Porting, What do you guys think?

[TS87FC3S]

I have an 84 12a that is apart for rebuild, im wanting to port but keep my intake.. rb 465 holley (individual runner) im considering stock primary ports for driveability and torque and bridge port secondary's with race exhaust port. What do you guys think and how hard would this be to tune, car is street car with numerous autox and road course days planned.

[N.RotaryTech]

I would say do it, since I had experience with a half bridge port, though it was a S4 13B.

I'm not experienced with tuning with carbs, but I think it would be pretty easy.
I tuned mine with the stock S5 NA ECU, throttle body and CAS.

If you go for it,
Be prepared for noise, bad gas mileage, and some light throttle hiccups.

Also be prepared for noise, on command flame shooting, and a fast revving engine that kicks like a mule up top. :)

And if you think you'll lose low end power, just step on the gas.

[TS87FC3S]

shouldn't i retain stock low end with the stock primary port, will the 465 cfm be enough? will timing be difficult seeing as the stock low end and highly modified top end?

[TS87FC3S]

or should i just go with a large extended port and mild to race exhaust and keep my 465cfm and exhaust since i will be cruising and normally driving this car as well as trck days

[PercentSevenC]

If you can keep the primary and secondary runners completely and totally separated, I'd say go half-bridgeport. Jeff20B just built a half-bridge 12A with a Nikki that had better road manners than my streetport. He liked the results so much he's going to build another one.

Here's a video of it idling, with and without the choke:
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[Jeff20B]

You should see the videos he didn't post of how fast this thing revs. Hey Percent, think you could whip up another vid and just post it to youtube so it can be linked here? The rev vids showing the tach and also the video showing the nice little cloud of activity in the carb, ok? Stick them together in the same video like the one you did above.

It was a great project. I'm glad I did it. I'm considering doing it again but I'm not sure about all the details yet. I'll see how things work out after a different engine goes together over the next few weeks. Then I'll revisit the idea.

[TS87FC3S]

You should see the videos he didn't post of how fast this thing revs. Hey Percent, think you could whip up another vid and just post it to youtube so it can be linked here? The rev vids showing the tach and also the video showing the nice little cloud of activity in the carb, ok? Stick them together in the same video like the one you did above.

It was a great project. I'm glad I did it. I'm considering doing it again but I'm not sure about all the details yet. I'll see how things work out after a different engine goes together over the next few weeks. Then I'll revisit the idea.

How is Your setup configured, did u street port primarys, how big did u go on ur exhaust port and bridges.. are you using the stock nikki? (sorry alot of questions just wnt to do it right the first time) also how did u set timing?

[Jeff20B]

Of course I did NOT streetport the primaries. I feel diabolical1 missed the mark on that recommendation to you. No offense to him but he seems to sort of cruise all around the forum popping in here and there to offer advice. It's usually good but sometimes not so much. You know the old saying "jack of all trades master of none." He's sort of a jack of all trades over there. Him and that rxtacy guy. Great guys, very helpful, but sometimes incorrect like Racing Beat. :banghead:

The rubbery low end of streetports? If they are all he's done over the past several years, then says he feels no difference from his streetports vs stock ports, how big are his streetports? Maybe really small, or super weak. When was the last time he drove stock ports? :rofl:

Also you've gotta ask yourself who has done a half bridgeport recently? Who had awesome results? Who is just handing out armchair (or computer chair) advice? See what I mean? If you're gonna do streetports, there's a lot of advice out there. But if you're doing half bridgeports, and you seem genuinely interested in doing some, maybe follow my advice. I don't mean to sound conceited (or maybe I do). Results speak.

I've recently driven a full stockport with 12A turbo exhaust timing (we used 12AT housings so they were already ported from the factory). Then I drove a freshly built massive streetport 12A. Then the half bridge 12A with STOCK primary AND STOCK secondary port timing and mild ported exhaust. All three with Nikki carbs. The differences were very different, dramatic and very educational.

The fully stockport with 12AT exhaust timing was powerful in the low end and has plenty of high end too. Basically 4k comes up quick on the tach and you either upshift or punch it to open the secondaries and keep going. Nice, pleasant daily driver engine with some fun factor. Stock SA22C 30 pound flywheel by the way. Kinda heavy, but still usable. Some sort of header exhaust with a magnaflow out back.

