PatrickT

Hi there,
Im using my S4 TII only occasionaly on the street, and I started competing in time attack last year.
Till now my engine block is completly stock.
I upgraded some things around like a T04/T3 turbo but in the stock turbine housing.
FMIC, Koyo, K&N, 750 / 1000 Injectors , Rtek 1.x , SAFC, AFCR, Wideband, Exhaust temp.

I think I was at about 300 hp , but on track I had to go massive rich to get the egt low. So I lost a litte bit top end power...running 12-14psi

Recently I got a spare engine and I think of porting this one for track purpose.
It looks in very good shape, and has 8bars of compression.
In the past when I drove the car to work I thought about street porting it, but now when I dont drive 5000miles a year, I think about bridgeporting it (half BP).

My aim is to get where the FC endurace race car was with 400-450 hp, which also had a BP I think.

But then I read that many people say a extended street port makes the BP obsolete !?
My plan at the moment is going some kind of 1/3 J-Port , to reduce the overlap but suporting flow like a half BP

Target is:
intake open : 45°BTDC
intake close: 70° ABDC
exhaust open: 80° BBDC ( something street portish)
exhaust close: 48° ATDC (stock)

Maybe Im aproaching it to much from a piston engine.
I did valve timing simulations in the past for Mercedes Benz, but a rotary "may" work completely different.

What are your thoughts ?

PS: I like a wide powerband, currently Im using 3500-7500 rpm on track
and it should still be driveable there. Power is ok to come later ^^

Greets, Patrick from Germany

diabolical1

iTrader: (3)

streetport if you want to keep running your current turbo, and i would probably say forget about the 450 HP goal. i seriously don't see a point to bridgeporting (half or full) on your current turbo. i'm no authority though.

however, if you choose a better turbo to build around, then you'll open your options and the port choice is yours.

my thoughts on this are perhaps you took something out of context or your sources are wrong.

j9fd3s

iTrader: (3)

well #1, check with the rule book, in the US running a ported turbo would put you on track with Nascar...

getting big power seems to be less about the port and more about the combination of parts, ie the turbo, exhaust, etc.

for instance we did a small streetported S5 T2 engine, with NEW housings/rotors, so it was a very japanese style build, with a 60-1@12psi it did 392rwhp. Aaron Cakes full bridge did 392hp@12psi.

or there is Max's car too https://www.rx7club.com/time-slips-d...-rwhp-1000747/

PatrickT

Yes, I think with the T3 turbine, I wont benefit much from the BP....
My plan is to just break in the ported engine with my current setup.
And when I know everything works, and I still have money to spend ^^ I thought about switching to something like Aaron Cakes GT4088R and a standalone ECU.

I just dont want to do all the mods at once, maybe I mess something up and lose a lot of money.. :-/

The regulations on the time attack I participated are really simple.
There is the street class, I drove in, where the engine block has to be stock.
Only intake and exhaust may be changed. And I think I made the most out of it as my engine is stock from the throttle to the turbine. ( 3" turbo back )

And there is the pro class, where everything can be done.. :P
But you are right, there are also other events that have different regulations..I might have a look on them...

-Patrick

j9fd3s

iTrader: (3)

the T3 is too small for a BP, and actually just looking at dyno sheets, its very hard to prove the BP even adds hp, Aarons car is part of that proof, all of that work, and it has the same HP as an S5 engine that was completely stock, except the port, and 60-1 turbo.

if you go way back, tony farkas's car did 499rwhp with a bridge, and Jrats car did 501hp with a street port, same boost

PatrickT

Ok but Aaron has a GT40...or what do you think is "wrong" with his car ?

I read somewhere that a BP engine wont start with a stock ECU...is this true ?
..and why ? ... because of timing ?
because this could make my plans more difficult (but I may have a solution for this )

j9fd3s

iTrader: (3)

i don't know that anything is wrong with Aarons car, it just happens that a small street port on an otherwise completely stock engine and a 60-1 is a really good combination.

the trick is the combination of parts, the turbo, exhaust port, and ecu all need to work together.

i bet a bridge port would start on the stock ECU, but it might not run that well. a proper bridge is going to want less fuel in some places and more in others, timing on a stock ecu is going to be really aggressive too

with a stock computer you really need to build a combination that works WITH it, and not against it.

PatrickT

last weekend I inspected the spare engine I have with an endoscope
as I never saw a rotary from inside
here is the result:


sure I know how it works, but I never had a reason to open mine,
which is a good sign when I think of how many piston engines I had to "open"

It can be clearly seen, that even in a stock engine the corner seal is almost "half in the air"
And on the opposite side there is the secondary port, which I wanted to bridge port...

