Eliminating Restrictor Plates?

 Daytona, Engines, rear-end gear, Restrictor Plates, Talladega, transmission  7 Responses »
Oct 052012
 

Every return to a restrictor plate track brings suggestions about how we might eliminate the restrictor plate.  Restrictor plates serve the very necessary function of limiting car speeds at Daytona and Talladega so that the cars stay on the ground.  The negative is that they remove throttle response.   One suggestion from some readers that I hadn’t heard of before suggested that NASCAR could just change the rear-end gearing parameters to shift the power curve and reduce horsepower that way. Will that work?

The amount of horsepower an engine make depends on the rotation rate of the engine.  The faster the engine runs, the more combustion events and the more power generated.  This works up to a point, because if you rotate the engine really fast, you start having problems getting enough air into the engine and the power goes down.  The graph below is for a typical unrestricted engine that makes its maximum horsepower around 9300 rpm.

In order to cut the horsepower back to what you’d need to run safely on a plate track, you would need to restrict the engine to run at about 450 hp – which would mean the engine would have to rotate at about 4500 rpm.

Looking at the curve above, it’s evident that the engine is designed to run at its peak horsepower.  What dictates that curve?  Cylinder displacement, engine configuration, head configuration, etc.  But mostly  NASCAR determines the curve because of the rear end gear rules.

NASCAR engines run up to about 10,000 rpm (revolutions per minute).  Rpm is a unit that measures how fast something rotates. It’s like miles per hour, but miles per hour corresponds to a linear motion rather than a rotational motion. The minute hand on your clock, for example, makes one revolution every hour. The seconds hand makes one revolution per minute.

The circumference of a typical tires is around 88 inches.   Every time the tire rotates once, the car moves 88 inches, so 1 tire rpm = 88 inches per minute.  You can convert this into miles per hour.  Since I chose a nice round number like 88  inches for the tire circumference, it works out to a really simple equivalence:  1 tire rpm = 1/12th of a mile per hour.  This means that if you want to go 200 mph, the tires have to rotate at 2400 revolutions per minute.

The power curve above shows that the engine makes the most horsepower at 9300 rpm.  This produces a problem:  the engine is driving the car at 9300 rpm and the wheels are rotating at 2400 rpm.  That’s why you have a transmission and a rear-end gear, as illustrated at right.  The diagram shows the gear ratios for a Borg Warner MM6 manual transmission and a GU6 3.42 rear-end gear, as might be found in a Corvette.  Note that NASCAR cars are not allowed to use any gear that increase the rotation rate between the engine and the wheels.  No 5th or 6th gear, either.  1:1 is the best you are allowed — which means that the rotation rate coming out of the transmission is the same as the engine rotation rate.

At maximum speed, the transmission is using a 1:1 gear, so the only reduction occurs at the rear end gear.  A 4:1 gear means that one gear makes four rotations for every one rotation the other gear makes.  If the engine is rotating at 10,000 rpm, and it passes through a 4:1 rear-end gear, you have 2500 rpm at the tires (which is 208 mph).

The whole point of this discussion is to keep the cars at lower speeds so they stay on the ground.  Let’s say you want to limit the cars to 190 mph – that requires the wheel rotate at 2280 rpm.  We don’t want more than 450 hp, so the rear-end gear has to take the rotation rate from 4500 rpm to 2280 rpm, which means 4500/2280 = 1.97, so you need essentially a 2:1 rear-end gear.  (Just for comparison, a typical rear-end gear is 3.3-3.9, depending on the track.)

So it is possible to gear the car down so that it simply doesn’t produce as much horsepower.  It is a better solution than what we currently do?

Restrictor plates work by reducing the air coming into the engine, which means you can give the engine less gas and thus you produce less horsepower.  Gearing down would reducing the horsepower by making the engine run in a much-less efficient range.

One consequence of a lower rpm is that you would have really back problems with knocking.  Knocking happens when the air-fuel mixture auto-ignites (ignites before the spark plug fires).  Knocking is much more likely at low engine speeds because the the combustion happens so much more slowly than in a fast-running engine.

