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i know your Rx-7 is ported, but i honestly don't remember if you said you did it, so forgive me if this is something you already know. however, one of the first stages you go through in the porting process is to score the housing with your template. you basically have to trace the limits of the lines you're going to cut. you will want that to be as precise and consistent as possible. the commercial templates are made of thin metal sheets, but the plexiglass is a DIY method.
Originally Posted by Benjamin4456
Edit: Just to run with my previous post, what effects would a taller port have - this is 'porting fundamentals' after all, so I'm still curious. And if anyone would be willing to answer the questions about the port lip along the oil seal track I'd appreciate it.
on your question about the template, you probably now have something like what i described above with the 12A i built. it felt okay ... to me! that said, all we're talking about here is another sheet of plexiglass - you haven't touched the housings yet. actually, not even another piece - just flip it around and make the correction on the other end of it. the dowel points are fixed. obviously, you'll have to label which side is which with something that won't fade or get washed away though. just for fun, maybe download a degree wheel and try your hand at figuring out timings for both. opportunity knocks ...
however, my take on it if you want the 74 spec, then you should take the extra few minutes making the correct template, as opposed to an approximation.
as for the other question, the lip it sounds like you're describing is probably the area where Mazda wanted to create a little extra turbulence to keep the fuel atomized. on the Renesis engines they called the AWP (anti wet port) area.
The pineapple intake ports did cut into the oil seal track slightly which is part of the finesse I was talking about in that i did not cut into my oil seal track at all. Theirs was a racing engine while mine was meant to be more streetable. And yes my exhaust ports do go up to and a little bit beyond the smallish 12A sleeves in the upper corners. I wasn't happy about it but I was not the person who cut them, so I just went with them and they seem to drive the turbo very well despite the overlap. The overlap might actually be helping to spool it quicker. I believe my engine is pretty sensitive to backpressure, as all ported engines are. The bigger the ports (or the more overlap you have, the more sensitive. A stock port can run with a potato in the tailpipe (not really).
I gave the degree wheel a shot and it looks like my port closes about two degrees later than 74 spec. So if 74 spec closes at 50 then that would make mine approximately 52. I probably didn't measure correctly though because if stock is 40, there was definitely not 10 degrees between the stock port and 74 spec, more like 7 degrees. Oh well, it gives some context at the least.
So it sounds like I shouldn't touch the part of the port against the oil seal track for multiple reasons, and that my 'modified' 74 spec port will probably be just fine with perhaps a small power increase...? Are we talking much of a hit in the torque department, or will it be negligible? Going back to the very beginning of this thread, I had mentioned that I was willing to take a small decrease in torque if it meant more power, just making sure that that decrease in torque won't be more than small (a lack below 2k seems entirely manageable). It looks like this is similar to at least two of your setups so if y'all are saying they were/are good in your experience, that's enough for me.
Originally Posted by diabolical1
actually, not even another piece - just flip it around and make the correction on the other end of it. the dowel points are fixed. obviously, you'll have to label which side is which with something that won't fade or get washed away though.
Unfortunately I already have done this, making the above the second port on this sheet. The first was a bit... ugly...
i know your Rx-7 is ported, but i honestly don't remember if you said you did it, so forgive me if this is something you already know. however, one of the first stages you go through in the porting process is to score the housing with your template. you basically have to trace the limits of the lines you're going to cut. you will want that to be as precise and consistent as possible. the commercial templates are made of thin metal sheets, but the plexiglass is a DIY method.
I didn't do the job myself but I am familiar with the process. I've only seen people use steel plates to score the housing. Plexi seems a bit expensive but at least it's thick and you can see through it to confirm you've got things right. The plexi actually looks thick enough that you could use it with a plunging router to start the port. That's something I'd do in woodworking at least...doubt I would try it on a housing.
I gave the degree wheel a shot and it looks like my port closes about two degrees later than 74 spec. So if 74 spec closes at 50 then that would make mine approximately 52. I probably didn't measure correctly though because if stock is 40, there was definitely not 10 degrees between the stock port and 74 spec, more like 7 degrees. Oh well, it gives some context at the least.
So it sounds like I shouldn't touch the part of the port against the oil seal track for multiple reasons, and that my 'modified' 74 spec port will probably be just fine with perhaps a small power increase...? Are we talking much of a hit in the torque department, or will it be negligible? Going back to the very beginning of this thread, I had mentioned that I was willing to take a small decrease in torque if it meant more power, just making sure that that decrease in torque won't be more than small (a lack below 2k seems entirely manageable). It looks like this is similar to at least two of your setups so if y'all are saying they were/are good in your experience, that's enough for me.
basically, the intake closing time has a huge impact on the rpm the power peak occurs, all else being equal. the later the closing time the higher the peak, and the more you loose at the low end.
going from 50 to 52 is a pretty small change, but you would expect to trade a little low end for a little high end. keep in mid that if you went to like 60, you can loose everywhere, because you loose the low end you expect, but the nikki can't keep up so you don't get the gains either.
