I was reading through the VLR and Rok GP manuals, and something caught my attention. This is from the Rok GP but I believe the VLR says the same thing.
“Prepare fuel. Vortex engine works with commercial gasoline, leaded or unleaded, as well as racing fuel, with minimum 95 ROM.”
If we convert that to the R+M/2 octane rating commonly used in the U.S., that’s 91 octane. Yet, I see a lot of racers running 110 or even 112 octane fuel. This raises a question: why are we using such high-octane fuels when the manual clearly states the engine only needs 91?
Higher-octane fuel is designed to prevent detonation in high-compression or highly advanced timing setups, but these engines don’t seem capable of utilizing all 21+ points of octane, even with increased timing. Using unnecessarily high-octane fuels could leave power on the table.
For example, VP C9 (96 octane R+M/2) seems like a better fit. It’s closer to what the engine requires while still being a high-quality fuel. Over-advancing timing to justify 110/112 octane could lead to peak pressure occurring too soon, potentially reducing performance.
So, what’s the deal? Are we overdoing it with high-octane fuel because of a misunderstanding, or is there some other reason to justify it? I’d love to hear your thoughts and experiences with fuel in VLR or Rok GP engines. Has anyone tested lower-octane fuels like VP C9 or even straight 91 (ethanol free)? What were the results?
Welcome to the world of American consumerism lmao.
Any and all 2t racing engines (no matter how tuned they are) can run on unleaded 98 RON and were designed as such (especially monomake platforms like the Rok)
The utilization of a spec unleaded 102 RON fuel at international level is for standardization and to allow for chromatographic checks to be carried out for tech inspections reasons with samples.
There is no reason other than comercial benefit through partnership deals to use anything above 102 octane fuel, let alone leaded, which causes inumerous health effects.
Based on everything I understand, I concur with everything that @Simone_Perego says. I have a Rok GP, which I just converted to a Super Rok, and I run my local premium pump gas along with some VP Octanium (concentrated race fuel) and it runs great just like all of the other two stroke racing engines I’ve used the same fuel for. Unfortunately for the majority of karters this isn’t a great option because they’ll want to run whatever fuel is regulated in order to not be disqualified (race days) or for the sake of tuning on practice days. (using a different fuel for practice and race days not being a great platform for consistency). I don’t race, so I don’t have to worry about it and can bag the bucks and convenience.
Fuel partnerships, i’m not sure if that’s very common in the US?
It’s just easier to tech (and keep on hand) a single fuel for multiple classes. As alluded to, additional octane does not hurt anything so the headroom is nice to have.
Lead\TEL though… that really needs to go…
Overall looking at the entirety of engine used in karting here. I think that’s a fair assessment.
I’m fairly sure there’s some exceptions in the US. Mod and stock motos for sure needed additional headroom as they were detonating on MS98 (MON 96). At that point C12 became the main fuel (MON 108). Probably didn’t need to be as big of a leap, but C12 seemed to be more commonly available.
Eastern 93 AKI fuel is 98 RON or higher.
Western 91 AKI fuel is 95 RON or lower.
As for why VP 101 or Sunoco 260 GT is not used as the western racing fuel - when it came out it was more expensive than leaded fuel and sanctioning bodies haven’t kept up with the times
Just speculating here, could the disciplines of motorsport typically run in the U.S. play a factor in what type of race fuel ends up being used? Karting now use engines that are of lower compression than what used to be, so we can get away with running a lower octane fuel, but that may not be the case elsewhere.
In terms of participation, Oval and Drag racing in this country is many, many, many, times larger in size compared to kart racing (our discipline of kart racing is almost non-existent when comparing size). I would imagine leaded race fuel is much more ubiquitous and a lot more available simply by the number that are racing big, modified, high-compression engines on the oval tracks and drag strips across America (if they’re not running methanol).
That may not seem relevant for us, they can do their thing and we can do ours. But if you’re a kart club, track, or sanctioning body that needs to spec a race fuel and buy it in bulk, I could see how they may be inclined to go with a race fuel that is more widely available, despite other fuels available with an octane rating more appropriate for our motors, not to mention safer.
I’ll admit I have no knowledge as to how karting bodies deal with fuel brands when selecting a race fuel, but I could imagine that happening.
Apologies, i meant to say “all 2t KARTING racing engines”, i did not consider other disciplines in my statement.
Just speculating here, could the disciplines of motorsport typically run in the U.S. play a factor in what type of race fuel ends up being used?
This is a fair consideration, altough it does not make sese to not request a cheaper and less harmful alternative to leaded fuel when engaging in discussions with a fuel supplier for a single supply agreement.
This leads to my initial theory that mandating a more expensive (leaded, in this case) fuel means a higher margin on the sale of each drum, or a higher lump sum income from a sponsorship deal (depending on the revenue share that is agreed between the organizing body and fuel supplier).
The problem of the US of course being its sheer size and lack of overarching sanctioning body mandating a singular spec of fuel for the entire country, meaning engine tuners have to
a) Constantly ask what type of fuel the engine in question will run, and tune accordingly, which leads to
b) Not focus on one path of R&D as the difference between fuels is too big (due to percentage of lead content, octane rating, aditives and everything in between)
A solution would be for all promoters to at least agree on values for a maximum octane number, maximum oxygen percentage and unleaded, and then allow for each of them to make comercial agreements with who they deem fit.
These two are valid alternatives with very similar chemical properties :
I know in my area as far as race fuel goes the leaded fuel is about 2/3 the price as the unleaded. Part of this is due to the fact that they have the leaded in bulk and the unleaded only in 5 gal pails. Pump fuel is cheaper obviously, but 91 AKI isn’t good enough for race engines in my experience and that’s as good as it gets here.
So here in Canada (Ontario) this a debate wtihin the local clubs. I started ti run VLR last year for my 2 boys and it was supposed to be an entry level class and run 93 pump gas, the other tracks continued to run the 110 race gas and when members came over it was open fuel. The guys running at the front all ran 110 fuel, but thats because most are part of race teams, but al long as you adjust the timing you can run the pump with no issues. Now next year there is supposed to be so interclub series, problem is one club runs sunoco 110 the other runs VP 110, and some run pump 93…Which one is the spec gas? Its all about $$$ and at $160/pail of gas both clubs will fight to supply there fuel
I think there might actually be a preference among American karters for leaded gasoline, even if they were given a choice at the same price. The only exception would be if they allowed both fuels in one class and people figured out that the oxygenated unleaded fuel made more power.
