rx7 SE

iTrader: (5)

I've been doing some searching around the thread but can't seem to find any information on how well stock ports on a s4 TII will flow. I'm trying to calculate how well my turbo set up will mesh with my stock ports but it is difficult if I don't know the approximate maximum flow rate of stock ports. If there's anybody who can tell me how much power they made on stock ports that would be more than helpful too!

Thanks guys

~Ant

jjwalker

If you can find the square port area and the runner length (runner length doesn't include the plenum behind the throttle body) then you can get a close figure as far as flow rate is concerned at any given rpm.

rx7 SE

iTrader: (5)

I'm under the impression that not only the area of the ports but the bends and turns within the irons the ports take will effect the maximum flow as well, which is something I don't have the ability to measure. In my case it would be more time and cost effective to see if someone has reached the maximum potential of the stock ports and hence the maximum flow rate I would assume.

From an engineering perspective I feel knowing a rough estimate of that number would help greatly in planning ahead /deciding on what turbo to run, how much boost, expected power output, fuel requirements, etc. etc....once again, saves time and money....and stress

MaczPayne

iTrader: (5)

The intake manifold plays a big role in flow as well.

I don't think there's an easy way to calculate this on paper, you'll probably need to build a flowbench.

gawdodirt

Intake manifold is important only if it is in restrictive conditions. You could have a fire truck hooked to a garden hose and it will still only flow what the smallest restriction/cross section will flow. Oddly enough, this given is applicable to N/A and pressurized.

gd

rx7 SE

iTrader: (5)

Wouldn't you think the ports would max out in flow before the manifold since they have the smallest cross sectional area?

arghx

iTrader: (3)

max flow at what pressure ratio? increase the boost and you will flow more air

rx7 SE

iTrader: (5)

This website is siding more around 30 lb/min http://fc3spro.com/TECH/TURBO/compmap.html although that seems a little low even for stock ports..

Evil Aviator

The engine's max flow rate without boost is about 16lbs/min, so I am not sure why you think 30lb/min is low.

Tell you what, just post the following info and I will give you a ballpark flow rate figure so you don't need to hurt yourself with higher-level physics...

- What is your intended max boost level?
- Are you using a stock intercooler or aftermarket front-mount intercooler?

rx7 SE

iTrader: (5)

Let's see....I have a BNR stage III hybrid which flows about 40-47 lb/min max and I plan on running 15 psi once I settle on injector size and which EMS upgrade. I'm also running the stock top mount intercooler in conjunction with a coolingmist progressive water/meth kit to keep AIT's down under boost with such a small intercooler.

Thanks,

~Ant

arghx

iTrader: (3)

I don't know about on an s4 T2 with no turbo, but a stock Rx-8 can flow almost 30 lb/min without a turbo. Attached is a log of engine sensors on a WOT run for a completely stock Rx-8. Peak mass airflow, as measured by the MAF sensor (stock car so the reading is correct), is 225 grams/sec. Using a conversion of .1323 lb/min per gram/sec , that's 29.5 lb/min at 8300rpm. Peak volumetric efficiency (labeled "Calculated Load %" here) is 109% at 6000rpm. Volumetric efficiency is defined here as measured mass airflow divided by theoretical mass airflow under standard conditions. Note that the throttle position reading pegs at 66% for WOT.

Based on those Rx-8 numbers, I would be surprised if an s4 T2 really flowed as little as 16 lb/min without a turbo. That's only about 120 grams/sec. What's really interesting is that the Rx-8's 225 grams/sec is almost exactly the same amount of air my buddy's '05 Subaru Legacy 2.5GT flows with full exhaust and higher boost (16ps) on stock turbo. Rotaries flow a lot of air, even if the engine geometry is not the best for torque production or fuel economy.

sc0rp7

iTrader: (3)

The stock top mount will be your restriction IIRC...

Evil Aviator

A stock-ported TII engine would flow about 16lbs/min at 6500rpm without boost. To double-check the number, we can estimate horsepower @ .55 BSFC and 12.5:1 AFR to come up with 140bhp, which is pretty close to an S4 NA 13B at the same rpm. At 7500rpm redline it would flow about 21lb/min without boost. Under the standard Garrett turbo map conditions (85degF and 28.40inHg) it would not get to 30lb/min without boost or porting. Math: (80cid * 7500rpm * 85% EV)/1728 = 295cfm * 0.069146lbs/cf = 20.4lb/min.

