Sorry for the long post but for some reason I got inspired to write an article.
Quit Blaming the Engines
An article on runtime vs. mileage.
Runtime has become a major issue in the 1/8th onroad world in recent years. Finishing a five minute main without a fuel stop has become extremely difficult to do at many tracks. Many people are quick to blame the latest high horsepower engines for this but I’m here to tell you that’s not entirely the case. Today’s engines are more efficient then they have ever been yet we still can’t make time. So what is to blame?
First of all, let’s take a look at our terminology to see where some of the misconceptions come from.
We often talk about fuel mileage since this is the most common way of expressing the concept. It is also nearly meaningless to us in the RC world. Mileage is expressed as distance covered divided by the amount of fuel used such as miles per gallon. This is a very useful number to know when running a race over a fixed distance; however, we do NOT have a fixed distance to run as our races are timed.
Runtime is how long (in time, not distance) the car can run on a given amount of fuel. Since our races are timed, this is the number we need to be concerned with. Unfortunately, it is affected by a couple different factors. The first one is obvious; fuel mileage. The better the mileage, the longer the car can run. But mileage has distance factored in to its determination so that brings another factor into the runtime equation:
How much distance can we cover in the given amount of time?
What does that mean? It means that any change that makes the car quicker will REDUCE our runtime
even if the mileage stays the same. How can that be? Well, let’s take a look.
Imagine a car that runs 20.0 second lap times and can to do exactly 15 laps on a tank of fuel. It will run out of fuel as it crosses the finish line with 15 laps in 5:00.00. It is burning 8.33cc of fuel per lap (feel free to substitute “lap” for the distance of the lap such as 2000 feet. I’ll stick with lap for simplicity.) So we are happy that we are making five minutes but as racers, we want to go faster.
We make a chassis adjustment to the car that gets it handling better. It now runs 19.9 second lap times. If the mileage stays exactly the same at 8.33cc per lap, it will still run out as it crosses the line to complete the 15th lap; however, it now completes that 15th lap in a time of 4:58.50 and is unable to complete the 16th lap. Of course, since the car is handling better we are probably getting those faster lap times by using more throttle and reducing mileage as well but for these purposes, let’s assume the mileage is exactly the same. We are now failing to make a 5 minute runtime even though our mileage didn’t change. It is very important to understand this difference between runtime and mileage for the rest of this discussion.
This is also why slower drivers that are a lap or two off of the TQ pace have far less trouble making runtime. It’s not because they don’t have the high HP, fuel sucking motor that the pros have, it’s because they are travelling less distance.
So how does this explain the drastic reduction in runtimes over the last ten years? Well let’s take a look at the three big culprits I mentioned earlier:
Ten years ago I was racing on slick, dusty, bumpy parking lot tracks. Even the few permanent tracks around were small, slick and tight compared to most tracks today. The average speeds on these tracks was much lower, therefore we were not able to cover as much distance in five minutes so we didn’t need to get very good mileage to still make runtime. I used to make 6 and sometimes even more minutes on a tank with no trouble.
We racers always want better facilities to race at. So we get bigger, faster, swoopier, smoother, higher grip tracks sprayed with all kinds of traction enhancing concoctions. This leads to faster average speeds and more distance covered within the given amount of time so runtimes drop.
Of course the fact that we are spending more time at full throttle will also reduce mileage but again, the runtime would drop even if the mileage stayed the same. This holds true for the rest of the factors as well so I will not mention it again.
Manufacturers are constantly improving the handling and performance potential of the cars. I don’t know about you but the Shepherd I run today is capable of MUCH faster lap times than the Picco or Mugen I ran ten years ago. So even if I ran the exact same engine and pipe combo from ten years ago in my Shepherd of today, I would see lower runtimes than I did then.
In my opinion, the Protoform 909 and bodies like it are a HUGE factor in the reduction of our runtimes. Sure the increased aero drag is probably hurting the mileage a bit but it’s the faster lap times that these bodies have created that are killing our runtimes. The performance difference between a 909 with a jacked up rear body mount and 1999 era Paris Lola almost touching the rear tires could be as much as .5 a second per lap. This means that just a change in bodies has led to being able to do 1 to 2 more laps in five minutes and thus, greatly reducing runtimes.
So what about the engines? Well, today’s engines do make a bit more power than ten year old engines but the difference isn’t all that great. I have an old RB C4 that can still run within two tenths of my latest full mod 35 + 21 with the same pipe and fuel combo. And oddly enough, seem to get about the same mileage with the same combo. Yet we still struggle to make time. Let’s take a look at what we used to run ten years ago compared to today.
Ten years ago:
RB C4, 30% nitro, 9mm venturi, no INS box, fuel hog 9886 pipe with Pico conical manifold.
Sounds like a real gas hog now doesn’t it? Yet I had no trouble making time with this combo then. I have run this combo in recent years and except for slick little parking lot tracks, it doesn’t make time today.
Novarossi Flash, 16% nitro, 8mm venturi, INS box, three chamber 2015 pipe.
Look at that would you. With that much lower nitro, the smaller venturi, an INS box and a three chamber pipe we should be seeing much better mileage yet we still struggle for runtime. The truth is that we ARE getting better mileage but the increased speeds brought on by the other factors I have mentioned have reduced our runtimes.
So I offer up this challenge if you don’t believe me. Dust off that old Picco Integra or Serpent Vector or MRX2, put a period body on it mounted just like it would have been back then, drop your current motor/pipe combo that won’t go 5 minutes into it and head to the track. I bet your runtime problems will be gone unless it’s a really fast track but even then it will get MUCH closer to 5 minutes than you were. If the track you ran on ten years ago is till around, take it there. If you used to go 6, I bet you beat it now unless you’re driving has improved significantly since then.
<sarcastic comment said with a smile to follow>
So the next time you run out on the last lap, stop blaming Novarossi or your engine builder. Put the blame where it belongs. With Mugen, Serpent, Shepherd, Kyosho, Protoform, etc. and all the track builders throughout the world.