urquhartglen

hi guys just askn has anyone found what i have. i had a 4port (tall port) 12a with half bridge and it was ok. nice lump etc. not huge power but ok. i got sick of that and built up a 12a 6port full bridge. the end plates have a bridgeport for each of the ports and centre plate has normal type of bridge, (so there are 6ports and 6bridges in total) along with the ports opened up to std tall port size.(not alot of room in a 6port untill u hit water.) I LOVE IT way better than the tall port half bridge. nicer down low and revs and screams way better in top end. it is much faster off line and in top end than the tall port half bridge.... idles at 2100rpm and is lumpy as.... and im using same carb and dizzy etc as on the 4port... i asked around before porting it etc and was told not to bother as they crap.... pleased i did as im very very happy with it.... it is as fast on road as mates 13b full bridge with a ida... im useing a rejetted nikki carb and elec dizzy with two" headers to diff then 2.5" over into a rear muffler... in short it pulls harder from idle all way through the revs to 10,000rpm better than the 4port. AND yes i have the bearings and carbons etc etc etc to be able to rev it that high.... power drops off at 10,800 rpm so no point going over 10grand

theNeanderthol

iTrader: (1)

Wow! cool idea! I have never heard of anyone doing this, but there are many here who have much more experience than I do.

When people say "don't bother" most people give up on the idea. But you didn't and it sounds like it really paid off!! awesome! Can you post any photos of your port work? or of the car? You said it makes good power even low in the rpm range, how streetable is the car?

rotarydude

iTrader: (2)

I would like to see some pics of the port that you did. So if I understand correctly you used the center iron(housing) off a series 3 12a? Interesting I would like to hear more esp if you where to dyno this I would love to see graph

Unevolved

iTrader: (1)

I'm interested in the specifics of this as well.

urquhartglen

the engine came from a 1985 mazda cosmo. 12a 6port.
had it on dyno at 1100km only to check for any lean spots so didnt get a graph of power. did make 167.2hp at back wheels tho. (mate had his 12a tall port half bridge on same dyno and got 134hp) ill put up sum photos of the porting i did when i find them soon.
even tho it idle at 2100ish it is very very streetable only really lumps on decel or when cruzing at or under 3000rpm. i use it as a daily driver and my wife uses it as well.. doesnt foul plugs and starts easy even tho it has carbons in it... it is loud but thats my fault as exhaust needs better mufflers. the reason i think its better is all in the air flow speed at low revs. as the port runners are small on a 6port (when compared to a tall port etc) and the carb also has smaller primary ventures etc. they are only 17mm primarys and 21mm secondarys. primary jets are factory .9 and secorday jets are 1.5mm. spark plugs are bp8es.. timing is unlocked and set nearly as factory.... on youtube type in (1978 12a bp) it will come up. sorry about sound as was taken fron a cell phone and rx is too loud for my photo to record. will put up better video soon.... the centre plate is not from a s3 as over here they all had the injector holes in them. none of my engine is rx7 is all cosmo. you could do the same as what i have done with a s4 s5 6port 13b... ill post photos later doday of ports etc etc i did.... can also copy and send porting template if any body wants one... ive done the hard work and got it right as couldnt find any porting templates so made it all up as i went along(wrecked a couple of plates doing it hahaha) im the only one i know with a 6port bridgeport and my other friends that have rotarys love it and the way it drives.... keep eye out for photos. what you guys want photos off as have a few of that engine going together etc

Keeble

iTrader: (3)

wow, only 167 for a bridge?
my old stock port 12a was putting down 113 with 170k miles on it.

interesting project none the less

urquhartglen

yea 167 not much but like i said wasnt there for power run just to check mixture... they wernt paying any att to the power and didnt try... car wasnt reved over 8000rpm on dyno as was only 1100km old at time

el_rotary

iTrader: (3)

It does make great power! I am not taking anything away from this thread but, theNeanderthol I have somewhat the same style motor in El Paso street driven. Small world I guess.

