rx7tt95

Obviously, the right combination of both will yield the best results. However, if one were to concentrate on one or the other, which helps more in the power department, porting the intake ports or exahust ports on a turbocharged 13B-REW?

As I understand it, porting the intake side moves the entire powerband upwards and creates greater emissions. More airflow is created through greater revs, etc...but vacuum and idle suffer, of course dependent upon port size. I would think that turbocharging overcomes intake side restrictions to a certain extent and that a turbocharged motor would benefit more from heavy exhaust porting. I'm looking at this not so much in terms of an all-out race engine, but a powerful, flexible street engine to be used for roadrace stuff. Opinions appreciated!
Michel

bcty

EXHAUST! totally

RETed

Intake.&nbsp The exhaust ports are big enough.


-Ted

BDC

Both, although the main point of interest is the intake ports' casting. It just flat stinks. What do you expect from a mass-produced item, right?

The exhaust port is pretty durn large but I believe has room for improvement. However, the major area of concern is the intake port outlet and tunnel pair. Concentrate 80% of your energy there.

Intake and exhaust ports are both important; they're complimentary of one another just like every other modification in the engine bay that changes how well the engine's able to gulp in and expel a single stroke of air.

B

BDC

HEre's a few pictures of how I do exhaust ports: As you can tell from the pictures, there's not a whole lot you can do unless you decide to go a bit out there and change out the exhaust sleeves. Otherwise, all you can really do (within reason whilst keeping in mind to not increase port overlap) is to clean the port up and increase the port timing by taking a bit out of the bottom of the port itself to have the port open earlier in the exhaust stroke.

http://bdc.genxracing.com/EnginePorting

I'll post some intake porting pictures as soon as possible to give you an idea of my own gripes I have w/ the factory casting and how leaps and bounds can be made by givin' some TLC to those things.

B

rx7tt95

Cool. Thanks for the info guys...so basically I'm looking at moving the powerband up if I want to see additional hp based on intake and exaust porting alone. There's no way around it. Take your time posting the pics. Just trying to learn a bit here.
michel

RETed

I dunno what your set-up is or what kinda power shift you're looking for, but we usually just turn up the boost.

Exaggerated power shift can easily be induced by a bridge port.



-Ted

rx7tt95

Ted,
I was curious as to what would yield the greatest benefits on it's own. I still want a meaty midrange and I don't want the bottom end to go "too" soft :-) Roadracing, turning up the boost can mean a very short-lived engine. I may only run 12psi on a roadrace course and 3-8psi more on the drag strip depending on what my final setup will be and the car will see lots of street time as well. Just trying to take an educated approach to deciding which way to go.
Michel

Rotortuner

BDC
Those ports look realy good. I like the way that you dident change the opening time of the port very much. I think it is pretty important to now go down on them very much but instead do what you did there clean it up and go up and out. Good work and thanks for sharing.

CJG

RICE RACING

Here is my take on the question, You cannot make the exhaust port large enough!

I take out the sleeve and open the port as much as is possible without letting the seals drop out or the water run in, up as mucha s possible and as wide as possible, I only lower the port floor around 2mm.

My engine in street trim (full 3" exhaust, air filter etc, pump gas) on 20psi boost makes 540BHP@7500rpm (@engine) and has 460Nm of torque from 5500rpm to 8000rpm with peak of 524Nm@6900rpm ..... Greater porting overlap gives you a flatter torque spread in whatever rpm range you tune the engine for mine is within 88% of the peak torque over a 2500rpm range, which matches the std gear ratios very well once you are in 2nd onwards.

Porting the exhaust to it's limits has worked for me, and I would never leave the port anywhere near std dimensions ever again on a performance rebuild.

If you are running a std ECU and not willing to rev to 8000rpm then porting to this extent is a waste of time.

