Pontiac GTO Forum banner

1 - 11 of 11 Posts

·
Registered
Joined
·
417 Posts
Discussion Starter #1
Hey Guys,

I am looking to take the 66 up to BIR this weekend to make a few runs on the 1/4 mi. While I can do a great job setting the car up to turn left, I have never been on the 1/4 mile!

My intent is to just go and have some fun, seeing what kind of speed I can get with a non-race setup on street tires. But... to get the most from what I have, what are your thoughts on tire pressure and air-bag pressure?

Here are the basics:

--4spd
--3.31 Chevy 12 bolt
--rear air bags with separate air lines
--255/60/15 Goodyear GT street radials.

Any other suggestions?

Thanks! Hopefully the car will make the 2hr drive back home afterwards...
 

·
64-67 Expert
Joined
·
8,561 Posts
I'm no pro drag racer, but from what I've read, you want a bit more pressure in the passenger side bag. I'd start with about 8psi in the driver's side and 12-15 psi in the passenger's side bag. As for tire pressure with street rubber, I'd drop it down to 25-26 psi....if you go too low you risk spinning the tire on the rim or breaking more driveline parts, if you hook up really solid. You might want to start out by leaving at about 2500-3000 rpm with some feathering of the clutch to help traction. In a 1966 article I have, they drag test a near new '66 GTO and their launch technique was simply to drop the clutch at 5200 rpm off the line. They had slicks, though, and netted mid 12's with the bobcatted car. If you dump the clutch at high rpm, all you'll get is a lot of wheel spin and a slow time. It takes a lot of practice, and a lot of trial and error to get the best out of the car AND the driver. I think the biggest thing is timing your leave....you don't want to red light, but you don't want to wait for the green, either. It's an exact science. Someone with much more experience than I is sure to chime in with some good advice, though.
 

·
Former Super Moderator
Joined
·
9,919 Posts
Drive around the water burnout area and keep the tires dry for the burn out. With treaded tires the water will run down the treads at the starting line and you can actually start out in a puddle. I was dropping the clutch at about the second to last yellow light before the green. Also I could not come out of the hole hard as I would just light up the tires, so I would just leave the line like I was at a traffic light and then nail after the car got moving.
I drove about 2.5hrs to the strip, ran all day, and drove home after words. :cheers
 

·
Super Moderator
Joined
·
5,744 Posts
:agree Rukee's experience with a 4-speed car hits all the significant points.
The challenge is keeping the tires right on the edge of breaking loose without actually spinning. It's a property of physics that it takes less force to keep a tire spinning than it does to start it spinning, so the ability to ride that edge will net you the best launches and best e.t.'s.

Once you learn how to do that, the second piece of the puzzle is tuning your reaction time. You want the car to be moving such that the second staging beam "reconnects" the exact instant that the green light comes on.
(There are two beams, pre-stage and stage. As you roll forward, the tire breaks the pre-stage beam first and turns on the top bulb of the tree. As you keep rolling forward, the tire breaks the stage beam and lights the next bulb. Depending on how large your front tires are, you've got "some distance" you can roll and still keep both bulbs lit. "Deep staging" is when you roll forward far enough that the pre-stage beam turns back off, but the stage bulb stays lit. If you allow the stage bulb to turn off before the tree goes green, that's a red light and you lose. If you take a nap and let a bunch of time go by before launching the car, you can run a perfect e.t. and still get smoked.)
You have to learn how to be consistent - picking a point in the tree count-down where you launch the car such that by the time the engine has responded, taken all the slack out of the drive train, started the car moving, and the car has moved far enough to turn off the stage bulb.... all that has happened such that the bulb goes out the instant the tree goes green. When you see your reaction time printed on your time slip, that's how much time passed between the green light and the stage bulb turning off (because your front tires moved out of the beam).
You want that to be a very small number - like .040 or less - and learning how to do that every single time requires a car that's consistent and a driver who knows exactly how "far" to roll into the beams and how to begin the launch at exactly the right time in the countdown. It's not easy, especially with a gallon of adrenaline dumped into your system from the excitement.
One approach is to always launch your car at exactly the same time. (Like the instant you see the last yellow turn on) and then "tune" your staging depth to adjust your reaction time. Stage "shallower" (don't roll in as far) if you're going red, stage "deeper" (roll in farther) if your reaction times are too long.
Depending on your car and your own physiological reaction times, you might have to adjust your 'starting point' to go some time on the middle yellow (when you see it start to go out, etc.) or later on the last yellow if you and the car are both extremely quick.
How important is it? Very. A difference of .01 at the tree can translate to a margin of .1 at the finish line.
It's why some racers invest in expensive electronic delay boxes and transmission brakes. With a delay box/trans brake car, you set a time into the box and then you always "leave" on the first yellow (because humans are more consistent that way). The delay box will then continue to hold the trans brake until the set time has passed, then release the trans brake and allow the car to launch.

