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Old 12-06-2010, 02:56 PM   #1
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Default Quit blaming the engines, mileage vs. runtime.

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?

1. Tracks

2. Cars

3. Bodies

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:

1. Tracks

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.

2. Cars

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.

3. Bodies

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.

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.
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Last edited by wingracer; 12-06-2010 at 03:39 PM.
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Old 12-06-2010, 03:44 PM   #2
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That's something to think about, I think you're right.

Nice post!
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Old 12-06-2010, 03:53 PM   #3
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As mentioned in another topic I was lucky to messure some today's engines and I must say that the Flash Tuned 2009 is made for getting as much mixture in and combusted gasses out. The crank intake and the total exhaust port are huge compared with an engine from a few years ago.

I can imagine why this is. A few years ago the EFRA did go to the 7 minutes qualification with a mandatory pitstop, in other words we did need engines running 3.5 minutes and not 5 minutes. The race of devellopping faster engines was started.
Yes, I do believe it is for a part with the manufacturers as we all know the 2013 is an awesome pipe getting 5 minutes so why isnt there a new EFRA legal 2013 like pipe or a Novarossi/Picco alternitive?

Yes, todays grip made by the new cars, GTP bodies and insane clutch setups is draining fuel.

1+1=2 so I think evryone has a part in it. We are setting the rules and the manufacturers making products to them.
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Old 12-06-2010, 04:08 PM   #4
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nice read, more plz
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Old 12-06-2010, 04:15 PM   #5
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Quote:
Originally Posted by Roelof View Post
As mentioned in another topic I was lucky to messure some today's engines and I must say that the Flash Tuned 2009 is made for getting as much mixture in and combusted gasses out. The crank intake and the total exhaust port are huge compared with an engine from a few years ago.
And yet, I bet you that if you measure the ACTUAL MILEAGE, not run time but mileage, the Flash with today's typical set-up would actually have better mileage than a top motor from 8-10 years ago with a period appropriate set up.

Remember that while the Flash may not run as long on a tank, it is in a faster car on a faster track so it is covering more distance.

Look at it another way. Let's go to a track ten years ago. The TQ is 15 laps, 5:01.00 and no one has runtime issues. Nearly everyone could go at least one more lap. After this race, the track owner makes a change. From now on, qualifiers will not be five minutes, they will be 15 laps. Whoever does 15 laps in the quickest time will be TQ.

Fast forward 10 years. Exact same track, exact same format but all our modern gear. Are any drivers running out of fuel? No, they have no trouble going 15 laps. Of course, they are doing those 15 laps in 4:20.00 now. Even if they can still do that one extra lap, they are still running out around 4:40.00. Fuel mileage is practically the same, but they can't go 5 minutes.

You say the Flash is designed to only go 3.5 minutes yet I see Flashes go 5 all the time, on tracks as slow as the ones we raced on 10 years ago. And it's not the timing. I have a mod motor from 8 years ago timed just as high that had no trouble making time then. The Flash gets better runtimes than many of my older motors.

The point is that the motors are actually getting as good or better mileage than they ever had. It's everything else that has killed runtimes.
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Old 12-06-2010, 04:27 PM   #6
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I've heard that Novarossi MFs(Massimo Fantini mod) could do 5 minutes plus 1 lap back in the 2007 worlds in Argentina. Im talking about engines that made the A main, at the worlds.
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Old 12-06-2010, 04:57 PM   #7
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Quote:
Originally Posted by Thybaut View Post
That's something to think about, I think you're right.

Nice post!
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Old 12-07-2010, 12:35 PM   #8
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NIce read, I believe it as well. I'm gonna take an RC300 to the IFMAR Championships and run away with the title! With the 8min plus run times I'll be running, they won't know what hit them!!
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Old 12-07-2010, 02:28 PM   #9
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On everything you say I have to agree with you, however I still think the engines have a bigger part in the runtime issues then you say they have.