So I figured that regardless of if I go 74 spec or my modified version, I'll need to remove some material so I went ahead and started. Here's it so far. Please point out anything that I should keep in mind or change.
Edit: So j9fd3s, it sounds like my small change will be fine, that is I'm willing to have a slight upward shift of the power band. If anyone would like to give their input I'd appreciate a second opinion just for my sanity's sake.
- maybe make your tape layer a little thicker (think: the old prevention vs. cure adage)
- don't go all the way to the scribe on the closing edge. i like to leave a little room so that when i start the blending process (with the sanding drums) i can use that to take it to the scribe
- don't go for "glass" on the intakes, but go for glass on the exhausts
- i didn't see where you discussed runner work, but the shorter radius can be smoother than the longer one
Ok cool, thank you. Could you elaborate a little on the shorter vs longer radius runner bit? I think I know what you're talking about but I'm not certain. Also, should the very edge of the port be similar to stock (relatively abrupt) or should it have a small bevel/slope up to the final closing edge? Obviously I'll be sure to deburr the edges I've cut, but beyond that?
Last edited by Benjamin4456; 06-21-19 at 04:37 PM.
basically, the edge of the runner that is contiguous with the opening edge of the port is the shorter radius. the side directly across, that's contiguous with the "bowl" is the longer radius. i was just saying you can make the shorter side smoother than the longer. for the longer side, you can remove or "knock down" the flash, but leave some texture to it, if that makes sense.
leave the closing edge shaped like Mazda had it, but yes, definitely "dull" it a bit. nothing should be getting caught on it with "this" port, but again, why take chances?
Here's my port so far. It's just the rough cut so of course there are some divets and the like. Should I bring the edge of the bowl down at more of a sharp angle, should it be curved as it goes up to the port, straight? Should the new port essentially come up from the existing bowl floor at an angle/slope, or should the wall be moved slightly so that it's more similar to the stock port with an almost 90 degree corner? Did that make any sense?
What about making the runner slightly wider (seen in the below photo) near the corner so that the transition from runner to port isn't quite so abrupt.
Many questions but I'm learnin' . Thanks all for the help, glad to finally be at the point of porting.
Last edited by Benjamin4456; 06-21-19 at 05:27 PM.
So questions from my previous post still stand, but I'm almost done with the rough cuts on all the intake ports so pretty soon here I'll be at a standstill (I'll do the exhaust for the mean time, but the goal is paint tomorrow so if anyone has some free time to answer the above and below questions that would be greatly appreciated). That said, I looked back over this thread and saw the picture provided by Qingdao as seen below:
So this is from a 'side on' perspective, but considering that how this is the same as the stock ports in essentially all directions, should I be attempting to imitate this for the closing wall? I feel as though that would get awfully close to water jacket. That then brings me back to my previous question of should the port wall on the closing side be as straight as possible - without breaching the water jacket - or should some curve be incorporated which I see more commonly on larger ports where there simply isn't enough material for a straight shot. And by straight I don't necessarily mean 90 degrees upright, more so just the shape of the wall. The angle is something I'm still curious about though. I'm hoping that came across clear enough. I can rephrase that if need be.
Well life doesn't revolve around forum's, so due to y'all's preoccupation elsewhere I went ahead and decided to try and make a 'final' port. Now it doesn't have to be final if anyone notices something that could be improved, but I attempted to keep things within the point of no return so hopefully it's not beyond help if something's amiss. The port does have some slope/curve to it, but not that much and I tried to "visualize how the air wants to flow" as someone said way back in this thread. For the final surface I used a 42 grit sphere stone on a low speed so that it would skip a little, making extra certain that it didn't skip its way to somewhere it shouldn't have been. Regardless, I think the finish came out nicely and it is relatively similar to the original cast surface.
Now then, I guess I should actually show the port. I took a good number of pictures so hopefully the shape can be understood in relative clarity. Here's a link to the album: 12A Porting. That link should work, but if it doesn't let me know and I'll fix it.
Criticism and suggestions welcome.
