Porting, What do you guys think?

TS87FC3S · 05-05-2011, 10:21 PM

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 · 05-06-2011, 07:44 AM

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 · 05-07-2011, 11:00 PM

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 · 05-07-2011, 11:26 PM

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 · 05-08-2011, 12:38 AM

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:

Jeff20B · 05-08-2011, 02:53 AM

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 · 05-08-2011, 08:22 AM

Quote:

Originally Posted by 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.

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 · 05-08-2011, 02:52 PM

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.

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?

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.

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 · 05-08-2011, 03:06 PM

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 · 05-08-2011, 05:12 PM

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 · 05-08-2011, 05:53 PM

Measured from what?

Jeff20B · 05-08-2011, 06:27 PM

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 · 05-08-2011, 06:29 PM

Quote:

Originally Posted by 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.

Lol thanks you have been the biggest help on this project

TS87FC3S · 05-08-2011, 07:30 PM

damn jeff you see my new issue

Jeff20B · 05-08-2011, 07:47 PM

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?

05-05-2011, 10:21 PM	#1
TS87FC3S Ask Me About My WANKEL!!! Join Date: Jan 2010 Location: Missouri Posts: 127 Rep Power: 16	Porting, What do you guys think? 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. __________________ 1984 Rx7 Gs - stripped interior re speed coil overs, tokico blues, re speed crossmemeber and mustang rack, diamond star racing wheels 1988 Rx7 Se - Sold 1988 Rx7 GXL - Sold

05-06-2011, 07:44 AM	#2
N.RotaryTech Home-brew Rotary Join Date: Feb 2008 Location: GooseCreek SC Posts: 552 Rep Power: 18	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. __________________ '89 RX7 GTU, half-Bridge-port S4/S5 NA, E6K, Full RB exhaust, weekend warrior. '83 RX7, The "this might take awhile" project. '87 RX7 GXL, Rest In Pieces. '98 Subaru Impreza Outback-sport, rx7 rescue vehicle, down for repair. '94 Ford Ranger, daily.

05-07-2011, 11:00 PM	#3
TS87FC3S Ask Me About My WANKEL!!! Join Date: Jan 2010 Location: Missouri Posts: 127 Rep Power: 16	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? __________________ 1984 Rx7 Gs - stripped interior re speed coil overs, tokico blues, re speed crossmemeber and mustang rack, diamond star racing wheels 1988 Rx7 Se - Sold 1988 Rx7 GXL - Sold

05-07-2011, 11:26 PM	#4
TS87FC3S Ask Me About My WANKEL!!! Join Date: Jan 2010 Location: Missouri Posts: 127 Rep Power: 16	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 __________________ 1984 Rx7 Gs - stripped interior re speed coil overs, tokico blues, re speed crossmemeber and mustang rack, diamond star racing wheels 1988 Rx7 Se - Sold 1988 Rx7 GXL - Sold

05-08-2011, 02:52 PM	#8
Jeff20B Rotary Fanatic Join Date: Mar 2008 Posts: 215 Rep Power: 18	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. 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? 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. 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? Last edited by Jeff20B; 05-08-2011 at 05:15 PM.

05-08-2011, 02:53 AM	#6
Jeff20B Rotary Fanatic Join Date: Mar 2008 Posts: 215 Rep Power: 18	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.

05-08-2011, 03:06 PM	#9
TS87FC3S Ask Me About My WANKEL!!! Join Date: Jan 2010 Location: Missouri Posts: 127 Rep Power: 16	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.. __________________ 1984 Rx7 Gs - stripped interior re speed coil overs, tokico blues, re speed crossmemeber and mustang rack, diamond star racing wheels 1988 Rx7 Se - Sold 1988 Rx7 GXL - Sold

05-08-2011, 05:12 PM	#10
Jeff20B Rotary Fanatic Join Date: Mar 2008 Posts: 215 Rep Power: 18	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.

05-08-2011, 05:53 PM	#11
TS87FC3S Ask Me About My WANKEL!!! Join Date: Jan 2010 Location: Missouri Posts: 127 Rep Power: 16	Measured from what? __________________ 1984 Rx7 Gs - stripped interior re speed coil overs, tokico blues, re speed crossmemeber and mustang rack, diamond star racing wheels 1988 Rx7 Se - Sold 1988 Rx7 GXL - Sold

05-08-2011, 06:27 PM	#12
Jeff20B Rotary Fanatic Join Date: Mar 2008 Posts: 215 Rep Power: 18	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.

05-08-2011, 07:30 PM	#14
TS87FC3S Ask Me About My WANKEL!!! Join Date: Jan 2010 Location: Missouri Posts: 127 Rep Power: 16	damn jeff you see my new issue __________________ 1984 Rx7 Gs - stripped interior re speed coil overs, tokico blues, re speed crossmemeber and mustang rack, diamond star racing wheels 1988 Rx7 Se - Sold 1988 Rx7 GXL - Sold

05-08-2011, 07:47 PM	#15
Jeff20B Rotary Fanatic Join Date: Mar 2008 Posts: 215 Rep Power: 18	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?