| Author | Message | ||
| Frank Parker (Parkerfe)
Intermediate Member Username: Parkerfe Post Number: 1696 Registered: 9-2001 |
No, a TR has a Flat V12 just like the Boxer. The only boxer street engines I know of are from Porsche. | ||
| Jeff Green (Carguy)
Junior Member Username: Carguy Post Number: 158 Registered: 10-2002 |
So that means my Testarossa has a boxer engine? | ||
| Mitch Alsup (Mitch_alsup)
Member Username: Mitch_alsup Post Number: 318 Registered: 4-2002 |
Consider a twin cylinder engine with pistons arranged at 180 degrees to each other: let us look at two crankshaft arrangements, a double throw crank at 180 degrees/throw, and a single throw crank. An engine where there are two throws on the crank will have the pistons at TDC at the same time, at BDC at the same time. This engine will not move to the left or right because the weight of the moving mass stays centered over the center of the crank shaft. BMW motorcycle engines use this arrangement, so do 6 cylinder porsches. Same two cylinder arrangement, but the crank has one throw. Here, when one piston is at TDC the other is at BDC and vice versa. The center of mass moves with the crank shaft. This engine will lurch left then right as the pistons move along their stroke. This motion looks like a boxer throwing punches. And that is why it is called a boxer. | ||
| PSk (Psk)
Junior Member Username: Psk Post Number: 73 Registered: 11-2002 |
Hehe, would be a rough little engine (BMW flat twin) if they both fired at the same time ... be like a single. In the end who knows, it really is just a term used by journo's ... and the sales people. Pete | ||
| Steve Magnusson (91tr)
Intermediate Member Username: 91tr Post Number: 1363 Registered: 1-2001 |
Tim N -- I agree that the term "boxer" has been diluted by Ferrari, Subaru, VW, etc. to now only mean "flat" (to the point where it's hard to even research what "boxer" used to mean). Pete -- I believe the R-series BMW motorcycle engines were the origin of the "boxer" designation (but I don't know whether the cylinder ignition sequence is alternating or simultaneous) 1923 BMW R32 R32 engine cross-section (I love the size of the connecting rod throws) | ||
| Tim N (Timn88)
Intermediate Member Username: Timn88 Post Number: 2120 Registered: 6-2001 |
These definitions are all confusing as hell. I thought a boxer engine was anything that was flat. | ||
| PSk (Psk)
Junior Member Username: Psk Post Number: 67 Registered: 11-2002 |
Interesting:
Thus if this is required for a true boxer engine, then an Alfa Sud engine ALSO is not a true boxer engine, as both cylinders do not fire at the same time. Many books refer (correctly?) to the Alfa Sud engine as a boxer ... I do not know of any engine then that could be classified as a true boxer on this definition. Pete | ||
| Mitch Alsup (Mitch_alsup)
Member Username: Mitch_alsup Post Number: 314 Registered: 4-2002 |
"Does anybody know what the 312F1 Ferrari engine is, ie a boxer or 180 deg?. I know that it only has 4 main bearings compared to the 7 in the road engine." According to "Art and Science of Grand Prix Driving" Nikki Lauda: The 312T2 engine was a pair of inline 6 cylinder engines mated on a single crank. This means that two con rods share a common throw. "Boxer/Flat 12 vs. 120-60 deg V12: +Lower CG, Better balance. -Wider. " The only real issue with the BB and TRs is that they designed the transmission to sit under the engine, raising the engine, and with it, the center of gravity and (negitively) influencing the handling characteristics. | ||
| Steve Magnusson (91tr)
Intermediate Member Username: 91tr Post Number: 1358 Registered: 1-2001 |
A true boxer crankshaft typically isn't as stout/rigid as a 2-con-rods-per-throw crankshaft when restricted to the same overall length (since there's an additional web of material between the throws taking up space and adding effective "length" to the boxer crank lowering its torsional rigidity) -- not a big deal on a small displacement 36hp air-cooled VW 4 cyl or a small motorcyle design, but not the greatest on compact high-output 8+ cyl designs. Add-in the extra machining/complexity Pete mentioned for the boxer-style crank and you can see why the auto industry quasi-unanimously adopted the 2-con-rods-per-throw design early on. An air-cooled VW Volkswagen 4-cyl has a boxer style crank, but I'm still not sure that I'd even call it a true boxer engine design since opposing cylinders don't fire simultaneously (although the opposing pistons do reach TDC simultaneously). | ||
| PSk (Psk)
Junior Member Username: Psk Post Number: 65 Registered: 11-2002 |
