NASCAR fans: why not limit octane?

[Malienation]

I’m reading The Physics of NASCAR, which is about, well, the physics of NASCAR race cars. I’m especially intrigued by the steps NASCAR has taken to keep speeds down to safe limits. They use restrictor plates, limited gear ratios, etc. to keep speeds down to safe limits.

Why don’t they just limit fuel octane? According to the book, they use 98 octane gas. Why not mandate, say, 87 octane fuel (or some other reasonable number) and get rid of that restrictor plate crap, etc? It’d be cheaper, too. What’s the logic here?

[SmartAleq]

Because octane doesn’t do what you think it does.

A higher octane rating on fuel denotes that it is harder to ignite, which is why a high compression engine requires a higher octane fuel–the fuel is compressed more, which makes it hotter before the spark ignites it. If you compress a lower octane fuel too far it ignites before the spark, causing the engine to “knock.” NASCAR engines run at high compression rates, so putting lower octane fuel into them would probably cause the very expensive engines to grenade. Not so good for safety, overall.

ETA: I laugh when people tell me they’re “treating” their low compression engine vehicles to premium gas, because all they’re doing is putting in gas that won’t ignite completely, thereby wasting money twice–once by paying more per gallon, then again by dumping it unburned out the exhaust system. Cute!

[Malienation]

@SmartAleq

NASCAR engines run at high compression rates, so putting lower octane fuel into them would probably cause the very expensive engines to grenade.

Uh, you’re making my point. Forcing the use of low octane fuel would in turn force lower compression ratios…yielding less power.

[SmartAleq]

No, the compression rate is fixed by the volume of the cylinder and the amount of travel by the piston. The engines have a high compression rate, because of they way they’re built, and no amount of changing the fuel will make it different. It’s like saying a two liter bottle of pop can be changed to hold a different amount of liquid merely by changing the liquid. It will always be a two liter bottle.

This might be helpful.

[Malienation]

@SmartAleq

No, the compression rate is fixed by the volume of the cylinder and the amount of travel by the piston. The engines have a high compression rate, because of they way they’re built, and no amount of changing the fuel will make it different. It’s like saying a two liter bottle of pop can be changed to hold a different amount of liquid merely by changing the liquid. It will always be a two liter bottle.

This might be helpful.

What I mean is that engine builders will be forced by necessity to design their engines with lower compression.

[SmartAleq]

Not gonna happen–for instance, have you ever wondered about the “SC” portion of NASCAR? It used to be that the cars were actually stock cars, that is, production vehicles that were only allowed to be modified to a certain point but were still recognizably the same cars as people were driving on the road. That’s so far in the past that it’s ludicrous they even refer to those things as “stock cars” at all.

Besides, if they really wanted to slow those boogers down they’d make 'em turn right…

[Malienation]

@SmartAleq

Not gonna happen

Again, why not? If you have to limit speed somehow (and obviously they do), why screw around with restrictor plates, gear ratios, etc? Why not mandate drastically lowered octane fuel and let the chips fall as they may? Sure, engine builders will have to move to much lower compression ratios (maybe 9:1), but how is that worse than fussing with restrictor plates? Of course, maybe 87 octane is too drastic a change…but the principle seems to me a no-brainer. Lower octane means different engines yielding less power and thus slower speeds.

Right now, engine builders create highly powered monsters and promptly suffocate them with restrictor plates. How is this better?

[bubba_jr]

[QUOTE=SmartAleq]
No, the compression rate is fixed by the volume of the cylinder and the amount of travel by the piston. The engines have a high compression rate, because of they way they’re built, /QUOTE]

Your missing one key point, it is very easy to manipulate the volume of the cyclinder while maintaining the travel. Dished pistons, larger volume combustion chambers, not that hard to manipulate.

Being a getting to be X-nascar buff. I do believe they actually implemented a compression rule about 10 years ago, they were routinely running 14-14.5:1 or so and now they are running 12 or 12.5:1. I could have told you a couple of years ago, but Nascar just isn’t the same anymore. Many years ago they were running 20:1 plus on the restrictor plates, diesel territory.

On the octane, they did drop from 105 or 110 to 97 just a couple of years ago, and I think it was just last year, they took the lead away.

Also about 10 years ago, the busch (now nationwide :rolleyes: ) cars were limited to I think 9.5:1, and they allowed them to go up to 12:1 or so, a jump from roughly 450 to 650hp. At the time it was the difference between a $10k and a $40k motor and took a lot of teams out of business and also made the cars handle a lot more like a cup car, which I do believe is how all the “busch-whackers” came to be.

To the OP trying to figure out Na$car is like trying to figure out a redheaded stepchild. They make no sense and seem more concerned with EGO than safety. If somebody suggests it they won’t do it, until they can profit from it.

