I am a little confused. the stock nikki flows around 300cfm. the 12a only needs 130-150cfm or something around that. so what is the point of making the venturis bigger and adding bigger jets to the nikki carb or upgrading to a holley or so on? unless you make the engine displacement bigger, it shouldn't need more air for N/A. where would the nikki carb mod that paul yaw does be a benefit? I am talking no porting or mild porting, either one. thanks for any help

 

130-150cfm
??? where did you get that #

 

Yeah, I'm confused on this number too. At redline, the Nikki can barely flow enough air for the engine. By allowing the air to pass more freely into the engine, you get more power. Hence the reason most people add a bigger carb.

 

i got it from using a calculator on the internet, but then i read somewhere that rotary engines displacement is different. Someone said you need to multiply the # by 2. so does this mean a 12a 1.1L is like a 2.2L piston engine in air/ fuel requirements? thanks, sorry if i am screwing this topic up. i don't know someting i ask.

 

yea, they move about as much air as a 2.2, closer to 2.3

1146X2=2292CC

 

thanks that helps me understand a little more. what about a port job? how much more cfm of air is needed for a mild port? thanks

 

all porting does is allow it to breath easier. Each rotation of the e-shaft the engine tries to pull in X amount of air. the port allows it to get closer to X by having larger breathing tubes if you will. the whole idea is to get it to have less vacuum in the manifold. think about boosted cars obviously no vacuum so they run faster. the closer you can get to 0 vacuum on an NA the faster the car will run. But then again you have to consider port timing and stuff and thats over my head, i would guess relatively close to the same cfm. a way to think about it is CFM= rpm*displacement. obviously you would have to do some conversions. a stock engine if producing 0 mani vacuum would need 323 cfm at 8000rpm.
thats assuming you plug in 1146cc for displacement. if you plug in 2.3L it would be like 647@8000 rpm. I would think it would be 1146 since 1rpm= 1 turn of e-shaft= 1 rotor face *2 rotors.

 

feel free to correct me, its just always the way i've figured it.

 

thanks that gives me a better idea of it.

 

2 ignition events every 1 rpm, so 2x the fuel and air is required and thus the 647cfm figure.

 

wow! i think this is the oldest thread bump yet.

 

im new here can you tell?

 

From what I have read....a 13b engine is measured out to be 2.6 Liters they way they measure for some racing sanction bodies. So, the 2.2 L or 2.3 L falls in line with that.

 

The 12a with stock exhaust, timing, and porting will only be able to handle about 300 cfm. Once you free up the exhaust, advance the timing a bit, and get rid of the rats nest it will easily take a lot more cfms. Thats why we use aftermarket carbs and hog out our nikkis.

 

sort of. if you put the CFM measuring device on something like the exhaust tip, or the air cleaner tip, you would measure something like 300cfm.

however the manifold is setup like an individual runner style, to which the cfm equation does not really apply. in an IR setup each barrel needs to handle the instantaneous demand of the rotor. we go more by physical size in these cases.

its why we had the 300cfm is all the engine needs, but it makes more power with a 600cfm carb argument

if you like, my P port only flows about 400 cfm total, but the carb is 350 per barrel

 

look at Stock Racing cars....NASCAR... the major difference in the two racing bodies is the Carburetor size.. The Saturday cars, (nationwide or whatever they call it now) and the CUP cars (Sunday racing cars) Cars on Saturday run a 390 CFM carburetor... the cars on Sunday, (I know they are FI, now).... run an 850 CFM throttle body (or carb, if You wish)... basically everything else is the same on the two classes of cars.... the cup cars are good for an extra 150 hp with that bigger carb... with all other things being equal. So, more air=more fuel...... = more BANG!!!

 

If it were only that simple. Those motors are way different as well. Theres nothing like stock in NASCAR since the 70s.

 

In both NASCAR motor cases, the carburetor/throttlebody/restrictor-plate is the path of greatest resistance. In the case of a stock 12a, the intake manifold and porting cannot consume any more air so enlarging the carburetor but dropping it onto the stock intake manifold does virtually nothing. Replace or hog out the manifold at the same time and you'll see gains. Port the motor and you'll see more gains.