BlastinSideways12A

I am well aware of the specifics regarding the use of Rx8 rotors in a pre-Renesis NA 13B but I'm posting this thread to share an observation and seek feedback regarding something that I haven't heard discussed and have spend half the day searching for.


What seems to be the general consensus:

Rx8 rotors have shown no significant power gains in all-motor race setups such as peripheral port engines despite their higher published values for compression ratio and lightweight.

The above makes sense as a small increase in compression would not have a significant effect on power outside of the margin of error. Drivability and fuel economy are other matters completely but they aren't really even a factor in most race engines...


Moving on...

The intake port timing on the Renesis engine is a considerable change over that of the S5 NA 13B from the 89-91 Rx-7.

The numbers are as follows:

Renesis:
Primary port timing: open 3* ATDC close 65* ABDC
Secondary timing: open 12* ATDC close 36* ABDC
Aux. port timing: open 30* ATDC close 80* ABDC

S5 NA 13B:
Primary port timing: open 32* ATDC close 40* ABDC
Secondary timing: open 32* ATDC close 30* ABDC
Aux. port timing: open 45* ATDC close 80* ABDC

The major difference is the intake opening which is much earlier on the Renesis. I believe that the Renesis rotors enable this for 2 reasons. First of all, the obvious, the beveled edges which pass over the opening of the port. Another reason is the fact that the Renesis rotors have the sideseals located outward in relation to earlier rotors. This enables the intake ports to extend outward on the side housings, opening the ports even earlier. 3* ATDC for the primaries and 12* for the secondaries. This translates into primaries which open 29* earlier that the previous model and secondaries which open 20* earlier...

To compare to the timing from the Racing Beat streetport for a 4 port:

Int open: 25* ATDC Int close: 60* ABDC

These numbers still leave an extra 22* for the primaries and 13* for the secondaries.



WHY NOT...

Use the rotating assembly from an RX8 and use the opening edge from each of their ports as a guide to street porting the older 13B housings. This would give a rotating assembly capable of a reliable 9,000 RPM and more aggressive timing then street porting traditionally yields. This would enable a slightly more powerful NA without the inconveniences of a bridge ported engine. I know of a few older 13B engines making over 200 RWHP with older rotors and a street port.

I'd like to hear some input...

I have a good set of housings from a TII and an NA... The eccentric shaft and rotors are not usable though so I am considering the Rx8 components for an NA build. I have already decided against turbo-charging, I don't feel the need to, nor do I have enough tuning experience to bother at this point. I also have sets of both S4 TII intake manifolds and S5 NA intake manifolds. Right now I am leaning toward using the TII housings with the S5 NA manifolds. I will weld up the lower manifold then re-grind the runners to fit perfectly to the 4 port configuration. That way I will be able to take advantage of the manifold having less bends and the VDI.

Additionally the engine will be run with a Megasquirt and PROBABLY be used in my 85 GSL (unless I can find a clean 86-88 base to swap TII suspension, brakes, and limited slip into). I also have a TII transmission so that the extra power won't cause any problems in that department.

BDC

Good thread. These observations would seem to indicate that power is generated by opening the port earlier as opposed to the common thought (and what I call a misconception) of closing them later. As the engine spins up, the physical amount of time the chamber has to swallow a chunk of air becomes less and less, therefore making it more difficult once a certain RPM thresshold is passed for the engine to continue making torque. Opening the port earlier moves this thresshold up in the RPM band, I think. This is what I quantify the main positive effects I've seen with bridgeports and their ability to continue generating torque and high horsepower at comparably higher rev's (very early port opening on the eyebrow cut). Looks like the Renesis achieves this. Certainly worth researching more. I wonder if it's possible to mimick the early port opening on the side plates of the 13B/13BREW in similar fashion. I've not taken a close look at them myself to see. But, all in all, this does comport with the theory I've held of porting that earlier opening vs. later closing is where the benefit really comes in.

B

BlastinSideways12A

Thanks for the compliment... For the TII housings I would probably close the secondaries at around 65* ABDC. It would be nice to have the ports open significantly earlier without going to a bridge for my application. I want something that will be street friendly and last a long time.

Also, as you said it seems that the later closing would improve high RPM power at full load at the expense of power under nearly every other condition. Under conditions of light load the effects of lowered dynamic compression would reduce power.

