The Technical Questions Thread

[Ferrer]

Another one, I see that the Phantom used to use the 6.75L V8 but now uses a 6.75L V12. Other than smoothness, engine size, balance, and I assume revability, what sort of other characteristics will change about the engine? Higher redline? What about peak torque and hp? Keep in mind I am speaking in generalities.

Thanks in advance.

The new Phantom never used the old Rolls V8. It has also used a derivation of BMWs V12.

[LeonOfTheDead]

The new Phantom never used the old Rolls V8. It has also used a derivation of BMWs V12.

same for the Silver Seraph

What is the torque split on Lambo's AWD system and can it be varied a la some other systems?

in the Murcielago, iirc, about 6% fo the torque goes at front wheels normally, up to 40% (or maybe even 50%) when required

[Kitdy]

The new Phantom never used the old Rolls V8. It has also used a derivation of BMWs V12.

I am aware; I meant an old Phantom, the Phantom VI, or even other 6.75L Rollers. Shoulda been more precise in my statement I suppose.

[Ferrer]

I am aware; I meant an old Phantom, the Phantom VI, or even other 6.75L Rollers. Shoulda been more precise in my statement I suppose.

Ah yes well. Probaby one of the main reasons was that I don't think BMW owned the rights of the old V8 and that the V12 was far cleaner.

[LeonOfTheDead]

Ah yes well. Probaby one of the main reasons was that I don't think BMW owned the rights of the old V8 and that the V12 was far cleaner.

I think it was related to the fact that even the previous Silver Seraph used that V12 from BMW, so probably, as you said, they didn't acquired the rights leaving them to VW

[Kitdy]

Ah yes well. Probaby one of the main reasons was that I don't think BMW owned the rights of the old V8 and that the V12 was far cleaner.

This does not answer my question much - I'm more concerned with the technical differences between the V8 and V12 - I suppose emissions is one of them. I guess I was really wondering more hypothetically the differences between vaguely ideal and equally sized V8s and V12s.

[Ferrer]

This does not answer my question much - I'm more concerned with the technical differences between the V8 and V12 - I suppose emissions is one of them. I guess I was really wondering more hypothetically the differences between vaguely ideal and equally sized V8s and V12s.

That aside, the V8 and the V12 are quite different. One is (was) a turbocharged pushrod engine with 2vpc and the V12 is a modern normally aspirated unit with direct fuel injection and 4vpc.

However as far as the ultimate smoothness is concerned I'm sure the V12 is better, since it's a more inherently balanced configuration than the V8. And as for the power, well the V8 is turbocharged so despite the deficit in technology it can make it up with boost.

[Kitdy]

That aside, the V8 and the V12 are quite different. One is (was) a turbocharged pushrod engine with 2vpc and the V12 is a modern normally aspirated unit with direct fuel injection and 4vpc.

However as far as the ultimate smoothness is concerned I'm sure the V12 is better, since it's a more inherently balanced configuration than the V8. And as for the power, well the V8 is turbocharged so despite the deficit in technology it can make it up with boost.

Carfolio seems to indicate that the V8 in the Phantom VI was naturally aspirated - as I'd figured and I was more comparing the NA version as it's more like vs like even though the two would be vastly different.

No less, my question about theoretical engines remains.

[LeonOfTheDead]

Carfolio seems to indicate that the V8 in the Phantom VI was naturally aspirated - as I'd figured and I was more comparing the NA version as it's more like vs like even though the two would be vastly different.

No less, my question about theoretical engines remains.

I think I've already answered somewhere in this forum the differences between engines with the same displacement but different number of cylinders and vice versa, same displacement per cylinder but different number of them.
I don't have my notes and books on the subject here with me now, so I'll pass the calculations and precise ratios, but theoretically, which is quite far from the reality, a V12 would be more powerful than an equally sized V8 or even V10, V6, I4, B6 and so on.
that's true only in an ideal word, and with similar engines taken into count, so forget about comparing a turbocharged one and a naturally aspirated one.

