non-pp 26b?
 

First off, sorry that this is not 20b related but I think it's the best place to ask this question. Most 26b builds are PP motors. "Standard" 26b (non mazda made) setups use two intermediate housings with modified stationary gears. Problem is these housings (unlike the 20b center housing) have 2 (smaller) secondary ports instead of a secondary and primary (larger) port. I suppose now would be a good time to throw some pics in to make this a less boring read but it's late and I'm lazy... maybe tomorrow :D . These just get filled in when running PP housings.

But say you want a 26b which utilizes the side ports... you now have restricted flow for the two center rotors, and increased flow for the outer two rotors. So my question is, is there any way to mitigate this problem? Say with porting? As far as i can see there's not enough material to port match the outer primaries. Using 20b center irons is not much better as it makes the motor longer/heavier and there are not off the shelf shafts (that i know of) which would let you do this.

So am I missing something, or are people just FORCED into a PP configuration with a 26b? :dunno:

Thanks, Heath

Mate, I think you hit it on the head, most people are forced to go PP for a 26b.

There's no where near enough meat in a port match a standard centre plate up to a primary and secondary.

Getting a second 20B intermediate plate would be the go if you when that route, but get a turbosmart one (billet) so weight isnt the issue.
Still then no current ecentric shaft's on the market to suit your needs.

And once you have done all that you would probably port the hell out of it anyway... so then most would just go one more and get the PP anyway.

A good while ago I spoke with Kiwi-RE about this and they said that most of the 4-rotor kits they sell are side (non-PP) port configurations. I didn't get into specifics with them about flow distribution with porting and what not, so I can't really offer much there. Supposing that several side port 26Bs are running though, as they said, it would seem to suggest that it's definitely possible.

I know that autotech's 4-rotor is side port fed. Might consider dropping them a line. If you do, please report back with whatever you find.

The reason I ask is because (as we all know) a PP motor does flow more than a side port motor. There's just more opening to flow through. However, the huge hole in the side of the housing does cause issues with port timing which really show their head at low rpm's. Definitely not a streetable motor. What I've been intrigued with recently though is the semi PP setup.

Now I know it sounds stupid to make a big fuss over the side ports, and then go punch some holes in the housings anyway, but hear me out. When you add up all of the flow area (small semi PP + primary + secondary) you actually end up with more flow than a straight PP, while the smaller hole in the housing doesnt affect overlap as much and therefore driveability isnt as bad as a standard PP (more like a bridge). So on those two accounts (more flow, better idle) the cross flow semi PP seems to be the best setup to me. It would be even nicer if you could open the semi PP ports individually, but for reasons I wont go into, it would be rather difficult to pull that off. The only other option I see is reducing the size of the outer primaries to the size of a ported secondary.... that is really the only way I can see it working. :scratch: Also I wonder about not having a circular hole for a semi PP motor but instead a half-circle (flat side down) so that timing could be more delicately controlled than what you are forced into with a circular shape.

if you really like the idea of a semi pp without the problem of unbalanced flow, then just have only one side port. plate 2 and 4 will be used, all the others blocked off. then have a nice 1.5 sized pp and you're done.

but then again, who the fuck would build something as expensive as a 4 rotor without going all out?
lots of people unfortunatly... the QSR bmw has side ports. so does this random 4 rotor on youtube which has two FD upper intakes.

I'm not sure why you'd use the term "unfortunately". The QSR 4 rotor is the most powerful rotary engine on the planet. . . pretty hard to say that they're doing very much that is regrettable.

I thought that a side port 4 rotor would be the ultimate in power combined with tip in throttle driveability.

I was thinking just go with the RB aluminum side housings for all and have them ported out the same even if you have to fill in some of the runners on the end housings.

If it doesn't have enough power in this configuration toss a turbo or four on it...

now THAT'S what I'm talkin about :D

IDK, I think it would be the best of both worlds. There is a point when "going all out" (full PP) ends up being a worse choice doing things moderately lol. unless you have a race team, I dont see the need for an all out, PP, ceramic seal, super ultra custom done motor. The goal for any NA 20b (or 26b for that matter) is to increase driveablilty, reliability, AND increase HP. If that wasnt the goal then I'd think a nice turbo 13b would suffice as you end up with the same power.

