Doesn't he adjust the throttle blades after the burnout? Fuel flow maybe? I'm just 18, and living 10 minutes from Bristol Dragway I grew up watching Fuel cars. (IHRA to start out with )

 

No, the little allen is actually a small (like 1/4") wrench that is used to back off the jamb nut on the **** that adjusts the throttle blade opening. This adjusts the idle. Most crew chiefs adjust the idle using the fuel side (fuel shutoffs), but some, Dick LaHaie is one, adjust the butterfly angle.

The EGT's are only for data collection. None of the Pro ranks can make changes during a run by data recieved. It is only a record/playback system.

 

Cool info.

Why do they need to adjust idle? How would that affect the
performance of the engine during the run/burnout?

I would think with the huge runner volumes, the engine would
want a fairly high idle to keep from stalling out.

Do you mean, they adjust the opening 'limiters' on the throttle
blades to allow for max. flow during the run?

I've heard many times (on TV), the announcers will mention,
"enabling the second magneto".

What's up with that?

 

Well, the idle has a big effect of how the car launches. Since they launch from an idle, too high and it smokes the tires, and too low and it doesn't 'get up on the tire' and get the wheel speed necessary. They usually like to idle at about 2500 rpm.

The opening 'limiters', as you say, are on the other side of the injector and once set, they are never changed.

Well, I don't know what they mean about the second mag, because we always ran both mags all the time. I think they used to do that a while ago, but I don't know if many teams still do it.

 

"Well, the idle has a big effect of how the car launches. Since they launch from an idle, too high and it smokes the tires, and too low and it doesn't 'get up on the tire' and get the wheel speed necessary."

I figured there would be a rev limiter to set launch RPM, and clutch
adjustments to dial in the power.

From what I gather, the driver applies a brake and clutch pedal.

Once the tree lights up, the brake and clutch are released.
The car launches based on idle speed and clutch slippage?

 

No, there isn't a rev limiter at all on those cars. There is so much fuel going into those engines that there really isn't a way to use one. Drop the spark like most units do, and it will drop a hole or hydro-lock, and if it drops a hole, it's hard to pick it back up.

Well, there is a clutch pedal and a brake lever (hand brake, right side). When the driver pre-stages, he/she holds the brake and lets off the clutch fully. There is enough clearance set in the cluch that it will not engage fully with the pedal all the way out. Then the driver 'goes to the high side', which means he turns the fuel pumps all the way on with a small lever on the left side of the cockpit (They do the burnout with the pumps only about 5-10% on). This is when you hear the cars get quieter on the starting line-they have 100% fuel volume and a little load on the engine. The driver then bumps into the lights (still holding the brake), and when the lights go yellow, he mashes the gas then lets off the brake and holds on to the steering wheel while going for the ride of his life and hoping that it doesn't blow up!

 

Good call on the hydo-lock. I've read that TF motors ride on the
verge of hydro-lock.

It never occured that cutting spark would do more damage than
good.

"dropping a hole" seems like a term to describe a misfire condition
and the difficulty of getting the plugs to fire once they've been
fuel soaked and cooled down?

 

Yep, that's basically it. When a car drops a hole, you can see it by all the raw fuel spewing from the pipes. Most of the time it won't pick back up, but there are instances where it will. I remember watching video of one car (can't remember which one) where it dropped and picked up the same cylinder 3 times during the run. That is very rare and nobody really had an explanation for it.

 

So when it drops a hole you lose downforce from the burning in that pipe, right? Shouldn't that loss of downforce steer the car into the dead hole? With a hole going on and off that's got to be a bugger to keep between the lines.

On a more sour note, do you have any info on the cause of Darrell Russell's crash? I heard NHRA is talking about minimum tire pressures for the new tires, 85% nitro vs 90%, and maybe some more driver protection re: intrusion. Does that say they lost a rear tire?

 

You won't read about this in National Dragster, or hear about it on TV because the details are too gruesome. Darrell was wearing all the latest safety gear, including a HANS device as well as the new 'C' shaped stiff Nomex pad that fits tightly between the rollcage and the drivers helmet, preventing any side to side movement. The car chassis did mostly what it was designed for...when the wing broke it automatically pulled the chutes, and the chassis split just behind the driver. A Dragster chassis is also designed to split just in front of the driver capsule, but it didn't in this instance. What killed Darrell (this is very sad) is part of the wing strut went flying through the rollcage, through his helmet and through his head. If you watch the video closely you'll see a giant piece of the wing strut jabbing out the side of the rollcage. You'll also see the Safety Safari guys going crazy when they get to him, because they new before they pulled him out it was pretty much hopeless. Very sad situation.

 

OldSStroker,

If I'm not mistaken something blew up and took the tire with it. I only watched the video once or twice but that's what it looked like happened to me. I've been looking for a vid online but to no avail.

 

Yeah, you actually see the car being 'steered' in the direction of the dropped hole more in a funny car than a TF car because of the chassis design (engine placement) and header design. I'm sure on that run it was a REAL handful!!

No, I doubt NHRA will ever release the actual cause of the crash or his death. Everything that is out there right now is just hearsay and speculation.

One thing I do know is that Goodyear has been trying to get NHRA to slow the cars down for some time now. The tire in it's current design (size) is not capable of the speeds these cars are running. Goodyear has said they would pretty much have to re-design the wheel to get them to withstand the 330+ mph speeds. They say for the tire to hold up, the wheel would have to be about 34" in DIAMETER and have a short-sidewall tire on it. The obvious problem there is that the assembly as a whole would be extremely heavy and it would make mounting/dismounting a royal PITA. Not to mention they would not be able to launch how they do now.

 

This is turning out to be quite an informative post.

Here's a question and my thought. I'll need all of you to pick it apart.

I've heard that top fuel motors run about 5:1 static compression
(coming from Dean Skuza on PHR TV).

Rumor has it, boost reaches 60 PSI.

If the effective compression adding that much boost equals xxx PSI,
what is the difference between running 20:1 static compression
with maybe 25 PSI of boost?

Is this because with a lower static compression, the swept volume
is greater than that of a higher static compression?

By adding 60 PSI of boost on 5:1 Static Compression, it is possible
to jam more charge into the cylinder?

That would mean the air/fuel mixture would expand to a greater
volume once ignited and produce higher cylinder pressures for
best torque per power stroke?

Educate this naturally aspirated brain please

 

90% nitro (or 85%) burning blown TF or FC engines aren't really much like our normal gasoline eating NA or even blown gas engines.

Thoughts:

Low static CR gives more clearance volume so there is more room for nitro. Remember these things almost hydrolock (fill the clearance volume [CV]) with fuel. The nitro releases oxygen when it reacts. I guess more CV allows more liquid fuel to be injected without hydrolock if it doesn't fire.

Swept volume (displacement) remains the same, at least until you hole a piston.

More nitro (and more air) = more power. If NHRA drops the max % to 85 from 90, will the guys try to pump in more even if it meant more CV and less static CR? Anyone know what they did when it went from no limit to 90%?


As an aside, I understand that the pressure in the blower expands the case enough that the gears the drive the rotors go from almost an interference fit when not running (tooth of one gear full into into root of mating gear) to almost not engaging when at full rpm and boost (teeth just barely touching at their tips).

Everything is edgy at these power levels.

 

I would love to know; how far would a fuel motor run if the driver held the throttle open past the 1320' mark? What would be the first thing to fail?