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Dragbike.

General Engine Building Discussion

Talk about engine building here. New products, tricky questions or showcase your work - If it's engine building related it's welcome here.


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Hi. First I want to thank you for your excellent courses. Even though English isn’t my first language, I had no bigger problem to understand the course. The result of the education I got from you is that I got my own dyno and tuning has become a big part of my business. (I am working with motorcycles) Mostly flashing but also live tuning.

Now to my question. I have started building a drag bike with an 1800cc twin. The bike is going to run with turbo/methanol. The question is what injector size I will need? What is to prefer, 2 or 4 injectors? No one seems to know when I ask, or should I say everyone knows. It really seems like they are guessing, and that is why I am asking you. I hope you have got some good suggestions. I will have two engines delivered to my shop in a few weeks and I am really looking forward to get started with the build. If you like I can keep you updated when it comes to the engine build.

Thanks and I wish you a really happy new year. Lars Sundberg Sweden.

Hi Lars, and thanks for the feedback! Great to hear you're enjoying the courses.

Methanol is a great fuel but you need to use a lot more of it in order to achieve the correct air fuel ratio when compared to gasoline. In rough terms I multiply whatever fuel demand I need for gasoline by 2.5 times if I'm moving to methanol. I can't give you specifics because it would require an idea of the power level you're expecting and what rpm you're going to run to. 1800 cc is large for a twin so you'd almost certainly want to run two injectors per cylinder (possibly even 3) in a staged fashion. The aim is to be able to provide the relatively small amount of fuel required for idle, while still being able to keep the engine happy at full power.

For a really rough and ready rule of thumb, I assume that you need approximately 1 litre of gasoline per minute for every 200 hp you want to make. That obviously becomes 2.5 litres per minute on methanol.