Use early tall port intermediate plates from a 12A. They flow enough and can be ported a lot. Pay attention to coolant seal location.

+1

not to pick, but i think you have that backwards. :)

i give this some thought every so often. obviously i can't afford to build 26B so i don't spend an awful amount of time thinking about them, but they do intrigue me ... and that sound!!! personally, i think it's just a matter of practicality, in the sense of simplicity as opposed to cost. i think the inherent uneven flow characteristics of a full side port 26B (without using 2 20B big housings) is solved simplest by going with full peripherals. perhaps i'm speaking too soon, but i've never seen a completed 26B project intended solely for street use. so PPs would not be a problem per se to those that have gone that route.

anyway, for the side port issue, i'd be inclined to agree with Jeff20B's approach. one may also consider playing around with porting the primaries while not messing with the secondaries much, if at all. i think both avenues could be viable if you tune and use the thing within reason - i.e. resisting going to extremes in both tuning and use. i mean 6 out of 8 ports would be virtually identical and i have seen photos of some REW primaries that "appear" to rival stock secondaries in sheer size (though i obviously can't tell timing information on them).

you also mentioned possibly going semi-pp as a way to avoid potential full PP issues. personally, if i ever found myself with the budget and opportunity to build a 26B, i think i'd be tempted most to try this configuration. funnily enough, i'm not convinced i'd be tempted to turbocharge it though. i especially liked your idea about manipulating the shape to aid in control of port timing, overlap, etc.. that actually fits right in line with some of the ideas i've scribbled in my notes on future 13B-based semi-pp projects.


great topic.

The 4 rotor engines that use side port in NZ and Australia happen to use 1974 RX4 Irons because primary and secondary are almost the same as far as inlet size and with a bit of porting can be made the exact same size and as far as opening and closing of the port both primary and secondary they are exactly the same which means that they can be ported to the exact same size again and be perfectly balanced as far as flow goes ,,the rx4 irons are still available in NZ and australia and as far as I know Racing beat has a few left overs as well last time i called.

I talked to Jim Mederer about this at the last Sevenstock and he was confident that the aluminum intermediate housings would not handle the load from the required additional stationary gears. The two aluminum f/r side housings they offer have extra meat around that area and a few extra bolts to hold it in place. He said this was discovered while casting the side housings similar to stock (first versions) after they found cracks radiating from the bolt holes for the stationary gears. The intermediate housing was not designed to accommodate that additional load and the new f/r side housings were redesigned just for this.

That didn't stop him from suggesting I buy a set and give it a try :rolleyes:

Gordo, I agree. A think tank section would be very very cool... right now threads like this kinda sorta fit in a section, but not really. I'd love a place to go to just bounce around ideas for NEW setups. Maybe this idea will get some traction.

Regarding the controlling the secondaries on a semi-pp... what do you mean by secondaries? Does the semi-pp fall into the secondary category? I mean, you could run independent throttle bodys, but there are a few problems with trying to seal off the semi PP holes to temporarily turn in back into a "side port motor" . namely, no matter where you put the throttle body (as close as you want to the port opening in the housing, as the apex seal crosses that threshold you create a gap where pressure/vacuum from the next rotor face interacts with the previous one. Now, do it fast enough (like high rpm) and the air cant move back through the gap fast enough... slow rpm it can and creates a crappy idle among other problems. As i understand it you can cure the problem by opening that port for a shorter duration, a smaller size hole, or changing at what point the leading edge of the rotor crosses that threshold. The semi PP attempts to address all 3 of those concerns as compared to the larger full size PP.

Now, further refinement of the port shape may lead to even better results, however its going to be alot harder to create a non circular hole and a non circular press-fit sleeve. Plus you have three parameters to adjust/experiment on so it would really take alot of either trial and error, or some smart thinking/calculations to come up with a better port shape. I have a few ideas... but really a circular port is probably used so frequently just for convienience sake.

