exhaust port major chamfer...

Any form of normally aspirated power mods.
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exhaust port major chamfer...

Post by 350matt » Fri Jun 15, 2018 10:50 pm

Gents

this is worthy of discussion I feel



I did something similar to mine but didn't take it this far
thoughts?

their site also has some interesting stuff on it, cermet coated side plates? aluminium side plates?

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Re: exhaust port major chamfer...

Post by 13Black » Sat Jun 16, 2018 12:14 am

I saw that - haven't got round to seeing how much further they go compared to a RB street port but I'll see if I can post up some rough percentages when I do. They're a company that does appear to know what they're doing though :D would be nice to have some power figures to go with it, I suspect not an enormous gain over a standard SP but every little helps certainly.
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Re: exhaust port major chamfer...

Post by 350matt » Sat Jun 16, 2018 9:04 am

The video does go into a surprising level of detail, so there's enough direction there for someone....

but yes as ever a back to back power test would be nice but that doesn't seem to happen on this platform

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Re: exhaust port major chamfer...

Post by Project-RX8 » Wed Jul 04, 2018 11:22 am

ooo... interesting...

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Re: exhaust port major chamfer...

Post by RobinPZ72 » Sat Nov 10, 2018 12:30 am

Yes that makes total sense also a lot is done by CNC, so a consistent profile all the time! There bridge port is lovely tool

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Re: exhaust port major chamfer...

Post by Velocity_Dan93 » Sat Nov 10, 2018 9:55 am

This concept is already being incorporated on some porting in the U.K. on FB engines :)
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Re: exhaust port major chamfer...

Post by 350matt » Sat Nov 10, 2018 9:56 am

Oh yes , care to spill the beans on whose work?

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Re: exhaust port major chamfer...

Post by RobinPZ72 » Sat Nov 10, 2018 11:02 am

Those Dam beans!

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Re: exhaust port major chamfer...

Post by 350matt » Sat Nov 10, 2018 7:50 pm

and does it work?

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Re: exhaust port major chamfer...

Post by 13Black » Sat Nov 10, 2018 8:24 pm

Who knows, dynos can't be relied upon ;)

I looked into their exhaust port a while back and it does seem to offer a decent chuck more area over Racing Beat's templ9s, on the surface at least.


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Re: exhaust port major chamfer...

Post by MadTaz » Sat Nov 10, 2018 8:37 pm

13Black wrote:
Sat Nov 10, 2018 8:24 pm
Who knows, dynos can't be relied upon ;)

I looked into their exhaust port a while back and it does seem to offer a decent chuck more area over Racing Beat's templ9s, on the surface at least.



RBREC.jpg
Despite what the missus may say, bigger doesn't mean better ;)

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Re: exhaust port major chamfer...

Post by 13Black » Sat Nov 10, 2018 8:44 pm

MadTaz wrote:
Sat Nov 10, 2018 8:37 pm
Despite what the missus may say, bigger doesn't mean better ;)

I think I've proved that to her if anything :angel:
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Re: exhaust port major chamfer...

Post by 350matt » Sat Nov 10, 2018 10:00 pm

Bududom tish!

to my mind the area increase is secondary to the fact it starts the turn earlier and so reduces angle and so the pressure drop over the port 'should' be a lot less

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Re: exhaust port major chamfer...

Post by PeteH » Sat Nov 10, 2018 11:54 pm

I'm with Carl on this one. It's not as simple as "bigger is better". I wouldn't be surprised if the REC port actually reduced power. For reasons.

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Re: exhaust port major chamfer...

Post by 350matt » Sun Nov 11, 2018 8:18 am

I'd be surprised if that was the case Pete they seem like a reputable firm and its quite a bit of effort to go to for no gain

I think its telling that the profile of the port also seems to follow the RB port and its just the entry point of the port that's been modified so the opening area of the throat is probably unchanged but hopefully the pumping loss over the port is improved

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Re: exhaust port major chamfer...

Post by PeteH » Sun Nov 11, 2018 9:31 am

They are very reputable, and seem to be one of the best rotary engine firms in the world. But that doesn't mean this modification definitely adds power. If you sell mods based on the potential power increase they will generate then you have to prove it. I've never seen any proof from REC that this mod works. There is no dyno run data. There is no indication of the downsides and compromises that might come with this mod (And there are always compromises and downsides).

Remember, REC didn't develop this for no gain. The gain is that they are a business, and they can charge customers, and earn a profit. That doesn't automatically mean the customer also makes a gain..... I'm sure that sounds cynical, but it's just business reality. And REC probably developed this porting with the best of intentions, hoping it would genuinely add power. But that doesn't mean it actually works. Trust REC if you like, but I only trust dynos.

The thing I like about RRP's work is that they prove everything. Everything is dyno'd, and they don't release any modifications until they are shown to work. Then they tell you the compromises as well.

Each to their own, and all that, but nothing's going on my car until I know it works. No-one's got any idea what this REC port does, because REC haven't said, haven't provided any information, and certainly haven't provided any proof. In fact, this port method isn't even explicitly mentioned on their web site.