Another consequence is that my engine design friends tell me that they can probably tweak an engine, within the rules, to produce more horsepower at 4500 rpm such that NASCAR would have to further change the gear and run the engines at 3500-4000 rpm, which exacerbates the knocking problem.

I wondered whether taking the engine speed down might increase throttle response, but none of the experts I spoke with thought that it would.  The problem, they say, is that as long as cars are running at full out power, aerodynamics will dominate plate tracks.  You’d have to decrease downforce and increase drag to really make a difference.

Finally, there’s an aesthetics issue.  The sound of an engine changes with its frequency.  If you went to Indy and we blindfolded you and asked you tell us whether the car on the track was a NASCAR racecar or an Indy car, it would be easy:  Indy (and F1) cars sound like mosquitoes.  They run at about twice the speed of a NASCAR engine.  If you forced a NASCAR engine to race at 3500-4500 rpm, the car would sound like it was in pain – you’d get a low moan instead of the engine sound associated with 9000 rpm that we’ve all come to know and love.

If you were paying attention, you ought to be wondering why you couldn’t just run at very HIGH rpm – the power curve goes down on each side of the peak, so you could have the engine run at 13,000-14,000 rpm and output 450 horsepower.  The problem on that side is that NASCAR initiated the gear rule so that teams wouldn’t have to deal with the incredible stress on engine parts that have to run at those very high speeds.  High-speed engines would significantly increase the cost to teams – it would be cheaper in the end to just let them build a dedicated open (not restricted) plate track engine.

In conclusion, yes – gearing down would work in theory, but it would introduce its own unique problems that would offset the advantage.

Why was Michigan so hard on Motors?

 Chad Knaus, Engines, Hendrick Motorsports, Jeff Gordon, Jimmie Johnson, Michigan International Speedway, Tony Stewart  3 Responses »
Aug 232012
 

The Hendrick engine shop had four failures at Michigan.  The 24 and the 14 reportedly both had valve spring failures.  The worst was the 48, whose engine went south while leading with only six laps remaining.  Jimmie Johnson drove the car up to the hauler and walked back to his motorcoach with his helmet on, not talking to reporters.

I don’t blame him, especially when you realize how close he got before the motor let go.

High, Sustained RPM

Michigan is one of the tracks where the speed at which the motor rotates stays constant throughout an entire lap.  Watching the numbers from the television, most motors changed from only 7800 to 8500 rpm (revolutions per minute) throughout a lap.

Engine Diagram

Number of laps, or even miles are not the best way to gauge engine use because there is a huge difference between running at 8000 rpm and running at 3000 rpm.  What’s important is how many times a part is called upon to do it’s job.

The valves (one intake and one exhaust) are raised and lowered by the rotations of the camshaft (as shown above).  The camshaft is driven by the crankshaft.  When we say an engine is running at 9000 rpm, we mean that the crankshaft makes nine thousand rotations every minute – or 150 rotations every second.

Here’s the critical part:  The camshaft makes one rotation for every two rotations of the crankshaft in a four-stroke engine.  At 9000 rpm, the camshaft is running at 4500 rpm, which translates to 75 openings and closing of the intake (or exhaust) valve every second.  This means that the valve spring compresses and expands 75 times each second.

This is a linear phenomenon.  If the engine runs half as fast, each of these things happens half as many (37.5) times each second.  The faster the motor runs, the more movement, the more rubbing of parts and the more opportunity for pieces to break.

Watch the numbers this week at Bristol – you’ll see a much larger difference in speeds as the drivers slow down through the corners and accelerate through the straightaways.  Even more importantly, watch the changes in engine speed coming up next week at Atlanta, where you’re going to see similar high, sustained speeds.  The same issues will be in play for Charlotte and Texas.  This may just have been a case of a box of sub-optimal valve springs, or the engine shop may have been trying a more aggressive setup in preparation for similar track in the Chase.  I’m not worried – they’ll get it figured out (if they haven’t already).

By the Numbers

Let’s do a quick calculation.  The race time was 2 hours, 46 minutes and 44 seconds to run 201 laps.  There were 35 laps of caution, so (35/201=)17.4% of the race was run under caution and 82.6% of the race was run under green.

