D-4S Thread

[serialk11r]

Oh shite never knew about that. I guess I learned something new today.
Then...dry sump? Is that a possibility? The engine in the FR-S is very low...this car has a lower CoG than a Porsche Cayman but with a lighter engine, which means they were pretty clever about placement. A Porsche Cayman has DS though so...

OH and this reminds me, I wonder how Valvematic engines get along without DS, as there isn't ever a manifold vacuum, and not nearly enough flow at low speeds. I suppose all BMW cars are dry sump? M series run it for sure, and every new non-M series is Valvetronic equipped.

[old greg]

Originally Posted by serialk11r

Then...dry sump? Is that a possibility?

Not at this sort of price point, and it wouldn't really reduce the amount of oil vapor in the crankcase anyway.

And on the topic of CG height, there is very little improvement to be had from a dry sump system on most engines. Production car engines have rather large diameter clutches and flywheels that limit the height of the engine once the oil pan is no longer the limiting factor. And on a flat engine you also have to consider the exhaust manifolds as well.

A dry sump is all about maintaining adequate oil pressure under sustained high g cornering. Lateral acceleration causes the oil in a wet sump to slosh to the side of the oil pan, potentially allowing the oil pickup to feed air to the oil pump (causing very bad things to happen to your crankshaft and rod bearings). This is especially an issue on a horizontally opposed engine, as oil will tend to pool in one of the cylinder heads during a turn. This will cause the level of oil in the sump to continually fall, making a loss of oil pressure more and more likely the longer you maintain a high-g turn. More than a few Subaru engines have been killed this way.

[Marrk]

The oil-air separator and catch can go before the pressurized part of the system? Is that correct?

[TheBetterMethod]

The catch can connects between the PCV valve and the intake tract.

Pressure pushes the vapor out of the crankcase through the PCV valve, then into the catch can, where the vapor drops out.
The clean air flows out of the catch can into the intake tract.

[Marrk]

Originally Posted by TheBetterMethod

The catch can connects between the PCV valve and the intake tract.

Pressure pushes the vapor out of the crankcase through the PCV valve, then into the catch can, where the vapor drops out.
The clean air flows out of the catch can into the intake tract.

Right. But the D-4S is a pressurized system. The fuel rail is pressurized.

[serialk11r]

Originally Posted by Marrk

Right. But the D-4S is a pressurized system. The fuel rail is pressurized.

Fuel rail != intake manifold? ...
There's a positive net flow of air into the engine, so this still works.

And regarding dry sump, what do people do when they want to track a car with a wet sump?

[TheBetterMethod]

Fuel pressure has no baring on the pressure in the crankcase which is caused by blow-by.

In any fuel injection system (multiport, direct or otherwise) the fuel is pressurized to feed the injector. The injector is nothing more than an electronic valve with a nozzle. The direct injectors run on higher fuel pressure levels so that the fuel can be injected into the pressurized cylinder. Also the higher pressure makes for better atomization of the fuel.

The only thing that pressurizes the crankcase is the blow-by gases. The PCV system doesn't compete with the fuel pressure in the fuel rails.

[markitect]

Originally Posted by serialk11r

And regarding dry sump, what do people do when they want to track a car with a wet sump?

Most cars on most tracks are wet sumps. The pump sits in enough oil that you won't run out of oil unless you reach some number of Gs for some amount of time. The big question is how long is that amount of time (basically if no oil is making it into the pan how long before the pan empties).

On Most tracks you don't have turns with enough G's for long enough time for you to run out of oil in the pan. Just make sure you aren't at the minimum oil level and you will be fine.

If your concerned you can do any of the following
1. Get an oil pressure gauge, and keep an eye on it (warning light is a good idea).
2. Baffle the oil pan, with trap doors so oil doesn't leave the pan in high Gs(Toyota/Subaru will do this, but that doesn't mean it can't be done better)
3. Add an oil accumulator, so we have some more time before you stop getting oil sprayed.(less then $300)
4. Dry Sump (more like $3000)

[Dimman]

Originally Posted by PAImportTuner

He hasn't owned a sports or high performance car with DI. He does not know that carbon build up on DI is almost 3 times the amount on normal PI vehicles. Unless the manufacturer implements a system to wash away the intake system every couple thousand miles it will continue to build up.*

*Not even BMW has made a system to "wash away" carbon.

That is one of the points of D4-S' port injection. And why it is superior* to regular GDI systems, like their original D4 direct-only system.

* That is actually what the 'S' stands for.

[Marrk]

^^^ Dimman, I don't understand.

[Ryephile]

He's trying to reiterate the point I made yesterday in saying that the port injectors keep the carbon build-up to a minimum while retaining the benefits of the direct injection setup.

[Marrk]

Originally Posted by Ryephile

He's trying to reiterate the point I made yesterday in saying that the port injectors keep the carbon build-up to a minimum while retaining the benefits of the direct injection setup.

Point taken. But on a car that both the manufacturers and the buyers hope will have the sh*t flogged out of it, what sense does that make? I've read that WFO and high-revving will increase carbon build-up.

I'm not buyin' this car to run it down to the market for a loaf of bread. If you know what I mean.

Thanks.

[serialk11r]

That is a good point, if you're always driving it at WOT then the direct injectors will be used most of the time, giving more opportunity for buildup.

But you're not always going to floor the gas, at least I hope you wouldn't be for the safety of the people around you on the road, and that's when the port injectors "wash" your intake valves So at the very worst, it won't be as bad as a typical VW GDI system.

[Marrk]

Originally Posted by serialk11r

That is a good point, if you're always driving it at WOT then the direct injectors will be used most of the time, giving more opportunity for buildup.

But you're not always going to floor the gas, at least I hope you wouldn't be for the safety of the people around you on the road, and that's when the port injectors "wash" your intake valves So at the very worst, it won't be as bad as a typical VW GDI system.

Ah! Now I get you!

Thank you, sir!