The Big Fuel Test Part 4: Race Fuels Fight Back

This article is the fourth of five in our Big Fuels test series (Article 1–IntroductionArticle 2–Boostane, Article 3 – Meth Injection), which spans 13 different test fuels, octane additives and injection systems tested on a supercharged C7 Corvette. During this article, we will review four of the most popular race fuels we could get our hands on. When we began this test, we surveyed our customer base and asked what they wanted to see us test. We ended up with a variety of fuels from VP Racing Fuels. The test group we’re discussing here did not include our ethanol-based fuels, which are tested in the next and final article of this series.

The test group included the following race fuels for our shootout:

This group of race fuels taught us quite a bit about why choosing the right race fuel for your engine combination is even more important than you think. Before we began this test series, the very term “race fuel” carried a different meaning than it does for us now.

When we think of race fuel, the concepts that jump into our heads (as the tuners responsible for making maximum safe power) are typically more boost, more spark, and thus more power with race fuel than pump gas. We think this way because race fuels often provide such capabilities. Often, but not always. When we asked which of these race fuels people thought would make the best, safe power through a survey of our customer base (performance shops), one of the best replies came from Jason Zajac of J&J Speed Shop in Elma, NY, who said: “Real hard to blow up anything on VP C16.”

Unfortunately, this was followed up with another reply from a different person whose friend’s C5 Z06 just blew up while on the same fuel, but tuned by another shop. This indicates that it’s not the fuel–it’s the knowledge of the tuner working with the right fuel for the right application that makes all the difference in the performance of the vehicle.

They are, after all, race fuels. The very term conjures up these ideals of more power instantly, and more safety margin for the engine. In our heads, it must be true because, well, race fuel. But is that the reality? That’s the point of this testing series, and specifically this segment of the series.

As we learned, you must choose your race fuel wisely. This does not mean that we found a bad race fuel, but we found out that race fuels need to be chosen for their intended purpose, not on their names, and not even just on their octane ratings. Too much octane for your application and you lose power before tuning, while too little makes minor or zero improvements over pump gas. Octane isn’t even the only factor.

That’s right: we’re saying conclusively from our testing that some race fuels won’t make much more power than 93 octane pump gas. They know it; we know it, and now you know it. In fact, here’s a chart showing how our test group of race fuels performed before being tuned for the race fuel. Also important to note here is how much more power they made over pump gas (which produced 574 rwhp) after tuning.

No, it isn’t the race fuel company trying to cheat you out of your hard-earned money. The truth is that the consumers aren’t educated enough to choose properly or even know the difference between the race fuel blends. Can you honestly say that we, the dyno tuners, typically know enough about the different fuels to know which would work better than others in a specific application? I can count less than ten tuners that I personally know who could answer that with an absolute “yes.” We all “should,” but most don’t. Most fall back to that old adage, it’s all “race fuel” and we lump it all together. Not good.

Looking at the results in the chart above, would you have known that putting C16 in the tank without tuning would have made far less power than pump gas did? Most of the time, the guys tuning your car are professional tuners, not fuels engineers.  Knowing why the fuels behave how they do is really the key here. The bigger issue here is the customer who doesn’t know this, and with a car tuned for pump gas actually goes to the drag strip, empties out the pump gas and pumps C16 in. That’s the guy who goes slower than his tuner suggested he should given his dyno numbers. That’s the guy who doesn’t know any better and needed proper tuning for the fuel he pumped into the tank.

Making this issue even more challenging, there exists a mere handful of industry experts with knowledge in this area, and it’s even harder to get those experts to give out proprietary information on why or how the fuels really make power.