2 hours, 46 minutes and 44 seconds is 10,004 seconds.  82.6% of that is 8,263 seconds that were run under green.  If we take an average of 8000 rpm, which is 66.6 revolutions of the camshaft every second, the average valve and valve spring went through half a million up-and-down cycles.

Jimmie Johnson ran a top happy hour lap of 36.323 seconds.   Assuming an average of 8000 rpm, each lap at that speed adds another 2,421 cycles of the valve spring. Six laps means he was short 14,526 out of over a half-million cycles.  Think about sixteen valves and valve springs that make well over a million (including practices) successful executions and come up short by a few tens of thousands.

No wonder Johnson didn’t want to talk to the press.

 

Recent Restrictor Plate Posts

 Aerodynamics, Drafting, Electronic Fuel Injection, Engines, radiators  No Responses »
Jul 062012
 

Radiator Temperature vs. Pressure Setting of Pop-Off Valve

Why Radiators are so Important at Plate Tracks – The radiator pressure rules seem to change a lot at plate tracks:  here’s why…

Why Bump Drafting Seems Harder in 2012  A summary of why bump drafting done incorrectly causes so many problems

What’s a Pop-Off Valve?  One of the easiest last-minute changes for NASCAR to make is the pressure relief valve (a.k.a. the “pop-off valve”).  Here’s everything you need to know about how that affects drivers’ ability to draft.

Pocono: The Shifty Triangle

 Engines, Pocono, rear-end gear, transmission  No Responses »
Jun 092012
 
Gears2

NASCAR engines like to run at about 8000-9500 rpm (revolutions per minute); however, the tires on the car rotate around 2400 rpm at 200 mph.  The gearing in the transmission and the rear end gear reduce the rotational engine speed, with different gears providing different reductions.  When you talk about the size of a gear, you’re actually talking about the relative sizes of a pair of gears.  The gear on the left in the diagram has 20 teeth, while the gear on the right has 10 teeth, so this gear would be a 2:1, meaning that the smaller gear rotates twice every time the larger gear rotates once.

If the engine is running at 9000 rpm and goes through a 3.0 gear, the result is a 3000 rpm revolution.  Pretty straightforward calculation.  A car is just a little more complicated because there are two sets of gears. All that means is that you multiply the two gears together to find the effective reduction in speed.  In the diagram above, if you were in first gear, 9000 rpm coming from the engine would be 9000/(2.66*3.80) = 890 rpm at the wheels.  Note that the fourth gear is the smallest it’s allowed to be in NASCAR:  there’s no change in rotational speed.  NASCAR doesn’t allow overdrive, which would be a number less than one.

There is actually no rule against shifting – but there are rules about which gears you can use in the transmission and rear end gear.  The third hear in the drawing that third gear is 1.14, which is the gear you use at Pocono.  At a place like Michigan, you’d use something more like a 1.30 gear.

It’s a seemingly small difference in numbers, but it makes a really big difference in how useful third gear is on the track.  Let’s say you’re running 8500 rpm in fourth gear.  That translates to 2237 rpm (186.4 mph) at the wheels.  If you have a 1.30 gear, running the same speed of 186.4 mph, the engine would have to turn at 11,050 rpm, which is well beyond the range in which engine builders start to get ulcers.  If you want to use third gear and keep the engine at 9000 rpm, then the maximum speed would be about 150 mph.

On the other hand, if you’re only running a 1.14 gear, running at 186.4 mph requires you to run at 9,690 rpm.  All of a sudden, third gear gets useful on the track.

Remember that horsepower and torque depend on the engine speed, as the graph at left shows.  There’s a sweet spot (a peak) where you get maximum horsepower or maximum torque.  (The position of that peak changes depending on how the engine is built and tuned.)  One way of changing the engine rpm is changing speed.  Another is changing gear.

