The Technical Questions Thread

[culver]

Here is an OK picture kind of showing the difference.
http://upload.wikimedia.org/wikipedi.../B6-v6_180.png

In the boxer engine the opposite piston pair moves in opposite directions. So the pair is either moving towards or away from each other. This helps balance out the movement of the pair of pistons. In a flat V setup the opposite pistons move together (both right or left at the same time). This would normally create a very bad imbalance and is why you would never see this setup in say an opposed twin engine. However, since the V12 is basically 2 I6 motors the left bank and right bank are each balanced so the switch from I6 to V12 doesn't affect the balance of the system.

A boxer V12 would be possible but it would add a bit of length and extra machining cost to the motor. The machining cost would be because you have more crank journals to machine. The length would be because you simply can't pack the connecting rods as tightly if you don't share the crank journal. I believe all of Porsche's opposed 12s were also flat V12s rather than boxer 12s.

[NSXType-R]

Originally Posted by culver

Here is an OK picture kind of showing the difference.
http://upload.wikimedia.org/wikipedi.../B6-v6_180.png

In the boxer engine the opposite piston pair moves in opposite directions. So the pair is either moving towards or away from each other. This helps balance out the movement of the pair of pistons. In a flat V setup the opposite pistons move together (both right or left at the same time). This would normally create a very bad imbalance and is why you would never see this setup in say an opposed twin engine. However, since the V12 is basically 2 I6 motors the left bank and right bank are each balanced so the switch from I6 to V12 doesn't affect the balance of the system.

A boxer V12 would be possible but it would add a bit of length and extra machining cost to the motor. The machining cost would be because you have more crank journals to machine. The length would be because you simply can't pack the connecting rods as tightly if you don't share the crank journal. I believe all of Porsche's opposed 12s were also flat V12s rather than boxer 12s.

Thanks a lot for the info!

[Kitdy]

I just read that Ducati's 2-1-2 exhausts? Would not a straight 2 exhaust be freer flowing?

[TVR IS KING]

I don't really know where to ask this...So here goes. Is it easy to get mold out of floor carpet? And how would this be done? My beloved '88 Pulsar has some mold in the floor, I'd really rather it not be there. There doesn't seem to be any source of water either.

[fpv_gtho]

I dont know how you'd get it out short of physical removal. Maybe theres some product out there that can kill/neutralise it without having to deal with holes in the carpet or stumping up for a new carpet.

[pimento]

Exit Mould? Worked in my shower...

[culver]

Originally Posted by Kitdy

I just read that Ducati's 2-1-2 exhausts? Would not a straight 2 exhaust be freer flowing?

Speculation here, it's likely a better setup for exhaust scavenging over a wider RPM range. In general straight pipes are only well tuned for 1 RPM setting. Combining the flow from multiple cylinders is often better for a wider range of speeds. The break back into 2 might be for packaging. Sometimes cars will use dual mufflers because they package better than a single larger muffler. It's possible this bike is doing something similar.

[Kitdy]

Originally Posted by culver

Combining the flow from multiple cylinders is often better for a wider range of speeds.

Why is this?

[2ndclasscitizen]

It's both a packagaing and styling issue. Ducati have had twin exhausts for ages. As for packaging, because of the L-twin layout it'd be hard to run two full exhaust pipes and a decent size. They'd also be pretty fecking loud.

[Bob]

Originally Posted by Kitdy

Why is this?

the amount of time a pressure wave take to travel from the exhaust valve to the end of the muffler and back is fixed by tube length (sort of, but also affected by other things like gas temp) but anyway, that means that if each cylinder has its own exhaust, it will work really well when the low pressure part of the wave hits the exhaust port when its open, and really poorly when the high pressure wave hits the exhaust port when its open. That means you have a very peaky powerband.

Running two exhausts into one tends to let them cancel each other out, resulting in a flatter powerband.

[NSXType-R]

Quick question- what's happening in a 911 when there's liftoff oversteer? Is it just because of the momentum of the engine because of a transfer of weight from the rear wheels to the front wheels?

[johnnynumfiv]

Originally Posted by NSXType-R

Quick question- what's happening in a 911 when there's liftoff oversteer? Is it just because of the momentum of the engine because of a transfer of weight from the rear wheels to the front wheels?

I can ask at work since we take care of a few racing 911's, but I think its because you are unloading the suspension and you loose some traction on the back tires.

[LeonOfTheDead]

Basically when your braking (that's the case, mainly), there is a "transfer" of weight to the front wheels.
The thing with all cars is that this way the rear end is "lighter" and can be moved elsewhere more easily.
The thing with 911s is that even if the rear end is "lighter" (that's because the gravity force is partially contrasted by the transfer of weight) it still weight a lot, more than in other similar cars, and therefore even if moving it it's easier now that it is partially suspended up in the air (if we could say so) what you are doing is moving a big mass which is eventually more difficult to manage and handle.

[TheScrutineer]

When you come off the throttle you are freeing up the rear and transfering weight to the front. With a 911, unsettling it and transfering the weight to the front is going to result in oversteer. Because a 911's engine is unusually mounted overhung at the back, it acts as a pendulum meaning oversteer can be a little quick and frightening. This is especially true in old 911s (pre 996). With a little skill it can be corrected and put a smile on your face.

High speed oversteer in the wet on the road in an old 911, the likely hood is you will die!

[NSXType-R]

Thanks a lot guys!