stickshifta

Hey guys, I am looking for a little advice on my upcoming build. I am building a 1990
B-2200 Pick up. I have already built and swapped a S4 13b into it. It was on the road for about 8 months, but now I am looking for more. I would like to build a N/A motor producing between 220-240 HP. I will be running racing beats Holley carb and manifold (always pre-mixing). This manifold doesn't allow me to run the actuators for the 5th and 6th ports, so mine are frozen open with pineapple ramps installed in the sleeves. I am also running their long header with 2 1/2" pipe back. I also have a dump on the header for track days (mostly what I am building the truck for). I am also running twin MSD 6A boxes with blaster coils.

I was thinking I can achieve my goals by building a half bridge motor, with eyebrows on the frozen 5th and 6th ports only. The truck is mostly for the track but must still be able to drive it down the road from time to time. I have plenty broken down motors so I am not in need of parts.

My questions are how much overlap I am going to need (I don't expect it will be much). Recommendations on size and shape of my exhaust ports, squared off or oval. Lastly do I need to make any changes to my current set-up in the truck.

Any help you guys can give me would be helpful.

peejay

Don't bother with the six port irons, find some 4-port end irons (12A or T2 depending on rest of engine) and build those.

Really, I was happier with a street ported 6-port than my half bridge. It made more power.

I would NOT use a dump pipe, unless you are okay with retuning the carburetor when you take the dump cap off, and then retuning again when you put the cap on. I used to play with one and found that the carb needed to be jetted a lot richer with the cap off.

You may also find that a bridge engine will not tolerate mufflers that are restrictive enough to make a dump pipe worthwhile. That is to say, exhaust restriction KILLS drivability, and once you find an exhaust solution that is free flowing enough to have good street drivability, you'll probably find that there is no worthwhile power gain to having a dump pipe.

stickshifta

has anyone ever done a half bridge with eyebrows only on the primary (center) iron? if i went this direction i could leave my street ported end irons.

john smack

iTrader: (12)

^ I had a 12a like that and it worked fine

Falcoms

On mine I ran eyebrows on both the secondary and aux ports on my s5-N/A block, leaving the primary's just with a large street port. It yielded amazing drivability on the street, and a nice, broad powerband for the road course. The main issue was the VDI intake was nearly 3 times the length it should've been for that engine. All said and done I was making 200hp at the flywheel with the stock VDI intake, no sleeves for the aux ports, VDI valve wired open at all times, and though I didn't realize it at the time, 8.7:1 s4 turbo rotors. With a weber or holley intake and carb setup, along with the 9.7:1 rotors, I'm sure 240hp would've been quite easily obtainable.

here's the ports just initially roughed in:

stickshifta

Did this port job req. a J port in the housings? can you give me an idea how much distance you left between the grove for the coolant seal and the edge of your eyebrows?

Falcoms

if you're using used plates, it's easy. you have a darkened area where the rotor housing sits on the side plates. I didn't do a j port or anything fancy, just a couple of eyebrows, leaving about 3/16"-1/4" material for the bridge to support the corner seal. I always used the darkened area as the reference mark for where I cut to as I don't really believe in cutting the coolant seal and track unless it's an often rebuilt track-only engine, and even then it's not really worth it to me.

TonyD89

iTrader: (10)

Except the darkened area won't show the leading edge of the trailing side seal. You gotta watch that the whole thing doesn't become unsupported.

stickshifta

Again looking at your picture, did you open a passage between the two ports in the bowl of the main port? If so why?

84stock

iTrader: (5)

I believe that passage is already existant.

I would bridge just the primaries...

And add nitrous

84stock

iTrader: (5)

And you might be thinking about something like this

http://www.youtube.com/watch?v=qOzQzOmwRsU

stickshifta

Also i was considering doing a small full bridge. Do my eyebrows on one my primary (center) iron have to match the same intake timing?

84stock

iTrader: (5)

Do the eyebrows on the primaries on the end plates only!

peejay

I did that originally on my GSL-SE block and was unimpressed. When I took it apart to redo the coolant seals, I opened the bridges up to the same height as my old TII block. They go halfway up into the aux ports. I was still unimpressed, but it was at least somewhat better.

