I ported my center iron on my half bridge 12a project. After comparing it to online photos I'm worried my bridge between the ports is too thin and could break under stress. Or a seal or spring could pop easier. What do you think? This is my first rebuild and port job so I want to make sure it's right. The bridge is about 3mm wide with a slight bevel and the port does not overlap under the rotor housing. (The edge where the housing meets the ported area has maybe 1/2 a mm of iron left, as you can see it is a bit reflective in that spot in the picture). Most bridge ports i see completely overlap under the housing and almost to the water jacket.

Basically I'm not worried about how much more power can i make if the port was bigger or if I had a thicker bridge. I want to make sure it won't break under stress being that it's a tad thin.

Should I just scrap it and buy a new iron? Port that one further under the housing and leave the bridge thicker?
[IMG]file:///C:/DOCUME%7E1/Nate/LOCALS%7E1/Temp/moz-screenshot-2.png[/IMG][IMG]file:///C:/DOCUME%7E1/Nate/LOCALS%7E1/Temp/moz-screenshot-3.png[/IMG]

 

I just ordered a new iron. Should I leave the main port mostly alone and port the eye brow closer to the jacket? Leaving maybe a 6-7mm bridge?

 

For some reason the image is no workie for me.

 

You posted the documents from your local computer. it wont work that way. You need to place them on the internet somewhere like your ISP or PhotoBucket for example.

 

I go no thinner than about 5mm.

I mark the whole area with Sharpie, set my dial calipers to 5mm, and scribe a line based off of the original port opening line. No problems yet.

 

It was supposed to get the image off of Verizon PIX place. Guess it's buggy. But yeah, it's about the thickness of an apex seal (3mm or so). I'll retry on this new iron as soon as it shows up. I'll make sure it's at least 5mm thick. How far under the housing should I port it? I've seen some people port it so far it is hair thin against the water jacket groove. I want it to last more than a year though. My plans for the engine is to keep the reliability of the street port with a very small gain from the half bridge, but I mostly just want a little brap.


I'm also curious how the engine will run with my setup on my stock port... Currently I have

-Nikki (Sterling of course) Racing Beat carb hat, running factory secondary jets and slightly larger than factory primaries.
-New factory fuel pump
-PaceSetter header (I know, crap... but it flows better than stock)
-Racing Beat mini silencer
-Factory connecting pipe
-Racing Beat power pulse muffler
-2gdfis, BUR7EQX leading, BR7EIX trailing, recently replaced NGK wires (plugs will be replaced with new ones when the engine goes in obviously)
-EFI fuel filter.


I'm considering a lightened flywheel, just because there's no better time to replace that then with the engine out.

I know I would gain a bit more power out of my porting with a better header and less restrictive muffler, but can I run a medium half bridge on my current setup?

I know I will need a new fuel pump and regulator. Suggestions?

 

why are you porting the primary instead of the secondary plates??

 

that's what i wondered.

i suppose he just wants the brap brap of the bridgeport without the actual gains of bridging the secondary. loss of fuel mileage and loss of low end torque for minimal gains in the top end.

 

 

I could see a mild, small secondary bridge for the brap without too many of the sacrifices. Especially if you close off the small primary to secondary port in the intake manifold.

 

This would be my idea of a small secondary bridgeport to retain some streetport driveability and have the brap along with modifying the intake as mentioned earlier (not an actual port job, photochopping project). Would assume a marginal increase of power in upper rpms.

 

The way I see it, if you're gonna do a bridge, cut it at least as tall as the runner.

I'd like to do a half bridgeport 12A (on the secondaries). I'll follow peejay's advice and make the bridge 5mm thick and cut the hole large enough to go into the rotor housings a little. Then bevel the rotor housings. Flip the rear rotor's apex seals so the little triangle piece stays in place. Oh and most importantly I'll use a separate runner intake manifold so there's no communication between primary runners and secondary runners.

Exhaust will be an RB road race header into a long primary exhaust. It will collect to 2.5". The collector location will be determined later.

 

This is one of my bridgeports



http://www.youtube.com/watch?v=09_ukjxh-zM

 

there is reasons sometimes port the primary as bridge instead of secondary

if you by laws is limited to the stock carb,,, and your car is a HB cosmo

1: stock carb secondaries will already be undersized on decent extend port ,, why bother bridging here when the extend will do it just as well over a wider spread of RPM

2: HB cosmo is middle mounted on BOTH sides of the primary plate
this is a unique engine plate avail only on 12a 6p, 12aT and 13b 6 port GSL-SE / RESI engines originally fitted to HB cosmo

these plates have the WORST /SMALLEST port casting and stock port of any primary plate
you do not have the option to use any other plate due to the need for both engine mounts

you cannot even mild port these plates to anything as much as even a stock shitty s1 rx7 NO middle plate
the solution is to port the inlet manifold primary runners and to add a small bridge to the stockish primary port
( you will be limited in the bridge height by the width of the runner casting )

the primary ports can be angle cut on the housings and the motor built from centre plate outwards to turn the small chip wedge out towards the secondary ports

then at least you could use the potential of even the stock carb

i have done this even with cross-ported type inlet manifold
and it does bridge idle,, but its not super aggressively lumpy if you cruise
i suspect it may actually be more grumpy if the cross-port under the carb is eliminated








pics demonstrate the centre plate in question with angle cut housing
( red line is highlighting the arch cut into the runner and under the bridge to promote airflow by radiusing the airflow path )

on this plate this all amounts to about as much as you can port both extend and bridge before finding water jacket

as is,, considering this car must run standard carb to be legal,, and limitations of the middle plate
this is as good as you can port them
( the secondaries used on this engine are full template mazdatrix extend shape )


as a comparison,, here is what you would do if you actually had a decent 3B/R/R5 combo of earlier plates to work with

 

You don't lose low-end torque, except for the very bottom of the range (sub-2000rpm). As matter of fact, you gain quite a lot.