In order to clarify this issue, I collaborated with Freddy Turza, Technical Manager with VP Racing Fuels. Freddy was adamant that customers must know how they plan to make power in order to figure out what fuel is right for them. For example, if the engine will be using mild boost (6-12 psi), then the fuel requirement will be different than a super-high-boost application. Things like octane–which dictates the resistance to autoignition–are a part of the equation, but only a part. Other items such as oxygenation are important too. Not just how much oxygenation, but what was used for the oxygenation process–ether, ethanol or something else? We’ll be exploring more about the makeups of the fuels in the next and last article of this series, which will be focused on ethanol-based fuels. Given our lengthy conversation about all these variables, I came to appreciate VP Racing’s willingness to actually talk with its customers, to answer the question of: “which race fuel is right for me?” If in doubt, call the tech line, and leave ego behind. After you get a few recommendations, buy a little of each and actually take the time to see what works best with your combo – and figure out why. Some combinations hate slow burning fuels, and some work great with them. There’s not one answer to fit all applications, and with so much potential power gains on the table, why aren’t we doing more of this testing in our industry?

Speaking of power, let’s get back to some results. Below is the least impressive of the results, a comparison between 93 octane pump fuel versus VP Racing’s C9 race fuel.

Performance Numbers:

We found that VP Racing’s C9 gained the least power and torque (+5 rwhp, +7 lb-ft of torque) compared to our baseline of 93 octane pump gas. It liked an air/fuel ratio of 11.5-11.8:1 and just 18 degrees advance. Looking at the charts, we see that this race fuel made nearly the same power and torque before and after tuning and only a little more power than pump gas. We were certainly surprised to see this, given our standard impression of race fuels as a way to generate more and safer power. What was wrong? Why didn’t we need to run much more timing than we did with 93 octane pump gas? Why were we seeing knock at similar spark advance as 93 octane pump gas?

VP Racing’s C9, as it turns out, is a great race fuel, if you are running a homologated class of circle track racing somewhere in America. While I’m not sure who exactly is required to run this race fuel in their series, it really doesn’t matter for our purposes, or most of yours either. The purpose of this race fuel is clear–it isn’t to make more power than pump gas. It’s to equalize a bunch of racers in a class, to prevent them from having an advantage running different fuels over one another. Sometimes this has also been done in class racing to protect corner workers’ health, as in the past some racers have even been known to make their own “cocktail” blend of fuels, causing nausea and other health issues for race officials.

In this case, in the name of science we tested the fuel because of the octane rating, and we wanted to see what would happen. Fortunately we always start with a mild tune and bump up to see safe improvements.

Moving on to bigger results, let’s review MS103 (103 octane) and MS109 (105 octane) together. While MS103 made 602 rwhp peak, MS109 made 604 rwhp peak. However, it should be noted that both fuels produced exactly the same Average Horsepower across the range when compared to each other–so let’s show you how they did on average against 93 octane.

Below is the 93 octane baseline (solid lines) vs MS109 (dashed lines) AVERAGE dyno chart. It’s not what you’re used to seeing (Peak charts), but this is a better way of looking at power gains across the entire RPM range. Tuning was a breeze–these fuels needed just a few tweaks to be maximized. This included adjusting the stoichiometric point to what the VP Racing specs call for, as well as spark adjusted upward (from 15 degrees on 93 octane pump gas) to 22-23 degrees with MS103 and a preferred AFR of 11.7-11.9:1. MS109 preferred 21 degrees of advance, with a slightly leaner AFR of 12.0-12.4:1 at full throttle for maximum safe power.

MS109 produced 604 peak rwhp and 422 average rwhp. Excellent power gains and easy tuning made it a great contender for the overall win, but we still have the old school leaded C16 fuel, which was designed over 20 years ago, to go over next.

C16 is the slowest burning fuel of the bunch – but still king of the non-ethanol based race fuels. Old-school C16 fuel made 605 RWHP, just 1 more horsepower than MS109. With a very low Reid Vapor Pressure (a measure of the volatility of gasoline) it doesn’t turn into a vapor for burning easily, and required 24 degrees of spark advance, compared to 93 octane pump gas needing only 15 degrees for maximum safe power. Reid Vapor Pressure is, more specifically, an absolute measurement of how much vapor pressure is exerted by the fuel at 100 degrees Fahrenheit. ASTM-D-323 is the test if you are interested in looking it up. Below are the peak results after tuning.

