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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.