j9fd3s

i notice that mazda between the turbo 2nd gen, the cosmo and the 3rd gen keep making the runners larger; the cosmo is HUGE, but the port timing/opening stays almost the same

Sesshoumaru

http://www.yawpower.com/techindx.html



good site





thanx for the help I am understaning the concepts a bit more.



I hate living in a world of equivalent trade............

Lynn E. Hanover

The 6 port is an example of the attempt to keep runner velocity high all through the RPM range. As the revs get high enough to develope a breathing problem with the small primary ports, the secondary ports begin to open. The period of time that the intake ports are open goes way up and this allows good velocity to be maintained in both sets of runners all through the RPM range.



You have read on this site that some people have run the secondary ports 100% of the time, and in short order, they have gone back to the stock setup. Total runner velocity is less than half of what it should be, and the engine becomes lazy and soft at low revs. The mid range is poor as well, and you cannot cover the gear changes with anything like the power that should be available. So you end up with a top end only engine, that gets to its top end very slowly. Not a good combination for fun driving.



There may be a tendency to think ourselves into a corner on this stuff, or worse, combine data points from incompatible situations.



The turbo versus nonturbo engines are only similar in basic design. The breathing problems that limit the NA engine around 300 HP with less than 14.7 pounds of boost, (one bar) are not present in the turbo engine.



Think about this. Torque times (X) RPM = HP. This is Mr. Watts formula for determining how much work is being done. Or, in plain talk your ET. There is an accounting for mass. An accounting for time, and an accounting for distance.



One way to increase HP, is to force the engine to produce more torque at a given RPM, or the same torque at a higher RPM. When you look at a HP graph you see the HP peak as a function of RPM. So this is the intake opening time being shorter and shorter as the RPM increases. The cylinder filling goes down with RPM increases (smaller aperture time) just like a camera. So the upper limit of a NA engine has much to do with inlet runner length (tuned length) and the turbo engine is limited by the mechanical strength of the engine components. Even though the new engine may return Mazda rotaries to the USA, it will not be caught producing 900 HP with its tuned length induction system. That will be left to the turbo engine.



The only difference is that more than 100% cylinder filling can be maintained to the highest RPM attainable. Short aperture times limiting breathing, is simply overcome with added pressure. Suppose for a second that we could develop an engine that could live at 12,000 RPM. Ceramic rotors, Titanium crank, every bolt a precision fit dowel pin. The advantage is that cylinder filling thanks to the turbo(s) could be over 100% through 12,000 RPM, and if you can do that, the torque at that RPM could still be quite good. Now refer to the formula.



Torque X RPM = HP. Even if you loose a few foot pounds to internal friction and cylinder filling, that 2,000 additional RPM will still give you some monster HP numbers. I am thinking 1,500 HP easy.



The point is that the NA engine will never have more than 14.7 pounds of boost. That is only available at sea level. The new engine uses tuned length induction to attain more that 100% cylinder filling over a broad range of RPM.



This has to be one of the most incredible pieces of automotive engineering in 50 years. But it was a compilation of known data points. putting it all together was the achievement.



Lynn E. Hanover

bill shurvinton

This is where I like the way the Euro 6-port is implemented compared to US. We have no sleeves, allowing more freedom in the runner porting and the secondary butterflies on the LIM that replace the rotating sleeves are closed by vacuum, not opened by back pressure.



Only problem is that they block a good chunk of the runner up with the spindle.



I am convinced that there is a great street engine trying to get out with the 6-port, especially now that fly by wire throttle controllers are readily available as are ECUs that can control them. One day....



As to the NA power limit, it is purported that Guru racing in Australia have a monster bridge port combined with a 2-part eccentric that is producing some 360+HP at well over 12,000RPM. Way non-streetable, but interesting. I haven't seen dynonumbers to basck up the HP claims, but the car the engine is in certainly seems to win races.



Bill

83turbo

Okay, so I recently read an SAE paper from Mazda (~1984 or so) showing a J-bridge ported 12A making 270 ps at 8000 RPM. 270 ps ~=265 HP. This should scale to ~300 HP @ 8000 RPM for a 13B (correct?).

VE at peak HP was substantially below max VE of the engine.

1 - should it be possible to alter the porting so that best VE is moved to a higher RPM, resulting in more power @ 8000 RPM? (presumably narrowing the power band)

2 - if the VE depicted here at 8000 RPM can be maintained at 12000 RPM, assuming the same BSFC, 450 HP should be attainable at 12000 RPM.

