Nihilanthic

I can address a few things, already:

The port size, and shape, and location determine the VE at which rpms. The cam and valvetrain of piston engines does. Later opening/closing ports, open longer, more area, work better at high rpms. Lower ones favor shorter duration, 'advanced' timing, and smaller area. So, basicalyl, a port job increase VE, so does a ported heads/new cam/bigger valves. Exhaust and intake are the same on each engine type.

The rotary is less thermally inefficient than a piston engine, so there ya go. in that regard.

Also, the amount of displacement per stroke is... well... the engines size! the VE is how much of that displacement you fill up. You want to operate in the rpm range where the VE is highest, because that will give the most torque, and brake specific pressure, bla bla bla.

Now, F1 engines rev high for one reason only - they are REQUIRED to have low displacement (3.0 liters, right?) and the way you can make more power without turbos or superchargers is to rev higher. You dont make more torque, but if you rev it high and multiply it out with a transmission, you have more power. Also, they have the intake, exhaust, and cam profile set up for high VE at high rpms. You cant have high VE at *ALL* rpms unless you do a staged port job like a renesis, or a VTEC-like piston engine. And even then youre still trading off ultimate efficency if you just focus on one area to work with... so no wonder that the F1 engies have ******* lowend than a periperial ported giatnt-turbo 10A would.

But yeah... I really need to find out the Brake mean effective pressure (I hope I got that right) and VE of rotary engines (which I dont know!) and how the trade off of hotter, faster exhaust gas for less thermal efficiency effects how turbos work with it vs piston engines.

But, well, its essentially comparable to a 2.6 liter piston engine, aka a skyline engine.

maxcooper

Piston has better thermal efficiency because its combustion chamber surface-area-to-volume ratio is lower, and thus it loses less heat out the sides of the combustion chamber and into the oil and coolant.

-Max

peejay

My N/A 12A should make about the same power at the same RPM.

Less displacement, natural aspiration, cheap gas.

The turbo was mainly there to make up for the chokeriffic small ports and luxury-car-quiet exhaust system.

speedturn

iTrader: (1)

A rotary has to open the exhaust port and start dumping the exhaust sooner than a piston motor, or else the pressure inside will begin doing "negative" work on the e'shaft. That is why the rotary exhaust temperatures are so much higher than a piston motor; it is because there is still a lot of thermal energy left inside the not fully expanded hot gases when they are dumped out. (on any engine engine, expanding the hot gases and coverting that thermal energy to shaft work lowers the temperature of the gases.) That is also why the thermal efficiency and the gas mileage of a rotary are worse than piston motors.

Nihilanthic

I see.

That might also explain why we see GT35 instead of GT30 turbos being used. when I look at the charts that compare displacement and such, youd think a GT30 would fit better. This is going with 2.6 liters displacement, of course.

YellowT2

iTrader: (1)

One other thing I didn't see mentioned is that rotaries don't have valves getting in the way of the intake and exhaust airflow. That has to help getting more air into and out of the combustion chamber with the same intake manifold pressure (especially at high RPMs).

Also, being able to spool a larger turbo not only reduces the air temp coming out of the compressor, it also reduces the backpressure on the turbine side.

Nihilanthic

Well, obviously in the top end the bigger turbo is going to win.

But, the GT35R seems to be a 3-4.5 liter turbo, and a 400-600 hp turbo, given what the PDF from Garrett says. The IMPLICATION is a GT30R would be a better fit, because that graph has it as a 2-3 liter turbo, and 300-500 hp potential.

Is it even really worth using one, though? GT35R seems to spool up mighty early on the 13B, with stock ports... but I've yet to see a GT35R maxed out!

ronbros3

JUST a thought, a piston engine has the valves in the way of flow, they only open about .400-450, so they block hi-flow, a rotary has wide open ports with nothing in the way, so it seems it would just flow more for the same size port. Plus a lot more variables. RON

ronbros3

Opps! yellowT2 said that, sorry RON

ronbros3

And it would seem that a rotary could be at 200% VE with a big turbo ! RON

Nihilanthic

200% VE if you assume its a 1.3 liter... but its really a 2.6 :P

maxcooper

Rotaries also need more air to make the same power as a piston engine, due to the high BSFC. That means they need bigger turbos, too. The GT35R is a good match for the 13B, but depending on your expectations, it may run out of steam before you want it to. The GT35R "maxes out" at less than 600 BHP on the 13B. The same amount of air flow might make 600 BHP on a piston engine, but it doesn't make that much power on the rotary. Hence the availability of bigger kits like the GT40R for the 13B.

