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I've searched around a little bit and asked a few very well known Rotary porting experts and they pretty much all agree that opening the intake ports earlier and leaving the closing stock, would create better torque for turbo application.
Can anyone else add to this, I'm just trying to understand how/why? |
who knows. my ports open earlier and close later...
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on a non renisis engine the intakes open ~25 AFTER top dead centre. most piston engines open the intakes 25 degrees BEFORE top dead centre. the rotary is like that because physically the exhaust port being where it is adds overlap, and too much overlap is bad for emissions. the renisis has a different exhaust port layout, and that lets them open the intakes earlier
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Because boost aids in the expantion of the chamber. And the further you port into closing (porting up), the closer you port into the compression stroke, or at the least, maximum expantion of the chamber.
Brutal oversimplification, but may give you an idea of how it works. |
https://www.nopistons.com/forums/pub...DIR#>/wink.gif
Originally Posted by R.P.M.' post='843908' date='Nov 3 2006, 10:13 PM
I've searched around a little bit and asked a few very well known Rotary porting experts and they pretty much all agree that opening the intake ports earlier and leaving the closing stock, would create better torque for turbo application. Can anyone else add to this, I'm just trying to understand how/why? This is true for all engines, and is why bridge/peripheral porting is nice for rotaries, and tight lobe center camshafts are nice for piston engines. The idea is that you can get more port open time without having to close the port really late. The later you close the port, the more intake reversion you get at lower RPM, which hurts volumetric efficiency and thus torque. There an additional effect where you get more reversion simply because the airflow velocity in the port, and thus the air's inertia, isn't very high at lower speeds, so reversion is easier. In a piston engine, having more duration also allows you to get more valve lift. In a rotary which HAS no silly valves, you get the dual benefits of more port area, and a better geometrical shot into the chamber. It's like Stalin said, no action should have only one purpose https://www.nopistons.com/forums/pub...DIR#>/wink.gif |
Ahhh...well that makes perfect sense now!
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The closing, even of the stock turbo ports is after bdc on the chamber. Porting this up shifts the torque peak upwards in the rpm range. At low rpm, there isnt enough inertia in the incoming air to overcome the port being open into the compression stroke. As the RPM's climb, there is enough inertia to overcome the reversion, and the extended port timing increases the flow of the port, allowing for more high rpm power.
The earlier opening has another effect not mentioned. The chamber volume is increasing rapidly as the engine passes tdc. The closer to tdc you can open the intake port, the more force the rotor will be able to create drawing air into the chamber. On top of that, you still have the longer port timing. |
Originally Posted by heretic' post='843961' date='Nov 4 2006, 02:15 PM
https://www.nopistons.com/forums/pub...DIR#>/wink.gif This is true for all engines, and is why bridge/peripheral porting is nice for rotaries, and tight lobe center camshafts are nice for piston engines. The idea is that you can get more port open time without having to close the port really late. The later you close the port, the more intake reversion you get at lower RPM, which hurts volumetric efficiency and thus torque. There an additional effect where you get more reversion simply because the airflow velocity in the port, and thus the air's inertia, isn't very high at lower speeds, so reversion is easier. In a piston engine, having more duration also allows you to get more valve lift. In a rotary which HAS no silly valves, you get the dual benefits of more port area, and a better geometrical shot into the chamber. It's like Stalin said, no action should have only one purpose https://www.nopistons.com/forums/pub...DIR#>/wink.gif As I say focus on the port advance and not the close. Port size has little to do with it and causes allot of DEI harm do to reversion of the rotors especially in NA motors. If you port late a little later on the exhaust can help add a bit of overlap to combat the low RPM reversion from the loss of VE. |
how come nobody has put a lot of emphasis rpm, and intake manifold/runner length, plenum size, etc... lots more to it than JUST port timing.
different opening and closing will make power at different rpm ranges. generally, more overlap = higher rpm, less overlap = lower rpm. |
Originally Posted by guitarjunkie28' post='844040' date='Nov 5 2006, 09:04 AM
how come nobody has put a lot of emphasis rpm, and intake manifold/runner length, plenum size, etc... lots more to it than JUST port timing. |
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