BDC

From what I've always been told, Rice Racing, the idea is you should open the exhaust port earlier in the stroke yet retain the same, stock port overlap with the closing time remaining the same. What's the scoop with that? When I did this rotor housing, I did it free-hand from intuition as opposed to using a pre-made template.

B

BDC

Thanks a bunch. =)

B

RICE RACING

That is one of the MANY falacies that go around about forced induction engines !

When I did my engine I pushed the intake opening as far back as I could without the leading edge of the side seal droping into the opening on both the primary and secondary and lifted the exhaust port as high as It is possible (had to take the exhaust sleeve out) to get the most overlap I could while still retaining the low speed low load efficiency of the street port.

It does make a little less low end power than an engine with less overlap, but once revs are above 4500rpm, it takes off! I have never seen an instance where more overlap reduces power, in facts the direct opposite happens The only disadvantage is slightly higher idle, lower tolerance to realy restrictive exhausts, and not as much low end (below 3k) power, but once you are in the higher rev ranges you will have a better engine with a wider stronger power band.

Thats what I have noticed, I choose not to listen to the experts when I ported my engine, and I am glad I did not. Those same people told me that Peripheral port turbos do not work? Well most of those people are just sheep who follow everyone else and follow popular beliefs, sorry about the rant and rave but it is very common in my country to not heavily port turbo engines, why I do not know? I have had nothing but sucess with it.

RICE RACING

Oh, I also must stress, that to take full advantage of the radical exhaust ports, you need a proper fabricated tuned length header ( not a bull **** cast one!) and a good size exhaust housing (I use a 1.32 on a t04) Using this type of porting on a small exhaust housing like a 0.96 and a badly designed manifold is similar to like in the old days when we ran N/A rotaries, you need the less restrictive manifold/turbine to take full advantage of the increase in engine volumetric efficiency. And fully divided is a must !

relvinnian

> Insert dumb question below.

How do I remove the ******* exhaust sleeve?

RICE RACING

You need to remove or drill out the pins that hold the sleevs in, they are realy hard to drill out as they tend to be harder than drill bits ! but take your time, they will come out

Once you have these out the sleeve will slide out and you will be truley amazed as to how much you can open up the port

With the manifold side I run pipes that are the same diameter as the inner ID of the sleeve, with a thick flange plate I use an inverted funnel shape which acts like a transition from the large port runner area into the smaller pipe area, also you need to smooth out all the edges left in the area once the port is removed. You will have aheart attack once you finish porting, but trust me it works ! my dyno graph does not lie.

relvinnian

Thanks Peter.

I'll make sure I have a supply of bits on hand. BTW, my dremel hates you.

Dragon

Exaust port makes the biggest diffrence... Air in to the engine with a turbo is under pressure, it's going in no matter what, If you want more air then turn up the boost and shove in a denser air mass... The exaust on the other hand needs time to get out... It needs to be wider and open sooner and close later to get all the exaust out so it can pick up a nice clean charge of air and gas when it passes back by the intake port... The exaust port is the key to power on any turbo engine be it rotary or piston...

Now if your running N/A then you need to concentrate on the intake ports

rx7tt95

Definitely running boosted...I do want quick spool-up for roadcourse work and I can't really afford to wait til 4500rpm as those pesky supercharged/turbocharged Z06's will leave me at the exit of every corner. I wasn't planning on going with an over-exuberant a/r on the turbine as I'd like to see 10psi by 3K EASILY. Many of the comments have sort of validated my own thoughts (albeit in a more experienced manner!) on the exhaust side. I've worked with turbocharged pistons engines where many of the same theories apply although 70% of the restrictions found in a piston engine are in the heads alone! Boost overcomes that, but it doesn't make things very efficient. Dragon, your comments really made things a bit clearer. Keep the info/opinions coming!

BDC

Sort of, Dragon. There's a couple of problems here, however: One, shoving a denser air mass doesn't mean that'll be a workaround for the obvious downsides to the original casts of both the port tunnel and port outlets on the iron housings/plates. There's alot that can be done there to inrease the efficiency of the intake port in terms of keeping the intake charge cooler whilst retaining its velocity. And, velocity is the key to alot of this.

