Lexus developing million dollar super car - report

[Dimman]

Well that depends on the timing, right? What the 3 stages can do is to pump up the bottom like we are discussing but also the top end which will reduce the need for as large as ports. Plus probably somewhere in the middle. They can also be timed to jump over the bad waves.

[serialk11r]

The thing is this, the sound wave does not create a consistent increase in flow at all, it reflects back pretty quickly. The amount of time the valve is open is longer than the time the sound wave hangs around the cylinder.

It would be nice if someone like arghx7 could explain lol.

[Dimman]

Originally Posted by serialk11r

The thing is this, the sound wave does not create a consistent increase in flow at all, it reflects back pretty quickly. The amount of time the valve is open is longer than the time the sound wave hangs around the cylinder.

It would be nice if someone like arghx7 could explain lol.

He sort of did with a cylinder pressure over time graph. It's not the average pressure that matters but the final pressure as the intake valve closes. Also keep in mind that the pressure waves have a shape/length not just amplitude.

[old greg]

Originally Posted by serialk11r

How is carbon fiber fabric usually made? I know the layup and stuff is the biggest cost problem with CF, not the material itself.

It's made on a loom, just like any other woven fabric. The fibers themselves are made from Polyacrylonitrile (a string of carbon molecules with some junk hanging off the sides) fibers that are heated in air and then run through an argon filled furnace. It's quite an energy intensive process, so the material costs are actually very high in relation to steel or aluminum. But even with metal, the majority of the final cost comes from manpower and machinery.

Originally Posted by serialk11r

I wasn't talking about filling, I was talking about the fact that the ports are very high flow and the valve lift is likely huge, so there's very little charge motion at low rpm.

Since it has drive-by-wire ITBs, it's possible that the throttle map keeps the throttle plates mostly closed at low rpm and high load to generate tumble and localized velocity. With the injectors right below the TBs, this could create pretty effective air/fuel mixing despite the low port velocity.

[Dark]

Originally Posted by old greg

Since it has drive-by-wire ITBs, it's possible that the throttle map keeps the throttle plates mostly closed at low rpm and high load to generate tumble and localized velocity. With the injectors right below the TBs, this could create pretty effective air/fuel mixing despite the low port velocity.

Sorry for my noobiness, but I have a question.
Could you explain the differences of high and low port velocity especially in this case?

[serialk11r]

Originally Posted by old greg

It's made on a loom, just like any other woven fabric. The fibers themselves are made from Polyacrylonitrile (a string of carbon molecules with some junk hanging off the sides) fibers that are heated in air and then run through an argon filled furnace. It's quite an energy intensive process, so the material costs are actually very high in relation to steel or aluminum. But even with metal, the majority of the final cost comes from manpower and machinery.

Since it has drive-by-wire ITBs, it's possible that the throttle map keeps the throttle plates mostly closed at low rpm and high load to generate tumble and localized velocity. With the injectors right below the TBs, this could create pretty effective air/fuel mixing despite the low port velocity.

Ah, thanks. The assembly process for metal parts is less labor intensive though right? I mean, this weekend I went to FSAE and they said they switched from carbon fiber monocoque to tubular steel frame + CF/aluminum honeycomb panels to save (a lot) of time, and the frame was completely hand assembled of course. I guess stampings for a production car would require expensive machinery though.

And the throttle body fuel mixing sounds plausible, thanks. Do any engines use this for certain though? Seems like motorcycle engines could benefit or something.

[SupremeMoFo]

I just wish Toyota would put some more effort into fixing the handing of the rest of their day to day models... they should take a leaf out of Ford Europe's book.

[Dimman]

Originally Posted by Dark

Sorry for my noobiness, but I have a question.
Could you explain the differences of high and low port velocity especially in this case?

One analogy that gets used is drinking straws. Compare a big and little straw. With a little straw you don't need a lot of effort to move some water. So it moves faster with less effort. But if you want to drink a lot of water quickly it becomes very hard. In the car case the straw size is the intake port and the effort is (mostly) the piston's downward speed, which is rpm dependent.

So that's sort of how port sizing affects the velocity.