In our test group of VP Racing’s C9 vs. MS103 vs. MS109 vs. C16, C16 made the best peak and average power, making 605 rwhp, an improvement of 31 rwhp and 28 lb-ft of torque over 93 octane pump gas alone after tuning. With so much octane (120+), this fuel was also the worst at making power before being tuned, making 10 rwhp less than pump gas before we tuned it with 15 degrees of spark advance.

Results Summary

So let’s evaluate the overall results of all tests so far including the previous articles in this series. What would I pick from what we’ve tested so far? Well, the question is, are you based strictly on performance or budget? Are you OK with large up front costs, or prefer more ongoing costs? Let’s choose three and compare them: 93 octane pump fuel with BOOSTane added, VP Racing’s C16, and finally 93 with straight meth injection for this vehicle’s combination. These three represent the best performers of their respective test groups (additives, race fuel, injections) from our entire series.


  • 93 and BOOSTane: Inexpensive and presented large gains, with easy tuning. The additive is easy to carry to race events and you can run it only when needed with a hotter tune if you like, or run it daily driver-style as cost is relatively low. With some tuning, it produced gains similar to the best race fuels.
  • VP Racing’s C16: A known quality and consistency, and delivered more peak and average rwhp. Old school with a great track record of safety and power. Great choice when you are heavily invested in the powertrain and don’t like to risk issues related to fuel quality.
  • 93 with methanol injection: Presents the lowest ongoing costs as it’s used only as needed at wide open throttle. When testing during daily driving, we averaged one gallon per week used. Gains were highest of this group in terms of peak and average rear wheel horsepower. Also, this is the only choice of the three which reduced intake air temperatures.


  • 93 and BOOSTane: the only issue we could think of would be poor pump gas quality or variations may be an issue in some areas. This wouldn’t really hurt anything, but would limit overall gains.
  • VP Racing’s C16: Ongoing costs of $15 per gallon make this fuel cost-prohibitive for street use and tailored more to the high-dollar race engine builds. The known quality of the fuel for those engines makes it easy to look upon this as cheap insurance.
  • 93 with methanol injection: The highest up-front cost of the three at $500-$750. It can be prone to failures with cheap kits–causing engine damage–but this is rare and you should know this before you buy.

Tuning notes:

  • We rank the tuning difficulty of VP Racing C9 as  3 out of 10 – Easy.
  • We rank the tuning difficulty of VP Racing MS103 as 3 out of 10 – Easy
  • We rank the tuning difficulty of VP Racing MS109 as 3 out of 10 – Easy
  • We rank the tuning diffuclty of VP Racing C16 as 3 out of 10 – Easy

No special tuning was required, other than to change the Stoichiometric value for each fuel in the tune as listed in the Spec sheets of each fuel. The race fuels tuned easily and simply required refining the optimal air/fuel ratio and spark advance for each. C9 preferred 11.7:1 A/F ratio and 15 degrees advance, MS103 11.7-11.9:1 and 22-23 degrees advance. MS109 preferred 12.0:-12.4:1 A/F ratio and 21 degrees advance, and C16 preferred 12.5:1 and 24 degrees advance.

Stay tuned for our next, and last article in the series – where we test the final and newest fuels against everything so far. Ethanol makes its way into the ring, and we will compare this and summarize all our fuels, additives and injections to see what really is the best to use–and when to use it.


Article Sources

About the author

Bob Morreale

Bob Morreale is the author of several tuning related books and courses for The Tuning School. Bob began programming using BASIC in the mid-'80s in 2nd grade; and progressed to other languages, including HEX, self-taught. While Bob can program, he prefers to do tuning related R&D on new vehicles, writing courses and then teaching the tuning process. Bob has over 18 years of tuning experience, starting with the legendary turbocharged 1987 Buick Grand Nationals to modern LS/LT and Ford powered vehicles. Bob has also written numerous technical articles for industry-standard magazines and conducts “Tech Tuesday” video interviews for The Tuning School. Bob enjoys road-racing and drag racing.
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