Pocono features two very long (3000+ feet) straightaways and two very flat (6 and 8 degrees) corners.  This means that drivers pick up a huge amount of speed coming into turns 1 and 2.  Turn 1 (where drivers have been entering at 211+ mph) has 14 degrees of banking – but teams are going into the 8 degree banked turn 2 at 200 mph.  You can’t take the turn that fast, so there’s a lot of slowing down going on.  Instead of staying in fourth gear and letting the engine run slower, you can shift into third gear and keep the engine in its most favorable operating range.

 

 

Engine Issues at Talladega: Vapor Lock, Gas Cans and Oil Coolers

 Cooling, Electronic Fuel Injection, Engines, NASCAR, Oil, radiators, Talladega  7 Responses »
May 072012
 

An usual number of teams “ran out of gas” or had engine troubles during the Talladega race.   The TV analysts had some ready answers for what might have caused these problems.  Their extemporaneous theories tend to elicit sighs from engine builders, who know that problems can rarely be diagnosed at the track – and even more rarely by someone who hasn’t looked at the car.

A wonderful aspect of blogging is that we’re not called to have answers on the spot like the television broadcasters and we have the leisure of time.  Let’s examine some of those theories.

The Gas Can

SPEED reported engine builders suggested that the teams weren’t getting a full tank of fuel into the car and that’s why they were running short.  This doesn’t really make sense given how fuel mileage is calculated.

Prior to putting the gas in the car, the gas can and gas are weighed.  After the fueling is complete, the gas can and any remaining gas are weighed.  The difference between those two weights is the weight of gas that actually got into the car.  This assumes that all of the gas missing from the can made it into the car.  If gas is spilled, it will affect the validity of the calculations.

Sunoco provides the teams with the density of the gasoline – how much one gallon of gas weighs.

You can calculate the volume of gas using this information.  For example, if the density of gas is 6.073 lbs/gallon and you find that you’ve put in 133 lbs worth of gas, the volume of gas that got into the tank.

(Yes, I know I’m using weight instead of mass, but as long as both the density is given in terms of weight/volume, the ‘g’s cancel and we’re OK.)

Teams know from this how much fuel they actually put into the car and they base their calculations (and what they tell the driver) on these numbers.  So even if they aren’t getting a ‘full tank’, the crew chief is well aware of it.  It doesn’t matter whether the lack of fuel is due to human error or a malfunction on the part of the gas can.  This is not a likely cause of the fuel problems we saw Sunday.

There are two places that this might be an issue:  First – if the engineer does the fuel mileage calculations incorrectly, you’re going to have the wrong prediction for the number of laps you can run.  The problem with this is that it is highly unlikely that multiple groups from different teams made the same mistake in the same direction.  The number and breadth of problems suggests something more systemic.

The second issue is that the density of fuel depends on temperature.  Fuel becomes less dense at higher temperatures, so putting in the same weight volume would mean less volume fewer molecules. (Thank you Barry!) It’s a little confusing because all of the calculations the team makes are done in terms of gallons, but that assumes a particular density. I’m checking to see whether teams take this into consideration.

Vapor Lock

Another theory proposed on the network broadcast (as a result of a crew chief comment, I believe) was “vapor lock”.

What is Vapor Lock?

Vapor lock happens when liquid fuel vaporizes (changes to a gas) prior to entering the combustion chamber.  The pumps in a fuel delivery system are designed to pump liquids, not gases.  The fuel pump cannot pump gas well, so the fuel pressure drops and fuel stops being delivered to the engine.  Since engines don’t run without fuel, the car ‘locks’.

How easily a fuel causes vapor lock depends on its vapor pressure:  the higher the vapor pressure, the more susceptible the fuel is to vapor lock.  (Although it’s not relevant to Talladega (elevation 596 feet), vapor pressure increases at high altitudes and this may also cause vapor lock at high altitudes, even when the car behaves fine at lower altitudes.)

Does EFI and/or Ethanol Cause Vapor Lock?

Vapor lock is LESS likely to happen with EFI than with carburetors.  The NASCAR carbureted system ran at low pressure and lacked a fuel pump in the fuel cell.  Those factors made it much easier for the engine to vapor lock.  The EFI system runs somewhere around 70 psi and has a fuel pump inside the fuel cell, which decreases the probability of vapor lock.

