Tune For The Leave: Drag Suspension Tweaks For A 10-Second Chevelle

It’s been said that this is the golden age of horsepower and that is most certainly true. But in drag racing, power is only half the equation. The other half is the ability to plant all that power to the pavement and accelerate the car down the track. The concept is simple but the execution requires some knowledge and investment in trial and error testing.

Rather than throw out a bunch of theories, we decided instead, to dive into one car’s worth of experience and show you what we’ve learned launching a 3,600-pound pig of a Chevelle off the starting line. Most of the material here will focus on the first 60 feet of the drag strip. After about 100 feet into the run, even with more horsepower, there should be sufficient wheel speed to keep the tires glued to the track. So we’ll concentrate on the 60-foot times and what we learned tuning this A-body.

A big advantage for drag strip tuning is the ability to separate compression from rebound adjustments. Here, we’re stiffening the rebound adjustment by turning the knob clockwise. Each step offers an audible click. All QA1 double-adjustable shocks have a range of 18 clicks between full soft and full hard.

The other point worth making here is that this is still a street car. Our tires are sticky but still DOT legal and the suspension retains its stock trailing arm configuration. We could drive this Chevelle anywhere. We don’t – but we could. Let’s start with an overview of the package.

The car is our Orange Peel ’66 Chevelle so dubbed because of its backyard bodywork and paint. It’s powered by a 550 hp, iron-block 6.0-liter LS using a TCI Street Fighter 3,400 rpm stall converter in front of a TH400 trans. Out back is a Strange S-60 (Dana 60) with 4.10 gears, and (initially) 26×11.5-inch wide Mickey Thompson ET Street bias-ply tires. As you’ll see, we eventually coaxed this beast to run a 6.98 at 99 mph in the 1/8-mile with a best 60-foot of 1.57 using a taller tire. That 1/8-mile time is roughly equivalent to 10.75 to 10.80 in the quarter-mile at 122-123 mph. But, we struggled to get there since our initial runs were much slower and required a few suspension and tire changes.

On the rear shocks, Doug Norrdin from Global West suggested using a longer double-adjustable shock on the rear. The application is a 1990 S-10 truck using the upper crossbar mount for the early Chevelle. It adds roughly 2 inches of length to the shock travel.

Our ultimate goal is a quick car that can make multiple runs within a few hundredths of a second. If the car is not consistent there’s no sense in adding power if all it does is add to our traction problems.

As an example, some people think a car that runs 10.40s at 135 mph is really strong. But, a knowledgeable drag racer will tell you that a car running that mph has the power to run 9.90s to 10-flat. Likely this car’s slower elapsed time is the result of tire spin off the starting line which is where we will begin this story.

Our initial passes were disappointing running 7.30s to 7.40s at 96 mph. The 60-foot time was equally slow with a 1.84. The issues began right on the starting line with tire spin. Even with a limited amount of traction, the left front corner rose too quickly and topped out against the upper control arm while the right rear squatted badly.

Global West upper arms come with a standard bump stop but Global also sells this adjustable stop limiter with various shims used to place the stop exactly where you want it. This bolts to the bottom of the upper control arm.

This is a common issue with stock suspensions. We had previously removed the front sway bar and installed Global West upper and lower tubular control arms. In the rear, we added Global’s tubular lower arms complemented with Global adjustable upper arms. The change to the taller S60 housing moved the pinion angle up by roughly one-degree. The pinion angle should have been one to two degrees lower, but we didn’t realize it until after testing was complete. Finally, we added a set of QA1 Stocker Star double-adjustable shocks to allow us to separate the two forces of compression and rebound for individual tuning.

Under initial launch, engine torque lifts the left front and twists the body to force the right rear corner to squat which compresses the rear spring. Looking at the car from the rear, while the body is twisting to the right rear, torque is simultaneously attempting to counter-rotate the rear axle assembly which lifts the right rear tire. This may seem counter-intuitive because of how the body squats, but this unloading of the right rear is exactly what is happening. This is why the right rear tire always spins on non-posi equipped rear-wheel-drive cars.

This photo is not the best but notice the car is roughly 100 feet out and still heavily squatting on the right rear. When the car squats, it is essentially unloading the right rear tire. Installing the BMR anti-roll bar solved this problem.

Our first efforts were aimed at counteracting these forces by tuning the shocks. With a previous drivetrain, this car had less power, a tight converter, and less gear, so the tuning effects weren’t as critical. Now with more power, more gear, and a looser converter, this created a much harder launch – and tire spin. The QA1 double-adjustable shocks allowed us to make separate adjustments to the compression and rebound valving. Let’s define these terms.

When a car hits a bump, this compresses the spring and pushes the rod into the shock absorber body. This is called “bump” or “compression” movement of the shock. When a car accelerates, the frontend rises and extends or pulls the rod out of the body of the front shocks. This is called “rebound” or “extension”. We’ll use the compression and rebound terms.