If Guru is making 360 at 12k, is it VE or BSFC that is coming up short compared to a 300 HP engine? I would guess that heat loss to the cooling system goes down with increasing RPM, so any drop in BSFC would come from pumping losses.

3 - back to the first engine. The paper depicted 3 different porting styles, all with the same open/close points - side bridge (no rotor housing cut), J bridge (with rotor housing cut), and peripheral. J bridge seemed to have the best powerband, although peripheral peaked higher. Why would the peripheral fall short on torque through a good deal of the RPM band? It actually had less port area than the J bridge, so velocity problems seem dubious. The only BSFC graph shown was vs. BMEP at 7500 RPM, and it didn't explain the disparity at that point.

j9fd3s

yes, this seems to be a problem with the forums, we dont get all the info/circumstances nor do we know if its a valid sample...





ive kinda thought of a turbo as just a bigger na, and i guess bigger runners would be a plus if you can use em?



yes if you drive an rx8 where you can ring it out it feels a lot different that say my gsl-se, it never seems to run out of breath, even way up at 9500. i thought it had decent power too, i took one out at thunderhill in group 2 and i was passing people, despite the fact i was really hacking away at the wheel

Lynn E. Hanover

Well.............



I can answer those questions/statements, but it will take about 300 pages and a lot of research.



The short version is this:



VE stands for volumetric efficiency and is a figure usually smaller than 100% and is the displacement of a pumping system vice its actual output in CFM at a specific speed. There are pumps and compressors that don't spin, so there is not always an RPM to publish.



So if you turn an engine with very short port timing, very slowly you can get just about 100% volumetric efficiency less the swept displacement lost to timing.



There are systems that can use tuned port runner length an exceed 100% VE.



So say you have a one rotor that displaces one cubic foot per revolution after porting losses, at 100% VE at 1000 RPM it would be pumping out 1000 CFM. The new Mazda is over 100% over a large portion of it's operating range. It is tuned and red lined to not make it all available on the street. But it has good torque, so it covers the shifts well and "feels" strong. It is rated at 238 HP for us stupid US customers, but in other locations it can be had with much more right out of the showroom. It should have been noticed by now that the best VE, and best torque is just about in the same place on a HP graph. It all fits together does it not?



So that is VE.





BSFC, stands for Brake Specific Fuel Consumption. It is reported as pounds per horse power hour. Not much help is it?



That just means that for each horse power the engine generates on the dyno, it is going to consume x amount of fuel in one hour. Numbers below .40 are good. Numbers over .55 are bad. The good or bad are the fuel mileage at the test RPM.



So you would plot that as a curve that covers the whole RPM range, and you would want to investigate a wide range of throttle settings, as well as mixtures and ignition events. So to do a good job on just one engine change the mfrs may have a day or a week of dyno time.



It is sort of a measurement of how efficient the engine design is at recovering the energy in the spent fuel.



I care not how efficient the race engine is, and I doubt that you care either. You already know that if you keep your foot in it all night, showing off, you will need a fuel stop before work tomorrow. If you knew the BSFC for each time through the rev range, what could you do with it?



So the difference is VE. And having the best VE (usually close to best torque) closer to max RPM means more HP. Because the formula: Torque x RPM /5252 = HP means that moving the best torque up the rev range does two good things. It gives you an engine that can cover the shifts with better power down low, and it picks up peak HP.



How much torque must the Aussies have at 12,000 RPM to produce 360 HP?



Lynn E. Hanover

kahren

its 157.67 tq that seems pretty good, unless that number is at the flywheel then thats not so impressive.

White_FC

If your talking about us Aussies and high powered BridgePorts...

check out this link..



It's a thread all about intake setups and what not for the IPRA (racing class) bridgeport engines. (no cutting into the rotor housing at all)



a small bit of info from there..

"At the fly we made 180hp 3500rpm, 260hp 6000rpm & 303hp 10200rpm. "

Thats what I call a good powerband..



Ps that is not a figure from guru racing either, their engines do put out more...

Good read none the less.

83turbo

What I was more or less getting at with my questions was this:

We know that high VE is attainable over a wide RPM range - this much is

documented. Torque peak with a peripheral or bridge port can be fairly

high. However, 360 HP at 12k isn't actually alot of torque (at that RPM

- we don't know what the peak torque is). Any clues on what the VE is

at this sort of RPM, or what is realisitically attainable? Likewise, is

BSFC at stratospheric RPM inherently different from what you might expect

to see at maybe 8000 RPM?

Normally if you want to move the power band up to a higher RPM, you can

delay port closing a little more - does this trick keep working or is

there some point where you just aren't going to get any more revs out

of it? (like when piston speed outstrips the flame front in a piston engine)