First gen man

iTrader: (24)

Does anyone know the mass airflow rate of a 13b 4 or 6 port with stock manifolds? I've searched and dug around the internet now for awhile, and I can't find anything. I'm pretty sure I can't use the standard calculation for a piston engine. Maybe using a volumetric efficiency of 300%...
I was hoping maybe somehow, someway, someone, recorded a few mass airflow rates at various RPM's.
Or a second option, does anyone know an equation I can use on the rotary to determine mass airflow?

How is anyone selecting turbo's?

87 t-66

iTrader: (133)

most people ditch the afm and get a standalone when using an aftermarket turbo.

ifryrice

Way to read the thread...

Calculate it using the following:

2616cc displacement
4 cyl
4 stroke
~80% VE is a good start.

87 t-66

iTrader: (133)

i did read the thread smart ***. it seems that he is wanting this info to upgrade his turbo...

ifryrice

Yay for quoting out of context. Let's play make it obvious!

It would appear he's looking for a number related to flow rates.... I wonder why?

Hmm, trying to figure out how much air it flows.... ok.

Oh, maybe that's why.

What does turbo sizing based upon flow rates have to do with removing the AFM when upgrading turbos?

Evil Aviator

I am good at airflow number crunching, but quite a few forum members are good at knowing what has historically worked well with a given 13B configuration. What is your question?

arghx

iTrader: (3)

There is a sticky thread on this in the single turbo section of this forum.

displacement of 2.6 and VE of 85-90% are most common. and then most people run at a pressure ratio between 1.8 and 2.2 if they are using straight 93 octane fuel.

KhanArtisT

iTrader: (2)

ReTED's website calculated it as 30-40 lbs/min. More towards 40 if its been ported.

First gen man

iTrader: (24)

First off sorry for not seeing the sticky.. I didn't think this was being discussed since I couldn't find it. Hence the how is anyone selecting turbos? comment. Sorry again for that.

Thanks alot though. Using 2.6 as displacement makes good sense. I was thinking about doing it with volumetric efficiency just to be a smartass. This seems more proper though.

I have a standalone without a MAF sensor, and a 60-1 already. More or less I followed Evil Aviator's method of a few people do know what works well.

I would just like to see how close I am to full efficiency with this turbo finally. (if at all) Also I bring all of this up, because mostly I'm looking for what boost pressure to run. I've decided to push more boost than the 13 PSI I'm currently running and I wondered if going to 18 psi instead of 15 psi would maybe put me on a more efficient island.

Evil Aviator

The reason I didn't post a number like that is because the question was not clear, and it is really easy for non-engineers to misunderstand such things. For example, the 30-40 lbs/min that you posted is for a 13B that is running a fair amount of boost. The way I read the question it seemed like the OP was asking for the airflow rate without boost, as none was specified. Regardless, even once a number is determined, it seems like a lot of people still don't know what to do with it. That is why it is usually better just to see what other people have determined to work well, although I think it is good to try and crunch some numbers to get a better understanding of why one system may work better than another.

Don't forget that the compressor map indicates the psi at the compressor outlet, while the engine's boost is normally set to the psi of the intake manifold. There will be a certain amount of pressure drop between the compressor and the manifold depending on the plumbing and intercooler. To determine the drop you need to plumb a boost gauge somewhere near the compressor outlet, and then find the difference between this and the regular boost gauge attached to the intake manifold. If you would rather just take a guess as opposed to doing all that work, the drop is usually around 2 psi or so.

Given that, assuming the standard atmospheric conditions of the compressor map of 85degF inlet temp, 29.92inHg ambient pressure, 1.52inHg vacuum at the intake = 13.95psia compressor inlet pressure, and estimating the compressor outlet pressure 13psig manifold pressure + 2psig pressure loss = 15psig, then you can estimate your current pressure ratio ((13.9psia+15psig)/13.9psia) = 2.08 PR on the compressor map.

