My GTX3071r build

[Tmsracing37]

I am not going to set here and argue about piston design because both will work fine in the FSI. But having data on how rs4 injectors work at high rpms, higher rail pressure and very short window of time for fuel and air to mix, I believe it’s best to use a piston that can create more turbulence in the cylinder close to and at Top dead center for a better complete burn. The crowns do affect the turbulence in the cylinder and here is a good article explaining why.

Setting Your Squish Clearance





Something we emphasize a lot is the value of getting your squish clearance right. A proper squish clearance makes the motor both more efficient and less prone to detonation. When you're assembling your high performance motor project, this little detail is well worth the small amount of time and effort it takes to get it right. You'll have more power, better fuel mileage, and your motor is less likely to "ping" on you.



In the ideal world, your squish clearance should be set to about .030". Tighter than that risks piston to head contact; looser starts reducing the chamber turbulence effects that you're going for. Unfortunately, I don't think I've ever pulled apart a factory assembled engine that had a squish clearance of less than .050"! So you can see what a huge opportunity this is to improve on your motor.



So let's talk a little about what squish clearance is and how to adjust it. Put simply, a squish band is the area or areas where the piston comes in close proximity to the chamber as it passes through top dead center (TDC). Fuel trapped in this space gets squeezed out at high velocity and generates turbulence in the chamber. Turbulence in the chamber promotes better atomization and less separation of the fuel and air, encouraging it to burn

Link:
http://www.nrhsperformance.com/tech_squish.shtml

 

[Tmsracing37]

I am not going to set here and argue about piston design because both will work fine in the FSI. But having data on how rs4 injectors work at high rpms, higher rail pressure and very short window of time for fuel and air to mix, I believe it’s best to use a piston that can create more turbulence in the cylinder close to and at Top dead center for a better complete burn. The crowns do affect the turbulence in the cylinder and here is a good article explaining why.

Setting Your Squish Clearance





Something we emphasize a lot is the value of getting your squish clearance right. A proper squish clearance makes the motor both more efficient and less prone to detonation. When you're assembling your high performance motor project, this little detail is well worth the small amount of time and effort it takes to get it right. You'll have more power, better fuel mileage, and your motor is less likely to "ping" on you.



In the ideal world, your squish clearance should be set to about .030". Tighter than that risks piston to head contact; looser starts reducing the chamber turbulence effects that you're going for. Unfortunately, I don't think I've ever pulled apart a factory assembled engine that had a squish clearance of less than .050"! So you can see what a huge opportunity this is to improve on your motor.



So let's talk a little about what squish clearance is and how to adjust it. Put simply, a squish band is the area or areas where the piston comes in close proximity to the chamber as it passes through top dead center (TDC). Fuel trapped in this space gets squeezed out at high velocity and generates turbulence in the chamber. Turbulence in the chamber promotes better atomization and less separation of the fuel and air, encouraging it to burn

Link:
http://www.nrhsperformance.com/tech_squish.shtml

 

[mark920]

I went with mahle, they have an 8cc dish, however, had I not, I think wossner would have been my second choice. Ultimately I think part of the equation should also be weight, which no one has mentioned yet...

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[okswerve16]

The whole reason they orignally went with the crown piston is to run in fuel stratified mode or ultra lean mode, they would inject at the top of the compression stroke and the crown shape help keep the fuel in the center on the piston in the immediate vicinity of the spark plug only allowing very small amount of fuel to be actually injected resulting in less fuel consuption since only the very center of the piston held the fuel the rest of being very lean.

This was never implented like conglomerategti said, only homogenous burn, which is like normal injection where the fuel is injected during the intake stroke and is allowed to mix through the cylinder homogeniously through the intake and and compression stroke

 

[mark920]

The whole reason they orignally went with the crown piston is to run in fuel stratified mode or ultra lean mode, they would inject at the top of the compression stroke and the crown shape help keep the fuel in the center on the piston in the immediate vicinity of the spark plug only allowing very small amount of fuel to be actually injected resulting in less fuel consuption since only the very center of the piston held the fuel the rest of being very lean.

This was never implented like conglomerategti said, only homogenous burn, which is like normal injection where the fuel is injected during the intake stroke and is allowed to mix through the cylinder homogeniously through the intake and and compression stroke

So based on how our cars actually run, what benefit do crowned pistons actually have?

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[mrbikle]

read above......

and all of the VAG decisions were based off correct spray pattern... unless youre running s3 injectors, your spray pattern is shit.

