Kyrasis6

ok guys, I've pent the last 2 months or so reading about the different ports and stuff and am still queezy exactly how I want to port the engine and by how I mean much more than the style of porting.

The engine I'm building is a 6-Port S4 N/A. I'm doing a bridge on the 5th/6th ports. Tonight I got out a steel and traced a bridge on the Aux port and on the secondary port, slid the housing on rotor on, then took the housing back off and spun the rotor around a few times.

I plan on having the Aux ports functional but just looking at the timing where the secondary and aux bridge would open it looks like the secondary bridge would open a little sooner than the bridge on the aux port. Both are traced right up to the housing. So is this correct? It looks to me like I can reduce the overlap a few degrees by moving the bottom of the bridge on the aux port up. I'm not "planning" on bridging the secondary was just tracing it for comparison.

I just can't decide at the moment if I want to move the bridge up or down, close it a little earlier or later, extend it slightly into the housing, change the shape of the nose and tail, etc....

I'm definatly not going to just trace a brow, drill a few holes and cut out a slot.

I'm going to take the pieces into work tomarrow to strip and re-apply the dykem then retrace to make it more clear and post pictures so people can see what I'm talking about.

rotarygod

iTrader: (1)

This is the 3rd thread in as many weeks on this same subject. Please DO NOT do auxiliary bridgeports! If you want to go bridge, go all or nothing. In other words, bridge them all, change the ecu, change the exhaust, and change the intake manifold.

Just say NO to aux port bridgeports!!!!!

Jeff20B

iTrader: (13)

So no BDC style half bridge?

rotarygod

iTrader: (1)

BDC isn't bridgeporting 6 port housings and he's running a turbo. I'm saying not to do bridging on only the auxiliary ports on the 6 port motors. Don't do them especially if you are still running the stock intake, ecu (please no piggybacks either!), or exhaust. Flow is just crap through them. The 4 port engines on the other hand are much nicer for bridging. Even a small half eyebrow on one of their ports would be beneficial. I actually got into all of this about a week ago in another thread. Keep in mind that a naturally aspirated bridgeport engine and a turbocharged bridgeport engine behave very differently from each other. Boost makes up for many things. A supercharged bridgeport engine would even behave differently from a turbo engine as well. I am a supporter of Brian's work BTW as he is one of the few people that actually tries things to see what happens.

BDC

Hah, that sounds like a funny slogan for a signature. Maybe a bumper sticker or something.

B

NoviceRotaryTech.

I SAY YES TO AUX BRIDGE PORTS!!

rotatech

4 port engines = more power no question about it

anewconvert

iTrader: (1)

seriously, just a few topics down you will find the aux bridge thread RG is refering to.

I have an aux bridge, its not worth it. After I get my intake and exhaust sorted out Im going to have the engie pulled and fully bridged. there is no point to the aux bridge.

this is why: If you keep the stock intake to allow the aux sleeves to be functional then your going to lose a lot of power in the stock intake. The stock intake is a serious restriction for a bridgeport.

If you build a new intake then you lose the sleeves so you are taking on the compromises of a bridge port without all the power. If you are going to go through the expense of a new intake you might as well make as much power as you can in the process. Why spend that kind of money just to limit yourself to a small bridge of the aux ports?


Either half or full bridge, or go with a streetport. The aux bridge isnt worth the time. The ONLY reason i would do it is if I could build, dyno it, strip the engine and go to a half bridge to dyno it again just to put this Aux Bridge stuff to rest.


Ill say this again. I HAVE an aux bridge, with a stock intake manifold, and Im telling you its not worth it. If it werent for the fact that the car I bought came with the aux bridge I would have gone with a half bridge at the very least.

BC

Kyrasis6

You guys missed the point of the topic, it was not a discussion of which is better, it was a question on the length, location, and shape of a bridgeport.

I've been reading since november and have read all the posts about using the proper exhaust, intake, port sizes, fuel management, inertia ramming, etc.... Any competent engine builder is going to take these into consideration.

Since the post is already jacked I'll say that I agree with NoviceRotaryTech on most of his theories. Two things I have not seen mentioned yet are how the effects of overlap change with rpm and the effects of blowdown.

Inertia tuning is physics, the same laws apply on both rotary and piston engines you not only have the factor of the pulse waves but also the inertia of the moving gasses and just like in a piston engine they will do different things at different rpms, what you tune them for and how well they are tuned with the rest of the engine will determine their success.

