you prefer to try things out yourself and make things work, very few people do that these days. If I thought you would have listened I would have spoken up against doing this, but from all your hands on testing you would have done it anyway, I give you Kuddos for giving it a shot, though!

I cant wait to hear your next testing experiment, but be safe!:redface:

ks

 

[Alky V6]

I'm glad you didn't get hurt trying the Asymetrical crap! Shoppe has been telling people that for years and no matter how much I tried nobody would listen. He has NO experiece in drag racing and all he does is sit on his computer making formulas telling everyone what they should do based on his "calculations". Thats all his website is, formulas.

When you think about it, the LCA's are pushing the car (pulling under braking) and if one is angled differently than the other, then each arm will be pushing the car in a different direction so of course it's going to act differently and the more power the more it's going to affect it. What he's been proposing is dangerous and what would happen if the car really got out of the groove, how predictable will the car be trying to get it back under control?

I love the fact that you prefer to try things out yourself and make things work, very few people do that these days. If I thought you would have listened I would have spoken up against doing this, but from all your hands on testing you would have done it anyway, I give you Kuddos for giving it a shot, though!

I cant wait to hear your next testing experiment, but be safe!:redface:

ks

You're right, I suspected the car might pull to the left. I thought it rather odd that there was this theory out there, but no one had tried it out. That alone made me cautious of it. I was well prepared for the possibilities.

It was very obvious that the more power you tried to put to it, the more strongly it wanted to steer left. I was on and off of it a few times before I aborted the run. I wanted to give the theory a fair try.
It's very obvious that asymmetrical 4 link settings can affect the rear tire loading left to right. I just think that the difference in AS% to use from left to right is much more sensitive than Bill's theory suggests. As you can see, since installing this Moser axle housing, I always have and still am running a very slight amount of asymmetrical setting (3% difference) and managing to go straight.
Could a slight amount of more difference in AS% end up completely eliminating the need for any spring and/or ARB preloading? I think it's possible, but to get that exact difference would be too hard to narrow in on. You'd still end up having to use some amount of spring and/or ARB preloading for fine tuning the chassis.

Bill was right about one thing. The asymmetrical 4 link arrangement does dynamically change rear tire loadings relative to driveshaft torque input. As I rolled into the throttle and engine power ramped up, I could tell that the pull to the left increased proportionately to the amount of driveshaft torque input.
Even though it wasn't in the most favorable fashion, it was still very interesting to see the theory play out the way it did.

 

[KEVINS]

Don,
Could I by chance get a copy of your Perf. Trends file for your car? I'm curious to see how my UCA Bucket's would plot out with all the control arm options you have.

If not not no big deal. I seem to remember that I couldn't get other peoples files to open whenever they sent theirs to me so it may not work.

KS

 

[Alky V6]

Don,
Could I by chance get a copy of your Perf. Trends file for your car? I'm curious to see how my UCA Bucket's would plot out with all the control arm options you have.

If not not no big deal. I seem to remember that I couldn't get other peoples files to open whenever they sent theirs to me so it may not work.

KS

I don't know about sending the files, but I'm more than happy to list any parameters you're interested in.

Because of the slight amount of asymmetrical link setting, I use one file for the left side and one for the right.

 

[Alky V6]

Here are the final 4 link settings, left and right. I found a problem with the axle upper link locations. This caused a change in the left side IC position. 114 instead of 117 AS%. A 6% difference in AS% between the left and right side.
The extra upper axle housing mounting hole is just the stock axle housing location I use as a reference only. The Moser housing does not have that hole for an option.
The frame side holes are all stock location.

 

[Alky V6]

For those using the Performance Trend's 4 link calculator, here are the tables with the specifications.
The left side and right side files use the same specification found in the 'Other Car Measurements' table.
The 'Top Axle Bracket Locations' are the same for the left and right sides.