urquhartglen

its going back on dyno at sum stage as ive had a lot of questions about the hp of it... so ill have to wait see what it really does make. as it pulls hard all way to 10,000rpm. then drops off quickly. also the sleeves are removed from the 5th and 6th ports. and are back filled in the undercut to help with flow. as seat of pants feeling on road its pritty good. much faster than evos and wrx etc... can keep up with batmans. cant pull away but can stay side by side...... anyway i was just letting you guys know that i was thinking outside the normal as i think it payed off as im more than happy with the resuilts.... lookn for photos now

urquhartglen

cant find finished photos but there is sum from early on in porting testing stage to give you a idea of what i did... the centre plate photos shows std tiny port then other centre plate shows finished with a bridgeport. then photos of a std 12a 6port plate and the blue marks show approx what i ported out. the one that has been ported was a test one to c how far i could go.... the manifold is factory 6port before any match porting and vaclum stuff removed...


dont rubbish it. as this was just the test ones.... finished ones are the center plate and same as blue marks on end plate. BUT TIDY as these were rough markings

urquhartglen

this was my std 6port 12a before i striped it. and made it a full bridge

Naegleria_Fowleri

Very cool project.

diabolical1

iTrader: (3)

sounds like a pretty interesting little firecracker you've got. as long as it keeps you happy, you're ahead of the game.

el_rotary

iTrader: (3)

Looks good, I bridge-ported only the bottom part of the ports on the end plates because on the top port I insterted the sleeve and put the pinappleracing insert in it for better velocity. All of this was set in place 'open' with some kind of lock tight. Its too much fun!

urquhartglen

ive taken the sleeve out, but back filled the under cut were the sleeve sit. so get better flow like normal ports... and i thought bot only bridgeing bottom port as i couldnt find any info on any one doing bridgeporting on 6ports so i tested and tryed my own thoughts. 3000km into engine and im very happy

urquhartglen

engine as it is now, 3000km old

gready123456

i have a 12a 6 port also took it apart also pondering on what to do with it , i was wondering did u remove the actuators from the manifold and leave the 5&6 ports open fulltime,
and what mods did you do to the manifold, i might jus do this same bridge on all the ports also but i want to make a intake for it and do fuel injection and maybe turbo it what do u think ? , in terms of internals what do i realy need to deal with the high reving engine , i will do mods to gain higher oil pressure and i will do the water jacket mods also in terms of bearing what do i need to do ? i am planning to use RA's unbrakable apex seals , any help u can lend to me would be nice here are some pics of the engine








I need new rotors and a pair of rotor housings ( i am getting another 12a soon but 4 port ) so hopefully the rotors and and the housing are good
i also need to lap those plates i will try to hand lap them with a stone and some cutting paste and
see how it goes , i have seen some ppl use orbital grinders also ,

Jeff20B

iTrader: (13)

Don't go too far when you lap. You want to keep the nitrided surface. I won't be lapping mine.

For your rotors, you have to get the '83-'85 assembly because the front counterweight has a 45° bevel to clear the little lump in the front casting. The lump is on the other side of the aux port.

Don't you love how small the primary ports are? Even the secondary ports are small. The aux ports can be opened up as far as an FC. Maybe the secondaries too?

My plan is to use a set of GSL-SE/RE-SI end plates because my stock ones are bad. I have to keep the stock 12A intermediate plate because the intake runners are much lower than any other year. You'll see this difference when you compare a bunch of intermediate plates. Fortunately the top and bottom of the 12A 6 port's port is the same as the RE-SI end plates. That means it closes at GSL-SE/RE-SI spec. The only difference is the opening timing, which can be handled with a Dremel or die grinder. So when I'm done all four low RPM ports will have the same port timing. I can do this because I'm using a carb. You'll need to consider what you can get away with since you;ll be injected. I suggest a GSL-SE intermediate plate (dont get an RE-SI intermediate because its intake ports are just as narrow as the stock 6 port but a little earlier closing timing yuck!). My RE-SI aux ports will probably have to stay as they are becasue they're probably big enough; I do have the option of porting out to FC spec, but because I'm using a carb, my total port area must be taken into consideration. I'm affraid if I took it out to FC spec, it'd outflow my carb and my exhaust ports, not to mention the exhaust system in the car it's going in.