Last edited by Benjamin4456; 06-21-19 at 11:29 PM.
i took a look at your album. i think you generally have the right idea. considering this is your first job, i would say you are doing very well - very well indeed. when i think back to my very first job, it sucked!!! of course, i was pleased as punch with it then, but looking at my photos now, they were UGLY!!! i can't wait for the day when i have to open that engine again so i can revise them with what i've learned in the years since.
i'm a little concerned when you used the term "final surface" though. it is my opinion that you do some more blending. i actually clicked on a few of the photos and i could see some areas of unevenness and divots. also, i think you should go smoother when all is said and done - like a 120 sanding drum. you might even be able to get away with 80 if you want it rougher which i can understand, but 120 is about where i begin to trust the tactile sensations in my fingers. on the other hand, you may want to leave all the finish work until the end, then do all 4 at once. i don't know. it's up to you, but i take it that you're just working on this one now to get the feel, so doing the finish now may be a good idea.
with you mentioning that "42 grit sphere" as your final, i'm also curious to see the tools you're using.
Originally Posted by Benjamin4456
What about making the runner slightly wider (seen in the below photo) near the corner so that the transition from runner to port isn't quite so abrupt.
as i said, you have the right idea. yes, try to smooth out that little pocket where the runner starts to join the port. you can definitely do some work there, and it should make difference in terms of flow. also, if you look head-on, down the runner, you will see a similar "edge" on the lower end (near that lower tail area of the aperture), you should try to smooth that transition area as well. i'm not sure if i described what i'm saying very well, so i'll try to say t this way as well: basically you want to transition that upper and lower portion of the opening side of the port into the port itself.
Awesome, thank you, and I see what you're saying about the runner transition area. For the surface I suppose I was thinking of Jeff's (I think it was Jeff, different thread though) method of using a broken and/or lopsided stone to do the final surface - perhaps I took that idea too far, I'll go over it with 80 and 120 after I've done the runner transition to see how those turn out. Going with the surface finish and tools and all, here's a shot of what bits I've used so far since you're curious. I've done most of the work with the cylindrical burr and the sanding drum (currently 120) but I've used the egg burr for some of the corners and quick material removal, and then the ball/sphere stone is what I mentioned before (42 grit equivalent). The large sanding roll is a bit bulky and I prefer not using it, and I've found that the conical stone doesn't do much help either, but I used it a couple times when roughing in the shape.
Oh, and these are Dremel tools if that hadn't been ascertained yet. I do have a 1/4" die grinder, but I felt like the Dremel gave an arguably better and much more precise cut, even though it's probably a margin slower.
I'll get a shot of the surface after going over it with the drums pretty soon here so that I opinions can be shared regarding it. Do you, or anyone else, have any comments about the shape of the wall/port? I think for now I'll focus on getting this one port done so I can have an idea of the final goal (I've done a rough cut on the others already though).
I think I'll still do a little smoothing, but other than that, how's it looking? I used a 120 grit drum to finish it and also took some material out of the runner-port transition area.
Edit: Now that I'm looking at it again, it appears like I could probably take a little more material out of the runner transition, but I'll wait until I hear back from someone regarding it.
Last edited by Benjamin4456; 06-22-19 at 12:48 PM.
You might want to raise the roof a little bit. If you study a true 74 spec port, it is pretty high up there. Also I think T2 and FD secondaries are that way. Yours have a ramp shape. But be careful if you cut upward in the ramp area as you can get close to the water jacket. Don't cut through.
Could you rephrase the roof bit? I'm not quite sure what you are referring to. The ramp part I get though. I can definitely remove some more from the closing edge wall, but like you said, too much further and it starts getting close to the water jacket. Just to confirm, you are saying that I should remove more material from this area (pointed to in photo below) to make it less of a slope and more of a straight shot?:
The closing corner (the top right corner of the port in the above photo if I'm using the wrong term) does have some considerable slope to it, although it doesn't feel like I can go too much further without breaking into the water jacket. Should I try and pull some more material there too?
when I say raise the roof, it is more of a cliche, but what it means is to cut more material from the ramp part, or in other words, to raise the roof of the port a little more to make it a more consistent shape. If you study an actual factory 74 spec of 50 degree port, you will see what I'm talking about. However, I realize the Y and R5 irons don't have the same internal structure like the 74 spec ones, but do the best you can without cutting into the water jacket. And if you feel uncomfortable about raising your roof or the ramp area any further, stop here.
regarding the "roof" issue, i would vote to leave it as is. generally speaking, those housings are pretty stout, and can likely take the extra cutting, but you really don't want to risk punching through it.
Now do the Judge Ito side seal protecting next step. I like to take a small round file and break up the hard sharp edge you have created along the closing side. Also test the whole area with a box cutter blade or some other flat straight edge that can knock down nasty burrs. Side seals don't tolerate burrs.