 

[Alky V6]

The 'Bottom Axle Bracket Locations' are different for the left side and the right side. Here they are.
As you can see by the differences in the left side and right side mounting hole heights, it doesn't take much of a difference in height to cause an asymmetrical 4 link setting for the rear. That's why I stated earlier that it would be rather difficult to narrow in on a perfect asymmetrical setting and not have to use some small amount of spring and/or ARB preload to fine tune the combination.

 

[KEVINS]

Thanks for the info. I was able to do some plugging with some numbers and my torque box buckets won't work with a 12bolt only the factory rearends or the Ford 8.8, unless new holes are drilled in the buckets.

The 12bolt mounting ears are really high compared to the above rearends and my Buckets only produce an IC length of around 21" at best with the 12bolt even with the 3 holes supplied in the buckets...a taaad too short. lol...

ks

 

[Alky V6]

With the 'Bottom Axle Bracket Locations', the number 1 locations for the left and the right sides are the original mounting locations supplied by Moser with their version of the 12 bolt rearend housing.

 

[Alky V6]

Summary of changes to date

Total vehicle weight: 3290.5 lbs. with suited driver and full fuel cell load (15 gallons).
Percentage of weight on the rear axle: 45.75%
Percentage of weight on the left side: 51.57%
CG height = 21.7"
Starting weight distribution without ARB preload;
LF 955.5, RF 829.5
LR 741.5, RR 764.0
The ARB preload used with the above old weight distribution setting was 3 1/3 turns and was not included in the above weighing.
Present weight distribution, including 1/2 turn ARB preload;
LF 978.2, RF 806.6
LR 718.5, RR 786.7
LF spring preload increased 1/8".
RR spring preload increased with a .508" spacer under the spring and the stock rubber cushion at the top.
Ride heights equal in the front, 1/8" higher at the RR than the LR, with driver, helmet and fuel.
LR AS% set at 114.7%. (changed)
RR AS% set at 120.7%.
A slight amount of dynamic roll control in effect. (changed)
Pinion angle is set at .9 degrees upward angle from horizontal in anticipation of a 1-1.5 degree axle wrap up.
Front shocks (QA1 SA) are being worked from max stiff towards loose. Right now, the adjustment is at 19 clicks from full soft. Both front shocks using the same settings.
Rear shocks (Afco DA) set the same at 16 clicks comp, 8 rebound.
Both front and rear shocks adjust firmer by turning CW from full CCW position.
Range of the front shocks is 0-24 clicks.
Range of the rear shocks is 0-?? clicks. Top knob for comp adjust, bottom for rebound.
Front extension travel limiters set at approximately 2" including bumper compression. On an even rise left to right, the RF leaves the ground (3/4") before the LF.
RB preload is 1/2 turn. Static weight on the RR is 786 lbs.
Rear tire pressure at 9.5 psi. Front at 35 psi. 9.5 psi in the rear has been confirmed to be the best pressure to use.

 

[Alky V6]

The next plan is to set up the afterburner on a delay timer instead of the simple pressure switch that is now controlling the shut off point of both the primary and the afterburner systems.

As it's set up now, the primary nitrous system shuts down as soon as 175 kPa MAP is reached. The afterburner shuts down at the same time.
What I'm planning on doing is having the large primary system shut down at the same 175 kPa MAP level, but have the afterburner stay energized while the car is staged, and have it stay on part way through the 60'. The afterburner shut off would be on a timer relative to the transbrake release point.
If all goes as planned, I should have more boost relative to rpm to call upon through the important power ramp up in the first 60 feet of the run. This may allow more power to be used at and after the 1-2 shift point.
Wastegate and BOV control during staging and the first part of the launch will be critical in maintaining a steady launch rpm and map level, while maintaining a reserve amount of compressor speed to call upon for a quick step up in power at some point during the first 60 feet.

