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half bridge 12A, with a twist

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Old 04-29-11, 02:11 PM
  #226
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yea it even survived the hills in seattle be pikes market an its now covered in hepps of plastic
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Old 04-30-11, 12:36 PM
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Good. Keep the weather out of it. Shove some clean rags into the exhaust ports and cover the carb really well. Also cover the flywheel. They are unprotected iron and like to rust if rained on directly or exposed to humid air over a period of time.
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Old 05-18-11, 10:17 PM
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Originally Posted by Jeff20B View Post
Are they online?
Like pee in a pool, they are now:

Note: I had to stretch the original pic asymmetrically to get the 7.5, 51, and 41mm dimensions correct, but the bridge measures out about 1mm thicker than indicated. I have not laid this down on a housing yet, so YMMV, use at your own risk, no warranty expressed or implied, be excellent to each other, etc.
Attached Thumbnails half bridge 12A, with a twist-homologatedbridge72dpi.jpg  
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Old 05-19-11, 01:24 PM
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Wow, that bridge and main port look technically perfect. Thanks for remembering this thread and following up.
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Old 05-20-11, 05:50 PM
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motor is in going through the technicallities now
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Old 07-01-12, 07:30 PM
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Originally Posted by peejay View Post
I have not laid this down on a housing yet, so YMMV, use at your own risk, no warranty expressed or implied, be excellent to each other, etc.
Closing side is moved maybe 13mm higher and that's it, on a RX-7 12A end housing.

Interestingly, it exactly matched the aperture on the street ported TII housings I was running a few years ago. The bridge eyebrow closes at the same point as the one I made by-guess-and-by-gosh but the opening point is about 10mm lower than mine.

Neat stuff.
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Old 09-15-17, 02:30 PM
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Originally Posted by Jeff20B View Post
lol This thread wasn't about showing off a completed project. This thread was about the build progress. The PROGRESS. Which is progressing on time, on schedule. It's actually going kinda fast considering all that I've had to do to get the carbs working on the other engine so one would be ready for this half BP.
Jeff, what ever became of this half-bridge build? Did it work out?
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Old 09-15-17, 11:24 PM
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Yeah, I got word on its continued successes recently. It appears to be a great setup for the next owner. Kind of inspired me to look into building another.

This next one will have the advantage of several years of additional knowledge thrown at it and of course a hogged out Nikki! I'm also following the diagram peejay posted as accurately as I can. In other words, this one will be ported bigger than the first; the first was only stock port timing with eyebrows added. Pretty basic. Now I'm already at 74 spec with hogged runners. It looks pretty accurate to the diagram.
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Old 09-16-17, 12:45 AM
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Which diagram was that? I must have missed it.

I just think this half-bridge would be a great setup for my HPDE car. I commute a lot of highway miles with it and a few times a month hit the local race track. It sounds like keeping the dual stage Niki with monster porting on just the secondaries could creat a great idling and cruising car that really opens up at higher RPMs. ...assuming of course, all your theories behind it work.

Did you end up using the manifold that had completely separate runners? Any idea where that came from? I have an '85. Haven't pulled it apart to see what's there yet, but might be a good winter project. Port the motor and leave everything else as is, with a few tweaks to the Niki as I put it back together.
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Old 09-16-17, 12:17 PM
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Scroll up to post #228 that peejay made.

As for how a half BP will do on the highway, I don't know. It will probably brap.

The manifold came from an RX-2. But since then I've learned separated runners don't work very well, and I will not be repeating them here. The next manifold is also from an RX-2 and is already hogged out by a previous owner but doesn't have channels yet. I'll have to test it against one that has similarly hogged runners but does have channels. It's just a simple manifold swap to test them.

I don't have a time table for this project yet. Maybe a winter project like you said.
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Old 09-17-17, 09:26 AM
  #236
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Originally Posted by Jeff20B View Post
Scroll up to post #228 that peejay made.

As for how a half BP will do on the highway, I don't know. It will probably brap.

The manifold came from an RX-2. But since then I've learned separated runners don't work very well, and I will not be repeating them here. The next manifold is also from an RX-2 and is already hogged out by a previous owner but doesn't have channels yet. I'll have to test it against one that has similarly hogged runners but does have channels. It's just a simple manifold swap to test them.

I don't have a time table for this project yet. Maybe a winter project like you said.

the channeled intake is beneficial to the smallish nikki.

I ran mine on separate runners and got worse mpg, worse idle, way less low end, and even less top end.

I tested .5" and 1" open plenums and got great results at high RPM, and a much improved idle. At the cost of low end grunt and fuel signal.

the channels just help the secondary ports breathe when the secondary barrels on the carb aren't open. Without sacrificing intake velocity like an open plenum.

​​Hope that makes sense. I've successfully made some pretty fast cars using nikki's and simple OEM components.

​​
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Old 09-17-17, 02:27 PM
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It makes perfect sense to me.
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Old 09-18-17, 10:15 AM
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So if I plan to go HBP on my 12A. I need to channel my stock intakes? I already have a Jeff20B "Fat Nikki". I know the current owner of the HBP that Jeff20B previously build. Strong running car, has some BRAP and owner is pleased with the motor.
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