Then again, limiting engine horsepower and not changing anything on the car, your cornering speed is still going to be the same, which is where you are going to hit the wall the hardest. Or as Ryan Newman said, the new SAFER Car Of Tomorrow, wouldn’t have flipped at all, if it was the less safe old car. Higher center of gravity and all.

SmartAleq. I agree they should turn right more often, I went to Watkins Glen for 10 years straight, and gave up after the experience soured (restricted to a smaller area, less on track time, higher prices, couldn’t stand up in the stands, smaller beer coolers), the racing didn’t just get crappy, the whole experience did.

Thanx for explaining the octane thing, so many people don’t get it.

[FoieGrasIsEvil]

Won’t lowering compression ratios also affect acceleration?

I hate NASCAR, but I like fast cars even though I don’t own one, but it seems to me that the recent implementation of devices like restrictor plates are designed more to limit top speed rather than acceleration, which you would think a race like NASCAR has with only four turns per lap, would be more useful to the driver than ultimate top speed, which you wouldn’t be able to hold for very long due to the turns anyway.

When i drive my little stickshift, it’s readily apparent to me that accelerating through turns is the most important gain in a sport like NASCAR.
Wouldn’t lower compression ratios reduce sheer acceleration?

[Malienation]

[QUOTE=bubba jr]

@SmartAleq

To the OP trying to figure out Na$car is like trying to figure out a redheaded stepchild. They make no sense and seem more concerned with EGO than safety. If somebody suggests it they won’t do it, until they can profit from it.

So said the late Smokey Yunick. Now, there was a guy with an active mind.

What’s ego got to do with it, though? Are you saying that NASCAR might like the idea technically, but would never do it that way because they didn’t think of it?

[Rick]

@SmartAleq

Because octane doesn’t do what you think it does.

ETA: I laugh when people tell me they’re “treating” their low compression engine vehicles to premium gas, because all they’re doing is putting in gas that won’t ignite completely, thereby wasting money twice–once by paying more per gallon, then again by dumping it unburned out the exhaust system. Cute!

You really should read your cite before you post it. From your Wiki cite

The octane rating is a measure of the autoignition resistance of gasoline and other fuels used in spark-ignition internal combustion engines.

Got that? higher octane fuel is more resistant to autoignition.

It should be noted that octane rating does not relate to the energy content of the fuel (see heating value), nor the speed at which the flame initiated by the spark plug propagates across the cylinder. It is only a measure of the fuel’s resistance to autoignition. It is for this reason that one highly branched form, or isomer, of octane (2,2,4-trimethylpentane) has (by definition) an octane rating of 100, whereas n-octane (see octane), which has a linear arrangement of the 8 carbon atoms, has an octane rating of -10, even though the two fuels have exactly the same chemical formula and virtually identical heating values and flame speeds.

Nothing about the fuel not ignite completely, or pouring unburned fuel out the tail pipe.

Since NASCAR teams put in a new engine every week, lower compression pistons could be installed in time for the next race.* Lower octane fuel would lower the horsepower on the cars.

*However they would be dynoing like a madman to try and eek some extra hp out of their engine somehow.

[bubba_jr]

@Malienation

So said the late Smokey Yunick. Now, there was a guy with an active mind.

What’s ego got to do with it, though? Are you saying that NASCAR might like the idea technically, but would never do it that way because they didn’t think of it?

Yes.
Did you read Smokey’s books? Funny fantastic read, most not even racing related, easily a years worth of bathroom fodder.

Also after Dale Earnhardt died Smokey was on tv touting the softwalls that he came up with many many many years ago, but nobody wanted to know nothin’. It may have actually been in one of his books, I don’t remember, though he did die only shortly after Earnhardt died.

Remember the “Humpty Bumper”. Cheap, light, proven to seriously reduce G-forces and fit in the exhisting car. Big NOGO.

Just seems somebody comes up with an idea, Nascar says NO, then all of a sudden 2 years later its Nascar’s idea.

I may just be bitter.

[Malienation]

@bubba jr

Did you read Smokey’s books? Funny fantastic read, most not even racing related, easily a years worth of bathroom fodder.

Some of his technical stuff, yeah, although it’s been a few years. Didn’t get to read “Best Damn Garage in Town”, at least not yet. I’ll get to it…

BTW, I did one of those “drive a stock car” things at Dover, DE, a coupla weeks ago. Awesome.

[Airman_Doors_USAF]

People watch racing to get something different from what they can do themselves. If you reduce the compression ratios and the horsepower to the point that the cars accelerate like a 20-year-old Aries people will tune out.

Then you’ll get the guys like Smokey Yunick that will do everything they can within the rules (and some without) to fix things in their favor, so eventually it’ll end up that the teams will make up the horsepower gap and return things to the way they were, only more time and money will be wasted and fewer teams will exist. Then NASCAR will change the rules again and the cycle will repeat. Nest thing you know NASCAR becomes F1: boring parade laps and technology that does all the work.