Trots*88TII-AE*

Exactly why I said, "I thought". I am still trying to learn as much as possible, especially on these internet forums. I certainly don't see them as a joke, they are the biggest source of knowledge for me for rotary engines, and I haven't seen enough Mazda tech papers to be as knowledgeable as you I guess.







So then they must design semi-pp's with closing time in sync with the closing time of the sideports? The reason I was confused was I thought the same way about closing times, but figured the semi-pp's closing time would have been later than the sideports. It's all starting to make sense It would almost seem that stock side ports with the semi-pp would yield you better results vs. streetport, that way you could "stagger" the closing times based on the peripheral port being open or not.

cach22

Hey Mate,



Interesting theory, though the aditional overlap will mean that the intake stroke is swollowing more exhaust gas at low rpm than stock which is no good for power, though the big question is will the power gained by opening the port earlier outweight the power lost from the extra exhaust gasses in the inlet charge? The earlier opening may also give the engine a rougher idle. The other thing to consider is exhaust manifold back pressure. If you are running say 15psi boost with that turbo you will probably have at least 18psi in the exhaust manifold. so what will happen is the higher pressure in the exhaust manifold comapred to the lower pressure in the intake manifold means that the ehxuast gases will flow into the inlet ports which isn't good. The only way to improve that is to run a bigger exhaust housing



When i rebuilt my engine s513bt i umed and ahhed weather to port it or not as it was my daily driver and i decided to keep port timing stock though i made a flow bench and just tweaked the port runners. The advantage of the flowbench ment i could see if what i did made flow increase or decrease, though building the flowbench was another story lol.



You will easily acheive your 350+ rwhp with stock ports and your current turbo. I run the same turbo as you though i have an undivided 1.06 ex housing and off boost responce with this engine is really good, and the turbo is very responsive. I think your turbo would be even more responsive downlow due to the smaller a/r plus the advantage of the split pulse, just make sure your build the exhaust manifold with the shortest runners you can fit.



The other thing i was thinking i don't think you can open the inlet ports at 8 deg ATDC because there won't be enough meat to support the corner seals?



cheers



Lance

diabolical1

i can't speak for him, but perhaps he was including timing with rotor bevels?

i think i'm in the same place right now. i'm learning to curb my urge to go bigger with exhaust ports based on the (flawed) logic that more in should mean more out. i'm gaining more understanding of airflow as a dynamic (as opposed to static) concept each day.



it's funny because once i had completed my semi-peripheral housings and put the degree wheel to it, i started getting curious about some things. about that same time period, i also read a thread about a turbocharged full peripheral engine (i forget his screen-name at the moment) that had exhaust porting similar to mine and his power curve was not what he had expected. he hypothesized that perhaps his exhaust ports were probably too big, so naturally, it got me thinking. i spent a few months and wouldn't you know it, i had an A-HA moment ... i finally saw why big exhausts could potentially hurt a streetable powerband.



i'm dedicated to applying all the insights i've made since then to my "next" semi-pp project, but i still feel i NEED to put this one together first, if for no other reason than to follow through. however, i suspect it will provide some good and interesting data if i can just gain the needed wisdom to extract it.

j9fd3s

yes. in fact the Rx8 has the latest closing timing of anything mazda has ever done @80. even the P port closes @75!

j9fd3s

lmao! i remember when i put a degree wheel on mine, it was an "oh" moment. both ports are open together a LONG time... its like oh i know why its pissed off.... if you take the trailing plug out, and look in the intake, you can see light....



although it actually is kind of a sweetheart, it runs a lot better than i would have thought

thatpoorguy

In boost the pressurized air should force the exhaust gas out faster rather than sucking it in right? Or am I completely off?

bumpstart

i think the one factor most people overlook here is Exhaust Manifold Pressure ( EMP ) V boost pressure ratio

in most old school turbo's used on the street you would have a factor somewhere in the 2 or 2.5:1



-- no typo,, exhaust pressure is TWICE that of the inlet pressure in many turbos on song

if you are VERY good with exhaust, turbo manifold and wastegate and turbine choices you MAY get some near 1:1,, but never better



just a little bit of thought will tell you that the inlet and overlap period in some engines is now going to amount to exhaust gas dilution of the inlet charge

this is where a lot of people fail to cross the critical threshold of understanding the fundamental differences in turbo and NA flow dynamics



anybody who understands the concept of a miller cycle engine should now start to understand there is efficiency GAINS in having a late close inlet and a boosted manifold

somewhere there is a mazda SAE paper showing you the rise cycle of compression pressure in the rotor with the various inlet timings

they are radically different between late close and early inlet timing practices ,, the late close is easier on the the mechanical effort required during the initial compression stroke and has a radically faster rise in pressure during the final degrees of the crank during compression

this has implications on flame speed and ignition timing that few take the time to try and understand fully

and so the whole argument gets much more involved than appeared on outset of the OP's questions





basically a low overlap is better to reduce the exhaust dilution effect of the inlet while under adverse EMP/boost ratio

basically a late close allows the miller cycle effect to kick in,,, where boost won for "free" mechanical effort from the exhaust keeps the inlet in positive flow against compression late in the inlet stroke

and the win win is in the crank,, where it doesnt have to lose mechanical effort to do the initial stages of compression

,, effectively having an easy effort inlet stroke at the expense of the energy already lost to the exhaust

whilst this wins a radically different compression ratio rise in the compression stroke and thus demands a timing rethink due to that influence on flame speeds



i hope that comes through clear as mud ,, even if you have to reread it a few times

Liborek

I agree, but lets keep this discussion technically correct. Without measuring its just speculation. Also we donīt know at what EMP/IMP ratio things start getting really detrimental on given porting. Its clear that stock port will be most tolerant and full PP will be least. Of course EMP on given inlet boost goes up with RPMs.





This is wrong.



Turbine is propelled by heat, flow and pressure. Heat is something what rotary doesnīt lack. And flow and pressure drop... Small turbine will pass certain amount of corrected gas flow and will work with higher pressure drop. Bigger turbine will pass more corrected gas flow with less pressure drop. Main thing is that they will produce same torque for propelling compressor.



Rice Racing, and not only him, datalogged that on proper setup, EMP is just catching up with inlet boost towards max power RPMs. Also its not just matter of properly designed hotside - side of thing, but whole package including compressor and intercooling efficiency.



This is something what should be examined much more. For me personally, I would be interested in how much power is rotary engine able to extract from given compressor-airflow compared to piston engine with big enough hotside.