Vapor lock can happen within the engine (prior to the cylinder) or at the fuel pick-ups in the fuel cell.   The most likely place for vapor lock to be initiated would be at the fuel pick-ups because the fuel cell itself isn’t pressurized; however, the two engine builders I spoke to this morning both said that none of the data they have indicates that vapor lock was an issue in their cars.

Ethanol also makes it LESS likely that a car would experience vapor lock because ethanol has a lower vapor pressure than gasoline.  Ethanol-containing fuels are less likely to vapor lock than pure gasoline.

So What IS the Issue?

My sources suggest that high oil temperatures are causing the engine problems.  This problem is exacerbated by high outside temperatures and the reduced cooling inherent in the rules package that was implemented to prevent the two-car draft.

Two fluids help cool the engine:  water and oil.  Both are in turn cooled by the air coming in through the grille.  As the air flows in through the grille, it first encounters the radiator used for cooling the water circulating through the engine.  The air comes in at temperature Temp 1 and leaves at temperature Temp 2, where Temp2 is larger than Temp 1.  The air picks up some of the heat from the radiator and carries it away, which is why Temp 2 is larger than Temp 1.  (For more on this, see my blog on radiators)

Behind the water radiator is another cooler for the oil.  It also depends on cool air coming in through the grill.  The problem teams are having is that Temp 2 is so high that the air can’t cool the oil efficiently.  The problem is exacerbated because 1) the cooling air coming in (Temp 1) is hotter due to the outside temperature and 2) the air is warmer after passing through the water cooler because the engines are running hotter.

Thanks to the EFI data, teams can look at how the temperatures change in a much more detailed way than they could back when they relied on the driver relaying temperatures.  My engine guys report that they are seeing a difference of up to 50 °F between Temp 1 and Temp 2.  That difference is normally only 15-25 °F.  In addition, Temp 1 is higher to start with when the external temperature is high like it was at Talladega on Sunday.  (And like it no doubt will be in Daytona in July.)

Oil is a combination of different types of long-chain hydrocarbon molecules that unfortunately break down at high temperatures.  If you’ve ever heated oil on the stove above its smoke point, you’ve seen firsthand the decomposition of oil molecules due to high temperature.  The result is usually a gummy dark tar-like substance deposited on the pan surface.

The same thing happens with engine oil:  when it starts to decompose, it can’t lubricate the engine. An engine cannot run at peak power for very long without functional oil.

Yes, I did suggest that it would make sense to put the oil and water coolers in parallel instead of in series so that some of the cooler air would get to the oil cooler without having to pass through the water cooler first.  No dice – it’s been tried and deemed to be against NASCAR rules.

 

Plate Racing Rules: Getting Ready for Talladega

 Cooling, Engines, radiators, Talladega  No Responses »
May 032012
 

Most of the issues we were talking about at the start of the year regarding the measures NASCAR has taken to eliminate or reduce the two-car draft are still in play, so I thought I’d put the most important in one place as you start getting ready for Talladega this weekend.

One of the major changes is the radiator: The water capacity was decreased, which means that it can’t cool as effectively as it could with a larger volume of water. That limits how long cars can draft together in close formation, where the trailing car’s radiator is blocked and doesn’t get as much air circulating.

A related issue is the small, but extremely important limiter on the radiator called a pop-off valve This is one of the easiest last-minute changes NASCAR can make to adapt to changing temperatures — and new innovations teams have made to get around the current rules.

Finally, it seems as though bump drafting has gotten harder to do correctly. It’s all a matter of preventing cars from getting torqued. Literally.

Kansas Wrap Up: What Caused all the Engine Failures?

 Andy Randolph, Engines, Kansas, rear-end gear, transmission  5 Responses »
Apr 262012
 

The defining characteristic of the Kansas race was the surprising number of engine problems.  Many of those problems can be attributed to the change in rear gear from a 3.89 to a 4.00.  At  190 mph at a track like Kansas, your wheels make 2270 revolutions per minute (rpm).  If you watch the telemetry on the television broadcast, you know that the engine is rotating around 9500-9900 rpm.  Since the engine is attached to the wheels, there has to be something to change the rotation rate between the engine and the gears.

