Shainiac

iTrader: (7)

I've been reading around about bridges and half bridges and pro's and con's. Im just having trouble finding the information I am looking for. Could a half bridge be performed on JUST the 5th/6th ports while retaining functional actuators and sleeves. In my head this seems like a pretty cool, streetable setup for an NA. I would assume that at idle and low RPMs, idle would be stock-ish since there would be no airflow through these bridged ports. Any ideas??

Rx7_Nut13B

iTrader: (1)

Done that

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/frankenstein-motor-pics-inside-610501/

Shainiac

iTrader: (7)

AWESOME! Thats exactly what I wanted to see. Only difference is I am staying NA.

Sideways7

iTrader: (7)

From what I have read, keeping the aux sleeves operational will kill the flow potential to a bridge port. The stuff in the middle of the port (actuator rod or whatever its called, for example) disrupts the air flow a good bit. If you want to keep it for driving around town then go for it, but I think you will get mroe power from taking the sleeves out entirely.

Also, what you are talking about is usually called an "aux bridge" since it is a bridge on the aux ports.

anewconvert

iTrader: (1)

Have it. Not worth the time.



here is why. the stock intake manifold is unsuited for a bridge. The bridge will significantly outflow the manifold and you returns will be minimal. Further it will mess with the pressure waves that the stock manifold is designed to take advantage of.

If you are going to do the aux bridge you will need a new intake to take advantage of it. In that case the actuators for the aux ports goes away. now you have a tiny bridge that is open all the time, just like a full or half bridge. So you have a motor that has the compromises of a bridgeport without all the power.


So as rotraygod will say, as soon as he sees this thread and agrees with me (and arroncake too) if you are going to bridge, do it right. A the LEAST go with a half bridge that encompasses both the aux and secondary ports.

In my case i bought the engine as a fresh rebuild by RotaryResurrection with the aux bridge already on it. i didnt order the engine. SO its not wortht he money to pullt he engine and have it re-ported. So since I CAN keep the stock ecu and drive it just fine Im going to get a full exhaust, ITBs, and a standalone and be happy with what I have. If I eventually need a rebuild then I will get the secondaries bridged as well. That is the ONYL advantage to the aux bridge. you dont NEED the supporting mods to do it. You can run a stock ecu, intake and exhaust. It struggles for air past 7K rpms but it lets me upgrade slowly. However, for the cost of a porting job you are better suited to get the full exhaust, standalone and intake FIRST then get the engine ported, instead of the the engine first and everything else later.


BC

Sideways7

iTrader: (7)

Yep, Rotarygod is who first told me why its not a good idea for the reasons stated in your post and mine. Since then I have further read up on it and it just reinforces what he told me.

Shainiac

iTrader: (7)

I guess i didnt think about how restrictive the stock intake mani is. The main reasons I wanted to do the aux bridge were A) I want to retain the stock ECU. B) This is my daily driver so I want close to stock low end and fuel economy. C) Im not looking for gobs of power, and D) I have a blown coolant seal so I am rebuilding the motor myself this summer reguardless.

As far as being a waste of money, labor is free - Ill be on summer break. Also, I have a die grinder and an assortment of carbide bits and ect at my house.

I planned on buying street port templates for the intake and exhaust from Racing Beat or Mazdatrix. As for the bridge, i was just going to match it put the the housings and mark within the bounds of the sleave.

I guess my main question is, are the gains that much greater than a street port. I definately want to keep my actuators and sleeves intact, despite restrictions and less power. I could barely stand having to drive around when my ports WERE wired open.

Thanks to all for thier input. I hope im not coming off as a hard headed teenager. Im more of a practical person rather than performance oriented. (mainly because gas is expensive and Im getting ready to start college) Thanks again

anewconvert

iTrader: (1)

Heres the thing, and I am stating from 3rd hand knowledge off this forum, with a bridge you make MORE low end power than you do now. You make more power across the board. But compared the the top end it FEELS like you have lost power. I cant attest to this, but from what I have read others who have BP's this is true. many say that the definition of less streetable is in the eye of the owner and there are plenty of guys who daily their BPs.

For the aux bridge there IS a gain above 6k rpms. On my car it dies off quickly over 7k because I dont have a full exhaust yet. I have a collected header sitting at my house begging to be installed, and I bet that will cure most of the problem.