Blowdown is a phase right at the point where the power stroke ends and the exhaust stroke begins. The exhaust gasses are under extreme pressure and as soon as the exhaust port gets a few thousanths open they are going to go sonic and exit at extreme velocity, this is when a majority of the exhaust gasses are going to exit. This is the reason why making the exhaust port more round near the bottom makes a quieter port because the blowdown phase is more controlled, with a flat exhaust port floor the open area increases more rapidly and you get more of a bang than a puff. Most of the exhaust gasses and pressure is gone within a few degrees of the exhaust port opening the rest is pushed out by the rotor during the exhaust stroke. The exhaust gas velocity is going to resist it flowing back through the port causing reversion. At low engine speeds it will not have enough velocity to resist reversion and will contaminate the intake charge, which has been mentioned. At higher engine speeds though the exhaust velocity will increase because of blowdown and the higher speed of the rotor and instead of getting reversion you get a suction which is going to start sucking fuel in through the open port and will eventually get to a point where it will pull fuel right back out the exhaust. This along with the small bridgeport opening is going help keep the gasses flow in the right directions even if the pulse tuning of the secondary side of the intake gets screwed up. On secondary and aux side even though either bridge may never be fully closed your still going to get that return pulse slamming down the aux port. Most of the bridge on the aux would be open on the side that is still closing with a small opening on the other side so most of the pulse is still going to go where it should. You don't care about any pressure waves hitting the ports as they are opening or when they are fully open, you want the pressure wave to hit the port as it is almost completly closed so that hopefully you can get cylinder pressure slightly above atmospheric so you have extra ramming effect to overcome the compressoin that has already started, if within a good margin the port will seal before any gases can start flowing back out of the port.

Now we come all the way back around to my original topic if you carefully look where the rotor face is on the bridges (in my case the aux port bridge) you can see how reshaping the bridge slightly will reduce or elimate overlap and when that pulse is hitting the aux port as it is closing you can minimize the "leak" on the opening side of the next intake event. You could make the top of the bridge shorter or shapped a little different a small amount to help seal the rammed intake charge better at lower rpm.

Even if not doing an aux port I still see where a bridge on the secondary could benefit from some of this reshaping to reduce overlap and delay the intake opening a few degrees to help the bridgeport be a little bit more streetable.

classicauto

iTrader: (3)

But then why port it? You make the cuts to make power, or in my case, because you want to try it and want to have a really mean sounding engine. If you sacrifice the size of the cut (and thusly, any extra flow associated with it) then why even bother?

And in your case, to do an aux. bridge, you could leave the actuation rods in place so the entire port and eyebrow will be shut at idle and light load anyways so the point is moot unless you're talking about a 4 port engine or a full bridge on your six port.

but its always good to try new ideas and strive to make things better.........have you got any pictures of your proposed design?

Kyrasis6

We're talking about .020"-.030" inch worth of material in the right places not reducing the size by half or anything. I'll take some pictures of some of my ideas and then trace them out in AutoCAD for a clear image.

I'm still not completly sold on doing bridge on the secondary or the aux port, I want to do the aux port for the reason of shutting it off. But if the bridge on the secondary can be made more drivable I might just do that. My time is short at the moment though because we just started back on 12 hour shifts and I have a 1.25 hour each way to work

rotarygod

iTrader: (1)

Moving the bridge down or up does not change the overlap as it does not alter the opening time. The port opens from the outer edge but the closing side is the top edge. The bottom is not the opening side. As long as you have a bridge, you have overlap. Even the stock ports have a small maount of overlap.

Flow through the auxiliary runners is terrible. It is not condusive to making more power. This is even being verified by someone who owns one! Keep it a streetport and be happier with it in the end. Power will be just as high if not higher and you'll have none of the drawbacks. I've built only 1 aux bridgeport motor (and I usually don't admit it!) and that's was enough. That was about 10 years ago. Streetports are the way to go for street power unless you want to commit to a full bridge, new ecu, and new intake manifold and then you also commit to the part throttle issues associated with them. A bridge has no place being used on a stock setup. Doing a bridge on the aux ports and then keeping the sleeves in place to turn them on or off just isn't the good idea that it seems like it would be.

anewconvert

iTrader: (1)

+1

Kyrasis6

Rotarygod you've already stated those points a half dozen times, you arn't going to get anywhere saying them again or two or three more times and anewconvert's opinion has already been stated as many times.

As I've already stated any half knowing engine builder would have considered all of those points and as I have stated this discussion is not about what port is best for what application, it is about changing shape and placement of any bridgeport to make it more practical for various applications.