Opening the intake ports slightly earlier would allow tuning of the power curve through use of a custom intake manifold and exhaust header. Theoretically fuel economy could IMPROVE for highway situations. This port configuration would enable the improved duration without the negative effect of reducing the compression cycle. The additional overlap won't be a problem with the right exhaust and intake setup and a good stand alone tune.



In short it may be possible that power gains from the use of Renesis rotors may be obtained from the flexibility of port timing, rather than the higher compression and lighter weight that has failed to yield significant gain.

I'm tempted to investigate this and to try this out on my NA build. I'd love to achieve over 200 RWHP and over 20 MPG on the highway.

Black91n/a

Especially for racing the side seal being further out could have a positive impact on power by allowing bigger ports (see link for details), but I don't know if anyone's built an engine to fully take advantage of this yet. Although on the flip side you won't be able to side cut (scallop) the rotors as much and you'll loose a little there too. They also can't be lightened quite as much, but they have better weight tolerances than earlier rotors.

https://www.mazdatrix.com/sccaportrule.htm

BASTARD

iTrader: (4)

Here is my theory…(non turbo applications)

It is easier for the engine to suck air in during the first phase (opening earlier) of the intake cycle then in the second phase (closing later).

In the first phase the chamber is small and as the phase continues to the second phase it opens sucking in air…kind of like a syringe

But once you get to the second phase of intake (closing) the chamber is no longer getting bigger and therefore no longer sucking air in… it simply just moving what air it sucked in during the first phase to the combustion phase



just some food for thought... I could be totaly wrong

BlastinSideways12A

Thats a cool link, thought I'm not thinking in terms of bending racing rules or anything. I just want to drive the car on the street and on open track sessions. In addition, the air will take a more direct path by opening the port earlier rather than cutting into the rotor to achieve an earlier opening. Plus the compression won't drop, which is good for an NA. For a streetport application I wouldn't think that the rotors would need to be lightened since the rotors are already used at 9,000 RPM in a factory application. I would even be hesitant to run the engine at that speed due to the older apex seals that I would end up using being more massive than the RX8 apex seals. The RX8 seals shouldn't be used in the older engines because they are short and will bow when traveling over the peripheral exhaust ports. Of course carbon seals are an option but that will defeat any purpose of keeping the engine streetported anyway since the sealing will be so terrible at low revs.

BlastinSideways12A

Don't worry about being right or wrong, please if you have thoughts share them. I am by no means an expert, thats why I'm seeking as many thoughts as I can. This discussion is a great learning experience for anyone who is willing to participate.

To an great extent you are correct. Opening a port earlier will provide a greater improvement in volumetric efficiency than closing it later. However, if there is still a difference in absolute pressure between the intake manifold and the intake chamber air will continue to flow into the chamber regardless of where the rotor is located as long as the port is open.

At high RPM level, the rotor may open and close the port before the pressure in the chamber equals the pressure in the intake manifold (usually about 100MPa for an NA application) At this point the torque level will begin to drop off. Assuming that the restricting factor is port duration and not flow volume you may either close the port later or open it earlier.

To close the port later: This method will allow the engine to continue to make torque at a higher speed level but will have a negative effect on partial load conditions and lower engine speeds due to the reduced air flow volume, which means reduced air velocity. The BIGGEST factor dealing with the intake port closing is that the chamber volume begins DECREASING at bottom dead center... This is 50 degrees EARLIER than the intake port closes on a STOCK TII engine. Granted the airflow is not great enough to fill the chamber by bottom dead center so the port will continue to flow air after that point, especially under heavy throttle and high RPM. Flow velocity helps out here. Closing the port later will allow for greater volumetric efficiency at high loads and RPM levels. It will reach a point of diminishing returns though, as the later that the port closes after BDC, the more that you will be cutting into the effective compression of the air/fuel mix. This is what decreases mid-range, low end, startup compression, and cruising. As you can imagine, in a turbo-charging application this isn't a negative. In fact Mazda's 2.3 liter V6 did this and used a supercharger to this effect (miller cycle engine).

But what about opening the port earlier. Well in the Pre-Renesis engines this happens at about 32* after Top Dead Center. Streetporting will only get you to about 25* without worrying about the sideseal being compromised by the port. There just isn't that much room to go without bridgeporting the engine which will REALLY open the port early but will create some pretty crazy conditions not exactly favorable for most street engines (speaking in terms of NA) Overlap is the biggest thing in the bridge. (the ports of some J-bridge engines open as early as 100* BEFORE top dead center. By using the Renesis rotors we may be able to get the ports to open as early as 3* After Top Dead Center as the Renesis primary port does. This is only 3 degrees after the chamber begins to expand rather than the 25 degrees for most current streetport applications. A proper exhaust will reduce most of the negative effects from the additional overlap between the exhaust and intake.

