[Alpina_B3_Lux]

Originally Posted by bigdnno98

Just took a look at VACs site. It says they have N54 pistons, I'm not sure anyone has ever used them though. I guess you could say they're an option, just not sure I would want to be first at it.

E92Fan over at the UK section has been running upgraded pistons and rods, both from Pankl Racing / CP-Carrillo. Lower compression ratio (I think identical to the one Alpina uses on their B3 BT), much lighter materials on the pistons and titanium rods. Runs very well, he just doesn't have time to spend on his car right now unfortunately.

Alpina_B3_Lux

[J Boy]

Originally Posted by Ænema

I'm just saying that if the octane is there and the tuning is solid then the higher the compression the better the car will perform.

Not sure exactly what you mean by "the better the car will perform." but from what I understand, a lower CR will give turbo cars better peaks and take away from their low end.

[CaptainInsano]

Originally Posted by J Boy

Not sure exactly what you mean by "the better the car will perform." but from what I understand, a lower CR will give turbo cars better peaks and take away from their low end.

As long as they can make the boost. Lower compression allows you to run more boost (correct me if I'm wrong).

[J Boy]

I love this thread however, and it's also very interesting to read all the mixed reviews. Personally to those who are bashing on the RB turbos because of their less peak output than the singles, you have to remember these turbos are simply a direct swap turbo meant to be utilized with stock manifolds and housings. Of course a single will have a higher peak number but that isn't what the point here is...

Mad respect for OP and progress, not to mention the tune isn't finalized yet. The only concern I have is with the head, I would assume that the better flowing head would be giving the car a better top end? Also I thought the car would be able to keep revving past redline a bit with that head?

Like to see more results and progress though

[Sniz]

some big power guys!

[Ænema]

Originally Posted by J Boy

Not sure exactly what you mean by "the better the car will perform." but from what I understand, a lower CR will give turbo cars better peaks and take away from their low end.

In a perfect world(no limit on octane) the higher the compression ratio the more power the engine will make. Period.

However, with pump gas you run into an issue of the high compression ratio making the engine very likely to pre-ignite and detonate. So you take some CR out to make the engine less likely to knock.

[J Boy]

Originally Posted by Ænema

In a perfect world(no limit on octane) the higher the compression ratio the more power the engine will make. Period.

However, with pump gas you run into an issue of the high compression ratio making the engine very likely to pre-ignite and detonate. So you take some CR out to make the engine less likely to knock.

Makes sense. The reason I said that was because when going through a lot of different threads on other platforms people tend to run lower compression when making big boost however, when using big turbos, they typically don't build boost until later in the powerband. So with the lower compression ratios, they are losing a lot of their low end - mid range since they are making minimal boost.

Looking at the powerband of the RB turbos, they seem to be a very quick turbo and don't build large amounts of boost so I can definitely see where you are coming from.

[A4rings]

Originally Posted by J Boy

Not sure exactly what you mean by "the better the car will perform." but from what I understand, a lower CR will give turbo cars better peaks and take away from their low end.

Lower compression ratio allows for more boost.

[J Boy]

Originally Posted by A4rings

Lower compression ratio allows for more boost.

Yeeeeesssssssssssssssssssssssssssssssss

[Sigma 3]

Take a look at some of the builds on boosted e 46 M3 s . They are raising the compression as well. More boost does not always equal more power.

[Joshboody]

Air density is always more powerful then mechanical advantage, BUT both is even better. The CR limits are because of knock, but DI allows higher CR (less knock) so you really can't compare to PI.

[Ænema]

Originally Posted by Joshboody

Air density is always more powerful then mechanical advantage, BUT both is even better. The CR limits are because of knock, but DI allows higher CR (less knock) so you really can't compare to PI.

Yep, the thing to keep in mind is that CR will always be there regardless of RPM(I know, I know dynamic CR changes a little based on numerous factors but this basically holds true.) So that means you can help to offset poor off-boost performance by running a healthy CR. It also increases fuel mileage.