As for the intake mani you can pay about $600 for a shop to extrude hone the manifold. This will increase the runner cross-sectional area by something like 30%, so it will flow much better and you can keep the aux sleeves, but the sleeves are their own restriction and the intake runners arent the appropriate length for upper RPM power.

But honestly, you are better off just streetporting if you want to keep a daily driver. If you bridge it you should go all out with a full exhaust, new intake manifold, and a standalone, or dont bridge at all. The aux bridge isnt worth it. The gains will likely be better with a strettport than with a bridge. Even with just my aux bridge i HAVE to get a full exhaust. With a streetport you can get a RB downpipe and catbacka nd call it a day. With an aux bridge i need a new intake mani, hence the ITBs. With a streetport the stock manifold is sufficient. With a bride I need a standalone to take advantage of the bridge and to use the ITBs, with a streetport you can stay with the stock ECU.


A bridge of any sort really requires another $3500-$4500 to take full advantage of. A streetport is just a few hundred dollars extra. SAFC to tune the fuel curve and some exhaust work.

BC

Shainiac

iTrader: (7)

Would a descent catback and no cats really be that much of a bottleneck on such a small bridge? I already had a RP racepipe and perhaps an RB cat back perhaps a Dynomax (cheap, i know) system planned.

anewconvert

iTrader: (1)

that isnt the bottle neck. The stock exhaust manifold is.


BC

Shainiac

iTrader: (7)

Ah, suckage. Welp, I guess Ill keep weighin pros and cons until summer break comes around and I tear down my motor. Thanks all for the imput.

anewconvert

iTrader: (1)

no problem.


BC

Sideways7

iTrader: (7)

I think your best bet is a decent sized street port. I would actually say it is well worth the money to get it professionally ported by a well known person. With a proper street port it makes a huge difference. I had more power everywhere and noticeable more up top. It made usable power all the way to 7500 RPM, and this was with an s4 engine and s4 intake. For a street driven NA (ESPECIALLY a daily driver), a streetport is by far the best way to go.

rotarygod

iTrader: (1)

This is a topic that is a sore spot for me but I'll state it again anyways.

A bridgeport does typically (assuming it is setup properly) make more power down low and everywhere else over a stock port. HOWEVER this is at full throttle. Under light loads and rpms such as where you cruise and do most of your driving, they make less. Don't make the mistake of thinking full throttle power is indictive of how it performs everywhere. Even a dyno chart is only a 2D part of a 3D problem.

There are numerous reasons why this is a bad idea to do. I'm not going to get into them again but needless to say the last time we had this discussion we had a curious person who wasn't listening to those who have done it who said not to. All we heard was crap like "you only tried it once so you don't know that it couldn't work" and other such nonsense. If I couldn't make the first one work after much fiddling, I'm not going to waste time on another one! Instead I'm going to build a setup that works. Then of course we had the noob who knew nothing about rotaries who said to go ahead and try it and suddenly he was the person being listened to. Right...

CAN a bridgeport be made to work well with 6 port housings? Yes. Are you going to do it on a stock ecu, intake manifold, exhaust manifold, etc? No. Don't even waste your time trying. In the last thread on this topic, one person even said that just because every other person that's ever tried it (and there's definitely been more than a few) couldn't make it work properly, it didn't mean it couldn't be done. I'm not a betting man but I'd bet against their effort in a heartbeat. Too many people can't get over the fact that more is not always better. Bigger streetports are not necessarily more powerful than smaller ones. (Let's see what kind of crap I stir up with that one!). A bridgeport is not necessarily more powerful than a streetport. There are so many "if's" and exceptions to the rule. If you intend to keep your car street drivable, keep it streetported and even then don't go too large. The engine is more than just the size of a portjob. It's an entire system that is designed to work together in harmony. If one thing is subpar or improperly matched with everything else, the rest will perform badly with it. Don't under estimate the power of a good streetport. You'll get far more than you think you will. Please save the time and money and keep it simple. Unless you fully intend to do an ecu, intake manifold, exhaust system at the same time, don't do a bridgeport. And for the record, the guy in the link above who has an aux bridgeport done to his now turbo'd engine, he is a local here and while I do know him and get along with him, that car is having some big problems right now.

Shainiac

iTrader: (7)

Thanks a ton guys. I guess Ill call it a day, save some headaches, and stick with a tame street port