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Ok, y'all have finally convinced me that it's easy to go too large for a street car, particularly considering that my setup is not fully performance oriented. So now, as diabolical1 mentioned, I'm stuck with the issue of finding templates for 74 spec, although given that, my question is are there any templates already in production that would yield similar results to it? If there are I'm semi-partial to pineapple if only for the reason that I can stop by their shop and save some shipping (my budged is relatively limited so anything helps) - I've read that the pineapple medium and the RB "streetable" templates are quite similar if that gives any ideas. If not, perhaps someone has a template of the 74 spec ports that they'd be willing to scan and share?
I just realized that it hasn't been mentioned yet whether the intake and exhaust ports were altered for 74, or if it was only the intake?
You might stop by their shop and see if they have any 74 spec irons to copy as a template. Once you have that, making a metal template with the dowel pin hole openings would be easy.
i left the statement open on purpose because i wasn't sure how interested you were in making your own, but since KansasCityREPU said it, then yes, just see if you can get a hold of a turbo secondary (since they're more likely to have on of those) and a large enough sheet of plexiglass. bore your dowel pin holes at home, then take it with you and trace and cut the port. that's it.
and technically speaking (if i'm speaking out of turn, Jeff20B or j9fd3s can correct me) the port weren't "altered" until '76, or maybe '77. 1974 was the first year of the production 13Bs, so the port we're referring to was original, not a change. my guess is it got changed because of the emissions issues and that period in time.
Good thought about seeing if pineapple has an iron to copy. Diabolical1, what turbo port are you referring to? Also, only the secondary? Do you mean just clean up the stock primary and 74 spec the secondaries, or port match both the primaries and the secondaries to 74 spec secondaries? Or is there a 74 spec primary to copy too? Pardon all the questions, just trying to understand what you are referring to.
Not sure why, but that link you posted comes up as blocked or something - in other words I can't access it. Was there a copy/paste error or perhaps the is link dead...?
And just to clarify one last thing (for now...), the 74 spec ports are for 13B's and I'm working on a 12A. It sounds like there's no issues with using the intake ports across the different engines, unless I've misunderstood something - heck I first dabbled in the realm of rotaries only a couple years ago so I'm still learning (and will be probably forever ).
The secondary ports on the turbo side housings are supposed to be about the same size as the '74, the primaries for that and every other injected rotary are a different shape that is too small.
Picture from Mazdatrix comparing primary, secondary, and street ported secondary:
Here's a turbo secondary laid over a 12A:
You're going to want to grind out only to match the top portion.
The 76 Cosmo had the first of the 13Bs with the smaller 40 degree closing ports, and the tall runner intermediate plate to use a reverse runner manifold. These made as much power and a couple numbers more torque than the previous 74-75 REPU with a normal runner manifold. Same size 22mm primary Hitachi carb but the air bleeds on the Cosmo carb were smaller to work across a wider RPM range.
The 76 and later engines all had the taller intermediate runners to be backward compatible with a reverse runner manifold, but I think Mazda discovered there was a very good anti-reversion effect when they placed a normal runner manifold with the short primary runners on engines with the tall runners. As such, the early 74-75 irons have short runners and can work, but I prefer the tall runners of the later nitrided R5 and Y plates. I avoid using the early 3B and non nitrided R5 irons these days.
I've assembled a true 3B 74 spec engine and it was ok but that was years ago. I have a complete set of them sitting here but they are rusty on the outside from sitting in a field for a long time.
Ok here are the port closing degree numbers you all wanted to know about.
76 to 85 spec: 40 degress
74 to 75 spec: 50 degrees
T2 and FD secondary spec: 50 degrees (and same opening as 74 to 85 carb engines so a template can be made from these but don't port downward as it's not necessary)
RB "streetable" ports: 60 degrees
pineapple racing ports: 65ish degrees (I think)
What j-tso shows and says is very accurate about intake and exhaust ports.
I should mention my expereince with exhaust ports. The stock 12A opens at the same time as T2 but closes way early. I've found you can port a 12A exhaust upward by at least 2mm just enough so the bevel is gone, then recreate it. You must recreate the bevel to save the apex seals from bowing out at high RPM and slamming into a hard port edge. The factory bevel is there for a reason. I recreate it using a dremel with a sanding band.
