NHRA - National Hot Rod Association

At every NHRA national event, NHRA announcer Alan Reinhart offers fans the chance to send him an email with technical questions about the race cars, the tracks, and the procedures. As part of a semi-regular feature, we’ll share those questions and answers on NHRA.com.

Fan can write to Reinhart at announcer@nhra.com.

Here we go!

Noticed the wheels on Al Balooshi's Pro Mod wheelie bars are different sizes — not seen that on other cars and classes. I'm guessing there is a perceived torque advantage but any other thoughts? — Tony Wilson 

They always offset (stagger) the wheelie bars so that the right side is lower. The bars will "steer" the car off the starting line, and that offset is critical. With the Pro Mods, it is a bigger offset than Pro Stock as with more power you need a bigger stagger. 

It was getting to the point where the offset was so much that the bars were in a bind, so they decided to go with a smaller wheel on the left, and that opened the window for more adjustment without putting the bars in a bind.

Why do some Top Fuel cars have open-roof cockpits, some closed-roof? Wouldn't the open cockpit affect aerodynamics negatively? — Jake Lipinski

The canopy is allowed but not required. Some think it is safer, some think it could be the opposite depending on the circumstance. The canopy is heavier.

From an aerodynamic standpoint, there is very little if any difference. The windshield on an open car is high enough to direct the air over the opening, so there's no disadvantage there.

I’ve noticed that after the fuel cars finish their burnout and pull forward to pull the throttle stop, etc., the tuners appear to pull plugs from under the injector hat. What are these for? I apologize if you’ve answered this question before. — Larry Wilson 

That's how they adjust the idle speed. They are plugging or unplugging air bleeds. If you need to idle a little higher, you remove a plug to give it more air. Or replace one if you need the idle lower.

Because they can't adjust the butterflies for airflow like you would on a regular engine, that's how they do it.

I've noticed on the struts of Top Fuel cars and the rear of some funny cars there appears to be something similar to shoelaces, maybe about a foot and a half long. What is their purpose? — Rich Smitas

Those are the strings they use when they pack the parachutes. It's used to pull the tether through when they slip the cable in that deploys them. They don't weigh anything, so they just loop them around the strut. That way there are always right where they need them. I think it's kind of funny that many cars have two of them, even though they only pack one parachute at a time.

What is the purpose of the designated pairs in Stock and Super Stock, and how are they determined? — Rob Giroux

The purpose is to get them moving in the morning. Often nobody wants to be the first car down the track, so they would sit in the back off the lanes and refuse to pull forward until "someone else did."

The three designated pairs have to go first, then the rest will fall right in behind them.

They are the three slowest qualifiers and whoever they are paired with. One reason that it's common to have singles is because if you break while qualifying, you might end up last, so you are designated, and whoever you matched up with on the ladder gets the single, but still has to be one of the first down the track.

When the tractors are scrubbing the track with the tires that rotate backwards, does it matter if they are scrubbing rubber toward the start line or away from the start line? — Tom Amidon

It does not matter, and it has been analyzed to death, when they groom the track, it is like sanding a board. Going sideways would be different, but north and south (going with the grain), it delivers the same finish.

Ask Alan archive