AXMDR787BOY

That doesn't make it 2.6 litres...

Displacement is a measure of volume, that what you don't seem to understand. It doesn't matter how many times you spin it. The volume will never change.

You seem to have failed a basic geometry class somewhere so I won't even bother to explain how the 650cc figure is generated.

I am fully aware that there is no replacement for displacement; however, I dislike people that are self proclaimed "experts" that go around making claims about things they clearly have no understanding of.

Like I said, displacement is a measure of volume, nothing else.

I understand that, but that has nothing to do with the displacement of the engine.

What is you point here? You go a long way to say nothing.

Do you measure a sphere the same way you measure a cube? It isn't a piston engine; therefore, you cannot measure it as one. Let us go back to the point of all this. Displacement isn't a measure of air intake. It is merely a measure of internal volume. It is the same as a boat in water. Do you have to dunk the boat in water twice to figure out how much water it displaces?

This isn't physics this is simple geometry. The rotary engine is FAR more efficient volumetrically speaking than any piston engine. Fuel efficiency is another subject. While the underlying issue here is that DISPLACEMENT IS A MEASURE OF VOLUME not efficiency. Why can it spool a turbo like a 2.6? Because the rotary IS volumetrically efficient, pumping far more air than its piston counter part. Also the exhaust pulses are far closer together and come directly out of the combustion chamber into the exhaust. Thermodynamics is not the subject here.

It's good at what it does, move air. Can a prop engine move as much air as a turbo jet engine?

There are 6 combustion chambers though aren't there? So at any give time per rotor there is one face in the intake stage and one in the exhaust stage, this somehow changes the internal volume of the engine? You don't know how stupid you sound. This is geometry here.

Jesus, you are an idiot.

Nihilanthic

Do you not realize that if you closed all the valves in a piston engine at any part of its rotation, at all, right now, and took out the spark plugs and filled the cylinders with water, unless youre getting compression ring leaks you would have exactly HALF of the rated displacement?

The problem here is the WAY you measure displacmement doesnt match up with the way the engine operates.

A piston engines displacement is measured as the area of the bore times the stroke. It doesnt actually suck in that much air unless you spin it twice.

The spinning it twice thing is the key here youre not understanding.

The way MAZDA measures displacement is the displacement of ONE of the combustion chambers of a rotor, times the number of rotors. Fine. But, why did mazda decide to measure just one combustion chamber and not two? Are there not three?

For a piston engine, only half of the cylinders actually fire once every single rotation, while the other half suck in air and compress it. But they dont rate it at half of the displacement, do they?

The 13b engine is a 3.9 liter engine if it goes through its complete 1080° cycle. A piston engine is whatever its rated at per its 720° cycle. Mazdas displacement (which is effectively a 360° cycle...) times two, to make it by the same standard as what everyone uses and all the math is based off of, piston engines, is what I am suggesting.

A 2.6 liter 4banger would have a per cylinder volume of .65 liters. But, if you made the valves close all the way, the rings sealed, bla bla bla, should you pull the spark plug sand fill with water and measure the water, at ALL times it would be effectively 1.3 liters. Same for a 13b!

The thing here is the mechanics of the rotary and how they're quirky and dont match up with the math that was designed with piston engines in mind. That is the standard that everyone goes by, so the rotary whic h is a latecomer to already established rules has to adopt to it, not the other way around!

You have to compare EVERYTHING by the same cycle here, or the numbers dont match up. You know what BMEP is? Its "Brake mean effective pressure" - its a measure of how efficient the engine is and how well tuned, and its much better than something as paltry as "torque per liter". BMEP = 150.8 x TORQUE ÷ DISPLACEMENT (in cid).

Now, if you want to find that out for a rotary engine, you HAVE to do it by twice what mazda says it is, or it will not work. Why?, you ask? Its a well known and established fact that rotary engines are inefficient with handling heat of combustion to make power, and burning all of the fuel/air mixture. But, if you divide the torque x constant by half as much as the displacement actually is, you get a BMEP thats far too high for any N/A street motor. That doesnt add up, does it? Nope!