Gearing Up

That something is the transmission and the rear gear.  As shown at right (with the values given for a Corvette ZR-1), the engine rotation passes through the transmission and then through the rear-end gear before reaching the wheels.  A 4.00 gear means that the ratio of rpm in to rpm out is 4.00:1.  It takes four revolutions of the input to produce one revolution on the output.  If you have something rotating at 8000 rpm and you add a 4.00 gear, then the rotation is reduced to 8,000 rpm/4.00 = 2,000 rpm.

Note that NASCAR does not allow 5th or 6th gears and does not allow overdrive (when the first number is smaller than the second).  The lowest gear you can have is 1:1 in NASCAR.

Let’s compare running at 190 mph with the two different gears.  Last year, a 3.89 gear was used. At 180 mph, you’d better be running in 4th gear (which means 1:1 and the speed coming into the rear end gear is the same as that coming from the engine.  The engine speed required to go 190 mph is this 3.89*2270 rpm = 8830 rpm.  This year, with a 4.00 gear, you’d need to be running at 9080.  If you’re running 200 mph, last year you needed 9293 rpm and this year it would be up around 9556 rpm.  You’re basically running 250 rpm (or so) higher this year than last year at the same speed.

Andy Randolph, Engine Technical Director at ECR Engines tells me that engines were running at 9800 rpm for sustained times.  Although the engine rotates that fast at some places, doing it continuously places huge stress on the mechanical parts – that’s why most of the failures were due to mechanical breakage.  (Because I know he’s too modest to mention it, I’ll point out that none of the engines that had problems at Kansas were from ECR.)

The Math

For those of you wondering about where my numbers come from, here’s a calculation I did for Las Vegas.  The only difference is the slight variation in tire circumference.  If you plug in the numbers to the formulas and don’t get what I got above, I probably screwed up on the calculator.

Left-side and right-side tires have difference circumferences.  The circumference of a left-side Vegas tire in 2008 was 87.4″, while the right-side tires had a circumference of 88.7″.

To calculate how many times the tires rotate each minute, I first convert the speed into inches per minutes.  I know to use those units because I’m trying to get an answer in revolutions per minute, so I need to convert hours to minutes. I also know that every time a right-side tire makes one complete rotation, it has traveled 88.7 inches, so I’m going to convert miles to inches because I know I will need that later. Convert 45 mph to inches:

45 mph corresponds to 47,520 inches per minute. Looking at the right-side tires (for no particular reason), the car travels 88.7 inches every time it makes one full rotation. The number of times the tires rotate each minute is 536 rpm, as shown below.

 

 

 

Kansas: Temperature and Horsepower

 Andy Randolph, Electronic Fuel Injection, Engines, Uncategorized  3 Responses »
Apr 232012
 

There were a lot of engine problems at the Kansas race last Sunday — and a lot of theories as to why there were a lot of engine problems.  Let’s start with the cooler-than-expected temperatures on Sunday.

When the air temperature changes, so does the number of air molecules heading into the engine.  Colder temperatures make air more dense.  Since density is the ratio of mass per unit volume, a volume of air at a lower temperature contains more molecules than the same volume of air at a higher temperature.  The plot below shows how air density changes between 0 and 100 °Fahrenheit.

Before EFI, changes in temperature during a race posed a problem.  Fuel and air prefer to combust with a very particular ratio that is determined by stoichiometry.  Remember all the balancing equations you did in chemistry?  It’s the same thing.

Combusting two octane (a component of gasoline) molecules require 25 oxygen molecules.   The ideal air:fuel ratio is 14.7:1.  If you have one ounce of gasoline, you would need 14.7 ounces of air.  NASCAR engines run slightly richer (meaning a smaller air:fuel ratio).