I've got no vested interest either way. I'm just suggesting to people that if we want to chase genuine power then we need genuine proof. That shouldn't be too much to ask.

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Re: exhaust port major chamfer...

Post by 13Black » Sun Nov 11, 2018 10:22 am

This post contains assumptions and generalisations on the internet, you have been warned etc yada yada.

I haven't bothered to check the timing change of that REC port, but going off of a general 50' target BBDC exhaust valve opening time...and taking into account the extended stroke degrees of a rotary and converting it into 'piston speak' :-

From factory; a 192 only opens its exhaust port at 27' BBDC (quite late), and a 231 only opens slightly sooner at 33'.

The earlier peripheral exhaust setups get much closer to a 50' target.

So it's not out of the question to extend the opening time based on some engine fundamentals.

It's only a tiny piece of the puzzle though. What's more important is exhaust closing. We need another 20-30 degrees extended onto the exhaust closing time to get decent overlap and shut it off after TDC. I can't see that happening though, at least not without some ingenuity and downsides (cost, longevity?, emission failures).
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Re: exhaust port major chamfer...

Post by 350matt » Sun Nov 11, 2018 10:37 am

Fair enough Pete

I too would love to see a before and after dyno, its sadly very rare on this platform

OK off on a slight tangent though to pick up mr 13 blacks suggestion of variable overlap

how about a modified port just on the centre ports? and then modify a manifold to have a wastegate controlled exit pipe
that way the engine would run off the outer ports for idle and low speed and at high engine speed you open the middle ports up with the overlap?

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Re: exhaust port major chamfer...

Post by 13Black » Sun Nov 11, 2018 10:53 am

Nice idea, but in true rx8oc style: I don't think it'd work out very well.

Lots of faff, all for passing emissions while only making a bit more power. Where's the market?
If you need that power, you're probably not going to give a hoot about emissions as it'll be a trailered track toy or something.

Also wouldn't you still get overlap at low revs? Just with less exhaust flow? Wastegates probably not flowing very well either. And I don't know what kind of crosstalk you'd get between chambers with it shut, if any, but it's something my brain is trying to picture without coffee.
If I'm picturing that incorrectly then my bad.
I'm not sure how you'd modify the exhaust port to close later without munching a seal within the first 180 degrees of the engine's life.
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Re: exhaust port major chamfer...

Post by PeteH » Sun Nov 11, 2018 11:35 am

I'm not so negative about Matt's idea. The Siamesed ports are a big issue though. The shut valve would definitely cause horrible effects (I think the exhaust port opens just as the other rotor reaches peak pressure :shock: ). But that just suggests doing two valves, one on the front header, and one on the rear.

I wonder how much more retarded you could get the exhaust ports to close, before running into water galleries.... Then I wonder if the gains out weigh the complications.

I do agree with Nick, that such a mod would only be done by people that don't need nice slow speed behaviour, so just do the porting without the valves....

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Re: exhaust port major chamfer...

Post by 13Black » Sun Nov 11, 2018 12:14 pm

I did joke a little about revs new fancy race thingy being an exhaust bridge but it'd be interesting to see why it can't be done. I'd assume because of the housing chamfer cutting very close to the water seal being fine on the cool intake side, but having a squillion degrees of burning stuff running that much closer to it may pop it somewhat prematurely.
And then, you're only really gaining a couple more degrees overlap methinks.


If you really have that budget for more power, why not just spend a lil more and 13B-REW or 20B swap for yuuuuuuj more powerments.
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Re: exhaust port major chamfer...

Post by jondkent » Sun Nov 11, 2018 12:36 pm

I was wondering that. There must come a point when that is a more sensible route than trying to get an extra power. Does seem very expensive route to take for so little gain otherwise.

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Re: exhaust port major chamfer...

Post by delta0 » Sat Feb 16, 2019 9:42 am

It seems a lot of this porting is guess work/trial and error. Anyone aware of the methods/tools used to simulate this? Then we could get a better idea of how and when the gases need to enter/exit before cutting metal.
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Re: exhaust port major chamfer...

Post by 350matt » Sat Feb 16, 2019 9:53 am

I very much doubt that any of the rotary tuning firms have access to a GT power simulation, mores the pity

really does feel to me that the most worthwhile mod on this engine is to supercharge it - or add another rotor.....
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Re: exhaust port major chamfer...

Post by PeteH » Sat Feb 16, 2019 10:25 am

Tricky. I don't even think you can flow bench a rotary, because the rotor has to be in two different places for the intake and exhaust.

I wonder if any commercial engine software package has been designed with rotaries in mind.... Do you think GT Power can do it Matt?

We can use the principles of piston engines to define reasonable values for port timings and areas, and Mazda do publish some numbers for port area versus rotor position. So that helps.

I guess the only real ways to do it are:
1) Do loads of experiments and iterate to the best solution.
2) Spends big bucks on a general purpose CFD package, then spends months developing a full combustion model. Then spend many more months playing with port options to optimise the flows.
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