Now for velocity differences you can use a garden hose analogy. An open hose moves a certain amount of water rather smoothly but a little slow. Now if you speed it up by putting your thumb partly over the opening, the water sprays out faster. But the amount of water hasn't changed. In the cylinder head, the higher velocity air entering the combustion chamber moves around more and allows the air and fuel to mix better and burn better when ignited.




(analogy's are imperfect, and so's my full grasp of what the hell's going on, but this is close...)

[Dimman]

Originally Posted by serialk11r

Ah, thanks. The assembly process for metal parts is less labor intensive though right? I mean, this weekend I went to FSAE and they said they switched from carbon fiber monocoque to tubular steel frame + CF/aluminum honeycomb panels to save (a lot) of time, and the frame was completely hand assembled of course. I guess stampings for a production car would require expensive machinery though.

And the throttle body fuel mixing sounds plausible, thanks. Do any engines use this for certain though? Seems like motorcycle engines could benefit or something.

Motorcycles do do it, some with secondary butterflies controlled by the ECU. (Kind of like a modernized version of the old 4AGE and 3SGE TVIS system.)

Also something to think of about carbon fiber, is that the term is also now applied to short strands of carbon mixed in a resin or castable thermoplastic.

Look up Polymotor (I think). Carbon fiber engine block. But it's not what we think of as the woven stuff.

[old greg]

Originally Posted by serialk11r

Ah, thanks. The assembly process for metal parts is less labor intensive though right? I mean, this weekend I went to FSAE and they said they switched from carbon fiber monocoque to tubular steel frame + CF/aluminum honeycomb panels to save (a lot) of time, and the frame was completely hand assembled of course. I guess stampings for a production car would require expensive machinery though.

In the OEM production world, yes very much so. And yes, they use very big hydraulic presses with very expensive dies that wear out and need to be replaced.

In your FSAE analogy, it depends. Fishmouthing the tubes by hand is very time consuming and labor intensive, it's easily a month-long process for an FSAE team under normal circumstances. These days a lot of teams are outsourcing that to companies like Cartesian Tube that CNC bend/fishmouth the tubes based on solid models with about a ~1 week turnaround time if they aren't too busy. Assuming you have all of your jigs ready you could go from the UPS truck to a completed spaceframe in just a day or two.

[Dark]

Originally Posted by Dimman

One analogy that gets used is drinking straws. Compare a big and little straw. With a little straw you don't need a lot of effort to move some water. So it moves faster with less effort. But if you want to drink a lot of water quickly it becomes very hard. In the car case the straw size is the intake port and the effort is (mostly) the piston's downward speed, which is rpm dependent.

So that's sort of how port sizing affects the velocity.

Now for velocity differences you can use a garden hose analogy. An open hose moves a certain amount of water rather smoothly but a little slow. Now if you speed it up by putting your thumb partly over the opening, the water sprays out faster. But the amount of water hasn't changed. In the cylinder head, the higher velocity air entering the combustion chamber moves around more and allows the air and fuel to mix better and burn better when ignited.




(analogy's are imperfect, and so's my full grasp of what the hell's going on, but this is close...)

I kinda understand your analogies. Thanks, Dimman.
So you mean the high port velocity doesn't always mean air coming in the combustion camber more, right?

[quik1987]

Originally Posted by serialk11r

F1 cars have 7 speeds, not 6 :P The V10 is cool though!

How is carbon fiber fabric usually made? I know the layup and stuff is the biggest cost problem with CF, not the material itself.

I wasn't talking about filling, I was talking about the fact that the ports are very high flow and the valve lift is likely huge, so there's very little charge motion at low rpm.

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[Dimman]

Originally Posted by Dark

I kinda understand your analogies. Thanks, Dimman.
So you mean the high port velocity doesn't always mean air coming in the combustion camber more, right?

I think faster is generally better, especially given the same volume of flow. But too fast leads to frictional losses that can reduce flow. Plus there is something about sonic choking that I don't understand yet.

Always about compromise.

But overporting chasing a volume flow number (just CFM) with no regard to the velocity is what leads to shitty response on NA motors that don't make power til really high rpm. The trick is to increase flow AND velocity which is what separates the pro porters from amateurs. Or at least increase flow and minimize velocity losses.

Aftermarket domestic porting and motorcycle porting is far more advanced than the typical import performance porting.

[quik1987]

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