There's more to it than meets the eye, but it's also an opportunity to have a lot of fun while you're learning, practicing, and improving. :cheers


Bear
 

·
Registered
Joined
·
417 Posts
Discussion Starter #5
Geez Bear, thats a lot to think about :) I like the process back in high school better... Two cars line up on the line (painted across the 2 lane country road) and another guy drops his arms to go. Thanks for the advice everyone, I will plan on reporting back with how the weekend goes!
 

·
Registered
Joined
·
417 Posts
Discussion Starter #7
Well, it was an interesting (and fun) day! I ran the stock/trophy class, and my first run had a red light reaction time of -.002 (so close!) I had absolutley NO traction. It was like I had a single axle running in the rain. Worst part was I look over to my right as I was going to shift into 2nd, and the teenage girl driving a stock Ford Focus was right there! Fortunetly, the car hooked up at that point, and ran a 15.4 @ 98mph. I did beat the Focus...

It seemed like my posi was not even working, as the launch was slow & straight. I then added air to my right air bag, and lowered the tire pressure to 25lb. Since I had no idea where I was at after the first bad run, I estimated my time at 15.0. 2nd run reaction time was a little slow at .2, but the posi hooked up, and the rear of car jumped out with severe wheel hop. After getting that settled down, I finished with a 14.4 @101mph.

I was happy with the speed considering the slow launch and my mild-cammed motor. The 17 second buick in the other lane beat his time by .2, but was better than my + 1sec run!

Good news was that it was in one piece for the 110 mile trip home, which netted 16.5 mpg driving 60mph!

Defintely going to try this again!
 

·
64-67 Expert
Joined
·
8,561 Posts
Mid-low 14's is very respectable for a street car. Back when these cars were new, the times were similar, with experienced drivers. Not bad at all. And, more importantly, you're out there doing it.
 

·
Premium Member
Joined
·
217 Posts
I had that fun last week for the first time, just a test and tune night but so addicting! After the fuel delivery problem I had, I ordered a new Holley 850. Speed shop just called and said its in, can't wait to try it out! I had a great "gearhead" weekend as I got to meet and talk with Don Garlits and had him sign my GTO hat next to Arnie Beswick at a local show on Saturday then seats in the 10th row on the starting line for the Route 66 Nationals in Chicago (Joliet.) Took a few videos on my phone, including one at the finish line of John Force blasting by at 322 mph in his funny car, and another of Tony Schumachers engine exploding at the finish line of the top fuel dragster championship. It was awesome.
 

·
Registered
Joined
·
417 Posts
Discussion Starter #11
Had an open Saturday, so what better way to spend it than at the track? Since my last run, I had installed a longer duration solid flat tappet cam, but the biggest change came from added traction with new rear control arms, including adjustable uppers. Initially, my pinion angle was about 2 degrees in the wrong direction, now I have the trans & pinion at 3 degrees in opposite directions.

I ran a best of 13.94 on my street tires, so I was VERY happy to break 14! However, the street trophy class I was in cannot exceed 14.0. Here is my elimination run where I let a .008 reaction time go to waste! I was gaining too fast on the other guy and let out of the throttle a little too much and he edged me out.

GTO run - YouTube

Being an old circle track guy, I never knew this much thought had to go into a "street trophy" class at the drag strip!
 
1 - 11 of 11 Posts
Top