Hi
I am looking for anyone with the knowledge and patience to either explain, or guide me to any sources that are able to explain to me (in techical terms) why a turbo rated for 600hp will only deliver 400hp on a rotary car.
The reason i want this is so that i am able to get approved a single turbo conversion by the local authorities, and they have limits to how much a turbo can deviate form "max" to "actual" performance on a car.
For me this cause problems because we all know that a EFR 8374 will not deliver the piston rated "500-800hp" in a rotary car. So when i come in with a 800hp turbo, and a dyno chart saying 400, they will think i am approving the car in a detuned state and wont approve it.

So i need to make a solid and scientific case about the differences between piston and rotary in terms of air movement, to prove that the turbo does indeed max out at XXX in a rotary car. Can anyone help?

 

Well, the EFR 8374 will indeed reach over 500 whp in a Rotary, also the ratings are usually at the crank (BHP) so 500 whp is about 590 bhp on a RWD platform.

I'm sure @Howard Coleman and others can better explain why a Rotary needs more mass flow for the same power, it has to do with the thermal efficiency of the engine due to the moving elongated combustion chamber and increased heat loss compared to pistons.

 

Howard already explained it very well in post #1 here:

https://www.rx7club.com/single-turbo...e-e85-1056358/
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this will help too; 720° reciprocating cycle vs 1080° wankel cycle:

https://dsportmag.com/the-tech/educa...ary-vs-piston/

and its actually piston hp x 0.769 is ~ rotary hp

600 hp piston is ~ 469 wanking your wankel hp
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With a strong likelihood they won't accept randoms off the internet or automotive journalists as very authoritative, you might try to find appropriate SAE papers - which you usually have to pay for unfortunately - Mazda has done several from memory over the years and I recall others who dabbled with the inefficient device, presented a few too.

Other than that, one of the technical colleges here long decades ago, did have an old water brake with various engines at hand, including wankels, where you had raw readings and had to do the usual BSFC, BMEP, etc, calcs. If there's such a thing there in Norway and being quasi(?) government, with a love of record keeping, documentation like that might be far more palatable for bureaucrats.

 

www.academia.edu is a good place to find research papers. There are tons about rotary engines.

 

BSFC

As noted the reason a rotary engine makes less peak power on a maxed out turbo than a piston engine car on the same turbo is-

Rotary engines high Brake Specific Fuel Consumption (BSFC) at peak horsepower.

I takes more fuel (and the attendent air from a turbo) to make the same peak power as a piston engine car with lower BSFC.

Typical turbo piston engine operates between 0.60 BSFC and 0.65 BSFC at peak horsepower.

Mazda has documented its rotary engines 0.77-0.88 for the 13B-REW at peak horsepower.

You can clearly see that dividing piston engine peak HP BSFC by rotary peak HP BSFC lands you square in the rule rotary 0.70-0.75 multiplier ryle 9f thumb for peak HP off a specific size turbo compared to piston engine car.

 

and yet it makes more power relative to displacement than a piston engine. So it’s actually a twisted combination of factors that isn’t so simple as just this one thing or that one thing. The larger combustion surface area that absorbs more energy as heat, the long combustion chamber relative to torque arm created by the orbiting rotor and leading/trailing plug firing that creates a combination of both positive and negative work, and so on.

You can get into all that if you want, but as per the other reply in a different thread; they’re just known quantities based on history/experience that bear out to be approximately true in general.
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Very helpful thank you!

 

it’s probably closer to 0.74x - 0.75x
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Exactly this. Rotaries are less efficient at converting fuel into power. Therefore, for a rotary to make as much power as a piston engine, it has to inject more fuel. In order to burn that extra fuel, it has to consume more air.