The shock’s job is not to “absorb” movement but rather to control the rate of change of this movement. So if our front shocks were extending (in rebound) too quickly on the starting line, it would help to slow the rate of extension – especially in the left front. To accomplish this, we increased the number of clicks on the rebound setting of both front shocks. The QA1’s have a range of 18 total adjustment settings (“clicks”). For our first session, we started with the shocks roughly in the middle of their adjustment on both compression and rebound and stiffened the rebound with 6 clicks (12 total) on the left front and 3 (9 total) on the right.

Later in the first session, we changed the rear shock setting by stiffening the compression setting on the right rear shock by four clicks for a setting at 12. The idea was to stiffen the compression side to minimize the squat on the initial launch. The combination of these changes helped the car run a much quicker 60-foot time of 1.718 with an 1/8-mile 7.14 e.t. This was a significant improvement over the initial 7.34 on run number two, but still not great.

Here is the BMR bar installed on the Strange S-60 rear axle assembly. The S-60 uses the same diameter axle tubes as a 12-bolt so it bolts right up. The only fabrication required is bolting the frame brackets to the rear crossmember.

While the shock tuning helped reduce the twist induced into the chassis, the real fix required a more permanent change with an anti-roll bar. We installed a bar made by BMR for the second test session. This is a massive 1 3/8-inch diameter solid bar that connects the rear axle to the crossmember with adjustable rod ends. We added this bar with zero preload, meaning we adjusted both rod ends with the same thread engagement with the car sitting on the ground with driver weight in the car. The downside to this bar is that it is a heavy rascal at 40 pounds.

In our second test session, we made some minor changes to the shock settings which along with the BMR bar improved both the 60-foot and 1/8-mile times. All these chassis tuning efforts were part of a separate test we were doing with a new TH400 transmission that John Kilgore calls his SuperLite 400. By the end of session two, we felt we had created repeatable numbers so the next change was to add the new transmission.

We found that increasing the compression stiffness on the rear shocks helped the car with a better 60-foot.

This trans uses the same ratios and the same torque converter but Kilgore reduces the rotating mass in the transmission by roughly 16 pounds. The idea is that this reduced spinning mass should allow the car to launch harder and run quicker. We expected this trans to put slightly more power to the rear tires so for the third session we also changed to a taller set of M&H 28-inch tall tires borrowed from our buddy Scott Gillman.

On the first pass in session three, the change to this new trans was especially noticeable in First gear. Part of this upgrade is a reverse valve-body shift pattern, positioning First gear where Third (Drive) used to be. This demands the driver pull the shifter back instead of pushing forward. Unfortunately, author/driver muscle memory pushed the shifter forward from First gear into neutral on the first pass. This resulted in the tach needle zinging past 8,000 rpm. No parts exited the oil pan so we thought we had dodged a bullet.

The anti-roll bar mounting links should be installed with the car at ride height with driver weight in the car. Sliding the bolts into place creates a zero preload condition, which is where we started.

On the second pass, the car now launched evenly with no more body twist. Before we arrived at the track, we softened the rebound on the front shocks to a 10 setting with the compression at four. This represents multiple changes, which isn’t really the right way to do things, but that’s what we did.

It was difficult to get the car to launch with the shorter 26-inch tall Mickey Thompson tires so we borrowed a set of 28-inch tall radials. The taller tire effectively reduces the overall gear ratio from 4.10:1 to around 3.81:1 but plants more tread area on the track.

The second pass was initially encouraging with a 1.644 60-foot that felt good. However, on the next pass, the car fell back into its old tire spin habits. We tried softening the rear compression setting to see if this would help but the car ran even slower, so for run four we returned the compression setting on the rear shocks and lowered the tire pressure from 19 to 17 psi and this helped to pull a 1.626-second 60-foot time. Considering that we had reduced the overall gear ratio with the change to the taller tire, this was a move in the proper direction.

With the shocks tuned and the rear anti-roll bar in place, we managed a best 60-foot time of 1.578 which is roughly 0.20-second quicker than where we started. Note the rear tire is not planted hard, which indicates we could run lower pressure and perhaps move the instant center location to “hit” the tire harder.

In the last pass of the night, the Chevelle delivered a 1.629-second 60-foot time on the way to a 7.014 / 99.71 mph pass. This was encouraging. All we had to do now was work on consistency. We can relate 1/8-mile e.t. to ¼-mile numbers by multiplying by 1.54. In this case, that equates to a 10.80. For a quarter-mile mph, we multiply the 1/8-mile speed times 1.24 which estimates our quarter-mile trap speed at 123.6 mph.

These adjustable upper control arms from Global West (arrow) can make adjusting the pinion angle easy.

Session four started out just this side of awesome. In the warm, late afternoon air, our very first pass produced its best 60-foot of 1.578 followed by a new-best 1/8-mile pass of 6.982 at 99.56 mph. But apparently this was just a tease because on the next pass the tire spin returned. Passes three and four were close with 1.62 and 1.60-second 60-foot times but the car could not duplicate the earlier quick 1.57 60-foot time

These support bars are critical and should be among the first changes to any Chevelle that will see drag strip abuse. This strut connects the lower front and upper front control arms to prevent tearing the welds in the upper crossmember. This malady is actually quite common in small-block cars. All early factory big-block Chevelles came with an OE version of this support.