Alfa Sud engine is a true boxer engine as both the front pistons reach TDC at the same time, thus both pistons a moving out and in at the same time. I assume this must have some sort of force balancing ... Naturally this means that the crankshaft is more complicated than a horizontally opposed crank (ie. the opposing cylinders do NOT share a crank pin). With a 12 cylinder engine I think the force balancing would not be such an issue as with a 4 cylinder, thus simplier, shorter and lighter crank design would be my priority. Does anybody know what the 312F1 Ferrari engine is, ie a boxer or 180 deg?. I know that it only has 4 main bearings compared to the 7 in the road engine. BTW: Great little engine the Alfa Sud boxer  , although heavy. Pete | ||
| Peter S�derlund /328 GTB -88 (Corsa)
Member Username: Corsa Post Number: 298 Registered: 4-2001 |
As all of you and Matthew stated: A "Boxer" needs to have paired pistons (on opposite sides) at Top Dead Center at the same time, while the Ferrari flat 12 has one at TDC and one at BDC? Makes sense to me. Boxer/Flat 12 vs. 120-60 deg V12: +Lower CG, Better balance. -Wider. What about Flat 12 vs. true Boxer then? And which car has a "true" boxer engine? Ciao Peter | ||
| Steve Magnusson (91tr)
Intermediate Member Username: 91tr Post Number: 1349 Registered: 1-2001 |
Yes (per my definitions) | ||
| Matthew F (Mateotnt)
New member Username: Mateotnt Post Number: 24 Registered: 7-2002 |
So, to clarify: A "Boxer" needs to have paired pistons (on opposite sides) at Top Dead Center at the same time, while the Ferrari flat 12 has one at TDC and one at BDC? | ||
| Frank Parker (Parkerfe)
Intermediate Member Username: Parkerfe Post Number: 1687 Registered: 9-2001 |
Matthew,I never said that a Ferrari Boxer was not a "true 180 degree" machine. See my prior post. I said it was not a true boxer engine, and it isn't. It is a 180 degree V12 or a flat 12. In fact, that's what Ferrari calls it in my car's manual literature. And, a V6, V8, V10, V12, V16, or whatever engines can be at what ever degree a manufacturer choses, not just 60 or 90 degrees as stated in your post. | ||
| Steve Magnusson (91tr)
Intermediate Member Username: 91tr Post Number: 1344 Registered: 1-2001 |
I think Subaru also plays a little fast and loose with the "boxer" designation in their literature/advertising. IMO the classic "boxer" definition is what TomD is calling "horizontally-opposed" and the "two con rods per crank throw" is the modern "V" configuration -- and I'd characterize both a true flat boxer and a 180 deg V12 as "horizontally-opposed". So the confusion comes from everyone using slightly different definitions... | ||
| TomD (Tifosi)
Intermediate Member Username: Tifosi Post Number: 2426 Registered: 9-2001 |
this was posted by mitch in another thread There are two kinds of flat 12s: a) horizontally opposed, and b) boxer. The horizontaly opposed has a porsche-like crankshaft (one con rod per throw--two throws 180 degrees apart per pair of pistons) where paired pistons more in opposite directions. Since each pair of pistons are perfectly balanced with each other, only rotational vibrations are induced. The boxer has two con-rods/pistons on a single throw. This style is a V with 180 degree firing order. This style is known as boxer, because these engines box back and forth, rotating on an axis perpendicular to the crankshaft (think verticle); left front to the left (say 2 mm), then right front to the right (again 2 mm), and repeat. As you know, a 12 cylinder engine can be balanced perfectly (1st order) when the bank angle is a multiple of 720/12 == 60 degrees. So there can be 60 d V12s, 120 d V12s, and 180 d V12. What is not known is that correct choice of rod length to stroke can result in perfect second and tertiary balance. Therefore, the boxer flat 12 is a 180 degree V12! See "Design and tuning of competition engines" | ||
| Matthew F (Mateotnt)
New member Username: Mateotnt Post Number: 21 Registered: 7-2002 |
I disagree with Frank's statement. Ferrari Boxer engines are indeed true 180 degree machines. Any 180 degree engine is, by definition, a boxer engine. Whether it is in a BMW motorcycle, a Porsche, or a BB. 180 degrees means that each cylinder bank is directly opposed to the other bank. Bengines are also known as "flat" engines, as in Porsche's older flat four. Most Ferrari V-12s, on the other hand, are in 60 degree vees, while V-8s are 90 degrees, because 360 (a full revolution) is divisible by these numbers. A boxer engine (the same as a 180 degree engine) is usually more smooth. Because it is "flat," it is also generally wider but less high than a V-engine. | ||
| Frank Parker (Parkerfe)
Intermediate Member Username: Parkerfe Post Number: 1685 Registered: 9-2001 |
A true "boxer" engine has the oposite pistons moving toward each other in the cylinders as in two boxers fighting. The 365GT4BB, BB512 and BB512i have the pistons moving in the cylinders as in other standard V12 designs, hence not true boxer engines. | ||
| Peter S�derlund /328 GTB -88 (Corsa)
Member Username: Corsa Post Number: 297 Registered: 4-2001 |
The 512 BB got a 180 deg V12. Could someone please explain the difference and pros & cons of these two 12 cylinder designs? Ciao Peter |