A bit more grinding and a small round file later... voila: 12A Porting (Final?). I decided that I was comfortable removing a little more material so I went for it and now there is almost no slope - except for the very perimeter and the closing corner that I mentioned before. It probably could have been brought out a little further, but that's as far as I felt safe with. Now then, three more to go... Thanks diabolical1 and Jeff20B for the commending remarks, honestly it turned out better than I had expected all things considered. Here's a shot for the forum:
For the exhaust I dropped the closing by about 2.5mm under T2 spec, stock width and opening. There was still plenty of material for an anti-reversion lip had I gone all the way to full T2 spec. They're not too pretty, but here's a shot of one just for documentation. The bizarre marks along the sides are just visual, you can't feel them. If there's anything I should fix about them please share, it would be a shame for a misshapen exhaust to be the demise of my motor... They appear fine (read functional), just not pretty and not exactly uniform (I have to admit that I greatly prefer intake porting over exhaust porting). Here, I'll just stop stalling. Below is the photo:
it looks okay, as far as rough cuts go, i guess. of course, this is a photo, so .... i don't know what the lines above and below are about, but if you stuck to the template you were given, then i suppose all should be good. speaking of the template, this was a 13B Turbo template, right? just curious about the width.
my take on it is this side is usually fairly easy to do, just cut the scribe and make sure to bevel the closing edge when you're through. there is usually a fair amount to do on the back side of it, and it requires more of a careful touch (compared to the intakes) when you're in there.
Well by that response it sounds like they need some more work...? It is a photo so I get how it's difficult to tell the shape and all. Don't pay mind to the lines, they were just reference for me. I used the T2 template but dropped the closing by about 2.5mm - stock opening of course. The logic behind that was Jeff's suggestion on using the 12A turbo exhaust port timing, which I couldn't find a reference to other than it's 38 closing (and based on my short experience with the rotary engine/degree wheel combo, I didn't trust myself to go off of just that). So I figured a slight drop from T2 ( which is 48 degrees if I'm correct) would yield similar enough results. I discovered that the RB street port also closes at about 48 so it seems like the 2.5mm drop is probably just about right considering my intake ports. I kept the width stock, and the bevel I added is very similar to stock too. I could clean up the slides a bit (both the bevel and the actual sides of the hole) if y'all think they need some more attention. I ended up doing the majority of the work from the front though, only going from the back for the sides where my Dremel couldn't reach at an angle.
Progress pictures? Sure thing. Here's one of a secondary port and then of course with today being paint day...
Of course the engine isn't assembled yet; just sitting together (don't mind the mess). The paint didn't come out perfect, but I didn't expect it to. Honestly I think it looks great even though the wind decided to pick up at some unfortunate times... There are a few spots that got missed a little, but it's going in almost the furthest thing from a show car (that'll change someday - not show car, but not '16 years in a field' by any stretch either) and you'll never notice the occasional flaws when it's in the engine bay - or so I continue to tell myself. Changing pace here, tomorrow is slated to be assembly day so quick reply comments will be appreciated regarding porting (I'll be starting after lunch most likely, but that would mean I need to have all ports finalized before then). In theory the grand engine swap will happen on Tuesday, but we'll see. If not it will get pushed off to Thursday afternoon or Friday.
I think that's about it for right now. Thoughts concerning the exhaust ports will be appreciated. Thanks all for the help getting to this point.
1. the opening edge is probably the easiest part to do, so once you have that where you want it, then just leave a little material for when you're doing your finishing.
2. the sides: you kinda want to use the sleeve as a guide, which is why i said the backside will require some work. i try to curve it so that it flows into the shape of the sleeve. the thing is, i really can't really remember the shape of the 12A sleeve though. i know it differs a bit from the 13B, so it might leave an unsightly "gap", but it's the shape that matters. for lack of a better expression, you kinda want to "funnel" the exhaust into the sleeve. that said, the important thing is to stick to the scribe, you have to keep in mind that you've already made the port wider, so sticking to scribe is even a little more important than usual. if you can get the funnel shape, fine. if you can't, that's fine, too.
3. for the closing edge, as usual, leave some material so that you can do the bevel and the finishing. i usually try to go with a high finish on them, but in all honesty, it's probably not necessary.
EDIT-
by the way, i like the paint job. i don't see the flaws you mentioned, but we are oftentimes our biggest critics.
also, good luck with the assembly. diligence is the key. try to arrange the parts in your work space in logical fashion and work through it that way. i remember doing one engine and somehow leaving every last dowel seal out because they somehow were not with everything else. so i had to disassemble, clean and reassemble the whole engine over 4 bloody little seals.
06-21-19, 01:00 PM
that said, all we're talking about here is another sheet of plexiglass - you haven't touched the housings yet. actually, not even another piece - just flip it around and make the correction on the other end of it. the dowel points are fixed. obviously, you'll have to label which side is which with something that won't fade or get washed away though. just for fun, maybe download a degree wheel and try your hand at figuring out timings for both. opportunity knocks ...