You can probably port up as far as true T2 spec on a 12A but you want to leave at least some of a lip between the port and the sleeve. The size difference is there not only to help dissipate some of the powerful super sonic pulse by allowing it to suddenly expand before it enters the header, but it also acts as an anti-reversion lip so can be useful if going turbo. Though i have to say my 12A with the pineapple ported exhaust ports has no anti-reversion lip and it does have a turbo. And it does perform just fine, spooling the turbo quickly. So I dunno.
j9fd3s once told me there was an experiment done in Japan where two FD engines were assembled and tested back to back; the only different being exhaust ports. One was stock while the other was ported out to where the sleeve was met, thus no anti-reversion lip or any room for expansion. The engine that made more power was the one with stock exhaust ports. Makes you think... Perhaps j9fd3s can fill us in on the details if I forgot anything.
okay, so the turbo reference was because of a thread Jeff20B had made quite a while ago where he had spec'd out the port timings and showed that the old 74 spec was very similar (if not the same) as the secondary port on the turbo engines. i will see if i can find that thread and link it as well. in essence what i was saying was you could copy a turbo secondary and use it on all 4 of yours.
yes, the 74 spec refers to the 13B from that year, but it doesn't matter for what you're doing. you're porting your 12A to that spec and it translates perfectly because the rotors and shafts only differ in width between the two. everything else is the same so the ports and timings will work for both.
EDIT:
Wow. 3 new posts since i first started typing this response.
Okay, let's see if I've got all this right. The turbo secondaries (which match the 74 spec closing) should be used for all 4 intake ports, but should only be ported up. The exhaust can be brought all the way out to T2 spec (only porting up again) and it's best to keep some of the anti-reversion lip at the exhaust sleeve. Intake ports don't matter what engine they were from (to an extent) as they only differed in the width of the rotor/housing - which is what I had been thinking, but thank you for confirming it.
So I decided to try printing those templates that j_tso posted and dang, they're actually to scale (printed on 8.5x11"). Props to you, or whoever, made them. I cut them out roughly just to get an idea of the sizing so here they are (the engine hasn't been cleaned yet so disregard the strange surface finish):
My questions are now, one, that exhaust looks rather large although I don't have any context so... is it? Also, does that exhaust template include the space for the bevel or not - as in, should the bevel be within the template or outside? I'm assuming within, just making sure. Also, I take it that the width should not be changed? And two, should the intake be brought inward (towards the stat gear) or outwards (towards the corner seal path) at all, or should it be left as is. I notice most templates go out towards the water jacket a little bit although this design doesn't appear to (I'm guessing that's because this is a copy of the stock turbo secondary). Again, just looking to learn.
Diabolical1, the link in your second post works; not sure why the first didn't. Both were interesting reads so thanks for posting them. I had actually stumbled across the exhaust one before but I hadn't read all the way through.
Thanks again for these replies. Oh, and if those two pdf templates are fine and all, is there any reason to go with the pineapple small exhaust?
My questions are now, one, that exhaust looks rather large although I don't have any context so... is it? Also, does that exhaust template include the space for the bevel or not - as in, should the bevel be within the template or outside? I'm assuming within, just making sure. Also, I take it that the width should not be changed?
The bevel should be within the template since they were directly traced over. It's generally recommended to not widen the exhaust ports so it doesn't reduce the amount of metal the apex seal rides on.
And two, should the intake be brought inward (towards the stat gear) or outwards (towards the corner seal path) at all, or should it be left as is. I notice most templates go out towards the water jacket a little bit although this design doesn't appear to (I'm guessing that's because this is a copy of the stock turbo secondary).
Porting inwards on the intake cuts into the oil seal path on the rotors, so leave that side alone. Porting outwards makes an earlier open timing, a bridge port is a much earlier opening. The danger in going too far outwards is catching a side seal tip.
Correct, stock turbo port opens the same time as a 12A.
i don't know if it's the photo or not, but that exhaust port looks like it closes way late - like one of the race ports. again, i would say if you can't get a less crazy template, then follow Jeff20B's advice outlined in post #32. my opinion is the job is more balanced that way.
fair enough. could just be the photo and my old eyes. maybe not fully flush against the housing??? anyway, i have the RB template, so i know it works. apologies ....
j9fd3s once told me there was an experiment done in Japan where two FD engines were assembled and tested back to back; the only different being exhaust ports. One was stock while the other was ported out to where the sleeve was met, thus no anti-reversion lip or any room for expansion. The engine that made more power was the one with stock exhaust ports. Makes you think... Perhaps j9fd3s can fill us in on the details if I forgot anything.
i have some friends of friends that work in Japanese rotary shops, and the stock FD exhaust port is tough to beat! the factory racing ports are better, but they have an exhaust sleeve that doesn't expand like the street car engines.
you can say what you want about Mazda's engineers (IMO they are pretty sharp!), but i nthe case of the exhaust port, its just a hole and all they needed to do was size it correctly, and they did...
or actually for what its worth, the 76-85 USA engines closed at 38 degrees, and the 74-75, 86-2003 engines, and 76-85 European and Japanese engines closed at 48.
