Whats the difference between Flat 12 and V12?

flat or boxer engine like BB512/Testarossa or Subaru or Porsche 911 has 180 degrees "flat" horizonaly opposed stroke between companion cylinders......that's why it's called boxer as it's like a punch counter punch. V4/6/8/10/12/etc has a "V" degree like 60/90/and all sorts of wierd degrees in F1 like Renaults 111 degree. VRod Harley is a V where a lot of the BMW motorcycles are flat.....RAdial is like the old Pratt & Whitney Prop planes with the cylinders opposing each other around like a pin wheel.........

Understand a bit better now?

 

Yes a benefit of a flat configured engine is that the weight of the engine is lower, and this helps with handling.

The benefit if a V configured engine is that it can be placed in a narrower engine bay. For example in an F1 car they can make it engine narrow to help with aerodymanics.

 

From purely a performance perspective, there aren't any dramatic differences. Said another way, you'll get similar specific output (everything else being equal) from a V as a boxer cylinder configurations. Surprisingly, however, the harmonic balance is usually slightly better (more moderate and even) with a V configuration. As suggested earlier in the postings, it's really about engine size/packaging, and, keeping the center of gravity as low as possible.

 

Wikipedia to the rescue!

http://en.wikipedia.org/wiki/Flat-12

They say what I was going to but better and certainly less work for me

 

D Moore - Scott's reference is important to read, for it points out that the difference between a flat and V-12 is not merely the geometry, but whether the opposing pistons share a crank journal.

Technically, the Boxer engine is a V-12, that happens to have a 180 degree V angle. The journals of opposing pistons are shared.

Jim S.

 

Jim, let me get this right, Flat is a V?

 

As I have always understood it, there is a difference between a 180 degree V and a true boxer engine. The 180 degree V has rods that share the same journal or rod throw so the pistons shuffle side to side rather than approach each other then go away from each other. A boxer engine has individual rod throws that cause the pistons to approach and depart as they reciprocate creating crank case pressures as they compress the crank case air. The 180 degree V eliminates this characteristic. Porsche's have boxer engines. I thought there was a difference between a TR and a BB engine like boxer vs 180 degree V. Is that true?

P

 

No -- both TR and BB are a 180 deg V-12 (just count the crankshaft throws on the SPC illustration). A true "boxer" engine design is Okish on a 4 or 6 cyl package, but, on 8 cyl and up, the crankshaft gets too "noodle-ly" (or must be very bulky to have the same stiffness and then the interia is high and the engine is not compact). Also more costly as you just have more crank journals to finish.

 

also boxers are more difficult (or rather more time required) to work on.

in the example of the evo vs. STi, the evo has pretty easy engine work, but the STi requires lots of pieces to be removed to do the simplist of jobs (like a spark plug change)

 

Yup! clear as mud. I know I'm missing something.

 

yep you are correct, there is no counter punch on a BB or TR like on a Porsche.....been schooled

 

An example from a car I was working on today..
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Cool, here's a true boxer I was working on today.....
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I'm not too familiar with Porsches. Is that a 962?

 

Fun reading. I learned something as well.

 

you are correct.

 

There is a very practical reason which ernie cited. It doesn't look to possible to me that a Ferrari Boxer engine could fit between the front wheels of of a front engine Ferrari, assuming you want to be able to go around a corner. My 330 GT has a pretty big turning radius as it is. Performance and center of gravity are nice, but front engined cars have a basic restriction!
I would guess there was very little time wasted on that decision, once the front engine configuration was chosen.

Cheers
Warren

 

Last time I looked Subaru's (and Alfa Suds) where front engined cars and they still manage to go around corners. A flat 12 is only going to be longer NOT wider than a flat 4. Pininfarina DID make a front engined 4 door prototype Ferrari with the BB engine ...

BTW: Do not get too excited about the Boxer term, one of the most abused or mis-used terms relative to engine design ever. After all even Ferrari mis-used it with the Berlinetta Boxer as as we have just discussed that flat 12 is NOT technically a boxer engine at all but a 180 degree v 12 as each pairing of cylinders DO share a crank throw.

Pete

 

Not comparing apples to apples.
If I unfolded my V-12 Engine to a Flat-12 (a fair comparison if only the layout is the issue) there is no way it could fit. But of course engines could be designed to fit any dimensional requirement, so yes, one could put a some kind of a flat 12 into my 330. But there would have to be some compromises.
Then there is Subaru - who claimed in their Ad a few years back that they had an engine "just like a Ferrari". One of my pet peeves regarding advertising claims.

Cheers
Warren

 

The engine bay of an Alfa Sud is wider than most ... I guess. Note also that Alfa Suds have macpherson strut front suspension that takes less room.

Anyway Pininfarina made it work , so it's possible, but maybe NOT in your cars engine bay.
Pete

 

The Porsche 917 flat 12 boxer solved the whippy crank problem by using a power transfer gear in the center of the crank (essentially 2 flat six engines joined together). That configuration helped with the stiffness of each half and resulting harmonic balance.

 

Actually, not wishing to be a smart pants, but the Alfa Sud (and 33) had the engine in front of the front axle. The gearbox was longitudinal behind the engine. This meant that the assembly was actually quite narrow in the area required for tyre turning clearance. The engine itself actually took most of the width of the car.
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