The three engines I run regularly are all fast as hell but the runtime I get with them vary quite a lot.

With the 2005 MF12 I can do 6 minutes, this engine still has the standard style crank which is a hugh fuel saver if you ask me.

With the Capricorn Lab E01 BC I can do 5:20-5:30, this is the fastest engine I have and has the most mods done to it I've ever seen.

With the RB R3 RC I can do 5:10.

When I still had a JP factory engine I was really struggling to make 5 minutes, but this engine revved like there was no tomorrow.

I can drive my qualifiers with a maximum deviation of about 0.2 seconds so this isn't causing it. The crank and burnroom have the most influence on runtime regarding engines.
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Old 12-07-2010, 06:25 PM   #10
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Quote:
Originally Posted by DS Motorsport View Post
On everything you say I have to agree with you, however I still think the engines have a bigger part in the runtime issues then you say they have.

The three engines I run regularly are all fast as hell but the runtime I get with them vary quite a lot.

With the 2005 MF12 I can do 6 minutes, this engine still has the standard style crank which is a hugh fuel saver if you ask me.

With the Capricorn Lab E01 BC I can do 5:20-5:30, this is the fastest engine I have and has the most mods done to it I've ever seen.

With the RB R3 RC I can do 5:10.

When I still had a JP factory engine I was really struggling to make 5 minutes, but this engine revved like there was no tomorrow.

I can drive my qualifiers with a maximum deviation of about 0.2 seconds so this isn't causing it. The crank and burnroom have the most influence on runtime regarding engines.
In Bold, that is completely right - to an extent with the crank.
The longer and/or earlier you have the crank opening (within limitations) can determine how much fuel/air mix you can get into the combustion chamber.

With the topic at hand, a friend of mine has a GRP engine, orange head, and at the track we run at, I run about par with him, yet he can do a few laps, start the race and finish with 1/4-3/8 of a tank left! Yet I start racing on a full tank and Im left with maybe 20-40 secs of runtime! Im not entirely sure if it was because I had a bad tuning (issues with my engine, RB T10) but that just shows that you can run more than 5-6 minutes on a single tank.
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Old 12-08-2010, 12:16 AM   #11
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Quote:
Originally Posted by DJ_Shakespear View Post
In Bold, that is completely right - to an extent with the crank.
The longer and/or earlier you have the crank opening (within limitations) can determine how much fuel/air mix you can get into the combustion chamber.

With the topic at hand, a friend of mine has a GRP engine, orange head, and at the track we run at, I run about par with him, yet he can do a few laps, start the race and finish with 1/4-3/8 of a tank left! Yet I start racing on a full tank and Im left with maybe 20-40 secs of runtime! Im not entirely sure if it was because I had a bad tuning (issues with my engine, RB T10) but that just shows that you can run more than 5-6 minutes on a single tank.
Are you both runnning the exact same cars, body, gearing, pipe, tire dia, etc?
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Old 12-08-2010, 05:26 AM   #12
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Are you both runnning the exact same cars, body, gearing, pipe, tire dia, etc?
Completely different engines bro - his is GRP, mine was an RB T10. I have a modified JLR Evo 3 which makes great runtime, so once I finish breaking it in, ill tune it up and see how it compares.
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Old 12-08-2010, 06:27 AM   #13
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GRP/Ninja engines are very fuel efficient. So what you are saying, doesn't surprise me.

The problem with that specific engine is that it doesn't hold the tune very well through out the day. It is very sensitive to humidity and temperature changes. Also, the carb is real tricky and it doesn't tune like a Novarossi.
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Old 12-08-2010, 07:03 PM   #14
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@Riketsu
Really??? I haven't seen that problem at all! Ive never seen him make any changes throughout the day, except for maybe a HSN change every few races, if that!
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Old 12-09-2010, 09:19 AM   #15
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Very nice read... thanks


Pass you soon...
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