And just to clarify one last thing (for now...), the 74 spec ports are for 13B's and I'm working on a 12A. .
so if we go back into the mists of time..... Mazda had the early 10A/12A engines, and these had port timing that was slightly different than the 76-85 engines. intake was something like 22/45 and the exhaust is 73/38?
then for 1974, there was a big redesign, 3mm apex seals, single distributor, and the ports were revised, to 74 spec. the 12A and 13B both got the same ports.
the next big change was in response to the oil crisis, and then they made the ports smaller for 1976 and they stay that way until the turbo cars show up in 1986.
the 1986-2003 Turbo engines are basically 74 spec, with a few tweaks, mostly to aid emissions.
You would be correct there. I didn't have enough hands to hold the camera and the template flush without blocking it (at least from that position).
So it looks like I should use the pdf templates and those will be my best, and least costly option. I've read some additional threads since and I've noticed that many make the secondary larger than the primary. Is this mostly for fuel injected engines or might it apply to all, or would there even a benefit for what I'm doing? I'm also curious if it would do any good to bring the port further towards the coolant jacket by just a hair or if that would provide either no measureable benefit or perhaps even a detriment. Would this differ for the primaries vs the secondaries?
Other than the above questions I'd say I'm fairly set on using the templates provided by j_tso (T2 exhaust and turbo secondary), only porting up on both the intake and exhaust of course.
Oh, and great info j9fd3s. Interesting stuff there. I guess that would be another point for using the T2 exhaust.
Last edited by Benjamin4456; 06-10-19 at 11:02 AM.
You would be correct there. I didn't have enough hands to hold the camera and the template flush without blocking it (at least from that position).
yeah, i'm not a huge fan of trying to judge things like that from photos. some people are great at it. i'm more hit or miss. however, the original source was here, at hand, to set the record straight. no harm. no foul.
I've read some additional threads since and I've noticed that many make the secondary larger than the primary. Is this mostly for fuel injected engines or might it apply to all, or would there even a benefit for what I'm doing?
i think most people do that for idle, at least, i think that's the premise. think smaller closing edge contributes to less duration, etc.
I'm also curious if it would do any good to bring the port further towards the coolant jacket by just a hair or if that would provide either no measurable benefit or perhaps even a detriment. Would this differ for the primaries vs the secondaries?
essentially you're opening it earlier. there are benefits and of course drawbacks. for the record, i'm a fan. however, in the spirit of trying to stay neutral while putting things in context, think of it this way: you would now have stock Mazda ports that are an improvement over your stock ports. you get more power and basically no drawbacks. making alterations to those dimensions are how you walk down rabbit holes. make sense?
So I did some thinking about the different sized secondary vs primary ports and I realized that due to my manifold having channels, both will be getting some flow regardless of whether the secondaries are open on the carb. I'm not sure how the FI throttle bodies work, but I'd assume that it's a two stage, fully separate system based on their port design. Given that, it would seem that the only change - if any - to be made to the profile of the secondaries vs the primaries would be a perhaps slightly later closing to let a larger total amount of air in to allow for the larger secondary runners and venturi's and all - then again there's still the channels so I don't know, just thinking out loud. I really don't know enough about port design to be coming to any solid conclusions here, so if anyone would like to chime in to aid or set me straight on this that would be appreciated.
At this point I'm essentially looking for if there are any possible improvements (to better meet my goal of accomplishing the greatest amount of NA power possible while still retaining streetable and enjoyable low end torque) that could be made to the set up that I have established so far. Diabolical1, you mention that you're a fan of bringing the outer edge of the intake port farther out, would you mind elaborating on that? What trade-offs would be in store if small changes - and what changes might they be, if any - were to be made to the 74 spec intake ports? Again, just thinking out loud.
Channels: both will have some flow, yes, but air also has velocity and inertia. It won't magically flow from a primary barrel over into a secondary runner. All the channels do is help with vacuum signal. The early manifolds were all separated runners and required a different tune on the carb. Mazda made an improvement to the way a rotary runs by adding channels to the manifolds in my opnion.
As for the EFI setups, those have a progressive secondary opening that begins to open at about 10% of primary opening - both arrive at 100% open at the same time. But the secondaries have an extra pair of butterflies that are to remain closed under vacuum until at higher RPM when the load is right and they can open. I think that is how it works. Some people remove them and then have a stumble if they stab the throttle. They say it can be tuned out but I dunno.