So I did a little research in google scholar and found this patent on the intake system of the S4 TII

Patent US4614173 - Intake system for rotary piston engine - Google Patente

There is the discussion about the area above 4000rpm , where in stock config the exhaust pressure is larger than the intake pressure.
(this may also be an issue if I bridgeport the engine)
And how they used the effect of exhaust pressure wave running up the intake by designing the intake runner length this way this wave arrives at the other rotor shortly before the intake port closes there.
So the exhaust back pressure wave improves the intake charge on the other rotor.

So this is not how a "conventional" intake runner design works, according to helmholtz resonance length.

There is a formula in the patent how to calculate the optimum length to use this effect, which is used in high revs only where it can be used.
Im assuming mazda calculated this for 6000 rpm
which would lead to a runner length of ca. 44 cm
Can somebody tell me the actual runner length, if this is correct ?
With this length there would also be a 3. order helmholtz resonance at 3700rpm which would fit to the torque curve of the TII.. (and a 2. order at 5500)

before getting to further calculations I have to verify the runner length ;-)

...to be continued...

-Patrick

j9fd3s

iTrader: (3)

there is an SAE paper about the intake design for the 6 ports (if you want, pm me). there are lots of graphs for different lengths and diameters, they chose 500mm as a length. i've been ASSUMING the T2 was the same, but i don't actually know.

there is also an S5 paper where they discuss the different lengths chosen for the NA engine

there is also an SAE paper where that do the same with a P port engine, however being IR and not the tournament effect type, its a little different, oh and the ports are kind of different too

but yes you're basically right, back pressure is higher than intake pressure, even on the NA's. the car isn't running quite yet but i am building one where i can check preturbo backpressure on a stock turbo, and i have a bunch of different compressor wheels to choose from, but the goal is 300hp.

anyways a stock port engine will put up with more backpressure than a BP/PP engine, adding overlap to the port timings makes it picky, i think its one reason why the stock ports work very well oh high hp turbo cars.

PatrickT

Ok, I saw the other patents for the NA engines,
but I posted this one, as it is the one I am focusing on.
In NA engine the exhaust pressure is most time higher than intake pressure because of combustion.

But in turbo engine, what many people deny, I believe in midrange when the turbo comes to work, the intake pressure may be higher than exhaust pressure.
This is where the turbo has its best efficiency.
So you would have a flow from intake to exhaust while overlap.
But in higher rpms, a wastegate turbo is to small in his design from being perfect.
The wastegate has to open, and the efficiency of the turbine gets worse, so the needed exhaust pressure to maintain the constant boost pressure rises because flow also rises.

This is how I understand the whole thing. I studied in mech. engineering with combustion engines and charging devices. And with turbo engines I was always looking of this effect which is called in german "positiv flush slope" ( word by word )

And it could be seen at the moment the turbo builds boost and some rpms on..




And this is what this picture tells in upper diagram.


https://dl.dropbox.com/u/98966921/Re...20english.xlsx

This is a excel sheet where I made my calculations. Even with the 500mm runner length you said, the calculated resonance rpms look reasonable.
But now try screwing with the port timings.

(I hope the links to my dropbox work, and the sheet is selfexplaining, use only the coloured values for playing.)

Ill have to measure the runner length part by part when Im at home on weekend...
...so far...

-Patrick

j9fd3s

iTrader: (3)

i think your understanding of the turbo is right on (i will be testing this shortly), back pressure in the exhaust in a rotary is bad. there is already a high content of exhaust gasses that get into the intake stroke, and high backpressure and lots of overlap would just make things worse.

you intake thing is neat, at this point you know more than i do about it!

i'd say you're on the right track though, the rotary is mostly like a piston engine, but it doesn't seal as well internally and doesn't like backpressure.

i think that's why you see people with stockish engines, and big turbos make pretty huge power, they get a combination right

j9fd3s

iTrader: (3)

oh and BTW the 500mm seems to be from trochoid surface to throttle plate

PatrickT

so going for a big turbo and by this reducing high rpm back pressure...
and making it spool by porting the exhaust to a more early opening... ?!

this should both reduce backpressure , right ?

I am now just thinking of how the "positive scavenging" could maybe be applied (turbo choice) to higher rpms, so overlay wont hurt...hmm

j9fd3s

iTrader: (3)

yep! small compressors take a lot of power to drive

PatrickT

I did some rough measurements,
Side housings, flange to port : 8cm
LIM flange to flange: 25cm
UIM flange to plenum: 18cm
sum : 51cm

so I'm assuming your 50cm may be right.

but I got the offset of the secondary runners wrong, its about 14cm
5cm offset would fit more for the primary runners

so for secondary runners L=1,14m
for primary more like L=1,05m

looking into my calculations I get the 50cm as a result, when referring to a offset of 12 cm and 5000 rpms






when reverse calculating with these values, I'll get of course the exhaust charging effect at 5000 rpms, but also an a 3.order helmholtz resonance at about 3600 rpms ( 2.order at 5300 )
this both seems plausible when looking at the stock torque curve:





although this is S5 stock curve ( lower one) but I think UIM and LIM are the same like in S4 ?!

