Automotive How Can I Optimize Airflow Across Different RPMs for My Motorcycle Engine Build?

AI Thread Summary
Optimizing airflow across different RPMs for a motorcycle engine involves understanding the relationship between engine design and air velocity. The engine in question has a bore and stroke of 56x47 mm and a compression ratio of 13:1, leading to specific airflow calculations at varying RPMs. The discussion emphasizes the importance of cam design in achieving productive airflow throughout the rev range, rather than focusing solely on peak horsepower. It is suggested to start with an existing engine design for practical learning before attempting a complete new engine build. Calculating mean gas velocities, ideally between 90 to 110 m/s, is crucial for maximizing volumetric efficiency.
puxley
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Ok so here it goes,
I have a motorbike,and as I am a learning engineer I want to build a second engine for a few reasons, firstly I want to go faster secondly I want to do all the work myself to learn, thirdly I want to become a better engineer and want to do lots of paper work to learn and see how close I can get predictions.

I can see this as a very difficult undertaking as there are many veriables but nothing like a good challenge to get things going.
My problem is I need your fabulous help.
And if anyone wants to give me some homework and reading please push me in the right direction.

Ok the engine will have a bore and stroke of 56x47
It is a inline 4. We will say it is running a compression ratio of 13:1.
So with that being said will need a clearance volume of 10.7081cc per cylinder.

This would mean (not including the clearance volume) it "could" move 3726.498 lm @14500 rpm and 514.007 @ 2000rpm now is where it gets tricky, I would like to try find a flow rate that is productive through the rev range, how would I find out the the best air velocity to do this as I'm not too interested about massive cross sectional area for peak Bhp.

I also will not be near a flow bench till Jan so this is all just numbers to aim for until then. As I understand it (correct me where I am wrong) once I have these rough numbers I can than look towards the cam design to try match them.

Sorry this is so long.
Thanks for reading.
Puxley
 
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Testing a complete new engine design cannot begin until the project is complete. Then everything will fail at once, or you will be unable to point the finger at one faulty component since they come in connected groups.

Consider instead an “apprenticeship” making replacement parts for an existing engine. Calculate everything you need to understand the existing engine design and parts specifications. Each component will be an analysis, design and fabrication job in it's own right. Mastering the skills necessary need only be done once. At every point you can swap out and test components.

Once you know what you are doing you will be in a position to design and make components for an improved engine. You might consider taking an existing two cylinder design and extending it to a four cylinder engine. Will you make your own pistons and rings or buy standard components ?

By progressively replacing old with new you will end up with a complete handmade engine.
https://en.wikipedia.org/wiki/Ship_of_Theseus
 
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No the Pistons and rings will be from a company that had them built for these bikes especially. I will be doing the machining of the ends of the new crank, the barrels the decking, and the head work, I mainly want to do the calculations to get a better understanding of how everything relates to each other, I have full confidence in everything except the head where the Calcs will be more for fun as I won't get any real world application until it's on a flow bench, thank you for your reply
 
According to the https://www.amazon.com/dp/0837603331/?tag=pfamazon01-20, p. 406, «The highest volumetric efficiency values are achieved at mean gas velocities of 90 ... 110 m/s (empirical values).»

The mean gas velocity is defined as ##v_g = 2ns\frac{d^2}{d_v^2}## where ##n## is the rpm, ##s## is the stroke, ##d## is the bore and ##d_v## is the valve diameter.
 
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Awsome thanks for the info!
 

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