I guess I could start prepping to build it tomorrow if I really wanted to. Gotta port out the intermediate plate first. Get the same port timing as the secondary ports in a typical RE-SI or GSL-SE. I just hope it doesn't outflow the tiny runners in the intake manifold.

coldy13

To lap them I like to spread the lapping compound on one plate, sit another on top and slide it around. Keeps them flat and does 2 sides at once.

rxtasy3

iTrader: (2)

^that's the way to do them when doing it urself.

to the original poster, should've done a full bridge on that 4 port 12a.

Elcocue75

I must say it looks nice!!, I have a 85 GSL and I am wanting to do the same to my motor. she has 85,750 original miles. I just haven't been able to do it with the way the economy was going but it's starting to pick up at work so now maybe I will have a green light to start working on my baby. I really can't wait I am itching to do a full bridgeport on my baby. I have heard negative comments on doing this but I have already made up my mind about this. how expensive is it to do this here in the states, I live near Houston, Tx?

urquhartglen

Just to note mate. ive had a secondary bridge and full bridge 12a 4 port engine before i built this egine... 4 ports are fine when ported if you are doing lots of high rev driving or racing etc. i found that round town it was bull **** with a bridgeport 4 port... MY 6 PORT BRIDGEPORT MAKES MORE POWER AND NICER TO DRIVE.
but thanks for the comment but ive tryed both so ill judge what i feel is the best...


Other questions. i removed stuff from maniflod and just tided up the castings etc inside and match ported it. i took the sleeves out of the 5th and 6th port. i use belzona to back fill the undercut were the sleeve sat to improve flow (i made 4 3mm drill hole about 2mm deep to give belzona sumthing to stick to) ive opened the centre plate port up to std 4port size and see the two blue marks in my photos i bridged like that. so got 6 separate bridgeports... I LOVE IT... bugger the 4 ports if you use the car often.... if you drive WAY up in revs then go 4 port as mine runs out of puff at bot 9000rpm... i have carbon apex. 3 window bearings, new housings and new rest is factory new seals but solid cnr seals...

urquhartglen

Good on ya mate. nothing like a ported rotary.. remember tho that she will want a bigger fuel pump etc etc. bridgeports love gas, along with any other porting.
when i was looking into bridgeporting my 6port everyone said DONT... but i did and i made my own porting templates as no one had any.. id be happy to post you a copy if you cover postage. and then you can do it your self/ im a engine recondioner by trade for last 10years so i built my own engines...
id say go bridgeport 6port. others would say no. but i have one and i bet they dont haha... funny how eveyone goes the same old path with rotarys,,, like yea get a 4port and go real big on ports etc etc etc. thats all good but i drive mine to work in town each day and it neary as nice to drive as a street port (extandport)
but it lumps and gets up and goes when you stomp on it(spins 1st 2nd 3r both wheels).. mine idles at 2100rpm but thats more to due with my carb i had. i have fitted a set of flatslides off a gsxr750 road bike now... **** its cool to drive now... and pulls nice and real strong and idles at 1800 with nice pluse.. starts off key etc etc

unsure of costs in usa as i live on other side of world in new zealand. cant help you there mate.... i have a few friends with rotarys over here. most are rx7 but sum rx2 and rx3s they are all bridgeported or j ported... (4ports) they have drivn my rx7 and all had good things to say about the power delivery of it and say its nice to drive without as many down falls as a 4port bridgeport...

but if you going for outright power eg max porting and ida or injection etc then go four port and they will flow better in the end but if you like to drive the car round town etc use your 6port. you will love it as i do mine... i can email you a video of it running.. go to youtube and type in (rx7 skids 360) my old 1.. new rx7 is my red one

urquhartglen

im happy to help with inlet porting templates and exhaust templates... also i have a shed full of 12a bits that i can sells... good plates both 4 and 6 port. good rotors and housings etc etc

Naegleria_Fowleri

Is there any estimate on the power it makes? I'm assuming a four port would make less power down low but more up high with a bridge port as opposed to the six port, but that's just going by everything I've read from previous attempts (more specifically, six port 13B vs. four port 12A both bridge ported). I'm really interested in knowing how much power it puts to the ground.

I think that this is a really great project to have. I wish that six port 12A's (or even four port 12A's at this point) were far easier to come by so I could experiment with stuff like this.