If you look at the 60-1 compressor map and follow the intersection of the 2.00 PR and 40 lb/min lines, you will see that your boost level hits the top of the center efficiency island. Any more boost would move your system outside of the efficiency island. Therefore, your current 13psi boost setup is about as optimal as you can get. Kudos for you!
http://www.turbocharged.com/catalog/compmaps/fig9.html

First gen man

iTrader: (24)

Evil aviator, your a good help, thanks alot for all of that.

The new question is, does anyone have any actually airflow readings to compare this equation with? Anyone ever seen how much it flows with a MAF sensor?

First gen man

iTrader: (24)

No one with anything on my last question there?

arghx

iTrader: (3)

I have logs of a completely stock Rx-8 hitting about 220 grams/sec at 8000rpm as measured by a factory mass airflow sensor. So it's going to be less than that.

First gen man

iTrader: (24)

I convert 220 grams/per second to 29.1010186 pounds per minute. Correct if I'm wrong.

Also from what I have read and learned, most compressor maps are when you are using that turbo. Hence putting in your pisg level.. Everyone has been saying from 35-45 pounds per minute airflow, that sounds about right for a 20-30 lb per minute non-turbo engine to flow once turbocharged.

First gen man

iTrader: (24)

No one has confirmed any actual flow rates on street turbo setups or high boost types?
Whats the pounds per minute of a 35 PSI peripheral port?
Some of the turbos they use surge around 30-40 lb/min haha

I just want some actual proof of some numbers, and to find out what our record highest flow rates for a 13B are.

nycgps

iTrader: (4)

Someone had a graph before. forgot who.

I think SAE has papers about it.

j9fd3s

iTrader: (3)

we have this thread with the airflow meter voltage vs airflow graphs.... but no, nobody has measured anything since the internet.

2-N-D-pink

iTrader: (27)

To figure out how much airflow you need for your desired boost level here is a formula:

(Displacement) (RPM) (Volumetric Efficiency) (Pressure Ratio)/5660

Displacement is easy, use your displacement in liters rounded to the nearest tenth. For a rotary, we have to convert to piston math, so a 13B is 2.6L, a 12A is 2.4L, 20B is 4L.

Pressure ratio (PR) is boost-dependent, so it changes depending on what boost and RPM you want to run.


So, for example on a 13B-REW:

(2.6L) (8000rpm) (90%VE) (2.2)/5660 = 727.6

The number we just received is our CFM (Cubic Feet per Minute), which is a volume measurement of a gas, in this case, air.
So now we have an air flow requirement of 727.6 CFM. So what? Now we need to complete yet another conversion to get our CFM into lbs/min.

Formula:
(CFM) (0.069) = lbs/min

And our example:
(727.6) (0.069) = 50.2 lbs/min

2-N-D-pink

iTrader: (27)

I also found an "Engine Volumetric Flow Equation" in this web site. I cant remember which site led me to this. I think it was a link off ReTED site. It was a while ago and I cant remember but I think you have to download it.

Turbocharger Compressor Calculations


It says turbo compression calculator but it gives equations for Volumetric efficiency. Also, at the bottom of the page there is a link to a spread sheet. You can put your info and it does calculations for you. Read it through...its much simpler than it looks.

Furb

iTrader: (2)

Your calculation is wrong..
just multiplying the displacement by 2 is not the way to convert to piston figures

Also, rounding off figures before the formula, will give different results

From all the flowcharts ive seen, a rotary puts out between 30 and 40
30 being a stock 13B, near 40 is a bridgeported 13B

Your result of 50 is way too high

2-N-D-pink

iTrader: (27)

Is this on a turbo engine or non turbo? Please correct me if Im wrong. This is from what I understand and the information was through another forum. Some flow charts would help.

Another example from what I understand...Lets use a stock turbo II engine. The stock turbo II engine (at least the jspec from what I know) redlines at 7k rps and boost is 8 psig.

(PR) Pressure Ratio is defined as absolute outlet air pressure divided by absolute inlet air pressure. To figure out pressure ratio you would need this formula.


14.7 + boost pressure / 14.7 = (PR)
14.7 + 8psi = 22.7 / 14.7 = 1.5 (PR)


In this case 14.7 represents ambient air pressure at sea level.