Going by 2.6 liters, you get 155.87 psi. Actually rather respectable. Going by 1.3 liters, you get 311.74 psi. Thats absolutely ridiculous. No N/A engine is capable of getting that, youd have to be using nitrous, Supercharging, or Turbocharging to do so. Now, to put this in perspective, a S2K gets... about 185.59 psi. Thats very good for a street motor... honda engines are known to have high specific power, and as a side effect of how obsessive they are to get that high specific power they also get good specific torque (or BMEP), for comparison, a stock LS1 gets about 164.63 psi. Another respectiable thing.

Oh, and if you want to do this easier, just do torque/liter... feh.

Another thing you should look at a lot of the math out there for piston engines, a lot of them have a "/2" in them, the constant part of the equation is already divided by two, because it takes two revolutions to fill the whole engine, compress, ignite, and exhaust.

A rotary takes THREE, but 1080 degrees is not 720! To make it fair, youd go by the same cycle, 720.. or do all piston engines by a 360 cycle like Mazda uses.

Get it now? Mazda goes by how much the engine can move in one rotation. We all go by two. I realize your arguement for mere static displacement, but what id challenge is why only ONE rotor face, why not two? Why not all three? (Comparo time) A EJ25 is... 2.5 liters in 720 degrees of rotation. a 13b is 3.9 in 1080 degrees of rotation. If go by 720, a 13b is 2.6 and a EJ25 is 2.5. If both go by 360, the EJ25 is a 1.25 liter and a 13b is 1.3. If both go by 1080 then the rotary is 3.9 and th EJ25 is 3.75 liters.

Apples to apples, not apples to oranges. IF you really MUST believe that the rotary is a 1.3 liter, then its 1.3 liters, just twice as fast as a piston engine, so its effectively a 2.6 liter engine. But, its not somehow having 160-200% V/E, that I can assure you... without the use of forced induction!

Also, I figured Id add this in:
Mazdas way doesnt make sense, becuase if it is in fact a 1.3 liter its somehow 160-200% volumetrically efficient. A naturally aspirated 13b moves air just like every other engine thats all natural - VACUUM. It *SUCKS* the air in! You can get slightly over 100% VE with a vacuum based induction engine if you use exhaust scavenging (overlap) and tuned length of the intake runners, and various types of manifolds, or Peripherial Ports with velocity stacks. However, there is no ******* way to get air in there at 2BAR without a turbo or supercharger working at effectively 1BAR. Mazda arbitrarily decided to use just one rotor face x # of rotors to measure displacment. Thats fine. However, all the math has to be re-written for Mazda's displacement to work - because it does not make sense. The laws of physics dont change just because its a rotary engine.

Go ask a professor at a college to explain it, becuase Im sick of repeating what I say. It moves air at the same rate as a 2.6 liter engine and its not somehow getting 160-200% VE operating purely by vacuum with no outside compressors - and engine compression doesnt change the amount of air in it. You could compress it 1:2 or 1:100, its still only x # of liters in displacement. The intake needs if you size a throttle body or carburator is the same as a 2.6 liter, the exhaust gas coming out is just like a 2.6 liter, and *gasp* the tach signal is SUSPICIOUSLY like that if a 4 cylinder engine, having one spark event per 180 degrees.

****, if you still dont believe me, try to tune a megasquirt on it and say its 1.3 liters and see where your VE% tables lie. If its a 1.3 liter engine than the tach should read twice what it does now, or everything simply doesnt add up. And its not the laws of physics that is wrong, its the way mazda measures it.

NissanConvert

iTrader: (1)

sr20det + garret gt28 "disco potato" = respectible power, near stock turbo lag. the rb26 would be a silly engine to put in a seven you'd have to baby the throttle all the time. not to mention the expense of all the fabrication, plumbing etc. the rb20 has better torque than the sr20 weighs just a little bit more. when i was a nissan follower i wanted to go rb25. more displacement than the sr20, only 200lbs heavier than the ka24. less fabrication than the rb26. i'm not a real big fan of the ca18. i've never really seen anyone do anything impressive with it. so you lose displacement add a turbo... might as well just turbo a ka24.

as for the geometry, im not getting involved.

MrDirt

The CA block is the base platform for the RB series. I really like the RB20/25 as well, which is why I also really like the CA.

travisorus rex

Just exactly what does that make it?

