Discussion and questions related to the course Understanding AFR
I have engine, full race application: Honda B18C engine: CR 13.8, N/A, rpm range 6500-10500. I tuned it with blend of 10% nitromethane, 5% castor oil, 3% acetone, 2% water, 80% methanole, lambda 0.7. Engine is working fine, but I want to move further and increase nitromethane % up to 25-30%. Could you please, advise me the right and the safe way?!
1. Blend? I think with (30% nitromethane) to increase amount of castor oil up to 10%.
2. A/F ratio?
3. Ignition with nitrous? I think, 30% blend should rise MBT up to 6 degrees compare with straight methanol, but with nitrous (100-150 hp), ignition should be roughly the same like with straight methanole?
4. In your opinion, what is max % of nitromethane to keep engine from boom )))
Unfortunately I can't offer much advice on nitromethane as I've not utilised it myself. It's not a particularly common fuel outside of the upper echelons of drag racing in my experience. If you're going to increase the nitromethane percentage I'd recommend targeting a richer air fuel ratio to begin your tuning and see how the engine responds. You're best to have the engine so rich initially that you're on the limit of the ignition system's ability to light the fuel and then gradually lean it off and see what effect it has on power.
In terms of ignition timing nitromethane is a slow burning fuel that requires more advance but the dyno will tell you where MBT is. In this respect it's going to be no different to tuning any fuel. Likewise you're still going to need to retard the timing with the introduction of nitrous.
I can't give you a safe percentage of nitromethane to run. It's going to put a huge amount more stress on the engine internals and that's going to come down to how well the engine can handle these additional loads. For example what rods are you running? Is the block sleeved? Ultimately you're likely to also find that head gasket integrity is an issue, particularly if you're adding nitrous too.
I wish you all the best and please keep us informed of your results.