The massive streetport 12A was the largest I had ever done. The exhaust ports were to the sleeves. This engine has a lot less low end. I wouldn't say rubbery. I'd say weak. It did get some great power up high toward 7k, though. Maybe not the best daily driver but it starts up quick and runs cool. This engine is destined to get a blow through turbo so its low end isn't much of an issue right now. It should improve a lot with a turbo. Stock 83-85 27 pound flywheel helps while NA especially.

Lastly the half BP. :) I had something to prove with this. I wanted to prove BDC and peejay wrong and run an aluminum flywheel and still have great launching and driveability. They, or rather BDC recommends running a stock flywheel to help with launches possibly because the tiny bridges you're forced to do on 86+ engines suck, or maybe just HIS engines suck? Don't know. :) All I know is you can do really big bridgeports on 85 and older engines, so that's what I did. :coolgleamA:

What were the results? Better than expected. The aluminum flywheel was just fine. It only had a little bit of brap at low load and low RPM, like around 2k, which stock carbed rotaries also get. The idle was right at 1100 which is fine as that's where my supercharged camden engines idle with an edelbrock. Plus the videos of half bridgeports I've seen all seem to have a slightly elevated idle with a little bit of brap as well. Perfect! The launching, even though it had the lightest flywheel I could get at only 7.5 pounds by itself, was better than expected. It didn't seem to lose any low end, infact had way more than the large streetport with its stock flywheel! This half BP is far more rewarding to drive! You get to have your cake (low end power) and eat it too (high end power), for free (no boost required)! How can you refuse that kind of awesomeness?

I could not compare apples to apples directly with the stock ported 12A above, as it had a stock flywheel and the half BP had aluminum, but I can tell you its launching would probably be about the same, then take it up to 4k, pop open the mechanical secondaries and hang on! Way more noticeable usable power than the stockport with its heavy flywheel. The aluminum really affected things in a positive way. Very few downsides.

I guess there was one downside. A slightly richer idle had to be tuned for the half BP to be happy. It caused the spark plugs to become slightly blackened with carbon after only four heat cycles. Oh they worked fine; it just made them darker more quickly than I was expecting. A good direct fire ignition like DLIDFIS would help a lot here I suspect. Also the engine took a few seconds of cranking to start. I suspect this will improve over time as it breaks in. j9fd3s said his P-port used to take a while to start until it broke in. Fare enough. Also the rotor housings of the half BP had some missing chrome. The engine ran fine before it was torn down so I knew they'd be fine to reuse if I got some new atkins apex seals. Who knows, it may have acted EXACTLY the same way even if it wasn't bridged, you know due to the worn rotor housings during its first few starts. Seems logical. You also can't get 12A housings anymore so you gotta reuse when you can.

Anyway I hope this has been educational and answered some questions you didn't know you had.

As for you specific questions, stock port timing on all four intake ports. Cleaned and smoothed castings. Bridgeports similar to group B spec on secondaries only. Exhaust ports ported up 3-5mm and 2mm bevel redone (can't remember exactly how high I went but maybe it's mentioned in the thread). Timing was leading at TDC. Trailing was 10 degrees after. So basically stock with a ten degree split. The Nikki was rejetted to work on a separate runner manifold. That means the large difference in size from primary to secondary jets was reduced. So from 92 to 94 primary. The secondary went from 160 to 150, but then I went to 170 because the secondary runners breath so much more now. I also reduced the size of the secondary air bleeds to keep feeding fuel up to a higher CFM (RPM) than stock. So it went from 140 to 120. Try to translate this over to your Holley if possible. Good luck. Oh and keep your runners separated! Secondaries must not ever communicate with primaries, ever! That's the key to a successful half bridge that nobody talks about. Well, trochoid kinda touched on it, but he was using dual carbs so it's not entirely applicable.

Gonna start a half BP thread like I did?

[TS87FC3S]

You wouldnt happen to have any templates would you lol, im really wanting a half bp.. and im new to porting but will be doing it myself lol kinda nervous not gonna lie..

[Jeff20B]

No templates. I measured carefully, scribed in some sharpie ink, then used a drill to do most of the work. Not sure what others use. Then cleaned it up with a dremel.

I never did bridgeports before. I was nervous too. But it's good to expand your skills sometimes. Always better if it turns out well. :)

Now I'm kinda nervous about my next engine. Gotta BP the intermediate plate because I have to use a reverse runner manifold in the application due to a lack of space. I already ported this engine to 74 spec so I'm not sure if I'll run the carb out of flow. I do have a Holley 600 to use if necessary, but I'd rather stay with the stock hitachi because it ran wonderfully in this car before. I also have a 390 holley but it is set up to use an open plenum so that won't work on a half BP.