Ok, yea my choice of words on the topic and description was poor, really the title should say "changing shape" instead of "moving higher". And what I meant by opening from the bottom was as the edge of the rotor moves it starts to open up a bridge on the aux port starting on the bottom of the outside edge, from there the edge moves inward an up like folding over the top page of a packet of paper stapled in the upper left and corner.

Progress is not made by thinking the same things over and over, it is also not made by stating the problem, developments are made by stating solutions.

Kenku

Y'know what always irritates me about these things? Yeah yeah overlap... the only thing is that when the rotor gets to the point where the apex starts closing the exhaust port, the rotor's face against the combustion chamber is providing *far less* of an area for gas exchange between the intake and exhaust sides than the intake and exhaust port areas suggest. Mazda did some studies on this during development of some of the factory race engines; the specific thing I'm talking about is published in an SAE paper; number 900032 if you can get access to it.

NoviceRotaryTech.

Best post Ive read in awhile. Beautiful words man.

rotarygod

iTrader: (1)

You aren't getting it. You are not going to do anything appreciable as far as reducing overlap with a bridgeport with your idea. Even if you change it by a few degrees, that's all it will be and it won't be enough to matter. Your idea will not work! Please just give up the whole aux bridgeport idea. It doesn't work and anyone saying otherwise DOES NOT know what they are talking about. Why are you listening to a "novice" when people who have done it and have been doing it for over a decade are telling you not to? What is it with this forum and listening to inexperience? I'll never understand that.

Kyrasis6

I'll have some pictures tomarrow of ideas to improve an aux bridge it got dark before I could get clear pictures of the secondary bridge to start editing those. I'll also have some pictures I made doing some trace work showing how small a space overlap in a stock S4 6-port engine actually occurs in which as Kenku said is practically nothing. Frankly I don't care if it is futile or not if someone is going to do a type of bridgeporting they might as well spend an extra 5 min with a dremel to optomise it to the best of it's ability for what they want it to do.

As for the degrees, I'm sure many people reading this have seen the intake port page on rotary illustrated:

RotaryIllustrated: Intake Ports

Some of those port timings are different by as little as 3 degrees I'm sure that if you can delay the bridge opening by 3-5 or more degrees and or reduce the overlap caused by the bridge by about that amount or more there will certainly be a measurable difference for a street vehicle. We're not talking about spending an additional $200 to move the powerband down 500 rpm or something like you would a camshaft just taking a little time to shape the port differently.

NoviceRotaryTech.

Alright, Ive been sarcastic in this thread so far, sorry, but now I'm serious.

On this forum and any other forum, I, don't take advice / info to heart right away, untill a lot of opinions and different opinions have been considered.
The opinions on this forum are not set in stone, this is a free-for-all where some opinions are true and some can be false. I think every one should know this.
So don't be so offended if someones not obeying your opinions.
This is a thing I've come to know with this forum, like I said, I like to get a lot opinions, exhaust the possibility's, etc. etc. before I come to a conclusion.

So, I DO GET IT (what you've been saying about all this bridging, and appreciate the info) "rotarygod". I just want other opinions.
Nice touch with the "novice" comment.
Meaning behind my name is that I do want to be a rotary tech. and learn and experience all that I can, but I have some humility with the "novice" part so that I'm not mistaken as a self -righteous ******* who thinks I know better that the next person.

gxl90rx7

iTrader: (1)

well rotarygod is the only one here who has actually done it, so i think he has a fairly weightly opinion, and probably knows more about it than anyone here

rotarygod: please explain how "it is not worth it"? Is it not worth it, because an auxbridge doesnt make as much power as a full or 1/2 bridgeport? Or does it makes less power than a streetport? or was the power difference not noticeable from stock? I would reason that if the power difference is comparable to a streetport (granted intake velocities, etc are not ideal), it would be still worth it, because you still have the stock torque curve under 3800rpm, unlike a streetport.

Kyrasis6

all of that "this port is better than that port" stuff is BS because you have different applications that each is best suited for and ways to compensate for their downfalls. Ok street port, did you just blend the ports and not change the openings at all, did you advance the port earlier, close it later, increase the area or lift, did you slope in the short turn radius of the port more gradually, did you open up the port around the nose which will see higher velocities or near the nose which will see lower velocities??? All of these things can affect the "power" of a port where it is made and how fuel efficient it is. So no you can't say this port is better than that.

You can give 3 different ppl the same engine parts and tell them they can't modify anything except the primary ports, everything else must be exactly the same between the 3 engines and all of them could get different results depending on how each person ported them.