 

[Alky V6]

If the new afterburner strategy results in a fair amount of reserve power for the launch, then the rear axle gear ratio will be changed from the present 3.73:1 to something higher. 3.55 or 3.42:1. This will solve my 1/4 mile problem where I'm reaching redline for the engine way too early in the run.

 

[Alky V6]

Part of the problem of making a particular chassis setup work is having the chassis properly loaded by a certain amount of driveshaft torque.
Engine rpm and map levels need to be the same from one launch to the next.

 

[Alky V6]

An interesting thing to note about the 4 link settings is that as the rear end rises, the AS% dials down or lessens to affect a self correction. The same sort of self correction occurs when the rear end drops. The AS% increases to boost a counter force to the dropping rearend ride height.

 

[KEVINS]

Don,
If I can custom drill a set of torque box buckets to work with your chassis would you be interested in trying them? It would require the use of my control arms since they need to be shorter in order to fit into the buckets.

The control arms use a 1/2" hole x 5/8" thread rodend on the chassis side but uses a 3/4" thread on the axle side.

With the car lowered as much as you can and still have tire clearance I would set the geometry so the LCA's are perfectly horizontal with the ground then angle the UCA's down to move the IC back and I would need your chassis holes and axle holes to compute the new hole location in the buckets. Doing this usually improves topend stability and helps load the tires more.

Tim Robison went from 1.45's to 1.33's after bolting them on in his GN.

ks

 

[Alky V6]

Don,
If I can custom drill a set of torque box buckets to work with your chassis would you be interested in trying them? It would require the use of my control arms since they need to be shorter in order to fit into the buckets.

The control arms use a 1/2" hole x 5/8" thread rodend on the chassis side but uses a 3/4" thread on the axle side.

With the car lowered as much as you can and still have tire clearance I would set the geometry so the LCA's are perfectly horizontal with the ground then angle the UCA's down to move the IC back and I would need your chassis holes and axle holes to compute the new hole location in the buckets. Doing this usually improves topend stability and helps load the tires more.

Tim Robison went from 1.45's to 1.33's after bolting them on in his GN.

ks

An interesting proposition. The main problem is, because of the backspace of my current wheels and the resulting tire to fender well lip clearance, the car is already as low as I can get away with. I have less than 7/8 inch of running clearance between the edge of the tire tread and the fender well lip right now.

What sort of UCA length parallel to the car centerline are you talking about? If you can give me that dimension, I can use the sim to see how it might work out with the more horizontally located LCAs.
I'm sure you would also suggest a lower AS% to go with the shorter IC length?

 

[Alky V6]

Do you have a pic you can post of your buckets? I'd like to have an idea of how much fab work it would take to install it/them.

 

[KEVINS]

They bolt in but you can add a spot weld to hold them if you wanted to.

Here's a pic of the bucket installed installed on my GN:

http://www.baselinesuspensions.com/kits/gbodyinstall1.jpg

http://www.baselinesuspensions.com/kits/gbodyinstall2.jpg

http://www.baselinesuspensions.com/kits/gbodyassy.jpg

As a baseline I always recommend the LCA's be parrallel with the ground so if the car is lowered as far as you can go then use your existing holes to level the LCA's as much as possible.

I set set the IC around 36" and the AS around 120-130% when the LCA's are parallel with the ground.

From the 12bolt sitting in my garage the new bucket hole would be moved back and down.
Measuring from your existing UCA chassis hole the new hole would be located:
1.81 backwards (shorter control arms)
.53 lower

Also, one thing that's different in my measurments is your UCA lengths. I notice your length in your software is 8.375" but I use 7.5" on my car with the stock rear. Make sure the length you're using is the "projected" length parallel to the direction the car is moving and parallel with the ground not the actual length of the arm but I'll use what ever your car measures.
When using the new numbers for the drilled holes in the buckets the UCA length works out to be 5.69".

ks

 

[Alky V6]

Yes, Kevin, the lengths are projected lengths. I'll plug the numbers in and see how it looks. Thanks.