NHRA, why do they rebuild the motors after each run?

[DEL65]

I was at the Autolite Natls on Friday. Way cool. For years I have always wondered why they feverishly rebuild the nitro-fueled motors after each run. Wouldn't it be easier just to show up with 4-5 long blocks each weekend and just swap the intake/blower. Is there some NHRA rule that prevents it.

 

[Sacbill]

I know if they brought 4-5 long blocks they'd been invested for way a lot of money. My understanding is that they like to get the most use out of the parts they can, and rebuilding every time helps them to make sure everything's cleaned up and ready to go. In theory, they don't HAVE to rebuild the motor, but the nitro classes do, probably just because they're running the bejeezus out of them.

One interesting thing I learned a couple of years ago at a race is that Pro Stock DOESN'T like to swap or rebuild a motor during an event. They'd rather keep the same motor in, tuned just to where it needs to be. A new motor needs testing and tuning to get it just right, and they don't want to deal with that on a race weekend.

On a related note, why didn't you tell me you were interested in Sears Point? johnpro and I went yesterday, and we could have set it up to all go at the same time.

Maybe next year? RV? Full weekend? :toot

 

[tarafied1]

Here are some amazing facts about nitro-burning engines:
* Under full throttle, a dragster engine consumes 11.2 gallons of nitro methane per second; a fully loaded 747 consumes jet fuel at the same rate with 25% less energy being produced.

* A stock Dodge Hemi V8 engine cannot produce enough power to merely drive the dragster's supercharger.

* With 3000 CFM of air being rammed in by the supercharger on overdrive, the fuel mixture is compressed into a near-solid form before ignition. Cylinders run on the verge of hydraulic lock at full throttle.

* At the stoichiometric 1.7:1 air/fuel mixture for nitro methane the flame front temperature measures 7050 degrees F.

* Nitro methane burns yellow. The spectacular white flame seen above the stacks at night is raw burning hydrogen, dissociated from atmospheric water vapor by the searing exhaust gases.

* Dual magnetos supply 44 amps to each spark plug. This is the output of an arc welder in each cylinder.

* Spark plug electrodes are totally consumed during a pass. After 1/2 way, the engine is dieseling from compression plus the glow of exhaust valves at 1400 degrees F. The engine can only be shut down by cutting the fuel flow.

* If spark momentarily fails early in the run, unburned nitro builds up in the affected cylinders and then explodes with sufficient force to blow cylinder heads off the block in pieces or split the block in half.

* Dragsters reach over 300 MPH before you have completed reading this sentence.

* In order to exceed 300 MPH in 4.5 seconds, dragsters must accelerate an average of over 4 G's. In order to reach 200 MPH well before half-track, the launch acceleration approaches 8 G's.

* Top Fuel engines turn approximately 540 revolutions from light to light!

* Including the burnout, the engine must only survive 900 revolutions under load.

* The redline is actually quite high at 9500 RPM.

* THE BOTTOM LINE: Assuming all the equipment is paid off, the crew worked for free, & for once, NOTHING BLOWS UP, each run costs an estimated $1,000 per second.

The current Top Fuel dragster elapsed time record is 4.441 seconds for the quarter-mile (10/05/03, Tony Schumacher). The top speed record is 333.00 MPH (533 km/h) as measured over the last 66' of the run (09/28/03, Doug Kalitta).

 

[DEL65]

Thanks for the info, especially the facts. Amazing stuff.

Hi Bill, I didn't call you, because I went with the Modesto guys on Friday. It wasn't too crowded. Got some pics with Cory Mac, Tasca III, Mike Neff, and Jason Line. Although there were very few hotties to eyeball, it was a great day. I'll try to post a few pics.