The end result will be the same increased port duration of the traditional later closing without the drawback of the rotor forcing air OUT of the intake port under lower load and RPM conditions. This will allow better volumetric efficiency under most practical operating conditions, INCLUDING full-throttle High RPM, rather than ONLY full-throttle, high RPM conditions. With the proper header setup designed to most effectively scavenge exhaust at say, 4,000 RPM you could even have a nice, torquey setup. In short, opening the port earlier will enable the engine to not only continue to make torque at high RPM, but additionally to make EXTRA torque. Closing the port later under all practical NA conditions will not INCREASE peak torque, rather just increase the RPM level at which the peak torque is made.

I plan on both opening the ports earlier AND closing them (a bit) later. A stock Rx8 and FC 6 port engine closes the aux ports at 80 degrees ATDC. I plan on 60-60* ATDC with TII secondaries and about 55* on the primaries.

BLUE TII

iTrader: (9)

Looking at a Renisis port I think moving the sideseal allows for some of the earlier opening as well as the beveling, but it looks like they employed another trick as well.

It appears to me from pictures that they ported the lower section of the port for even more early opening despite the fact this puts BOTH sideseals into the port.

It looks like it is just for a short section at the bottom of the port where the outer sideseal is mostly supported below the port by the side housing.

Could someone that has handled the Renisis housings confirm this?

If you are doing this to 4 port housings then you may consider having the primary ports being the ones that close a tad later. The idea here is once the 2ndaries are closed you have the smaller runners/volume of the primaries to really get the velocity up to overcome reversion.

This effect is already there with the little aux ports/runners on the 6 port models.

Here is what I tried to have big high flow 2ndaries and small high velocity later closing primaries in my TII.





From this thread

https://www.rx7club.com/rotary-car-performance-77/pics-blue-tiis-engine-build-new-type-primary-port-489429/

BlastinSideways12A

Great to hear feedback from you all. This thread has already become quite informative. It should be a great point of reference for NA and high-comp turbo builders alike as it progresses. Its too bad Mazda hasn't and likely won't build lower comp Renesis based rotors for the big boost fans.

Black91n/a

If you're building an NA motor then you should use NA irons as they've got bigger ports and will give more power. 200whp on 6 port irons with a street port is hard enough already, don't make it harder on yourself with smaller ports.

BlastinSideways12A

After a good port job the TII ports can be made quite large. My main concern, however is the port timing. I'll post some pictures of each of the irons when I get a chance... Realistically 2 weeks from now...

Additionally, the secondaries on a TII are less restrictive than the secondary/auxiliary combo of a 6 port. Also, I've seen dyno graphs with both engine configurations and in general TII based engines have seen greater numbers. Both setups have potential and there are some great builder/tuners pushing over 200whp with both.

I should just fill the ports in with devcon and hack a hole in each rotor housing, then stick a tube into each, just use 9.7:1 rotors, and drive around idling at 1,500 RPM... o wait, thats the plan for the spare 12A parts...

BLUE TII

iTrader: (9)

I can think of 2 examples of NA motors over 200hp that used 4 port irons.

Total budget build up by Yawpower that used S5 TII side housings w/ mild streetport (~60 deg closing), race port exhaust, S5 TII intake manifold, S5 NA rotors and a fuel only controller. 210 RWHP

The other is a dyno graph of a 13BRE with a header instead of turbo.

I think that over 200hp and flow starts to matter a lot as opposed to just timing and velocity (6 port irons). The 6 port offers better driveability and can make decent power even with the restrictive stock emissions equipment.

BLUE TII

iTrader: (9)

Oops beat me to it- lol

Anyways, check out Yawpower.com

BLUE TII

iTrader: (9)

Mmm, but we can have it all (big boost and high comp driveability) once E85 is more prevelant.

The Renisis will do high boost very well once the detonation is overcome w/ effective octane as it has no overlap so the very high exhaust backpressure to push the boost will not be a problem as it is in the earlier rotaries.

BlastinSideways12A

That Yawpower engine made 210 RWHP with a 12A distributor controlling ignition! Wow...

Black91n/a

If you grind out the divider between the aux and the secondary ports you can have a large runner. You can grind it out all the way to the port or not depending on what you want to do.