Engines introduce a fixed volume of air, which means that the number of air molecules changes depending on the density of the air.  You would like a system that introduces exactly the right number of gasoline molecules for the amount of air being introduced.  A carburetor cannot automatically adjust itself to maintain that ratio, but the NASCAR EFI system can.  When the temperature at Kansas turned out to be 20 °F cooler than expected, engine tuners weren’t worried because the EFI automatically compensates for the changing in temperature.

In fact, cooler is better in terms of horsepower production.  The more oxygen molecules in the cylinder, the more gasoline you can inject and the more power you can make.  That’s the idea behind turbochargers – compress the air so that you have more oxygen molecules in a volume of air.

The change in horsepower depends on the square root of the absolute temperature.  You may remember absolute temperature from chemistry and/or physics class.  When you use the ideal gas law, for example, you can’t just plug in the temperature you read from the thermometer.

The Fahrenheit and Celsius scales were developed around things we experience every day.  Water freezing is 0°C or 32 °F.  Water boiling in 212°F or 100°C.  As we discovered more about the molecular nature of temperature, we learned that physics places limits on how cold something can be.  The coldest possible temperature corresponds to -459.67 degrees Fahrenheit.  Rounding that to -460 °F for simplicity, 0 °F is 460 on the absolute temperature scale.  You get the absolute temperature by adding 460 °F to the temperature from the thermometer.  A temperature of 57 degrees F would be (460+57=)  517 F on an absolute temperature scale.  A temperature of 77 F would be 537 F.

The change in horsepower is proportional to the inverse square root of the ratio of the two temperatures.

If I go from 77 °F (537 °F in absolute scale) to 57 °F (517 °F in absolute scale), the horsepower would be:

This represents a 1.9% increase in horsepower.  If the engine was producing 850 hp at 77 °F, it would produce 866 hp at 57 °F.  In a sport where engine builders working really hard to get 1 or 2 hp, this is a huge change!

Some people have suggested that the engine failures at Kansas were due to the increased horsepower produced by the colder temperatures.  My favorite engine technical director Andy Randolph (of ECR engines) tells me this isn’t the likely cause for the engine failures.

What IS the cause will be my next post. (And it’s not EFI!)

The Truth about Cell Phones, ECUs and Car Control

 Daytona, Electronic Fuel Injection, Engines, Keselowski Brad  4 Responses »
Mar 162012
 

It didn’t take long after Brad Kezelowski pulled out his cellphone during the 2-hour-long Daytona red flag for the conspiracy theorists to leap into action.

The argument goes like this:  Cellphones should be banned from the car because a driver could use his specially prepared cellphone to a) change the Engine Control Unit (ECU) and/or b) transmit data from the car back to his crew chief during a race.  We will not address the suggestions that the driver could use the cellphone to talk secretly to the crew chief during a race because anyone who has been in a race car or worn a helmet knows that’s just plain dopey.

Let’s differentiate between telemetry and electronics.  The word telemetry comes from two Greek words:  tele (meaning ‘at a distance’) and metre (meaning ‘to measure’).  Telemetry technically means measuring something (like the speed or acceleration) remotely, but many people use the word to include the ability to send information from the crew to the car.

Let’s start with the assertion that is the easiest to disprove:  you cannot control the ECU remotely.  Some people seems to have problems distinguishing between electronics and telemetry.  Just because something is electronic does not mean it can be communicated with remotely.  I can start my 2010 Fusion from inside the house by pressing a button on its remote.  My 1998 Ranger remote doesn’t even have such a button because the truck lacks the ability to receive instructions from a distance.  An app that sends a signal to a car doesn’t do anything if the car isn’t able to receive and interpret the signal.

The McLaren ECU is built specifically to preclude the ability to change any engine parameter without plugging a computer into the system using wires.  There simply is no way to change the ECU wirelessly.  When NASCAR initiated the switch to EFI, they worked with McLaren from day 1 to develop a system that would minimize any possibility of “cheating”.  If you want to keep someone from stealing something from your car, you can make sure you lock he doors.  The sure way to make sure it doesn’t get stolen from your car is not to leave it in the car.

No major racing series allows teams to talk to the ECU remotely.  Even F1, which used to allow it, realized that fans don’t want to watch engineers race absurdly expensive RC cars.  NASCAR drivers are not controlling their ECUs with their cellphones.