The same goes for a bridge or any other port for that matter. You also have all the other engine factors which change things, how many miles are on the motor and it's other parts, does it have a stock exhaust, collected header, independant all the way? Is it a 4 port engine, 6 port, stock manifold, custom manifold, short or longer runners, bigger or smaller runner diameters, shape of the manifold, the list goes on and on.

Heck 3 of our engine builders at my shop can all build the exact same spec engine with all the same parts with CNC machined ports, same tune and everything and there might be a 5 hp difference between all 3 engines on the dyno. Further more them build 5 engines each of the exact same spec and most likely you'll find that all the engines assembled by one builder tend to make more power than the rest. So just the fact that a different person with different skills built engine can make the difference between what works and what doesn't.

Rotarygod an others are say an aux bridge won't work, can't work, isn't worth it, will give poor results, blah, blah, blah. Well 5 years ago the engineers at our shop where saying we'll never make above 800 hp, it will never work we are wasting our money on development. We got a new director of operations, fired the engineers who said they can't or it can't, hired new engineers that said we'll make it work and 3 years later we are putting out 100+ more horsepower and are wipping *** at races.

NoviceRotaryTech, you don't get it because he doesn't get it.

Rotarygod admits that he only built one aux bridge ported engine which sounds like a staggering huge amount of effort. I would be ashamed to mention it too because it would give ppl the impression that I'm a quitter. You give up to easy and your attitude reflects it. If Wankle had your attitude the rotary engine would have never made it into a car.

I will now ask the admins to close this topic since it is not going anywhere. For those interested I'll post another topic with my pictures and won't bother asking opinions about them, I feel confident that my thoughts will yield posative gains, even if they are small.

Kenku

Well, what I was getting at by bringing up the overlap issue is... because of the data Mazda was getting (on full race-spec peripheral port housings!) on the actual effective amount of overlap, I personally am fairly skeptical about how much of the driveability issues of peripheral / bridge ports are actually due to what everyone thinks of as overlap. I have to wonder if it's not really just a matter of port velocity and late closing leading to reversion at low RPM.

I come at this from never having driven anything boosted, but on the other hand I've seen some wild "street"ports. For example, having a full EProd spec 12A dropped into my car and going and driving around (pretty enthusiasticially at times) to break it in, I'm willing to bet that anyone who didn't know better would call it a bridge; it misbehaved at low throttle openings, loped like a sumbitch, and didn't start pulling until 4k RPM. But despite the intake being opened up about as far as possible, the theoretical overlap isn't anywhere near that of bridge or peripheral motors.

So, what I'd be curious to see with experimentation is closing the bridge and conventional sideports not too out of line with where the 4-port motors do.

Aux port bridges... well, look. Like you said, any competent engine builder is going to take intake tuning and many other factors into account. The stock 6-port manifolds are completely unsuited for anything that's been ported. This isn't theory; having spoken to people running a Sunbelt modified manifold (which was cut apart, extensively internally modified and rewelded) even then high RPMs suffer (for the record though, they like the midrange of the whole package and have stuck with it)

Let's stop talking about this as aux port bridging; from my theories (untested, mind ye) a streetable (well, moreso) bridge would be on the secondary ports of the 6-port irons anyway, not the aux ports.

This makes me half tempted to start testing this crap. God knows I've got shitloads of 12A irons and housings laying around, and friend of mine is getting a Stuska engine dyno setup for rotaries...

Kyrasis6

Well let this die then.

Aaron Cake

iTrader: (1)

Not quite true. The bridgeported engine sitting in my RX-7 right now has aux bridges.

Originally I did it so that I could use the aux port sleeves to block the bridges at low loads but after realizing how pointless this is (for reasons already covered in this thread) I decided to just keep them open. The car still has the characteristics of a bridgeport but the flow is not near the flow you would get from a half bridge.

Keep in mind that my engine is turbocharged, so things are a bit different for me. The effect on turbo spool is extreme. It's unreal how easy this car spools the stock turbo (the stocker was on there just so I could break in the engine) and it's nearly impossible to keep out of boost as more then 20% throttle. I suspect it will have no problem spooling the upgraded turbo it will receive this summer.

I'm happy with my engine but next time I'm going to just go full bridge.

Latin270

Damn! I dont come here to often but it sux when someone comes and posts a question only to be hammered down by those who feel like rather than anwsering the question at hand, they'd much rather moan and whine about how many times the "question" has been asked before! If you dont want help a fellow memeber out then just click "back" and for get about it! Too many baby's around here! Lets start acting like men....huh! Now back to our program!