Before session five, we made more changes. We stiffened the rebound on both front shocks up two clicks to 12, leaving the compression at four. Later we realized we had never tested the rebound in the rear which was an oversight. The session began with great expectations that were quickly dashed after the first pass when the engine began exhibiting serious blow-by symptoms consistent with a broken piston. The breathers were puffing like a tiny steam engine and after the second run, we called it quits. We yanked the engine that weekend and discovered a badly broken top ring land on number 7 piston. This was the result of that previous over-rev.

Our testing came to an end with this result of our driver-error-induced over-rev. To paraphrase WWII general Douglas MacArthur “We shall return…”

If we use the 1.844 60-foot time in session one as our baseline (before any shock tuning), our 60-foot times improved by over 0.25-second through the addition of double adjustable shocks, a taller rear tire, and a rear anti-roll bar. Note that in session two we ran that 1.576 with the shorter tires but were never able to duplicate that time. We eventually came within 0.002-second with the taller tires after the trans swap.

It’s likely the car is capable of low 1.50 60-foot times with additional tuning, including adjusting the pinion angle. Armed with these ideas, we think the Orange Peel can squeeze itself into the low 1.50s. It’s all part of the game.

E.T. Charts

Session One

Run

60-ft

330’

1/8th

MPH

Comments

1

1.865

4.921

7.454

96.92

Spun badly, tires – 18 psi

2

1.844

4.851

7.34

98.40

Spun, tires – 16 psi

3

1.718

4.666

7.14

98.70

Shock tuning  – better 60-ft

Session Two

Added BMR rear anti-roll bar

Run

60-ft

330’

1/8th

MPH

Comments

1

1.576

4.773

7.661

88.91

Hooked – spun at 100’ 16 psi

2

1.807

5.019

7.586

95.92

Spun tires again

3

1.627

4.577

7.053

98.82

Shock tuning F & R

4

1.630

4.578

7.051

98.98

No changes –Best run

Session Three

Added Kilgore SuperLite trans and 28-inch rear tires were the major changes going into this session. Rear tire change from 26-inch to 28-inch changed the effective gear ratio from 4.10 to 3.81

Run

60-ft

330’

1/8th

MPH

Comments

1

1.975

5.168

7.788

94.72

Driver error, 28” tires

2

1.644

4.654

7.224

95.93

Short-shifted 2nd

3

1.998

5.524

9.837

51.88

Spun –lifted

4

1.626

4.564

7.028

99.46

2nd Best

5

1.757

4.716

7.184

99.40

Slower 60’

6.

1.629

4.557

7.014

99.71

No changes

Session Four

Run

60-ft

330’

1/8th

MPH

Comments

1

1.578

4.518

6.982

99.56

Best Pass

2

1.771

4.823

7.314

98.48

Tire spin

3

1.624

4.565

7.030

99.37

0.005 off best 60’

4

1.603

4.553

7.026

99.11

2nd best 60’ – lost mph

5

1.690

4.671

7.141

99.17

Slow 60’

60-foot times still inconsistent even with the taller tire, note mph slowed by session end – the engine was losing power.

Session Five

Run

60-ft

330’

1/8th

MPH

Comments

1

1.792

4.891

7.503

98.15

Engine blow-by

2

1.704

4.751

7.339

97.21

Broken piston

Shock Settings by Test Session

Numbers in parenthesis are changes during that session*

Sessions

Left

Front

Right

Front

Left

Rear

Right

Rear

Session 1

Comp

8

8

8

8 (12)

Rebound

6 (12)

6 (9)

8

8

Session 2

Comp

4

4

8

12

Rebound

12

9 (11)

8

8

Session 3

Comp

4

4

8

8

Rebound

10

10

6

6

Session 4

Comp

4

4

11

11

Rebound

10

10

4

4

Session 5

Comp

4

4

11

11

Rebound

12

12

4

4

Parts List

Description

PN

Source

QA1 double adj. shocks, front

TD-507

Summit Racing

QA1 double adj. shocks, rear

TD-804*

Summit Racing

Global West upper front control arms

TLC-42

Summit Racing

Global West lower front control arms

TLC-42L

Summit Racing

Global West lower rear control arms

TBC-4

Summit Racing

Global West adj. upper control arms

TBC-47

Summit Racing

Global West rear crossmember support brkts.

TS-47

Summit Racing

Global West bump stop limiter kit

TLC-1100

Summit Racing

BMR rear anti-roll bar

XSB-006R

Summit Racing

TD-801 is the normal application for a Chevelle. This is a longer rear shock to allow sufficient rear suspension travel – the application is a 1990 S-10 pickup.

About the author

Jeff Smith

Jeff Smith, a 35-year veteran of automotive journalism, comes to Power Automedia after serving as the senior technical editor at Car Craft magazine. An Iowa native, Smith served a variety of roles at Car Craft before moving to the senior editor role at Hot Rod and Chevy High Performance, and ultimately returning to Car Craft. An accomplished engine builder and technical expert, he will focus on the tech-heavy content that is the foundation of EngineLabs.
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