The RENESIS numbers in your readout are higher because:
- The intake air temperature is below the SAE standard.
- The RENESIS flows more efficiently than the 13BT, which is one reason why it makes more horsepower without a turbo than the 13BT does with one. Technically the RENESIS is slightly supercharged.
- The RENESIS has a higher operating rpm.
Math: (80cid * 8310rpm * 102% EV)/1728 = 393cfm * 0.07567lbs/cf = 29.79lb/min.

I am guessing at some numbers here, and I am ignoring small factors like air moisture, but the numbers should be good enough for a compressor map SWAG.

They only seem to flow a lot of air because they have a horrible BSFC, and therefore it takes more air (and fuel) to make the same horsepower as a piston engine, lol.

Restrictions are relative. The only reason I asked for the intercooler type is so I can take a SWAG at the pressure drop in order to estimate P2c. FMIC systems can actually have more pressure drop than the stock top mount.

rx7 SE

iTrader: (5)

Great information guys, I'm glad the things I'm learning in class are actually used out in the field.

Anyway, so to say a s4 TII motor flows 16lb/min with no turbo I would assume that is because the motor itself doesn't have the displacement ie, torque to flow that much air under its own will? So that is why we slap turbochargers on these engines, but, is 30 lb/min the limiting factor for stock ports? Would that be a safe assumption, if that were the case then my turbo/exhaust setup will significantly outflow this motor .

That can't be the case because 30 lb/min is along the lines of 226 rwhp is it not, which is not that hard to get with just a stock turbo. I must be missing something then

arghx

iTrader: (3)

have you read this? https://www.rx7club.com/spec-tuning-154/how-size-matters-478915/

Chaotic_FC

heres a few..

first cars build thread:
keep in mind this is a REW, but it is an unopened engine..

https://www.rx7club.com/single-turbo-rx-7s-23/another-bw-475-project-816447/

results:

https://www.rx7club.com/rotary-drag-racing-167/stock-motor-enzo-racing-fd-goes-9-85%40142-9-mph-865403/

no stock intake here though..

theres also this car:

this is also a stock port, but a RE..

https://www.rx7club.com/showthread.p...hlight=tearbo2

results:

https://www.rx7club.com/single-turbo-rx-7s-23/my-goal-met-769rwhp-747542/

both around 700rwhp, one a bit above, and one a bit under.

now if somebody could post some data on the performance benifits between REW or RE plates and TII ones, we'd be getting somewhere!

Evil Aviator

What are you learning in class?

LOL, no, just forget all of that rotary engine uniqueness mumbo jumbo. It is a simple calculation of airflow based on displacement, efficiency, and mechanics, just like most other internal combustion engines. Let's take the math from my first example and break it down a little bit:

Math: (80cid * 7500rpm * 85% EV)/1728 = 295cfm * 0.069146lbs/cf = 20.4lb/min.

Given 13B engine = 80 cubic inch displacement

The rotary engine cycles all of its displacement each revolution of the output shaft, as do 2-stroke piston engines. A typical 4-stroke piston engine only cycles half of its displacement per output shaft revolution, so we would need to divide the displacement by half in this case, but fortunately we can ignore this step with rotary engines. Therefore, we can solve for cubic inches per minute by multiplying the displacement times the number of output shaft revolutions. I will choose the 7500rpm stock engine redline for this calculation, although you can solve for any rpm as desired. 80cid * 7500rpm = 600,000 cubic inches / minute.

Now we come to something called "Volumetric Efficiency" (usually written as EV, Ev, or VE). That is a fancy term to describe how efficiently an engine cycles air. Some factors like intake restrictions, poor suction, and burnt gasses lingering inside the engine will reduce this efficiency, while other factors like supercharging and tuned exhaust will help increase it. The 13B engine has a volumetric efficiency of about 85% at 7500rpm, which means it only cycles about 85% of the amount that we previously calculated. Therefore, we adjust the equation to: 80cid * 7500rpm * 85% EV = 510,000 ci/min.