Anyone care to share their thoughs? -Heath

for a more interactive discussion, here's a little to watch and read:
http://www.geocities.com/jeffguilfoil/semi-pp.html
http://www.youtube.com/watch?v=xEL9vzuig6Q

When we originally designed this subforum, the intent was to discuss rotary engines with 3 or more rotors, even though the title of the subforum may not convey that very well. See FAQ #5. ;)
https://www.rx7club.com/20b-forum-95/20b-faq-links-370451/

uh oh evil... dont let me talk about a 5 rotor! :D

I talked to Jim Mederer about this at the last Sevenstock and he was confident that the aluminum intermediate housings would not handle the load from the required additional stationary gears.

Bummer, but now that alum. int. housing is not a possibility the cost of doing a 4 rotor "right" just came down for me :).

Regarding the controlling the secondaries on a semi-pp... what do you mean by secondaries? Does the semi-pp fall into the secondary category?

Right! You can't close off a peripheral port, it is ALWAYS open to one chamber or two chambers and that is part why they can make so much power ie. intake velocity can overcome pulsation so much easier.

Soo, if you are smart you make the small peripheral ports your PRIMARY port as P-ports have been shown to make more power than side ports from 2,000rpm up.

You just go with a higher overlap but earlier closing small slot shaped P-port and go with crazy late closing side ports, because sideports are closed off from reversion into the next chamber by the rotor.

it may be difficult to make a non circular hole for a peripheral port, but with the right resources you can obviously do it (check my sig)... In the arrangement where you had a small peripheral port hole that you wanted to use in a secondary throttle opperation, it would be best to make the port short and wide, to eliminate pressure drop as the apex seal passes it.

You could make the port 1/4" high and 2.5" wide and it would still have lots of area.

Obviously it makes a tremendous amout of power, which is to be expected with a gt60.. but if you had the engine fully peripheral ported, or at least with semi-pps, it should be good for 2000hp with the same components..

Obviously it makes a tremendous amout of power, which is to be expected with a gt60.. but if you had the engine fully peripheral ported, or at least with semi-pps, it should be good for 2000hp with the same components..

I think you will see the wisdom of just a "tremendous" amount of power from sideports as apposed to an insane amount of power with p-ports if you get your set up running.

With too big of sideports or p-ports there is simply no control over the powerband. Give it 10% throttle in the powerband rpm and it has almost the same power as 100% throttle.

It is like how you can make a crapload of power with a restrictor plate after the turbo so race classes make you put it before the turbo- throttle plate ends up not so effective.

Hmm, I suppose you could get around this by putting your throttle plates before the turbo on a turbo P-port set up...

It's easier than you think, but only if you think outside the box that most everybody else is thinking in ....

13b rear iron with a secondary port
rotor 1
13b center iron with primary/primary ports
rotor 2
20b center iron with secondary/primary port
rotor 3
20b center iron with secondary/primary port
rotor 4
20b front iron with secondary port

You would have to machine out the holes on the front most 20b center iron plate to have tension bolts run through it.....and i doubt the "standard" 4 rotor shafts would work because the front center plate would be thick so that gets to be custom too.

It's a custom job no matter what, so you might as well do it the way that
makes the most sense for the intended outcome

we were looking at casting our own center plate.... but we're doing PP cause we're roadracing

Anything (as far as I'm concerned) that doesnt use an "off the shelf 4 rotor shaft" is out... as it would be extremely cost prohibitive :icon_no2:

If you think about it... the cost of an NA 26b vs turbo 20b.... i thnk the cost would not be that far off. Once you remove the cost of the turbo, intercooler, associated parts, cost of the 20b block and re(build) the 20b block. Grated there is the increased cost of the 20b shaft, the housings, dry sump, and cost to have it built.... but I think those two numbers wouldnt end up THAT far off.

you can use early '86-'87 front and rear irons with a 12a tallport centre,you can port the tallport centre to flow the same as the other secondary ports,giving the engine even ports all round. just have to machine the water seal grooves in the 12a iron.
its been done before.