The second issue has to do with port overlap. Even with the stock engine, there's a chunk of time where both the exhaust and intake ports are open at the same time. I'm unsure as to what all this causes, but guaranteed the intake stroke won't be clean and fresh; instead, it will have exhaust gas dilution of some sort in it.

B

RICE RACING

I am a circuit racer and I have driven 13B turbo's in all configurations, some with insane mid range power and others that are the complete oposite. For a circuit racer the biggest most undrivable car is the one that comes on boost like mad in the low rev mid range area, it makes the car near undrivable on the throttle as you try to feed in the power exiting the apex, then as you get near the 5500rpm and above region where you need the power to pull to 8000rpm you do not have it !

Once you start making serious power with a single turbo install, you will find unless you are running 12" wide soft racing slicks you will never be able to fully use your 3k to 4.5k full power in low to slow mid speed corners, then once you are straightening up and revs almost always average above 5.5k you have lost alot of the range that you "think" you needed so much.

The ONLY circuit track work where performance under 4000rpms is an issue is on Hill Climb tracks where you are using 1st gear alot, only then once you are in the 400+bhp range will you be able to harness all of this mid range power with full slick wide tires.

In a data log of almost any track where i have raced the total percentage of time spent in the rev region below 5000rpm is in the area of 10 to 15% and at very very small throttle openings or 0 throttle opening (during decel in selected gear for corner) You potential circuit racers need to analyse better what percentage of time your engine is realy working and you will see what areas you need to concentrate on to get best performance.

For a stock turbo, stock ECU, power challenged engine, then performance around or under 4000rpm may be an issue, for these people especially ones who have upgraded to a bigger single turbo you are realy wasting the potential of the 13B and are generally way off the mark in terms of an ideal race engine.

If on the other hand you want to limit yourself to a self imposed rev limit of 7000rpm or there abouts then getting a majority of your boost by 3000rpm will be an issue, you are realy wasting the potential of your engine by limiting the rpm to such a low limit.

rx7tt95, I am not having a go at you, I just wanted to point out what I have experienced with my engine combination through the years of running it.

rx7tt95

No problem. I want opinions which is why I asked. You do make sense and even with the stock twins I have to feather things coming off the corners. Generally I'm making more hp up to 4Krpm than singles where they just plain take off. They out torque me however. I do plan on taking things past 7Krmp :-) The V8's just have sooo much thrust coming off the corners (same corner speed) that I'm afraid a bottomless engine isn't going to do me much good. Even if I am making 475hp on top.
Michel

Dragon

lol, I'm not saying the intake port is usless or anything, just that the exaust port makes the biggest diffrence on a turbo engine... The anouther idea behind the exaust port is to get the exaust gasses will dump with great velocity and create a slight vaccume behind them in the chamber area then as the intake port opens it imediatly starts to insert it's fresh charge of air and fuel... The overlap actually helps pust out more of the exaust gases as intake fills the chamber on one side it pushes the exaust gases out the last part of the exaust port.. The idea behinde the bridge port is to start this process sooner... but no matter what you do there will always be some exhaust contamination left, the idea is to get rid of as much as possible...

bcty

so.. i was going to go with a big race exhaust exhaust port but i never thought of removing the sleves.. i'm an N/A and was wondering if a port that larger will be useless like RICE RACING is talking about? i wanted to go big cuz i heard that was ones of the biggest improvements.. i am going to do the intake as well.. i might do experemintal 2xbrige port.. i dunno yet though.. but i was curious where I would get best results in my exhaust porting! thanks

HWO

Thats the normal practise i hear from all the boy racer piston engine drivers in NZ, they cant seem to come to grips with the idea that CFM = HP not Boost alone.

Alot of members on this forum cant seem to get their head around it either.