 

[okswerve16]

read above......

and all of the VAG decisions were based off correct spray pattern... unless youre running s3 injectors, your spray pattern is shit.

Yes but VAG themselves changed the pistons design from crown to "flat top" (they have a small dish but i suspect it is for compression reasons) very early on for the fsi motors. AFAIK only very early model years had the crown pistons and then changed to the flat tops. I believe they originally intended to run in fsi mode but they never actually implemented it for the tfsi motors.

The the crown shape the flaps and the spray pattern are all designed to work for fsi mode, but since we only use homogenous burn mode they arent as necessary

 

[mrbikle]

Well we offered our opinion, our numbers will speak for themselves in the up coming race season

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[okswerve16]

Well we offered our opinion, our numbers will speak for themselves in the up coming race season

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Dont get me wrong I am not saying it is bad to use a crown style piston I am just saying that theoretically it shouldnt give an advantage over a flat top or sligtly dished piston with regards to homogenizing the fuel mixture since its intended purpose was for fsi mode only and they dont run in that mode.

 

[Tmsracing37]

Well we offered our opinion, our numbers will speak for themselves in the up coming race season

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LOL The old man saw this and started busting your balls.

Straight from Dick's mouth "What numbers? so far he's got 16 bent valves"

 

[mrbikle]

hahaha. touche.

 

[RRacerguy717]

read above......

and all of the VAG decisions were based off correct spray pattern... unless youre running s3 injectors, your spray pattern is shit.

The more distance you have for the injector to spray and the higher psi the rs4 injectors I've found they work better and better. Fyi with Johns stage 2 hpfp and capable intank pump my fuel trims went from +/- 3 to +/- .3 remember the rs4 injector fuel system was designed built with 2 hpfp working togther to provide needed volume and hpfp fuel pressure stays steady. Bob. G:thumbsup:

 

[Tmsracing37]

The whole reason they orignally went with the crown piston is to run in fuel stratified mode or ultra lean mode, they would inject at the top of the compression stroke and the crown shape help keep the fuel in the center on the piston in the immediate vicinity of the spark plug only allowing very small amount of fuel to be actually injected resulting in less fuel consuption since only the very center of the piston held the fuel the rest of being very lean.

This was never implented like conglomerategti said, only homogenous burn, which is like normal injection where the fuel is injected during the intake stroke and is allowed to mix through the cylinder homogeniously through the intake and and compression stroke

Yes but VAG themselves changed the pistons design from crown to "flat top" (they have a small dish but i suspect it is for compression reasons) very early on for the fsi motors. AFAIK only very early model years had the crown pistons and then changed to the flat tops. I believe they originally intended to run in fsi mode but they never actually implemented it for the tfsi motors.

The the crown shape the flaps and the spray pattern are all designed to work for fsi mode, but since we only use homogenous burn mode they arent as necessary

So why in the 2.0TFSI study guide, say the opposite?

 

[mark920]

The more distance you have for the injector to spray and the higher psi the rs4 injectors I've found they work better and better. Fyi with Johns stage 2 hpfp and capable intank pump my fuel trims went from +/- 3 to +/- .3 remember the rs4 injector fuel system was designed built with 2 hpfp working togther to provide needed volume and hpfp fuel pressure stays steady. Bob. G:thumbsup:

what's the Max bar that hpfpupgrade pump can put out? Another question if the fuel system can support it, what are the down sides to having a tune request 150+ bar?

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[okswerve16]

So why in the 2.0TFSI study guide, say the opposite?

The engine block its referring to is AXX code which is the very first fsi engine which is only in europe. AFAIK those engines could still run in in fuel stratified mode but never actually did.

INfo from a early press release "The North American-spec 2.0L FSI Turbo engine should not be confused with the similar European-spec FSI powerplant, which features a third mode of engine operation, stratified charge combustion, to allow short periods of extremely lean burn. In such low-speed, light throttle conditions, the very slight amount of fuel added to the mixture can result in stoichometric ratios as high as 65:1 (the normal ratio for gasoline engines is 14.7:1) and periods of exceptional fuel mileage. Because of North America’s lower fuel quality (which would require special catalysts to handle the extra NOx emissions from our high-sulfur-content gasoline), this technology is not yet available outside of Europe. True stratified combustion will be integrated into this engine, and other VW (and Audi) FSI powerplants, when the high sulfur content of U.S. fuels is decreased in the next several years."

So it seems only the very early engines has the crown shape which could still technically perform stratified combustion, since VAG had it mind when orignially making the tfsi as well as the na fsi.