Gearhead

iTrader: (1)

I'm needing to know what the total displacement of a rotary is going to be in 1 revolution. Would a 13B be 1.3 liters per revolution or every 2 revolution? I think piston engine displacement is every 2 revolutions. Example- a 302 cu in displaces 302 cubic inches of air every 2 crank revolutions assuming 100% volumetric efficiency. I'm playing with some calculations trying to decide what turbo meets my needs since it's time to pony up and get one anyways. Please don't tell me what turbo you have or what I should get. I just want to know the airflow. I want to play with the numbers and check flow maps. Gives me something to do in my spare time.
Thanks, Don.

[IMGhttps://www.rx7club.com/ubb/cwmsmilies/cwm15.gif[/IMG]

Evil Aviator

Yes, the 13B flows 1308cc/rev @ 100%Ev, while a piston engine would flow only half of its SAE rated displacement.

That's great that you are looking at performance, rather than hype, status quo, and shiny chrome. However, you will need to rely on experience (yours or otherwise) in order to complete your equation for a turbocharger. Compressor maps are great for getting a "ballpark figure", but they are based on only one particular A/R nozzle and one ambient condition (usually 0.069 lb/ft3, but who knows?). Also, the map will not help you with calculating the boost threashold, lag, and other application-dependant criteria. Definitely do you homework first, but I still recommend going to your local Mazda-smart turbo shop when it comes time to order and install the goods.

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88 RX-7 20B/T66 Money Pit
88 RX-7 TII Daily Driver
84 RX-7 GS Driving School Beater
00 F-150 Recovery Vehicle

Gearhead

iTrader: (1)

Thanks man, that's what I needed to know. I'm looking and listening to what you guys are doing for sure, but like you said... I'm not one to look at hype. I like to see facts in black and white. I know too many ppl that have this or that because someone told them it was the thing to have. I'm very hands on. I appreciate your response and would like to see your rides in person. Thanks, Don.

spyfish007

Well, why we are at it, how about some more questions. What is the volumetric efficiency of a rotary? What is the thermal efficiency of a rotary? Just wanting to look at some compressor maps and the above mentioned VE would really. Anyone? Any thougth as to what shows up in practical applications vs theory?

setzep

I asked this same question a few months ago and the big guys told me that a non ported 89-91 turbo block had a vol eff of 130% but didn't go into real detail. That was right before the big crash of the forum.

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Turbo.....the displacement replacement

spyfish007

I looked around on the net and it seems like a rotary can be anywhere from 50% to well over 100% volumetric efficient. I don't think a piston engine will do this. However, it seems that the thermal inefficiencies are the limiting factor in a rotary engine. Don't have hard facts, only some general thoughts from what I think I saw online.

RICE RACING

You need to know VE, BSFC, and a few other basic things to calculate out your mass flow and hence bhp you will get.

These are complex calculations that very few people in the world can calculate out in a accurate way for RE applications, the main reason is becasue they are dependant on many MANY DIFFERENT VARIABLES. For example a rear turbo housing a/r change has a large effect on VE of the engine, as does manifold design for example.

I have a large accurate data base of various combinations for n/a and turbo wankle engine applications, if you need a specific combination calculated out drop me an e-mail and I will get back to you with a calculation specific to you modifications.

ps. VE's for RE engines vary from 75% (std side ports) to 120 to 130% (for PP engines)

HWO

basically to figure out what your turbo needs to be, you work out how much HP you really want, find someone who is making those numbers and copy their set up, or adjust accordingly.