-Max

Nihilanthic

Right.. more lbs of air to make the same power when you look at a rotary vs a piston. That still doesnt quite make sense as to how our 2.6 is spinning up a turbo that Garrett says is for a 3-4.5 liter engine. Must be the giant exhaust PP?

And.. anyone tried a GT30R? When does a GT35R REALLY max out, anyone done that yet? lol.

Kenku

Garrett's also pretty vaguely approximate in the turbo sizes they give out. To someone without enough knowledge to intelligently select a turbo, a GT35R on a 3.4.5L motor would work and be pretty lag-free. But anyone else would just look at a compressor map.

Problem with the 30R is kind of... why? And it and the 35R really are constrained by the fact that they're running a T3 hotside...

Nihilanthic

T3 hotside constrains it how, exactly?

And, wouldnt a 30R be able to get almost instant spool? And cant it support 300-500 horsepower? :P

Kenku

T3 hotside can't flow as much exhaust as the larger frame turbine sections, so at higher horsepower levels it starts choking the engine. And a 30R could maybe support that kind of horsepower on some boingers... but any decent size rotary port will be putting more airflow through it at a lower boost level than it's designed for. So it may work, but a lot less efficiently, whereas the GT35R compressor is right about in its sweet spot.

Besides which, the 35R evidently has little enough lag as is, and is about the same price... and you'll not see many people going for a smaller turbo when a bigger turbo that makes more power, at a lower temperature, and spools well is no more expensive.

Nihilanthic

I see.

Whats with the "more airflow through it at a lower boost level than its designed for"? That didnt really make sense to me, but I'm anything but a turbo guru.

Bad2ndgen

Ok here are my thoughts. Please correct me if Im wrong.

A rotary engines displacement is 1308cc's however I don't think it can be considered a four stroke engine due to the fact that it injests this much air every revolution, making it more compairible to a 2-stroke, hence the 2.6litres. This is compounded by the fact that its only roughly 250ish deg. of engine rotation before the next rotor face is starting its intake cycle, making only 110 deg. before the next cumbustion event takes place. It seems to me that even a 2-stroke can't come close to this as far as efficiency of the rotating assembly. And just think of all those dead pistons being drug through there intake cycles by the rest of the rotating assembly. This is compounded again by the fact that they do create so much exhaust energy and are able to spool such large turbo's. You will find that piston engines can accually injest more air than the turbo's that they can efficiently spool can flow. That's why you see very high powered drag car's using things like nitrous to spool the same turbo's that we put on our street cars. And all turbo's are not created equil, I think that if you go learn even the basics of reading a compressor map, you will answer your own questions on boost VS power output. All I can tell you is that the turbo that Im putting on my drag car is capible of making the same power at 15#'s as a gt35r makes at 25+#'s. The rest you can figure out.

Justin
www.alienauto.com

maxcooper

If 500 HP is the top of the range quoted by Garrett, they mean on a piston engine that uses air and fuel more efficiently. It won't make that much power on a rotary. It would spool quickly, but torque would fall off at high RPM, which is where the rotary with a properly sized turbo (not one chosen based on piston-oriented HP and displacement ranges) will shine.

And people have been running GT35Rs on the rotary for a while now. I am sure people are pushing the limits. I think 470 WHP is the highest I've ever seen for the GT35R on a 13B. No one is asking for smaller GT turbos to run on their rotaries, but people are running GT40Rs, GT42Rs, and now GT35Rs with a T4 turbine housing (bigger than a normal GT35R).

-Max

maxcooper

The rotary does use a four-phase combustion cycle, just like a normal automotive piston engine (a 4-stroke). Each chamber goes from full small to full big (intake), back down to full small (compression), back out to full big (power), and back down to full small (exhaust) before starting over. It's just that each rotor has three chambers, each at various points in this cycle, at any given time.

It is like a 2-stroke in the sense that each rotor has a combustion event for each rotation of the main shaft. But in general, it isn't much like a 2-stroke other than that.

There is a combustion event for each rotor every 360 degrees (and thus 1 every 180 degrees for a 2-rotor). Each power stroke lasts 270 degrees (ignoring port timing, and just paying attention to the basic engine geometry). Yes, the power stroke is 1/4 of a rotor rotation, which combined with the 3:1 gearing of the rotor to the eccentric means each power stroke lasts 3/4 of an eccentric shaft rotation. Strange but true. Since each chamber is always actively in some phase of the 4-cycle combustion cycle, it does "drag around" the other chambers in the process.