So lets use the last formula for the stock TII engine.

(Displacement) (RPM) (Volumetric Efficiency) (Pressure Ratio)/5660

(2.6L) (7000rpm) (90 volumetric efficiencey) (1.5PR)/5660 = 434.0989399293286 (round to the nearest tenth) 434.1CFM

Formula:
(CFM) (0.069) = lbs/min

(434.1) (0.069) = 29.95 lbs/min



So now we can say that the stock TII engine puts out 29.95lbs/min. Raising or lowering pressure ratio will give you different answers. Also not rounding out to the nearest tenth will give you the same answer. Lets do another example..

Lets say in this case we are at 5000ft above sea level. At 5000ft psia = 12.2.

12.2 + 8psi = 20.2 / 12.2 = 1.7 (PR)


Formula:
(Displacement) (RPM) (Volumetric Efficiency) (Pressure Ratio)/5660


(2.6l) (7000rpm) (90VE) (1.7) / 5660 = 491.9 so were gonna say 492 CFM


Formula:
(CFM) (0.069) = lbs/min

(492) (0.069) = 33.94 lbs/min



From what I understand here is that if you are in sea level you would need more boost pressure to make the same amount of lbs/min as the second example. Unless this whole equation is fake and all non ported rotary engines make about 30lbs/min and ported ones are the only ones who can pass that. If thats the case what about non turbo engines.


Formula:
14.7 + boost pressure / 14.7 = (PR)
14.7 + 0psi = 14.7 / 14.7 = 1(PR)



Formula
(Displacement) (RPM) (Volumetric Efficiency) (Pressure Ratio)/5660

(2.6) (N/A redline 8000rpm) (90) (1) / 5660 = 330.7



Formula:
(CFM) (0.069) = lbs/min

(330.7cfm) (0.069) = 22.81 lbs/min



Hmmm. I think we should bridge port this engine. This will bring the rpm up.

Formula:
(2.6) (13000 rpms) (90VE) (1) / 5660 = 537.5

(537.5cfm) (0.069) = 37.08 lbs/min



One can get into further detail by figuring out absolute temperature. The link above shows you how. If this information is wrong, then whats the formula that your using for the rotary engine. Im multiplying 1.3L x 2 to get the displacement for the formula. If I use 1.3 as the displacement on the formula then the number that it equals out to is way too low...

Evil Aviator

Multiplying by 2 is correct. This is because the common formula is intended for 4-stroke piston engines that only fire 1/2 of their displacement for each rotation of the output shaft. Rotary engines and 2-stroke piston engines fire all of their displacement for each rotation of the output shaft. Therefore, your options for adapting the formula for rotary and 2-stroke piston engines are:
A) Multiply the displacement by 2 and use the formula as-is.
B) Or remove the 2 from the denominator of the formula.

Yes, the volumetric efficiency will be different for a rotary or 2-stroke engine, but that affects a different component of the formula, and the variable is adjusted as necessary by the user. Porting will also affect the volumetric efficiency differently at various engine rpm points.

The boost level will affect the flow rate. He used a 2.2 PR in the example, which is about 17 psi boost. This is why the flow rate is higher than what you usually see.

The number is also a little high because he did not account for pressure drop at the air filter inlet or inside the intercooler plumbing. This typically reduces the boost by about 2 psi. However, it usually doesn't hurt to use slightly inflated numbers when planning your system so that you have some room for error and future upgrades.

The 13B is actually rated at 1308cc (1.308L) displacement.

First gen man

iTrader: (24)

furb, you said you have seen flowcharts? How were these flowcharts made? Anyone else have actual evidence of what some 13b's have pumped?

Furb

iTrader: (2)

Flowcharts of turbochargers, not of the rotary engine itself

But the quotes stating flow between 30 and 40 come from rotary specialists that i have found throughout the years

lastphaseofthis

iTrader: (8)

Is this is the point of the thread? proof? records of highest flow rates?
or is there an under lining point?
B/c theres enough posts about this stuff to select a proper turbo for your desired power.

sounds like you're wasting everyones times over Semantics.