A max porting on a TII will be smaller than a max porting on an NA.

diabolical1

iTrader: (3)

not to totally discount fuel, but from what i gleaned from the Rx-8 Board, the major obstacle most people are having is the ignition system. it seems to be extinguishing spark. generally speaking, it appears the Renesis loves boost and is more tolerant of detonation when it occurs.

diabolical1

iTrader: (3)

as for the rest of the thread, regarding the original topic. yes, i do believe opening the intake earlier is where it's at in terms of a good torque curve. i'm not an engineer by trade, by i have been tinkering with these motors for a while (plus i can think spatially) and so far all of my theories seem to coincide with much of what's been said here by BDC and Bastard. i haven't gotten my grubby little hands on a Renesis yet, so everything i've learned is through reading, but i have plans for a project that will incorporate some of that Renesis knowledge and if i can, i will perform some tests and share whatever results i obtain.


by the way, this is a great thread. i haven't looked at the links provided yet, but if it hasn't been included yet, there is a great thread that Jeff20B started a while back that went into some of the points of port timing's relationship to streetable torque in N/A applications.

BlastinSideways12A

I may get the opportunity to freshen up a Renesis with new gaskets and o-rings in the near future. My dad and I are working on installing Miata suspension, brakes, and rear diff into one of his MGB roadsters and we have decided to install either an S2000 engine/trans or a Renesis engine/6speed. I'm sure you know which direction I am leaning... Anyway, I have discussed the carbon buildup of these engines with him and we have decided that it would be best to open it up to clean it up.

I see a great opportunity for some measurements and test fitting. Trouble is, I live about an hour and a half away so I can only work there relatively seldom.

BLUE TII

iTrader: (9)

OK, you could use the european 6 port plates so you can have a decent shape to the finished port for flow when you combine the aux port and the 2ndary port into one large port.

This siamesed port on an NA will peak around 10,000rpm minimum if you carefully design the exhaust and intake manifolds to lower the peak as much as possible (Dave Lemon's experience). This is partly because of the late port closing and partly because of the huge port runner from siamesing.

If you want a lower peak for reliability you can go with the 4 port irons. S5 and newer can still have closing later than 70 deg and the correct port shape due to extra material in the casting if you do want to get peak torque over 8,000rpm.

I am not saying you are limited to 200 RWHP and under with 6 ports by any means, rather that it is easier to get above 200 RWHP with 4 ports (stock intake manifold and mild intake ports).

Please prove me wrong with 200+ RWHP 6 port info so we can all benifit from how it is done.

BLUE TII

iTrader: (9)

Easily addressed.

I run 2 crane HI-6 and 2 LX92 coils for the leading spark plugs and stock on the trailing on my TII.

My experience is this set up will go through leading plugs quickly (~5-10k miles) but has enough spark to start the engine off of the assembly lube (Pump and injectors disabled) or run richer than 8:1 on pump gas at 1 bar boost.

BlastinSideways12A

The HUGE port volume is actually a drawback, especially since the intake manifold runner's cross sectional area is smaller than the port area would become so even when the air is moving fast in the intake, it will expand and slow down as soon as it reaches the larger area which would be created by grinding the entire port out.

An ideal setup would have the runner get smaller as it approaches the chamber, though only by a VERY small amount and in a very gradual fashion. This would result in the intake charge gaining momentum as it would speed up. The primary ports on the FC engines use this technique, though I'm sure that Mazda's primary concern was to improve the velocity near the injectors in order to improve fuel atomization at idle and cruise.

As I did mention before, I plan on modifying the lower intake manifold from an S5 NA to match the TII secondaries with a welder. I'll definitely test that setup with the VDI and compare it to a set of TII manifolds. I will be curious to see how each performs.

BLUE TII

iTrader: (9)

Exactly.

The siamesed 6 port set up that was made to peak as low as 10,000rpm used a custom large runner intake manifold and carb as it is either that or the complete stock intake and injection system in the class it runs.

BlastinSideways12A

I wonder how that port compared to the secondaries on a 13B RE...

I don't have the bankroll to enter into Cosmo territory yet so I've never got the chance to take one apart.

If I were to venture a guess I would say that the volume would be similar but the RE port closes quite a bit earlier. The later the closing, the more critical that intake velocity becomes because the momentum will counter the decreasing chamber volume before the port closes.

Black91n/a

You could leave the divider in place on the port and just grind it out in the runner to get a better ratio of port size to runner size. Just a thought.