-Max

Nihilanthic

Interesting... lol. How do T4 housings change the dynamics of a GT35R? This really is starting to make a big more sense now. I've played around with applets for turbo sizing, and the one thing that seems to elude me is finding a damn VE graph for a 13B-REW... if anyone knows that I'd love to know that! lol

I have an idea about how the turbo map works, but I dont exactly know what to draw on it to see how the turbo will behave. Knowing the displacement of the engine would help, but I dont yet know the VE of it at different rpms. Should I just use 80% in the applets for a conservative estimation? And how does that exhaust timing and the 'sharpness' of the exhaust pulse help effect spool? Is it a quantified thing or is it something you can just eyeball based on what you expect vs what you get?

And um... what field of engineering is this covered in? I havent yet picked my major

maxcooper

Mechanical Engineering, and specifically some class on internal combustion engines would cover it, if any courses would. But largely, you will probably have to seek information on rotary engines on your own (I doubt the coverage is very deep). Still, a mechanical engineering background will help you make sense of the information you do find. I'm not a mechanical engineer, though. I'm just an enthusiast with good mind for mechanical stuff.

-Max

Kenku

Realisticially speaking, unless you spend a lot of time on your own learning stuff, and taking the basics they teach you and applying them to completely different ends, a bachelor's degree in ME won't get you too much. This speaking as someone almost through his degree, and looking at grad schools. On the other hand, it *does* give you the background to start learning horribly cool technical ***** on your own...

To be perfectly honest, I just tend to use the 10hp per lb/min of air ballpark guesstimate to get an idea of things... 40lb/min at a pressure ratio of 2 is a usable datapoint, since I think it about corresponds to average streetport dyno runs at 1atm boost, and turbos that tend to have the efficiency plateaus around there also happen to be universally known as good rotary turbos. Use cheapass approximations to get horsepower at boost levels if you don't know it... if something makes 150hp NA (stockport-ish) at 1atm you'll be looking at 300ish. So you could get away with a 30R on a stockport motor and be in its efficiency range, but not many people bother with pricey aftermarket turbo setups on stockport motors.

... not horribly scientific, but useful and really easy to apply.

GT1-20b

A few good rules of thumb: a) What a Turbo flow map shows at 1 bar above atm. ( 2 to 1 press. ratio) on the 72 + % island, is roughly 70% of what is actuaslly needed to make that much Hp based in Lbs/Hr. of air on a Rotary engine.
In other words, a healthy Rotary will require about 1/3 more Air flow, or 50% more CFM. at the same P/R. than it's recipricating counterpart rated at, or putting out the same specific power reguardles of displacement.
b) Reguardles of VE., engine type, head/valve configuration, size or geometric layout. If it's an internal conbustion, (excluding Turbines)., then Hp is best calculated based on BSPC./Displacemnt, @ a given Rpm.
This gives an estimated Air Flow required for the target Hp. @ the desired window of operation, for a given engine. Then the Air flow required in lbs/Hr. or CFM. can be reversed engeneered for the correct compresor wheel that will deliver the Air needed at the desired P/R.
c) The mere fact thet a Rotary's OTTO cycle takes 1080 degrees to complete, or 50% longer per event, and that it fires once per revolution, like a 2 stroke, should open everyones eyes to the fact that it takes MORE AIR flow to make equal power from a Rotary. Requardles of size. d) About 100 Hp/Rotor for NA's & 200/Rotor for Turbo engines is reliable for streetable engines. Obviously, PP.'s & Radically ported Hi-Boost Turbo engines don't fall into this average. come to think of it, neither does "Reliability".
e) Last, Purpose built, money no object engines, such as those used in Pro Import Drag racing or Endurance racing, also fall outside these average parameters for calculating Hp. and Airflow #'s. Especially when enhanced with power adders, or regulated by restrictors in their Inlets.

Nihilanthic

any sources to find the VE% per rpm of a 13B-REW? lol. that would help me a lot in how to figure this stuff out!

One thing I wish someone would do is blow the dough on various turbos on various port jobs and just show the graphs of it all. But, that would require big $$$, and unlikely to be seen in the average import mag.

Maybe someone could talk MAZDA into that so they make the best possible 4th gen RX-7?