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1. Great work, Brett. Fun to see someone pushing the envelope and trying to innovate.
2. So the siamese is the ultimate restriction on renesis power?
I am almost positive the Siamese is the issue yes. If you have a look at how it is designed , compare the size of the port with the size of the first part of the siamese sleeve you will see there is a massive disparity . There is only one place for the backed up gasses to go , over the edge of the sleeve and into the opposite housing .
It only becomes a problem at this power point though .... Anything less and the problem is just the 10:1 compression ratio ...... which is an easy fix.
Would it assist the Siamese port spill over if the center runner of the manifold was also divided so the gases had to go farther before they could spill over? Or separated all the way to the turbo housing? (not getting into the complexities of making a manifold that way)
Would it assist the Siamese port spill over if the center runner of the manifold was also divided so the gases had to go farther before they could spill over? Or separated all the way to the turbo housing? (not getting into the complexities of making a manifold that way)
No .. You have to have a good look at the sleeve to see how it is designed ...... there isn't full separation at any point. The problem isn't gases turning around and going back up the other side . Its right at the first part of the sleeve, where the exhaust gases hit it at right angles, before it even gets to the open part of the sleeve.
If you imagine a pipe with a restriction in it ....everything before the restriction is at a higher pressure than everything after it . This is what we have at the Siamese sleeve except we also have ,BEFORE the restriction, a direct path around the sleeve to the opposing rotor. There is no way to effectively block the path without a total redesign of the iron ...yes I have tried !
To understand this you really need to look at a sleeve inside the port and think about where the restriction actually is. The port itself is not a restriction at all ...the sleeve is.
I did an approximate calculation that found the size of the port itself is more than DOUBLE the size of the passage in the early part of the sleeve . In this latest engine I made a few changes that got that down from 2x the size to about 1.4x the size . This was what I was hoping would lead to a breakthrough .................... It has helped a little, but it has not solved the issue.To do that would require that ratio be reduced to less than 1:1 (you still have the problem of trying to turn the gas 90 degrees which in itself will create backpressure) ...or total separation .
I know this is probably out of everyone's reach, but then again, internet advice is worth every penny you pay for it. REC (Rotary Engine .Com) has remade their own 20B center iron. I assume we would have to go that far to fix this issue, making a completely new center iron?
I know this is probably out of everyone's reach, but then again, internet advice is worth every penny you pay for it. REC (Rotary Engine .Com) has remade their own 20B center iron. I assume we would have to go that far to fix this issue, making a completely new center iron?
Well , I've tried a lot of ways to overcome it and what I have now is the best I've managed . I can't think how to improve on it from here .
There was a reason Mazda did such a **** job of designing that middle iron . To make it work any better they would have needed to lengthen the engine to get better exhaust flow from the middle , make a new longer eccentric shaft and possibly even fit a center bearing . Not only making the engine heavier and hugely expensive , but also not really increasing the power much over what they had already achieved by just making a few changes to existing patterns.
Can you share pics of your exhaust port modifications?
Sure
This is for the outer ports ....the thickness of the felt pen line is exactly how much I took out ,I also rounded the edge underneath .At the other end I just removed the ridges ...... pretty standard .
At the siamese end ....... I used a 4port plate instead of a 6 port plus I modified the sleeve to make it flow better .
See the difference in port size here ....
Soooooo ... Yes I made the Siamese exhaust ports SMALLER and got a better result ! I believe that if I could have made them even smaller still ,about half the size of the 4 port ports ...the problem would be solved for the most part .
I can't see this flow reversion happening to the same extent on an SC car as the flow will take the easiset path and vent to close to atmospheric rather than do a 180deg flip and go into the next chamber.
No ... I think you missed the key thing here . The Siamese port can be less than half the size it currently is and still flow the same amount of gas . That's because the port isn't the restriction ... the sleeve is .as far as the sc goes ... I don't believe there is any advantage .., because you actually need to make probably an extra 70-80 hp at the engine just to match what a turbo can do . At that level even though you are dumping to atmosphere..., you still have enormous restricton at the sleeve and reversion will still happen .
so the restriction is at the point of minimum cross section. still reversion will only occur when either chamber has a lower pressure than exhaust back pressure. yes it will probably will still occur on a sc engine but at what level and duration?
so the restriction is at the point of minimum cross section. still reversion will only occur when either chamber has a lower pressure than exhaust back pressure.
It still will get reversion, because how much backpressure there is in the exhaust isn't as important as how much pressure there is BEFORE the restriction. Low backpressure from the exhaust only changes the rpm and boost level that reversion occurs at.
I know this because I've seen what happens as I have reduced backpressure over the years ..... it should have had a much more profound effect than it actually did .
Originally Posted by rotarenvy
yes it will probably will still occur on a sc engine but at what level and duration?
Who knows ............... but we will never see a 400+whp Supercharged Renesis so the point is moot !
It still will get reversion, because how much backpressure there is isn't as important as how much pressure there is BEFORE the restriction. ...
this is the bit I'm not getting. so your saying when the sleeve is saturated the exhaust flows around the sleeve between the chambers to create the reversion?
Originally Posted by Brettus
Who knows ............... but we will never see a 400+whp Supercharged Renesis so the point is moot ! If you want to give it a go , make sure you have funds ready for the rebuild
I'd love to try but the cost of a new compressor puts me off trying and the likelihood it will end in a two year rebuild thread. especilly since i don't beleve in tuning or supporting mods
this is the bit I'm not getting. so your saying when the sleeve is saturated the exhaust flows around the sleeve between the chambers to create the reversion?
:
You need to look at the middle iron with the sleeve there and you will see that the sleeve has a gap all the way around it . It doesn't seal up to the port ----- the gap is 2-3mm all the way around. So air can travel from one side , over the top of the sleeve wall , around the outside of the sleeve and back into the chamber of the other rotor . This is never going to happen on an NA , but on a turbo , when you are pushing more than double the air through that tiny hole in the sleeve , the air will go path of least resistance which will be into the lower pressure chamber next door.
Good discussion on exhaust restriction. Any idea on ideal boost pressure to get the most benefit from the system. I have the hymee supercharger and I managed to get 200kw at the wheels with 8psi boost.
Possibly looking to increase the boost to 10 or possibly 12psi. I assume that these boost levels should be ok?
ok now I get you. porting makes this worse. blocking the air injection and a tighter fitting custom sleeve might help tho.
Yes any porting of the siamese ports makes it worse , making them smaller ...helps.
I have tried a tighter fitting sleeve (professionally inconel welded) ... it beat itself to death and I ended up with both a dead engine and a dead turbo ! I have also vented the air injection hole to the exhaust .
Bit late now ..but this might help others get what I'm talking about :
Good discussion on exhaust restriction. Any idea on ideal boost pressure to get the most benefit from the system. I have the hymee supercharger and I managed to get 200kw at the wheels with 8psi boost.
Possibly looking to increase the boost to 10 or possibly 12psi. I assume that these boost levels should be ok?
Should not be any problem at all but do run higher octane gas ! 20-30% ethanol will give you a decent safety margin.
The ideal boost pressure for maximum power from a particular system is : the pressure that still gives you the same incremental increase in power that you got for the first say 5-6psi . For my setup ... 13-14whp per pound of boost . When that starts dropping ... don't go any further. However your system is more likely to be limited by the SC than anything going on at the Siamese.
04-05-2018, 11:12 PM
especilly since i don't beleve in tuning or supporting mods 