Mikey

i like the idea

AXMDR787BOY

Dude, it's simple geometry. With a piston you take the bore and stroke and calculate the volume of the cylinder and multiply that times the number of cylinders. Viola! We have static displacement. It is a little more tricky with a triangle that follows an elipticroid pattern but is basically the same thing.

Displacement IS NOT a measure over time. It is a static measurement.

Nihilanthic

Hey braniac, heres the formula for how you calculate the airflow needs of a Piston engine:

CFM = (Displacement in cubic inches x max rpms you will run at)/1728*2 * VE%

BTW, 1728 is how many cubic inches are in a cubic foot. Guess where that ******* 2 comes from? The engine has to spin TWICE!!! Oh, btw, 1728 x 2 = 3456, if you look online for formulas to size this, youll see that constant if theyre doing it in CID.

Static displacement doesnt make sense the way mazda does it, because they measure only one rotor face, yet a piston engine has all of its piston faces measured. What gives? But at any rate, static displacement doesn't make sense.

*YOU* clearly dont understand, or dont WANT to understand (because 1.3 sounds so much better to you) what Im trying to say, but I'll re-explain it ANOTHER way to see if you get it.

A piston engine cycles air through all of its combustion chambers every 720 degrees. Thats why you have a times two in the constant you divide by for the CFM formula .

A 13b is a 3.9 liter engine per 1080 degrees. You spin it three times, go through all of the combustion chambers - the full cycle of a 3 rotor wankel - and its a 3.9 liter engine. However, the rate at which everyone goes by is 720 degrees, so if you go by 720 out of that 1080 cycle you get FOUR rotor faces, which is... ba da da dam 2.6 liters.

Thats why it sucks in air at exactly the same rate as a piston engine thats 2.6 liters per 720 degrees of crankshaft rotation.

Yeah, displacement IS a static measurement, but you really dont seem to be able to explain why mazda can rate their engine at 1/3rd the actual displacmeent of the engine! 3.9 liters obviously doesnt make sense, because it goes through all of its cycles at a rate 50% slower than everyone else. If you have a 2.6 liter piston engine it fills squeezes burns and exhauts all of its cyls in 2 rotations. A 13b will move 2.6 liters of air through four combustion chambers complete in2 rotations as well, hence why its compared to a 2.6 4banger, but it still has those two other rotor faces to go with.

Because youre comparing a 720 to a 1080 degree cycle its hard for some people who dont have enough background in physics to digest, but I can very well say its bullshit to go by ONE ROTOR FACE. Thats 360 degrees!!

If you want to change the arguement, that everything SHOULD go by what it does in one rotation, just like mazda does, the rated displacement of every piston engine in the world would effectively be halved. Youre confusing how mazda rates (one third ) of the displacement of a 13b with how it actually WORKS.

Now, Ill repeat AGAIN, you seem to either not understand (or not care to try to understand) my posts. A 13b is a 3.9 liter engine, except its ful cycle is 1080 degrees, or 3 rotations. Piston engines use a 2 rotation cycle. The only way its a 1.3 liter engine like mazda says it is if it does it twice as fast as everything else (which it doesnt, its really a slow 3.9 liter engine you DO know the rotor moves one third of a rotation per e-shaft revolution, right?).

So, yes, its 'complicated' to figure out the displacement of the swept area of one side of a lenerux triangle moving in an epitrochroidal movement. Spiffy. Thats NEVER been my arguement. Dont quote me as "blah blah blah" if youre unable to comprehend it. This isnt middle school.

AXMDR787BOY

Stop using air flow as the basis of your argument. This isn't about air flow.

There seems to be one thing you don't get. Rotary engines are measureed for THE WHOLE chamber, not individual rotor faces. This is why I asked if you measure a cube the same way you measure a sphere. You cannot compare the measure of the two in any shape or form.

If you measured the maximum volume for one rotor face in the peak of the intake/exhaust stage it would only be about 300cc's. So you can stop anytime now.

I am no rotary lover by any strech of the term. I don't *WANT* the motor to be 1.3litres. It is what it is. You seem to want it to be more than that. You are the one TRYING to FIND a reason.

This isn't a new arguement. Smarter men than you have accepted the facts for what the are years ago.

NOPR

[QUOTE=Nihilanthic]Youd be trading DOWN displacement... going from 2.6 to 2.0. QUOTE]

how many liters does your ford turbo 4 have?