A conversion factor is then introduced in order to convert ci/min to cubic feet/minute: (80cid * 7500rpm * 85% EV)/1728 = 295cfm

Since modern compressor maps are in lbs/min, we then convert cfm to lbs/min by multiplying by the mass of air at a given temperature, pressure, and moisture content. Since moisture content is such a pain to calculate, and it makes very little difference in mass, most field work ignores this factor. Since the Garrett compressor maps are based on 85degF and 28.40inHg pressure, I will use the standard mass of air under this condition in the conversion: 295cf/min * 0.069146lbs/cf = 20.4lbs/min.

Stock ports on a 13B flow about 90-92% EV between 3500rpm and 6500rpm, then dip down to about 85% EV at 7500rpm. This will vary with the engine series, 4 vs. 6 ports, the condition of the engine, etc., but those numbers should get you in the ballpark.

The important thing to understand here is that turbo boost will increase the air pressure, which will increase the mass airflow even if the volumetric airflow remains constant. Examples:

Ambient pressure: (80cid * 7500rpm * 85% EV)/1728 = 295cfm * 0.069146lbs/cf = 20.4lb/min.

2.0 pressure ratio (about 14psi boost): (80cid * 7500rpm * 85% EV)/1728 = 295cfm * 0.069146lbs/cf = 20.4lb/min * 2.0 = 40.8lb/min.

3.0 pressure ratio (about 28psi boost): (80cid * 7500rpm * 85% EV)/1728 = 295cfm * 0.069146lbs/cf = 20.4lb/min * 3.0 = 61.2lb/min.

As you see, nothing changed but the turbo boost and the lb/min flow rate. I ignored some factors like pressure drop, but that should give you the main idea.

Also, keep in mind that a turbo compressor map is a compressor map, which means that it deals with the statistics at the compressor inlet and outlet as opposed to the air filter or intake manifold.

RETed's airflow rate recommendations include an assumed boost level. This is because they are calculated by reverse-engineering the horsepower range of a typical 13BT as opposed to calculating the airflow rate from the base factors as I have done. Either method will work just fine for choosing a turbo. If you look at a compressor map, you can see that even if you are off by a few lbs/min it will not make much difference.

I would also like to add that Corky Bell's "Supercharged!" book is pretty good at explaining this to the layman. His "Maximum Boost" book is good for turbos, but unless it has been updated lately it uses the old cfm maps which fortunately are no longer in favor.

rx7 SE

iTrader: (5)

In depth response man! I appreciate you taking the time and explaining these things to me. I'm currently an undergrad in mechanical engineering with some motorsports on the side, so I've covered the basics including thermodynamics, fluid mechanics, materials, etc. etc. So in effort to retain everything that I'm learning at such a fast pace I apply it to our cars to see if everything works and how I can optimize these engines. You seem to have a lot of experience, I'm sure I have much more to learn

~Ant

Evil Aviator

Oh good, this will be a good experience for you. After you graduate and get a job in the industry you will be antagonized on a daily basis by people like me who are hired specifically to screw with you.

Have you seen this website? There are some minor math errors, but otherwise the information is pretty good.
http://www.gnttype.org/techarea/turbo/turboflow.html

I actually have no automotive industry experience, and the calculations I showed you are from my college classes back in the late 80's. For the last 20 years or so I have just used standard matrices or proprietary computer programs for all of my calculations. Fortunately, my current job allows me to make up my own programs, algorithms, and macros as I deem fit. Other than that, I try to keep current by crunching numbers on this internet forum from time to time.

We ALL have much more to learn. I have met some industrial legends who were shockingly lacking in some technical areas, which I have come to realize is part of being human.

Furb

iTrader: (2)

Porting improves performance, but doesnt mean you cant make good hp without...
just put on a bigger turbo and run more boost.
yes you will increase lag and intake temps, but you can make plenty of power.
J-rat had over 500hp on stock ports...

rx7 SE

iTrader: (5)

I didn't realize J-Rat was on stock ports....that is exactly what I was hoping to hear is someone make good power on stock ports. I may have to go bother him now

Furb

iTrader: (2)

J-rat WAS running stock ports untill a vacuum hose to his wastegate melted and he blew his engine...
Now he has a ported motor.