In the real world, petrol engines, especially NA ones, and even more those without direct injection, suffer of a too large bore due to flame quenching and other issues resulting in an extinguished flame front. That's why naval engines and power generators usually are diesel ones.
then, quite obviously, every cylinder requires a number of auxiliary mechanisms reducing the overall efficiency, so the more cylinders you have, the less efficient, mechanically, the engine will be.
that's why we don't have 2 liter V12, even if they existed. iirc, Connaught was programming a 2 liter V10 now that I think about it.
An high specific power is very difficult to obtain in a large displacement engine, for a combination of those two factors also, and the same is for its revving capability, due to the weight of the masses that has to be moved.

Consider the specific displacement with a 6 3/4 liter engine, a V12 is of course a better engine, from a theoretical point of view. but the differences between each engine could be so many that perhaps even an I4 could be better than the V12 in the end.
without even considering electronics.

[NSXType-R]

Hey, can a mod change the thread title? It seems a little stupid to be calling it "My" technical Questions Thread. Just lop off the My. It's better if the thread belonged to everyone.

[cmcpokey]

changed.. i was actually thinking of doing that yesterday anyway, but since you asked it just validated my thoughts. so cheers.

[NSXType-R]

changed.. i was actually thinking of doing that yesterday anyway, but since you asked it just validated my thoughts. so cheers.

Thanks. I never thought this thread would ever last this long.

[ruim20]

Question, do Top Fuel Dragster obey to any kind of limiting regulations? apart from safety? Engine size etc? i know that they had a limit on fuel nitro mixture.

Is Top Fuel the fastest a 'car' can accelerate?

[culver]

Question, do Top Fuel Dragster obey to any kind of limiting regulations? apart from safety? Engine size etc? i know that they had a limit on fuel nitro mixture.

Is Top Fuel the fastest a 'car' can accelerate?

Lot's of rules just like any other class. The engine displacement is set. The engines must use a belt driven supercharger, no turbos. They can not use computer controlled clutches.

To the best of my knowledge they are the fastest accelerating wheel driven car. That is some other things might accelerate faster but they don't do it via rubber on the road.

Here are some more fun ones:
This list has been around for a while and I don't know the original source

dunno if this a repost... search turned up nothing.
Top Fuel Facts...

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Some real cool facts about top fuel dragsters I stumbled across.....

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* One dragster's 500-inch Hemi makes more horsepower then the first 8 rows at Daytona.

* Under full throttle, a dragster engine consumes 1 1/2 gallons of nitro per second, the same rate of fuel consumption as a fully loaded 747 but with 4 times the energy volume.

* The supercharger takes more power to drive than a stock hemi makes.

* Even with nearly 3000 CFM of air being rammed in by the supercharger on overdrive, the fuel mixture is compressed into nearly-solid form before ignition. Cylinders run on the verge of hydraulic lock.

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

* At stoichiometric (exact) 1.7:1 air/fuel mixture (for nitro), the flame front of nitromethane measures 7050 degrees F.

* Nitromethane 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.

* 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 off its fuel flow.

* If spark momentarily fails early in the run, unburned nitro builds up in those cylinders and then explodes with a force that can blow cylinder heads off the block in pieces or blow the block in half.

* Dragsters twist the crank (torsionally) so far (20 degrees in the big end of the track) that sometimes cam lobes are ground offset from front to rear to re-phase the valve timing somewhere closer to synchronization with the pistons.

* To exceed 300mph in 4.5 seconds dragsters must accelerate at an average of over 4G's. But in reaching 200 mph well before 1/2 track, launch acceleration is closer to 8G's.

* If all the equipment is paid off, the crew worked for free, and for once NOTHING BLOWS UP, each run costs $1000.00 per second.

* Dragsters reach over 300 miles per hour before you have read this sentence.

Did you know …

… that the nitromethane-powered engines of NHRA Top Fuel dragsters and Funny Cars produce approximately 7,000 horsepower, about 37 times that of the average street car?