By the way, think of the timing of the reversion pulses that occur when the rotor passes by an intake port. Now think of it if the primaries are smaller than the secondaries. How much longer do you suppose it will take for the reversion pulse to come up and hit the bottom of the carb when the primary runners are so much shorter than the secondary runners? Do you suppose that it is ok to have secondary ports that close later than primary ports, based on the manifold runner length which is spacing the reversion pulses differently? I mean obviously the pulses will occur at slightly later times on the secondaries if the ports close later in the cycle. Does that make sense? Some food for thought.
Oh and can you please refer to ports by opening edge and closing edge so we know what you are talking about instead of saying the outer edge? Thanks.
As far as small changes, I've opened the primary port's opening edge about 1mm earlier than stock in the past and it can mess with the idle quality. That is 1mm which isn't all that much. Others have been opened even earlier with results as you might expect. Lumpy idle but mo' powah! It is a trade off.
Channels: both will have some flow, yes, but air also has velocity and inertia. It won't magically flow from a primary barrel over into a secondary runner. All the channels do is help with vacuum signal. The early manifolds were all separated runners and required a different tune on the carb. Mazda made an improvement to the way a rotary runs by adding channels to the manifolds in my opnion.
As for the EFI setups, those have a progressive secondary opening that begins to open at about 10% of primary opening - both arrive at 100% open at the same time. But the secondaries have an extra pair of butterflies that are to remain closed under vacuum until at higher RPM when the load is right and they can open. I think that is how it works. Some people remove them and then have a stumble if they stab the throttle. They say it can be tuned out but I dunno.
Ah yes, makes sense. Thanks for clarifying that.
Originally Posted by Jeff20B
By the way, think of the timing of the reversion pulses that occur when the rotor passes by an intake port. Now think of it if the primaries are smaller than the secondaries. How much longer do you suppose it will take for the reversion pulse to come up and hit the bottom of the carb when the primary runners are so much shorter than the secondary runners? Do you suppose that it is ok to have secondary ports that close later than primary ports, based on the manifold runner length which is spacing the reversion pulses differently? I mean obviously the pulses will occur at slightly later times on the secondaries if the ports close later in the cycle. Does that make sense? Some food for thought.
Huh, that's intriguing. I would assume that... hold on, I'm gonna do some quick math here. Lets say, just for comparison sake (in other words these are not true values), that the length of the primary runners are 10cm and the secondaries are 18cm in the manifold, and because the length of the runners in the block are essentially identical we will negate those. We're also going to state for this scenario that the air will be at STP to simplify the math and rule out other conditions. Finally it will be assumed that the reversion wave propagates at the speed of sound (yes, not necessarily true for reality, but this is conceptual so we'll go with it). Okay, so at 1000rpm we have an intake event on one rotor 1000 times per minute (oh and if any of this is wrong please call it out, I'd like to make sure that this is recorded correctly). This is the same as the eccentric shaft rotating once about every 60,000 microseconds. So now we can see that for each one degree of rotation of the eccentric shaft, it takes 117 microseconds. Since the intake events per time is equal to the number of eccentric shaft revolutions per time, each phase of induction take 167 microseconds to progress one degree (although due to the rotational path of the rotor, I don't believe this would be exact). With the same figuring, the time for one degree of rotation (not of the rotor, rather the eccentric shaft or phase of combustion) at 7000 rpm is 23.8 microseconds. The time for the reversion wave to travel in the primary intake runner is 292 microseconds and the secondary is 525 microseconds (using the values for length previously stated). In order to offset the time difference between manifold runners (233 microseconds), the intake closing of the primary would have to be delayed by about one and a half degrees to have the reversion waves arrive at the bottom of the carb at the same time at 1000rpm. However, at 7000rpm the primary closing would have to be delayed almost 10 degrees for the same effect. I can go over and check the math some other time, but for now I need to get on with things.
So, after all that it is clear that one, if trying to match the arrival times of the reversion waves delaying the secondary closing time would have the opposite than desired effect (which was clear without the math), and two, that balancing the time for reversion must be done to target one specific rpm (each increase of 1000rpm yields a time decrease of about 13.3 microseconds per degree of rotation). Well, I don't that helped to clear much up, other than to make me question whether an attempt to negate offset reversion timing should even be conjured. Jeff your food for thought went a little rouge here . Now of course this is all hypothetical and it ignores many other factors - this was probably the most straight forward it could be and therefore is not that accurate. Well that's enough of that for now. More food for thought I suppose...
