[FastLane]

Has anyone taken note of the 9.4:1 compression ratio found on the new Alpina B3 compared to our current 10.1:1 ?? Its acheived by utilizing Mahle pistons. This is a big step to adding larger turbos/allowing more boost without detination!

Thoughts? Comments?

[O-cha]

Originally Posted by FastLane

Has anyone taken note of the 9.4:1 compression ratio found on the new Alpina B3 compared to our current 10.1:1 ?? Its acheived by utilizing Mahle pistons. This is a big step to adding larger turbos/allowing more boost without detination on a normal port fuel injected car and does not apply on a direct injection car!

Thoughts? Comments?

Fixed it for you.

[WAYNEBO]

Interesting... the M3 and 335i are notoriously high-strung. Somebody do this mod.

[FastLane]

O-cha, your theory is sound on DIESEL direct injection NOT GASOLINE. Thanks for the fix! NOT!

With a gasoline DI, it could pre-ignite prior to spark but the chances would be minimal if your fueling through the powerstroke which is the added benefit of DI (more precise timing and quantity of fuel delivery). This pre-ignition, even a small amount with high hp application, can lead to engine deteriation due to the stress applied to the cylinder walls.

With a diesel DI you are already fueling through the combustion cycle (powerstoke) so pre-ignition isn't possible.

[O-cha]

You said detonation not pre ignition, not that it really matters since your wrong anyway. Theres minimal risk of either in DI, sure knock is not totally eliminated, but its not so bad that the engines untunable at higher boost.

You do realize you're talking about two different things right? Yea probably not.

[FastLane]

pre-ignition leads to erratic combustion which causes....DETINATION!

You are correct in that pre-igintion is not detination, but they go hand in hand. You are incorrect in stating the pre-ignition can be elimited in either application, its completey erased from DI diesel engines, thats one of the major reasons to go diesel.

For your comment regarding our engine's being safe at higher boost pressure, this is true to an extent. You wont see anyone running 28psi of boost with a stock setup because of the risk involved. The risk is exploading your engine, which is caused by .... uneven combustion which is caused by....many things like pre-ignition. You can advance/retard the spark to combat this though, oh and adjust your fuel amounts, and shorten/lengthen your injector pulse, oh and lets not forget to add some air in there....

Back on point, there is limited risk on detination in STOCK or even slightly modified DI Gas turbo engines but slap on a pair of TO4R's or Garret T66's and watch the pistons shoot out from your hood due to the uneven pressures associated within the cylinders!

Look at any direct injected forced inductioned (DIFI) engine that is very powerful and you will not see one that has a compression ratio higher than 9.9999:1, at least not one with a decent amount of miles on it

[O-cha]

Originally Posted by FastLane

pre-ignition leads to erratic combustion which causes....DETINATION!

You are correct in that pre-igintion is not detination, but they go hand in hand. You are incorrect is stating the DI can be limited in either application, its completey erased from DI diesel engines, thats one of the major reasons to go diesel.

For your comment regarding our engine's being safe at higher boost pressure, this is true to an extent. You wont see anyone running 28psi of boost with a stock setup because of the risk involved. The risk is exploading your engine, which is caused by .... uneven combustion which is caused by....many things like pre-ignition. You can advance/retard the spark to combat this though, oh and adjust your fuel amounts, and shorten/lengthen your injector pulse, oh and lets not forget to add some air in there....

Back on point, there is limited risk on detination in STOCK or even slightly modified DI Gas turbo engines but slap on a pair of TO4R's or Garret T66's and watch the pistons shoot out from your hood due to the uneven pressures associated with within the cylinders! Im talkin gettin 500+ whp!

FOR EXAMPLE: NISSAN R35 GTR: 3.8L V6, COMPRESSION RATION = 9.0 : 1

Detination is bad mmkay.


No seriously, wow at you saying pre ignition is the cause of detonation, if pre ignition is the reason your worried about detonation, actually I just don't know what to say to this without being banned.

The point is DI greatly reduces the chances of detonation.


If you're looking for 500whp, then by all means go for it guy, but you can get that with the stock compression ratio, there should be other things on your mind like the strength of the block, con rods, fueling ETC. Before its over you will be out at least 20 grand, have fun.




The GTR is not a direct injecton engine by the way.

[Evo8MRto335I]

The lower compression ratio is nothing new. BMW engineering and marketing decided to specifically put smaller turbos on the 335i to not have a car in the market in which would be associate with turbo lag.

During the testing they tried mid size turbos and they produce monstruous torque and HP, let me say it again insane power and torque(there is a video on the website talking about the engine ). The whole final output of the engine was vastly compromised by the choice of the turbos.

This engine would easily made 450hp from the factory with a couple of bigger size turbo trim at the cost of maybe 400-500rpm of turbolag.

The B3 does not surprise me at all, the engine is very capable.

[FastLane]

you posted before I could edit my previous post bout the GTR, bad example.

Again, you are correct that there are plenty of other mechanical issues to be concerned about but the point of my post was to note that we lowered the compression ratio and can run higher amounts of boost, safely, like on the B3 which runs at ~16psi (1.1 bar) and the most anyone around here runs is ~13-14.

Just a step in the right direction...

[O-cha]

You're missing the point man, you only drop the compression ratio when you NEED to, you don't NEED TO on a DI engine until much later.

So like I said if you're planning on going crazy with the engine have at it, but it's not something important to 99.9% of the people here and even if you were going to go all out you would run into other much larger/more difficult upgrades before you need to.

