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Fuel spec. For vp’s 50/50

Ethanol & Flex Fuel Tuning

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Discussion and questions related to the course Ethanol & Flex Fuel Tuning

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Hello, recently I’ve been trying to find the fuel specification sheet for the VP 50/50 fuel (50% Methanol 50% Nitromethane) since it’s not listed on the official website. Perhaps if there’s a way to calculate 2 different fuels with different stoichiometric ratios & different percentages please let me know.

Thank you.

Generally speaking, I'd want to know if it's mixed by volume or by weight, and I'd want the specs on each of the fuels being blended, and far more ideally the specs of the blend they're selling because stoich point is just one factor.

In your case, nitro weighs about double what methanol does per mol, so how the measure and determine a 50/50 mix is important. Machine mixing is often done by weight so I'd ask.

In this case, M1 specs might be correct for the methanol portion, they don't post nitro specs, on top of it being unclear how they're mixed. There are too many unknowns. I'd contact VP directly and ask.

Most likely you could throw stoich point of 3 into an ECU and get it running, but having proper fuel specs is the way to go whenever possible as the fuel model is so critical.

These are more discussion points, so DO YOUR RESEARCH, using multiple sources, as it's a potentially nasty, dangerous fuel that has a lot of potential for doing harm. There is a reasonably informative thread here - https://bobistheoilguy.com/forums/threads/homebrew-race-fuel.346024/

I think Mike meant an AFR of 3? Stoich' would still be lambda 1.0. In practice, you're probably going to be looking at closer to 0.8?

If you use the below values

Stoichiometric Air/Fuel Ratio

Gasoline = 14.7

Methanol = 6.47

Nitromethane = 1.70

It is in theory an easy calculation as you take 1 unit of eachand work out what their individual mass of air required is add them together and dive by two, eg

1 pound of methanol requires 6.47 lbs of air, 1 pound of nitro' requires 1.7 lbs of air, therefor 2 lbs of 50-50 will require 6.47+1.7 = 8.17 lbs of air and so 1lb of 50-50 will require 4.085 lbs of air.

You can also work that backwards to estimate the amount of fuel required if you know the air mass entering the engine.

The problem, as Mike said, is you NEED to know if it's a 50-50 mixture by volume, or mass(weight) because they are very different in density, and so there may be a big discrepancy if you use the wrong values. They also have differing expansion rates, for the same mass (weight) the ratio of the volumes will change with temperature - this is not really a problem chemically, but it WILL affect the overal air-fuel ratio.

You may also find it beneficial to read this useful primer - https://www.motortrend.com/how-to/hrdp-1304-what-is-nitromethane-anyway/

Pay particual attention to the detonation and other hazards of the fuel, such as it's corrosive nature, which can mean a complete replacement of the fuel system if it's not specifically made for the fuel.

TBH, though, from the question, I'm not sure you should be messing with this blend, unless you have a lot more experience than it seems?

Yessir I was saying 3 as in 3:1 would likely start the engine, not saying it's the appropriate value. Getting an engine started and optimizing a tune are quite different.

As Gord said you can ballpark the stoich point of a blend from 2 stoich points using a weighted average. This works for blending pump gas octanes as well, but when it comes to nitro and methanol the weight difference is massive so you'll want to know how "50/50" is determined.

With known good injector data, fuel pressure being accounted for, and an engine calibrated well on a known fuel prior, you could enter a ballpark stoich point for the new blend, switch fuels, then adjust the stoich point in your ECU until the engine hits lambda targets like it did prior, and consider that value likely in the ballpark of correct.

You're definitely jumping into the deep end with that fuel blend as Gord mentioned. If you haven't already, the progression I'd suggest is tuning for M1 methanol, then try M5, then try mixing up your nitro blend, then if you still want to try 50/50 go for it.

Ballparking the stoich point ends up being the quick/easy portion of sorting out a blended fuel because while the stoich point can be determined with relative accuracy in a few ways we've mentioned, blended fuels often don't behave like the weighted average of the behaviors of the fuels being blended, and these two fuels have rather different behaviors.

Thank you guys for the reply I’ll look more into this.

I was looking to use it in the future for N/A racing applications.

I’ll contact VP and see if they’ll help me out.

Please let us know what you find. Good luck!

Forgot, a couple of BIG caveats to add to the list.

You REALLY need to build the engine for this because the increased power/torque is from the increased cylinder pressure - obviously - so you need to consider it as being a high boost engine build. Depending on the fuel blend, you're looking at double, triple, quadruple or even higher pressures and you're going to need the hardware to support that - probable sleeves, head studs, pistons to suit that may be custom, connecting rods, probably crankshaft on top of the clutch and other transmission parts.

The second part is this fuel can be DIFFICULT to ignite reliably, and it HAS to be ignited because any misfire will leave unburned fuel in the cylinder and, while some will pass out the exhaust, it will take only a few cycles for a substantial amount to build up - this DANGEROUS because NM is susceptible to compression ignition, like a diesel, and the fuel in the cylinder doesn't 'burn', it EXPLODES (one of the reasons I referred to it as nasty earlier), and that will not only cause head gasket failure, it's been known to blow heads of engines, split blocks, pretzel con-rodss, end crankshafts through the bottom of the engine, etc. on top of the fire danger.

If you use this fuel, spend the money and make sure it has the voltage and amperage required for a STRONG spark!

Even something as simple as turning the engine over can ignite fuel residue! - These engine were probably using a 90% nitro' blend (I think that's the legal limit now), but they should give you some idea of why the fuel isn't for beginners - https://www.youtube.com/watch?v=FJwwXEZpXcI and https://www.youtube.com/watch?v=pqHPSxJ0LbE

I sent an email to VP and they responded with this:

Specific gravity @ 60F is 0.975

Stoichiometric A/F ratio = 3.65

I think that adding nitro gradually with pure M1 would be the best strategy

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