There is basically a very real chance this half BP 13B won't work out as well as the 12A did. But if I think about that, it probably will turn out not as well. So I should concentrate on the positive like I did while doing the 12A and things will work out fine.

[TS87FC3S]

Measured from what?

[Jeff20B]

From the port opening. Go read my thread on the other forum. I'm not here to educate you on how to do. I'm just letting you know that it is possible to port this yourself. But don't come crying if you screw up. You've been warned. :)

[TS87FC3S]

From the port opening. Go read my thread on the other forum. I'm not here to educate you on how to do. I'm just letting you know that it is possible to port this yourself. But don't come crying if you screw up. You've been warned. :)


Lol thanks you have been the biggest help on this project

[TS87FC3S]

http://i903.photobucket.com/albums/ac235/ts88fc3s/WP_000323.jpg

damn jeff you see my new issue

[Jeff20B]

I don't know what blocking those little channels would do. I don't know enough about holleys to know what to suggest. Maybe ask on the forum?

[TS87FC3S]

Would those channels cause an issue with a half Bp? and what kind of issues

[Jeff20B]

It would act like you did a tiny bridge on the primaries, so you get the drawbacks of a full bridgeport like bad idle, weak low end, poor fuel economy caused by the vacuum leak, but not any of the benefits.

[TS87FC3S]

That's what I was thinking

[TS87FC3S]

the hole in question hold water, so its acts as like a closed end vaccum source or something i think it can easily be closed off

Holley 0-1848-1 - Holley Model 4160 Adjustable Float Carburetors This is my carb just fyi

[diabolical1]

Jeff,
I read your post a few days ago and I decided I would not respond for a while because it's only natural to take offense to something like what you posted. However, I do appreciate constructive critiscism and I try my best not to fly off the handle on these Internet forums any more. So at this point, no offense taken. I sort of prefer you would have phrased it in such a way we could discuss (or argue), but I know we shared some thoughts with each other on the other forum, so I guess it's all good. :)

That said, I appreciate what you said and I will try to curb some of my enthusiasm from now on. These engines excite me and I WILL NOT apologize for that, but I suppose my zeal can misrepresent me at times. Engine threads are where I will likely "pop up" because all the other (stereo, rims, suspension, etc.) threads don't hit me at the heart. Engine and porting threads do.

I try not to come off as an "authority" so if I do, I apologize. I consider myself to be a humble student of the rotary engine - nothing more!

As far as this man's project goes, it seemed to me that he was trying to decide what port to go with. I did not realize that he was already leaning toward a half-bridge and I advised him accordingly. I know you and I met halfway on the other forum, but just to make it all clear, I did say go with a MILD streetport. Obviously a big street would have it's hindrances. It's just that I hate to see people post the hindrances based on a big streetport when a smaller one can yield "better-than-stock performance" and still keep stock manners.

i try to choose my words carefully. I can see where a big streetport would/could cause the "rubbery" low end, but I also figured you (of all people) would realize that there are a variety of ways to streetport a rotary. I made many templates for myself and in all honesty, I have not driven any of the really big ones yet, but when I give advice, I speak from the ones I have used. I am poised to build a big one this year. So maybe I will get that weak low end ... we'll see.

I maintain what I have always said. I have no personal bridgeport experience, so I won't try to speak as if I do. A friend of mine had one (a full-bridge) many years ago and he hated it on the street so my memories are filled with that. However, I do try to be objective with them. I will mess with bridges at some point, but right now my big port aspirations revolve around semi-peripherals and I will be spending my time and money accordingly.

As far as TS87FC3S's project goes, I hate to think that I came off as trying to force him into my way of thinking. I simply tried to illustrate other options, based on my experiences. If I failed, I'm sorry. I wish him all the success with his half-bridge and I still offer any support or advice I can. Hell, maybe someday I'll ask him for advice when I do my own bridgeport/half-bridgeport project. The bottomline is I try to engage in discussion - sometimes it works, sometimes it doesn't - but I'm happy with whatever he does as long as he is.

[fc3sfreak415]

hey jeff ive done free handed half bridge ports on 13b's and i have to say i kept the primary ports factory and just cleaned them up. and the increase is very notice able in power and i was happy with the out come :) glad to hear someone else lets god guide there hands to port there engine instead of using a template lol

[-xlr8planet-]

very informative. I liked it :D

[N.RotaryTech]

Just updated my signature. :biggthumpup: