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View Poll Results: Flat/Boxer vs Rotary. Vote for your fav
Flat/Boxer 3 100.00%
Rotary 0 0%
Voters: 3. You may not vote on this poll

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Old 02-11-2012, 07:51 AM   #1
knightjp
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Flat / Boxer vs Rotary

Reading up on the these engines and they seem to have their own following. Both show strong merits of good balance and smooth handling. However the boxer engines are used more in automotive applications than the Wankel.

Due to complete difference of these engines, I was told there are no real ways to compare them I guess. A small rotary engine does produce almost the same power, if not more, of a reciprocating engine double its size.

So far I've noted that the Rotary engine does lack in terms of low end torque, and fuel efficiency. However these are soon to be rectified in the up coming 16X engine from Mazda (so rumored)... Another factor are the reports of it being a high maintenance one.
So far I haven't found anything much about the Boxer engines in terms of maintenance issues, etc... I'm sure there are, I just haven't found any.

So lets use this thread as a fact gathering knowledge base... I wanna know the advantages and disadvantages of both from an engineering perspective to known maintenance issues and faults / flaws, etc...

http://www.youtube.com/watch?v=ATTPB...layer_embedded
http://www.youtube.com/watch?v=pZyDL...layer_embedded
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Old 02-11-2012, 04:33 PM   #2
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Re: Flat / Boxer vs Rotary

A very nice resource for Rotary engines.
http://www.rebuildingrotaryengines.com/
For are sure a lot of sites for the Rotary engine even though it only appears in one car... and a few engine swaps.
Have noticed that apart from the 2JZ motor from Toyota and Nissan's Skyline engines, Mazda's 13B and 20B 3 rotor are among the fav swaps for Tuners. I never see Boxer engines chosen for swaps that much unless the project car came with it in the first place.. Any reason why???
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Old 02-21-2012, 09:21 AM   #3
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Re: Flat / Boxer vs Rotary

Here are two new concepts for Rotary engines...

Doyle Rotary Engine

Liquid Piston Rotary

I wonder how these concepts compare to the Wankel.
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Old 02-21-2012, 10:56 PM   #4
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Re: Flat / Boxer vs Rotary

Very interesting videos
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Old 02-22-2012, 10:28 AM   #5
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Re: Flat / Boxer vs Rotary

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Very interesting videos
They're extremely interesting concepts. Frankly I'd like to see either of these concepts in an actual car. There are probably so many prototype engines being researched and invented, but here we are using 100 year old technologies just because its easier than trying something new.

I guess these guys should present their ideas to Mazda. Probably the only manufacturer who has the guts to try something new. Yes it nearly bankrupted them, but look at the RX7 and RX8... They worked wonders with those Wankel units...
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Old 05-01-2012, 07:55 AM   #6
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Re: Flat / Boxer vs Rotary

Probably a crazy question to ask, but... Can anyone explain why Subaru is only able to get 252BHP from a 3.6L Flat 6 and Porsche can get somewhere about 296BHP from the same size engine???
I know both are well engineered engines with DOHC, etc and have impressive reliability. I thought Porsche helped Subaru develop the EZ series engines, so why the big difference in power???
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Old 05-07-2012, 12:47 AM   #7
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Re: Flat / Boxer vs Rotary

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Originally Posted by knightjp View Post
Probably a crazy question to ask, but... Can anyone explain why Subaru is only able to get 252BHP from a 3.6L Flat 6 and Porsche can get somewhere about 296BHP from the same size engine???
I know both are well engineered engines with DOHC, etc and have impressive reliability. I thought Porsche helped Subaru develop the EZ series engines, so why the big difference in power???
You've gathered some interesting information about rotaries and boxer engines, I must say, I'm impressed

Though the power difference explanation is easy. It comes down to a few things.

Firstly, compression ratio. The Subaru EZ engine runs off of 87 regular octane with a compression ratio of ~10.5:1 (I think. Don't quote me on it), it also has specialized exhaust manifolds to increase scavenging; they are also unrestrictive and placed quite low overall on the vehicle, which gives good cooling characteristics. The Porsche on the other hand, does NOT run on 87 regular; it runs on a higher octane, and it also has a higher compression ratio for that reason... I don't remember the exact ratio of the Porsche engine, but the fact it's higher gives it more power.

Second; exhaust system. Simply enough, where are the two engines placed? The Subaru has a front engine whilst the Porsche has a rear engine. The rear engine will have a shorter exhaust that is more free flowing. It isn't a "better" exhaust manifold than the Subaru one, but it is more friendly to high-end horsepower because it is shorter.

Third; intake. While the difference in intake is minimal, the position of the engine also makes the intake systems of the vehicles different. As a proportional result, the intake of the Porsche also is more friendly to high-end power than the Subaru.

Fourth; tuning. Simply enough, it's a Porsche vs a Subaru. Of course the Porsche is tuned moreso for power and performance than being frugal and lean.

All these differences and other littles ones make up for the power difference.

Also, boxer engines do not have "similar reliability issues" such as a rotary engine has. The boxer is simply an inline engine that got chopped in half and flipped 90 degrees (so to speak)... It's still a reciprocating engine. It has it's benefits and disadvantages over inline/V engines just like rotaries do, as well as different forms of inline and V engines, but they do not have "different" reliability issues that a normal everyday inline 4 would have; unlike the rotary.

Edit: Woops, also wanna slip in and provide an answer for the "why are rotary engine swaps so common" question. The answer is also quite simple; they're small (adaptable to most engine bays), light weight, extremely high revving, produce a unique sound, and have a VERY big aftermarket; and while they are low on torque, they are usually swapped into lightweight japanese cars; which makes it so that the high revs and sufficient torque provide exceptional performance for the application.

You don't see boxer engines being swapped often because maintaining them is a bitch. Sure, they're also small and produce quite a bit of power; but just to simply change the oil of one requires the whole engine be taken out. Working on a boxer is a pain.
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Old 05-07-2012, 04:11 AM   #8
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Re: Flat / Boxer vs Rotary

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Originally Posted by elemein View Post
Edit: Woops, also wanna slip in and provide an answer for the "why are rotary engine swaps so common" question. The answer is also quite simple; they're small (adaptable to most engine bays), light weight, extremely high revving, produce a unique sound, and have a VERY big aftermarket; and while they are low on torque, they are usually swapped into lightweight japanese cars; which makes it so that the high revs and sufficient torque provide exceptional performance for the application.

You don't see boxer engines being swapped often because maintaining them is a bitch. Sure, they're also small and produce quite a bit of power; but just to simply change the oil of one requires the whole engine be taken out. Working on a boxer is a pain.
Seriously?? For boxer engines, you need to take the engine out just to change the oil?? I find that hard to believe.

If Rotaries are so popular in terms of applications in Japanese sports cars, and are easier to work on than Boxers, why are there no votes in the above poll..?

I love the rotary engines... Would have liked it if they made more low end torque...
But I'm not totally convinced that the boxer engine is a complete dog either..
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Old 05-07-2012, 04:47 AM   #9
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Re: Flat / Boxer vs Rotary

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Seriously?? For boxer engines, you need to take the engine out just to change the oil?? I find that hard to believe.

It's true because of the way they're designed. The block in a boxer engine is at the very bottom of the assembly, and alll the accesories are on top of it; basically making the top of the engine block unaccesible. Therefore to change the oil you need silly putty hands, or you need to remove the engine. The reason you dont need to do this for normal inline or V engines is because all the accesories are located on the sides of the engine; a boxer takes up a lot of horizontal space and cannot have many accesories on its' sides.

Edit: Though I forgot to include that this is not true for ALL boxer engines. Only most older designs and some newer ones. Some newer boxer engine designs have the oil refill system at a position that is accesible from the top of the engine. This is uncommon as the top of a boxer engine is, for lack of better words "a mess" normally though it is not unheard of. More modern Subaru's will have this, and probably some Porsche's too. Though I have never taken a Subaru engine out for an oil change, so I can't testify to the Subaru E series engine's, but I surely have taken old Porsche engines out.


If Rotaries are so popular in terms of applications in Japanese sports cars, and are easier to work on than Boxers, why are there no votes in the above poll..?

I voted in that poll myself, I was the second person to vote boxer. I too like rotaries, but they are not very torquey engines.

I love the rotary engines... Would have liked it if they made more low end torque...

There's a reason they produce lower torque It's mostly because of leverage. I could explain in more detail but I'm going to assume that you already know why they produce little torque at low RPM.

But I'm not totally convinced that the boxer engine is a complete dog either..

Certainly is not They're tough little engines
Replied in bolds

Though let me shed some light on the oil change subject; as even myself have started to try to recall which car needed the engine taken out to replace the oil; and I've come across an example.

Subaru Impreza '08 = NO external oil filter. Nonserviceable
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Old 05-07-2012, 07:01 AM   #10
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Re: Flat / Boxer vs Rotary

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Replied in bolds

Though let me shed some light on the oil change subject; as even myself have started to try to recall which car needed the engine taken out to replace the oil; and I've come across an example.

Subaru Impreza '08 = NO external oil filter. Nonserviceable
I bet the oil filter is designed to last longer than most considering it needs the engine out to change it. But I think that to change the oil alone you need not remove the engine from the car.
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Old 05-07-2012, 12:19 PM   #11
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Re: Flat / Boxer vs Rotary

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I bet the oil filter is designed to last longer than most considering it needs the engine out to change it. But I think that to change the oil alone you need not remove the engine from the car.
Changing the oil without changing the oil filter? A filter designed to last longer?

A filter is just that; it filters debri and impurities in order to keep the oil clean to a certain degree for as long as possible. The condition of your filter is directly proportional to the condition of your oil because your oil is continously being run through the filter (and impurities). If the oil is dirtier or equal to the amount of impurities on the filter, it will either shed it's impurities or pass through untouched.

Putting new oil into a car and not changing the filter will result in the filter giving it's impurities to the new oil; making it just as dirty as the oil that was in it before it; therefore making the oil change useless.

If you have a fish tank, imagine it like that. Changing out the water to control impurities and waste is great and all, but no matter how pure the water is, the second it passes through a dirty filter, it will pick up all the dirt the filter has.

Your oil is only as clean as your filter is basically.
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Old 05-08-2012, 04:25 AM   #12
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Re: Flat / Boxer vs Rotary

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Changing the oil without changing the oil filter? A filter designed to last longer?

A filter is just that; it filters debri and impurities in order to keep the oil clean to a certain degree for as long as possible. The condition of your filter is directly proportional to the condition of your oil because your oil is continously being run through the filter (and impurities). If the oil is dirtier or equal to the amount of impurities on the filter, it will either shed it's impurities or pass through untouched.

Putting new oil into a car and not changing the filter will result in the filter giving it's impurities to the new oil; making it just as dirty as the oil that was in it before it; therefore making the oil change useless.

If you have a fish tank, imagine it like that. Changing out the water to control impurities and waste is great and all, but no matter how pure the water is, the second it passes through a dirty filter, it will pick up all the dirt the filter has.

Your oil is only as clean as your filter is basically.
Thanks for the clarification... Didn't know that... Over here ppl only change the filters every other oil change... :P
Right now, I'm guessing that's bad practice....
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Old 05-08-2012, 06:27 PM   #13
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Re: Flat / Boxer vs Rotary

Lots of cars used to spec filter changes at every other oil change. A properly running engine won't generate enough crud to plug up a filter in the typical 5000 mile interval specified by many manufacturers, let alone the 3000 that people seem to live by. Its just become habit to change it every time.
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Old 05-10-2012, 07:36 AM   #14
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Re: Flat / Boxer vs Rotary

Saw this video posted on another thread... Just thought I'd share it... here...
http://www.youtube.com/watch?v=DiVXj...layer_embedded
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Old 01-26-2014, 09:49 AM   #15
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Re: Flat / Boxer vs Rotary

Sorry to revive such an old thread but i have to correct some seriously wrong info.

Now im only talking about subaru ej series engines used since 1989 in ALL subaru models.

There is no need at all to remove the engine to do an oil change. The oil filter is on the bottom of the block directly in the space inside the header. No tools needed to remove it. Jack the car, reach up and unscrew. I can do my oil change in about 20-25 minutes on a normal day.

Drain valve is also the lowest point on the entire engine so you can get a full oil drain without having to angle the block to do a complete change. I have a fumoto valve that makes the oil drain a joke.

This includes the 2008 imprezza, no it has the exact same oil change system.

They have changed the oiling system as of the 2013 fxt/brz (same new FJ series engine)


As for the reliability of the suby boxers... If you dont go for crazy power and do your regular oil changes they typically last about 160K miles before having head gasket issues. That is typically the biggest problem with boxers, is that the head gaskets wear out or at least start weeping oil after a long period.

There was two known engines runs that had issues... 04-05 head gasket problem ( manuf defect in the head gaskets) and in early 09 wrx/sti's due to bad #4 piston rings ( again manuf defect.. Both issues were fully covered under warranty).

The main reason why people dont swap to boxers is due to oiling issues. Under high G corners that are sustained for 5-7+ seconds the boxers get oil starvation in one or two same side pistons and the engine dies. To avoid it you need a dry sump which cost 3-5k or so. So they cost 2-3 times more then a 2jz series for usually less power. This is why the 911's cost more... They come with dry sumps from what i understand.
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