To the postrer, if youre going to put a damn turbo 4 in an RX-7, atleast do it right. SR20 is pretty retarded though, its still a high maintenance engine when you start pushing horsepower.

LT1-10AE

STOP THE BICKERING AND GET BACK ON TOPIC

I'm going to go on a banning spree if these threads keep turning into crap. Don't worry, it'll be a short spree.

driftex

i like the idea. i think it it is a little more reliable and there is also probably less of an over heating problem. Then there is the cool factor, as far as non rotary engine swaps go, this is the coolest (sorry V8 guys).

psychotic7

keep the rx7 light and nimble, like they are supposed to be. dont ruin them by putting huge gas guzzling v8's in them. the sr20 is a great canidate when it comes to engine swaps bc the aftermarket potential is crazy. though sr20's are rather expensive bc of the popularity. would an rb20 be cheaper? they have great potential as well.

LT1-10AE

Have you read anything at all regarding to weight differences OR fuel economy in V8 swapped cars? Didn't think so.

Research before you post.

psychotic7

i know they get better gas milage bc the rx7 is lighter but a turbo four banger will get kick *** milage and enough performance to satisfy anybody. i know its hard to believe but there are some people out there like me and half the people on this forum who dont like v8's. they swallow up all the engine bay room and trust me rx7 owners love that and they throw off the weight distribution and handling.

LT1-10AE

Again, you do not know what you are talking about. LS1/T56 FDs retain their original weight within the difference of the weight of a battery and corner weights are spot on.

Even using the iron block LT1/T56, my car is actually TAIL heavy by 60lbs. A tail heavy car that gets damn near 10MPG more than it's original configuration is a winner in my book.

So, that being said, you are welcome to your opinions and dislike of other engines, but stop spreading misinformation and myths. All it takes is a simple click of the "search" button above to find tons of information about V8 car weights, performance, handling and economy.

This section is for informing and helping others interested in other engine swaps, not for spreading false information. This isn't the lounge.

psychotic7

there is NO WAY at all, no matter how you look at it that a turbo four banger rx7 gets less mpg than a v8 and there is NO WAY it handles better....less weight=better mpg+better handling. all it takes is to pay attention in physics. with that said quit getting off topic and help the guy with his SR20 issue and quit trying to throw the unreliable gas hog at him. anyway dude, i say go for it, but be warned the sr20 has poor boost response, that is another reason i threw in the rb20

LT1-10AE

I never said anything about what engine he should put in his car. It's his car and his choice.

I have been challenging your claims of V8s being overweight and gas guzzling. You spread misinformation and I'm just here to correct you on it.

Nihilanthic

You clearly havent ever even seen published weights of how much various engines weigh. Also, because the weight is well behind the front years (the engine is behind the strut towers, and the transmission is behind the engine...) the weight addition is to the CENTER of the car.

You mean to tell me adding weight to the CENTER of a car messes up handling? Go look at what PMOI means if youre into physics so much. Also, the fact that his car is 60 lbs heavier on the *** end is FACT, not opinion/

Also, I just noticed you threw a RB26 in there. Youre taking a dump on v8s and you go put a heavier, longer engine in there? PUH LEASE.

Also, a v8 can get more fuel efficiency than a 4banger very easily. If its a Boosted engine and the off boost fuel maps are too rich, guess what? Bye Bye MPG. If you have a cam or porting there for meant for high airflow under boost, and/or at higher rpms, guess what? There goes your MPGs. You have to first look at all the variables, then isolate which ones matter for what youre trying to look at.

That said, a SR20DET running a good EMS (unless the stock one is good enough, Im not SR20 guy) will probably get good MPG. Then again, the 30 mpg highway reported by people who have done v8 swaps isn't imaginary. Its real. Youre being closed minded.

I myself am going with a turbo 4 - because the one Im going for is an even bigger bang/buck than with a v8 if youre willing to deal with the lack of torque off boost. And guess what else? Its BARELY ligther than a 302 or a LS1.

Check your facts, or use the search button. This has been addressed over and over and over, and the facts speak for themselves.

MaxDuo

Displacement is the number one thing to look at when swapping an engine in your car. Not mpg, hp, torque, weight, reliability, or fuel type.