6-port end housings just close too damn late! When the engine comes back apart, it's getting the primary runners opened up to FC spec (a little bigger, actually, since the port roof of the GSL-SE center is higher) and 12A end housings.

stickshifta

I would consider swapping out my end irons for 4 ports (T2, or 12a), but then my racing beat Holley intake won't work. I am trying to reuse as much of my original setup as i can. Will 12a end irons even work with S4 housings? and if i do that do i have to make a custom intake manifold?

peejay

You would need to source Turbo II end housings. I am playing with a GSL-SE block which can use the 12A end housings.

I also have a RB Holley manifold for a 4-port 13B, and I have a "special" manifold for a Turbo II that kicked all sorts of ***... so I guess i have the manifold situation covered no matter what I am running.

I can respect the need for using what you can get. For some reason the available TII carb manifolds are crazy expensive compared to 6-port or even FD. I'm just relating my experiences.

Falcoms

It was already pre-existing in the iron. As for the position of the bridge, I didn't actually measure it out or anything, I just based it on the way the seal tracks on the side plates were worn in. The "eyebrow" ports were about 3/16" wide give or take.

As for the suggestion of porting just the primary port, the reason I didn't do anything but a large street port on the primary and did the secondary and aux ports was so I gained the top-end performance benefits of a bridge port engine while maintaining a broader power band by actually choking it down to an extent. Think of it as a small block v8 camshaft with about 290* duration at .050, but with only .400 lift. Same basic principal. And those are just arbitrary numbers, simply for example.

stickshifta

I think i am going to go with Falcoms approach, a 6 port half bridge on the aux irons only. One thing i am going to do i little differently, i have the 5th and 6th port sleeves frozen in their ports with the pineapple racing ramps installed. so my thought is i am going to have to drill my eyebrows through these sleeves. does any one know of any reason this would give me trouble?

rotarygod

iTrader: (1)

I wouldn't do a bridge on the aux ports ever under any circumstance. They don't work very well and never will. If you absolutely MUST have a bridge port for whatever reason, use 4 port housings, a standalone ecu (or carb) with an aftermarket or custom built intake, and a very free flowing collected exhaust. If you can't do this, don't waste the time with any bridgeports.

peejay

What's funny is, my half bridge bridge GSL-SE block hates the exhaust system that I had on the half bridge Turbo II block. Same exhaust ports, same eyebrow *placement*, the main difference is that the current engine has relieved rotor housings and the Turbo II block did not.

So my next street bridge engine is going to NOT have relieved housings. After seeing what bridging did for low- and mid-range torque, I really don't want to go back to street ports.

rotarygod

iTrader: (1)

If I had a dedicated track car I'd probably try a bridgeport. I have to pass an emissions test so there's no point in going more than a streetport. I don't like loud exhausts anymore anyways. I think I'm getting old! I'm at the point now where I'd really just like to bolt a low boost supercharger on a stock 6 port and call it a day.

Falcoms

Mind you this is with the stock VDI intake and 8.7:1 rotors. I don't know about anyone else, but with that broad of a torque curve, the 6 port half bridgeport seemed like a great upgrade for any N/A RX-7 not willing to go to a 4-port setup.

stickshifta

Agreed, those numbers aren't bad. That makes me believe that with a similar bridge, a better intake, and internals i might be able to produce almost 200 wheel HP. Thanks for the hard data.

rotarygod

iTrader: (1)

Here's a link to an engine that has all stock intake ports, 9.7:1 rotors, FD rotor housings with stock exhaust ports, a Racing Beat exhaust, and a little bit of fuel tuning with an S-AFC. He could have a bit more power with an S5 intake manifold and could do much better with a custom built exhaust and complete ecu tuning. It's not about the intake ports. The aux bridges aren't a good choice. Abandon them. They suck. No one has ever made them work will and no one ever will.

https://www.rx7club.com/time-slips-dyno-128/s4na-dyno-157rwhp-970927/

RotaryEvolution

iTrader: (30)

i agree, i haven't seen a single person post an impressive sheet for a half bridge n/a that was anywhere remotely much above what the stock 6 port street ported irons can provide. even 170 at the wheels is managable without doing too much, without any bridge or custom intake.