Because the primary runners offset ist smaller, there is this exhaust resonance at a higher rpm of 5300 ( secondary at 5000 )
But in S5 engine they changed the primary port opening from 32° ATDC to 45° ATDC so this resonance point whould move down to 4500 rpm for primaries..
But as they almost eliminate overlap to primary intake by this, that effect may be removed on primary runners...

PatrickT

Now when street porting the intake for example
from intake opening 32°ATDC to 25°ATDC
and from intake closing 50°ABDC to 60°ABDC

this exhaust charging effect moves up from 5000 rpm to 6000 rpms, so it is still nicely useable at a higher power range
(helmholtz resonance is less effected)

but when moving to a aggressive early opening with bridgeport
with a 45°BTDC like I was planing, this effect moves up to 10000rpms O_o
I wont be able to reach that in my engine...

-Patrick

j9fd3s

iTrader: (3)

interesting, maybe that is one of the reasons the BP has mixed success?

PatrickT

Maybe, but I forgot it also says, that when intake opening period excedes 320°
this exhaust charging effect will be eliminated because of 2 cambers being exposed to the intake at the same time....

So when going bridge, this effect may be not useable, I guess I'll have to concentrate on lowering exhaust pressure and maybe only helmholtz resonance...

arghx

iTrader: (3)

Question: are you looking for a project to mess around with, (basically, a science experiment)? The best you can do is try to make some calculations based on what Mazda has already published for their 1 dimensional modeling. You're kind of going all over the place in your discussion here. For example, the point about exhaust backpressure increasing with rpm: if you look at the patent document from which that chart came, it actually mentions that the intake system was resonance tuned to use that backpressure.

Are you looking for a car that's fun and versatile to drive all around? Just keep the stock ports. In years of owning street ported motors, I'll say that the stock ports are underrated.

PatrickT

Right, and I further found out , that when going bridgeport, I wont be able to use this resonance from backpressure...so a as low as possible backpressure may be the aim.

I wanted to build this engine for track racing ( circuit )



Yesterday was the first time for me to open a rotary
I lifted the engine on a table and the first thing I discovered, was that the excentric shaft has a large axial play...about 5mm
I thought it should be only tenth of mm... so, not good news !?

Today I cleaned the parts a little and when inspecting them, I saw this:


notches at the edges below the sparks


grooves on the surface above the sparks





edges on the side housings (some porting thoughts there..)



the edges are not visible in this pic, but its quite a lot...

what do you think, is it scrap ?
I am a bit surprized it looks so bad, because it made 8bar compression...

-Patrick

j9fd3s

iTrader: (3)

the japanese high power builds would just have you replace all 5 housings, probably rotors. the rotary has more seals in it than a piston engine, and one of the problems with it is sealing. the best way to have optimum sealing is just to start with new parts.

however, the US style is to just reuse everything, and in your case, since this is an experiment, it might be the way to go.

the side irons should have step wear less than 0.004" (.1mm?). in the US we like to lap them smooth, however this removes the surface hardening, and by the time you reapply that, you could have just bought new.

the rotor housing surface is mostly inspected by looking into your wallet, if your wallet is empty, those housings look fine

really though the surface should be flat (they sag in the center), and as smooth as possible.

PatrickT

Ok, lets say its a rotary experimental
But do I need new seals ?
The engine had the 3 piece apex seals and Ill need the 2 piece type for BP, right ?

The complete seal kit will be still over 1k € or $
I would spend the money if the housings were ok...
but I dont want to throw it out of the window

The good thing was, my focus went again on the diffusor underbody ;-)

http://files.homepagemodules.de/b154...96p19741n2.jpg

j9fd3s

iTrader: (3)

the cheapest way i've found to rebuild these, is just to measure everything, and replace anything out of spec. you probably should do apex seals, just cause its a high hp build.

your parts list looks a little different, but you end up with a nice tight engine

MrGoodnight

iTrader: (1)

How about a Wu-port!
















Yes, that's a joke :P

PatrickT

Haha, yea
I wanted to do a PT-shaped port ( my initials ) ^^
but it looks like its getting a DP-port

Thanks j9fd3s, I will try to measure everything next weekend