Originally Posted by Jeff20B
Oh and can you please refer to ports by opening edge and closing edge so we know what you are talking about instead of saying the outer edge? Thanks.
Yep, sure thing. There I had meant to refer to the side of the port closest to the coolant jacket. I'm not sure if the 'side edges' of the port have a better term, but if so, I'd be glad to use it.
Originally Posted by Jeff20B
As far as small changes, I've opened the primary port's opening edge about 1mm earlier than stock in the past and it can mess with the idle quality. That is 1mm which isn't all that much. Others have been opened even earlier with results as you might expect. Lumpy idle but mo' powah! It is a trade off.
What exhaust port was that/those with? It's surprising that such a small change would yield such a difference. What kind of power you talkin' ? I'd fathom that in addition to the lumpy idle, some low end was lost too, yeah? Oh, and what sort of power could be expected from a 12A with the T2 exhaust and the 74 spec intake ports (or similar) on a hogged out Nikki and everything else up to par? Just estimates of course.
Ironically I just came across a thread very similar to this one that took place about five years ago... oh well.
Last edited by Benjamin4456; 06-11-19 at 09:09 PM.
We all call the edge closest to the coolant jacket seal the "opening edge".
A way to simplify the idea about reversion pulse timing is to imagine a stock 12A with pri and sec ports the exact same size. Now think of the stock intake manifold and how its runners differ in length. This means the primary pulse will arrive under the carb earlier than the secondary pulse. We can mentally manipulate the arrival times further if we imagine bigger secondary ports (later closing timing edge).
I would have to recommend 12AT size exhaust ports. Those give 10 degrees more open time than US spec and are really good with no danger to the apex seals. They open the same as T2 and US spec but close later than US spec but not as late as T2 spec. I don't know about going up to T2 spec on a 12A. I'd have to take a look at some parts to figure it out. Will it be too far for the 12A sleeve?
Yep, that was exactly what I had thought about, although I was curious about the math behind it to see how much of a difference the manifold runner length actually made in port timing (it's hypothetical, but still interesting to me at the very least). Does it even make sense to try and match the reversion pulses or is it not worth the effort. It would require one to find the rpm that would be most optimal for matched reversion (I would think that it's more important at high rpm due to the greater air velocity and therefore greater strength of the reversion wave, although I'm not sure - fluid mechanics is not a topic that I'm well versed on) and then port to accommodate. Is it something that should even be considered or are the effects too minute to take much effect?
About how far above the stock port closing edge is 10 degrees? Is the danger to the apex seals that on the longer duration port they have more time to bow outwards, or is it something else? I checked the sleeve this morning and it looks like the T2 port will come almost to the top, although I can't tell for sure. I can measure it when I get home today. Either way it probably wouldn't leave much of an anti-reversion lip/gas expansion step. While I was looking at it I noticed that the sides of the sleeve get narrower as you go up - when porting should the sides of the sleeve be ground so that the port is still the narrowest part or should they be left as is which would create a sort of venturi (or at least that's what looks like will happen)?
Edit: j9fd3s, the thread was this one: Porting a 12a with the op being Dave Martin. I don't believe I have come across a thread with Peter Tork, although I might have and just don't recall it.
Last edited by Benjamin4456; 06-12-19 at 10:32 AM.
Yep, that was exactly what I had thought about, although I was curious about the math behind it to see how much of a difference the manifold runner length actually made in port timing (it's hypothetical, but still interesting to me at the very least). Does it even make sense to try and match the reversion pulses or is it not worth the effort. It would require one to find the rpm that would be most optimal for matched reversion (I would think that it's more important at high rpm due to the greater air velocity and therefore greater strength of the reversion wave, although I'm not sure - fluid mechanics is not a topic that I'm well versed on) and then port to accommodate. Is it something that should even be considered or are the effects too minute to take much effect?
Edit: j9fd3s, the thread was this one: Porting a 12a with the op being Dave Martin. I don't believe I have come across a thread with Peter Tork, although I might have and just don't recall it.
with the Rx8 Mazda used a three stage intake, one for each set of ports. each stage, or set of runners has its own diameter and length. so the primaries are optimized for idle-3000 rpm (i think,), then the secondaries open, and take it to 5500rpm and then the third set opens. you could setup the 12A like that a little, you just don't get to optimize lengths, due to the carb
06-09-19, 10:49 AM
).
however, the original source was here, at hand, to set the record straight. no harm. no foul.