exhaust port major chamfer...

Any form of normally aspirated power mods.
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Re: exhaust port major chamfer...

Post by PaulAV » Sat Feb 16, 2019 10:30 am

Imagine a flow test bench could be used, bolt a plate onto each side /end plate with a connection for the metered air supply, similar to how you would flow a head, would involve separate flows for each port(inlet and exhaust for each plate) though
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Re: exhaust port major chamfer...

Post by delta0 » Sat Feb 16, 2019 11:03 am

PeteH wrote:
Sat Feb 16, 2019 10:25 am
Tricky. I don't even think you can flow bench a rotary, because the rotor has to be in two different places for the intake and exhaust.

I wonder if any commercial engine software package has been designed with rotaries in mind.... Do you think GT Power can do it Matt?

We can use the principles of piston engines to define reasonable values for port timings and areas, and Mazda do publish some numbers for port area versus rotor position. So that helps.

I guess the only real ways to do it are:
1) Do loads of experiments and iterate to the best solution.
2) Spends big bucks on a general purpose CFD package, then spends months developing a full combustion model. Then spend many more months playing with port options to optimise the flows.
Access to CFD packages isn’t a major issue. I have access to these. It is modelling correctly that is the challenge.
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Re: exhaust port major chamfer...

Post by 350matt » Sat Feb 16, 2019 12:00 pm

I think GT power could probably do it Pete
I've never had to do a simulation myself but we use it a lot at work and its excellent at cutting out a lot of guesswork / experimentation

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Re: exhaust port major chamfer...

Post by RobinPZ72 » Mon Feb 18, 2019 2:31 pm

I'm not going to get to evolved here, but all you need is how fast the rotor does a complete cycle or can we say revolution. then break it down into deg relevant to the engine cycles Suck, bang & blow. then find the time in seconds for each job. once you've done that there is formula, which have been around since the 60s, which will give you either your guess is not big enough for any meaningful gains or WTF and what have you done.

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Re: exhaust port major chamfer...

Post by PeteH » Mon Feb 18, 2019 5:57 pm

That's certainly the starting point, but it rapidly evolves into something hugely complex. This is a small part of the spreadsheet I use to calculate my engine mapping. It certainly considers the time available through the cycle, and it has some porting specifications in it. It can be a reasonable model, if it is parameterised correctly. But I wouldn't like anyone to think there are simple equations to calculate flows, losses, efficiencies, and the hundreds of other parameters that ultimately go into getting a well tuned motor.
Engine Power Spreadsheet.jpg

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Re: exhaust port major chamfer...

Post by 13Black » Mon Feb 18, 2019 6:06 pm

I'm particularly fond of 'Random Number To Convert Gas Mass To Power'.
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Re: exhaust port major chamfer...

Post by PeteH » Mon Feb 18, 2019 6:14 pm

I knew you see that instantly :lol: :lol: :lol: :lol: :lol: :lol:

This sheet is my mapping sheet, so I don't do the combustion calculations (they need to be done at stupid high frequency). I have another sheet that does those, then I produce that fiddle factor from those proper calcs. The fiddle factor is fine, and is adjusted via all the other VE values and so on. This sheet focusses on getting exactly the right gas mass, and therefore producing exactly the right AFRs, injector timings, dwell angles, etc.

It actually doesn't matter what torque and power this spreadsheet predicts. I get that from the other sheet. I only do it here so that I can have an idea of part-throttle behaviour.

So there. :P
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Re: exhaust port major chamfer...

Post by RobinPZ72 » Mon Feb 18, 2019 11:04 pm

The problem or difficultly arises when it’s a new concept, but a pre-designed mechanical object with known std dimension and other info. Isn’t that difficult to predict what’s going to happen but does require time and understanding fluid and thermodynamics. We did a study proving this some time ago where we calculated how engines would behave in certain scenarios and predicted when failure would happen using simple co-efficient of friction of the metals and oils use. It was one of the best studies I did as we had to get another specialist tutor in as the smart asst me myself and I tutor lost the plot and because he couldn’t do it no one could.

anyhoo that's enough from me!

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