[ArmyBimmerDude]

Originally Posted by Evo8MRto335I

The lower compression ratio is nothing new. BMW engineering and marketing decided to specifically put smaller turbos on the 335i to not have a car in the market in which would be associate with turbo lag.

During the testing they tried mid size turbos and they produce monstruous torque and HP, let me say it again insane power and torque(there is a video on the website talking about the engine ). The whole final output of the engine was vastly compromised by the choice of the turbos.

This engine would easily made 450hp from the factory with a couple of bigger size turbo trim at the cost of maybe 400-500rpm of turbolag.

The B3 does not surprise me at all, the engine is very capable.

What website is that?

[scalbert]

Originally Posted by FastLane

Has anyone taken note of the 9.4:1 compression ratio found on the new Alpina B3 compared to our current 10.1:1 ?? Its acheived by utilizing Mahle pistons. This is a big step to adding larger turbos/allowing more boost without detination!

I was a bit surprised by Alpina's decision. If they are to make the most power, they started with a solid method. But if they were worried about issues with the CR run in factory form, it may have been unfounded.

Running 9.4:1 is just slightly more (0.1 more) that the B5 S4 ran and could easily run 20 PSI+ boost, with supporting turbo, without significant detonation issues (provided the fuel and intercooling was there). I see no reason why 15 - 18 PSI on the N54 would be a problem provided the turbo's could support that, which they cannot at the higher revs. The cooling effects of DI is probably the largest contributor to being able to run the higher CR in the N54.

I would love to scope the phasing of the injectors and the ignition timing though; just to see when injection occurs versus spark. I suspect they occur fairly close together and with the fuel pressures involved, should atomize and cool quickly thus limiting potential detonation. But how much will need to be tested and disclosed which will not happen soon.

[FastLane]

I am commenting on LATER and you dont NEED to, but if you want great gains of power with the safety and security of an everyday car, upping the boost while dumping more fuel and air in it isnt going to do it (ie: BPU and a tune).

Not one of those Alpina B3's will go into limp mode when pushed. They did it for a reason.

Look o-cha, 99.9% of the people arent gonna care. You are definitely right. But 99.9% of the people here arent gonna have a 200+ mph, or 10 (11) second car.

This engine can put up huge numbers, the block is strong and its NATURALLY BALANCED (lets not get into how a 90 degree V8 and an I6 are the only nat'l balanced engine), so therefore, its a canvas for speed.

[O-cha]

Lol the cars are not going into limp mode because they can't handle it, it' s because it's a piggyback and shit happens when the ECU gets confused.

Also, the current tunes are not dumping a ton of fuel to suppress knock like you seem to be assuming.

Originally Posted by scalbert

I would love to scope the phasing of the injectors and the ignition timing though; just to see when injection occurs versus spark. I suspect they occur fairly close together and with the fuel pressures involved, should atomize and cool quickly thus limiting potential detonation. But how much will need to be tested and disclosed which will not happen soon.

That's the whole point, even if it was during intake the same effect would take place though.

[scalbert]

Originally Posted by O-cha

That's the whole point, even if it was during intake the same effect would take place though.

Actually, I want to know how close it truly is to the iginition. If they coincided, detonation would practically be eliminated. There could not be spontaneous combustion ahead of the flame front as the injector would essentially be feeding that flame front.

[O-cha]

Originally Posted by scalbert

Actually, I want to know how close it truly is to the iginition. If they coincided, detonation would practically be eliminated. There could not be spontaneous combustion ahead of the flame front as the injector would essentially be feeding that flame front.

You haven't looked at the video in my sig have you?

[scalbert]

Originally Posted by O-cha

You haven't looked at the video in my sig have you?

Never had but just did and still doesn't matter. A test rig with high speed video (and BTW, we have some pretty cool ballistics video's ) doesn't represent what is always occuring even under load.

I suspect that was set up for low engine speed. Do multiple injections occur at higher engine speeds?

Neat video, but what I want to know is the variation with changes in load.

[FastLane]

Shit happens isnt acceptable when shit is happening to everyone, capiche? Or when ur in the middle of a race, u cant say u lost cause shit happens.

What im tryin to get at (and not argue about) is that with a lower compression ratio on gasoline direct injection turbo engines, u have the best chance of maximizing potential hp. The Alpina lowered the CR on the B3.....why? I would love to know what else they did as a result, such as did they run leaner? adv/retard spark? are they running dead on stoich? why 16psi (turbo limited? heat limited?)?

[O-cha]

Originally Posted by FastLane

Shit happens isnt acceptable when shit is happening to everyone, capiche? Or when ur in the middle of a race, u cant say u lost cause shit happens.

You eluded to limp modes being indicative of your argument being correct. I corrected you by saying the limp modes have nothing to do with the engine being at it's limit, just the piggyback not tricking the ECU properly. I'm sorry if you don't understand that.

As for the rest, the higher the CR the more HP potential, everyone knows that, again, that's why you don't run lower unless you HAVE TO.

[FastLane]

Right unless you have to...why did Alpina HAVE TO lower their CR ? Why did they change the pistons?

[jpsimon]

Since when is "shit happening" to everyone? The majority of people DON'T have problems.

[O-cha]

Originally Posted by FastLane

Right unless you have to...why did Alpina HAVE TO lower their CR ? Why did they change the pistons?

Because like you the are stuck in the past.