Fuel economy on my first half-bridge was about the same as the large streetport 4-port 13B I ran before it and the early-opening streetport 6-port after it. About 20-22mpg on the highway. I only built the 6-port because I destroyed the half bridge's rear plate, I only had 6-port units lying around, and I wanted to try it. It was okay but soft on power like I expected. So I built another half-bridge engine! i just got it started yesterday and did some mild tuning on it today. The porting on it is a bit unorthodox but I want to experiment a bit.

I get excellent drivability and get the idle down to the ~1100-1200rpm range (still strong idle, too - 10-12 inches of vacuum) by having the engine idle entirely on the secondaries. The primary throttle (stock EFI manifold) gets shut entirely, the secondary stop screw is replaced with a long 10-32 machine screw (need to re-tap throttle body) and idle is rough adjusted there. The standard air bypass screw is then used for trimming idle speed in a roughly 100rpm window. The idea is, you want to minimize the amount of vacuum the bridges see.

The funny thing is, it won't brap. It just sort of burbles.

 

any pics of the port?

 

None very good. To visualize it, take a GSL-SE end housing, mark off the 5mm thickness for the bridge, and mark the height by going from about 1/4 of the way up the lower port to the top of the lower port. The window is maybe an inch high. Relieved to within a millimeter of the coolant seal groove.

I'm a little surprised that it idles as well as my TII half-bridge, which was ported on the same principle except no reliefs. I actually used my TII port as a guide, except obviously I couldn't go as high.

I plugged off the aux ports.

 

Peejay, what do "you" think of the mini bridge idea pictured earlier?

 

Do the secondaries and primaries even communicate at low RPM with a mechanical secondaries Nikki? I was under the impression that with a mechanical Nikki, the engine ran 99% off of the primary ports until you tapped them open. My reasoning was that the transition between mechanical primary and mechanical secondary would be too much for a bridged secondary port to handle at once. It would bog, or am I just over thinking? I figured a bridge ported primary would communicate or transition with a street ported secondary when the Nikki's mechanical secondaries opened up making it react smoother.

Opinions? Keep in mind this is my first ported engine so educate me.

Is there enough air flow between the primary and secondary ports inside the intake to communicate the two at low RPM? I have a 79 intake with a DIY port job with the bridged notch under the carb spacer ported and smoothed out.

Should I just street port the intermediate plate and B-port the front and rear plates? Then flip the seals like mentioned above?

 

The reason the secondaries get bridged is to preserve streetability. Should be no transition issues that you are referring to.

 

If you look at a stock manifold, the primary and secondary runners communicate freely with each other. The only division is between the rotors, and even then there is a tiny bit of communication between the two primary barrels.

I cannot stress enough that exposure of the overlap to vacuum is what causes rough running. You want to idle and cruise on the bridge! HOWEVER I don't have EFI with injection time endpoint control so I only go half-bridge so I can run the injectors in the non-bridged ports, so that they don't see the heavy reversion pulses.

Set up this way, the engine is kind of schizophrenic, since the primary and secondary runners are acting as separate engines. At idle and light cruise the air is almost all coming through the secondaries, with most of the primary air coming through the injector air bleed and the hole in the throttle plate. As throttle is tipped in, it runs more on the primary, until the secondary starts opening shortly thereafter. I was tooling around in the car on Friday, first time I drove the car in maybe four months, and noted that it was perfectly happy burbling at idle at 800-900rpm...

Drives in the city just fine, nothing special at all. Easy to drive with a puck clutch on the snow, too. (I was surprised at that myself Puck disk and stock pressure plate is very drivable combo!)

Referencing this:


My TII housings had eyebrows that had about the same bottom point but extended all the way to the top of the port. They didn't extend all the way down. They were 32mm high, if I remember right.

My current engine has the same bottom point and the rotor housings are relieved to within a mm of the coolant seal. You can take an '85-earlier engine's reliefs a lot further before hitting coolant seal groove! I'm pleasantly surprised that this amount of relief has not negatively impacted drivability.

One of my long-term projects is a full bridge 12A. It will have the late opening eyebrows but MUCH larger reliefs. Quad 48mm throttles, the works. Should be a blast.

 

Ok here's a few pictures of what I was busy on today... New center iron will be here on the 25th. It will be street ported to match the ones I did today.

How do they look to you? I have about 5mm of bridge and about 1.5 mm of iron after the seal groove. The port rests about 1mm under the housing when assembled.









and my small exhaust porting. I opened them up about 4mm on top and beveled the sides and bottom. Nothing huge, but I didn't want to go to far.