The second argument is a little more subtle because we all know that data can be read from the car during a race.  For the last 10 years, a company called SportVision has provided information to NASCAR’s television broadcasting partners using telemetry.  This information includes the throttle position, brake, rpm, speed and position of each car.  Prior to the introduction of EFI, SportVision got their throttle and rpm data from throttle position and shaft speed sensors in the car.  This year, rpm and throttle data are acquired directly from the ECU (which, incidentally, provides much more accurate data than the sensors did).

The question of intercepting data isn’t new with EFI: The company has been required by NASCAR to keep all data they collect out of the hands of the race teams since the program began.   SportVision encodes the data that is transmitted from each car.  If you were able to intercept the data, it’s not like you could open up the data file in Word and see a line like “4500 rpm, 147.6 mph, 80% throttle”.  It would be a series of ones and zeroes that would take some serious decoding in order to figure out what each piece of data was, much less what it meant.  This makes it difficult for anyone besides SportVision to intercept and make sense of the data.

Let’s assume for a moment, however, that a team did figure out how to intercept and interpret the data (and incidentally, you wouldn’t need the equipment to be insider the car – you could do it from well outside the car).  The SportVision folks told me that the sum total of all the data from the 43 cars competing in each race ends up being about 2 Gigabytes worth.  To set a scale:  One character is a byte and an average word is about 10 bytes.  One page of an encyclopedia is 10,000 bytes or 10 kilobytes.  The 2 Gigabytes of data collected during each race is 2 billion bytes, or 200,000 encyclopedia pages.

Each car provides about 46.5 million bytes of data, which corresponds to 4,650 encyclopedia pages worth of information each race.  For an average three-and-a-half hour race, a single car transmits information at a rate of about 3700 bytes (a third of an encyclopedia page) every second.  Handling this rate of data input and analyzing it in real time is nearly impossible.  In the words of one of the SportVision engineers, “If you find someone who can get the data and analyze it in real time, I want to hire that person!”  SportVision doesn’t even do real-time data analysis because of the huge amount of data coming in.  Even if you were able to intercept and read the data, analyzing all that data and getting something useful out of it (something you could use to make the car better) would be a huge challenge.

For the sake of argument, let’s assume that a team WAS able to intercept, interpret and analyze the data from the car in real time during the race.  What can they do with that information?  If they want to change anything on the ECU, they have to take the car behind the wall.  The time it takes to make the ECU change isn’t going to be offset by the performance advantage you might get from making the change.  The teams get all of the data from the ECU after the race anyway, so there’s absolutely no advantage to capturing it during the race.

Let’s also think about the practical.  If you had invested all this time and expense to develop the software and hardware necessary to intercept and transmit data from the car back to the pit box, don’t you think you’d tell the driver not to pull out his cellphone and make a show of carrying it in the car during a red flag in the most-highly-watched race of the year?

Here’s my biggest concern about cellphones in cars.  If you are going 180 mph and you stop suddenly, anything not secured in the car becomes a projectile with an initial speed of 180 mph.  Putting the phone in your firesuit pocket (yes, firesuits have pockets) is also not advisable:  Do you really want a hard piece of metal and plastic trying to embed itself in your leg? Or elsewhere?

Conclusion:  if you want to argue against cellphones in racecars, the best argument is the 180-mph projectile safety argument.  The drivers are not controlling their cars with their cellphones, they’re not intercepting data and sending it to the crew chief with their cellphones and, even if they were, there isn’t anything useful the crew chief could do with that intercepted data.  So let’s put that theory to bed for good and just enjoy some Bristol racing.

 

 

Engine Maps Explained

 Electronic Fuel Injection, Engine Map, Engines, Fuel Mileage  1 Response »
Mar 102012
 

In my last post, I detailed how the relays in the ECU system allow the system to flip to a default engine map.  This lets the team keep running, even when something fails, and it decreases the chances of the ECU doing something that blows up the engine.  Here’s a short explanation of what exactly an ‘engine map’ is and what it does.

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