… that one cylinder of the eight cylinders of a Top Fuel dragster or a Funny Car produces 750 horsepower, equaling the entire horsepower output of a NASCAR engine?

… that the gasoline-powered engines of NHRA Pro Stock cars produce about 1,200 horsepower, about eight times that of the average street car?

… that an NHRA Top Fuel dragster accelerates from 0 to 100 mph in less than .8-second, almost 11 seconds quicker than it takes a production Porsche 911 Turbo to reach the same speed?

… that an NHRA Top Fuel dragster leaves the starting line with a force nearly five times that of gravity, the same force of the space shuttle when it leaves the launching pad at Cape Canaveral?

… that an NHRA Funny Car is slowed by a reverse force more than seven times that of gravity when both parachutes deploy simultaneously?

… that NHRA Top Fuel dragsters and Funny Cars consume between four and five gallons of fuel during a quarter-mile run, which is equivalent to between 16 and 20 gallons per mile?

… that NHRA Top Fuel dragsters and Funny Cars use between 10 and 12 gallons of fuel for a complete pass, including the burnout, backup to the starting line, and quarter-mile run?

… that NHRA Top Fuel dragsters and Funny Cars travel the length of more than four football fields in less than five seconds?

… that NHRA Top Fuel dragsters can exceed 280 mph in just 660 feet?

… that from a standing start, NHRA Top Fuel dragsters accelerate faster than a jumbo jet, a fighter jet, and a Formula One race car?

… that a fuel pump for an NHRA Top Fuel dragster and Funny Car delivers 65 gallons of fuel per minute, equivalent to eight bathroom showers running at the same time?

… that the fuel-line pressure for NHRA Top Fuel dragsters and Funny Cars is between 400 and 500 pounds, about 20 times greater than the pressure on passenger-car fuel pumps?

… that depending on size and angle, the large rear wing on an NHRA Top Fuel dragster develops between 4,000 and 8,000 pounds of downforce?

… that the 17-inch rear tires used on NHRA Top Fuel dragsters and Funny Cars wear out after four to six runs, or about two miles? Some brands of passenger-car tires are guaranteed for 80,000 miles.

… that it takes just 15/100ths of a second for all 7,000 horsepower of an NHRA Top Fuel dragster engine to reach the rear wheels?

… that it's desirable for an NHRA Top Fuel dragster to race with its front wheels inches off the ground for about the first 200 feet of the run? This ensures proper weight transfer to the rear wheels, a crucial part of a good launch and quick run.

… that the nitromethane used to power the engines of NHRA Top Fuel dragsters and Funny Cars costs about $30 per gallon?

Sources: NHRA Communications and Technical Departments, NHRA race teams, motorsports equipment manufacturers (and boostedpimp)

And some more from Paul Van Valkenburgh

Horsepower measured from the driveshaft torque (actual measured power, not estimated or dyno) was 6000hp off the line and peaks just under 8000hp.

Engines run 40% more fuel than they can burn. The extra fuel is used to cool the motor. His article quotes 70gpm flow rate. But the fuel pumps are variable to control power. It takes 30hp to drive the pump.

The other article states that a HEMI motor couldn’t drive the supercharger. This article supports that saying it takes almost 800hp to drive the air pump. For calibration they spin up a 1700lb flywheel to 8000 RPM then engage a clutch driven overdrive that spins the supercharger 11,500RPM. Peak boost is about 50psi.

Downforces: As the car starts the tires wind up and the rear of the car drops. Almost immediately afterwards the rear starts to rise as the tires grow. The lifting of the rear of the car can add an extra 2000lb of downforce on the contact patch for a fraction of a second. The author also noted the force of the exhaust and said that he was almost knocked over while standing near a starting drag motor.

[Alastor]

Downforces: As the car starts the tires wind up and the rear of the car drops. Almost immediately afterwards the rear starts to rise as the tires grow. The lifting of the rear of the car can add an extra 2000lb of downforce on the contact patch for a fraction of a second.

That is interesting, there really is a lot going on at the tires during launch.