[BmwFanFL]

Though untuned, I have a question on the SSTT.

Many state that power is increased with higher octane fuel and the SSTT. However, with stock vehicles, power is not measurably affected above 91 octane.

To me, this implies timing is somehow affected by the presence of SSTT in a manner that is not experienced in stock vehicles. Yet, SSTT has no apparent access to timing information or control.

Is the engine retarding timing with the SSTT at 91 octane and less retard with higher octane? Alternatively, is it advancing the timing aggressively when the octane permits? If the latter, why would the ECU do this when boost is fooled by the SSTT and not in stock configurations.

Some aspect of the ECUs inputs must be triggering this adjustment. I'm interested in the mechanism at work here? Is it the closed loop fuel system, other action based on feedback from O2 sensors, knock retard due to knock sensors, or something else?

Inquiring mind wants to know....

[EastCoast335i]

^ +1

just put in 100 octane and im think there's a difference but it could also be preceived and not a true gain.

[BmwFanFL]

Thanks for the reply. My real question is what mechanism affects the timing (if any) to allow more HP at higher octane?

Octane mainly allows higher compression ratio and higher ignition (and non-ignition) temperatures. This manifests as power through earlier combustion timing (advanced) -- closer to TDC provides a greater combustion expansion ratio and better energy transfer. The trade-off for an engine control unit is maximize power, while avoiding early combustion or knock.

My main question is how does the ECU/DME decide to take advantage of this extra octane with the SSTT when it clearly does not under stock configuration? Is there a way to take advantage of higher octane without the SSTT-like boost effect?

[Ramos]

I thought you got more HP out of race gas (higher octane) even in stock form ??

[BmwFanFL]

Originally Posted by Ramos

I thought you got more HP out of race gas (higher octane) even in stock form ??

That would be a great answer to the question -- I'd heard it doesn't do anything on its own. I haven't felt any difference from 91 to 94 octane, but it could be a reverse placebo effect.

[Curt2000]

Timing is pulled if there is knocking in the engine...the higher octane you run the less knocking you get...the knock sensor is your mechanism that affects timing.

With the SSTT...since you are running a higher boost pressure there is a greater chance of knock...you can compensate for this by adding a higher octane gas...although I would say 91 w/SSTT is still well within stock knocking tolerance levels

As for 100 octane fuels, Octane has no real connection to performance, traditionally higher octane gasses are higher quality in all areas which equates to a better atomization, flame propagation, and over all power produced.

[BMdblU]

I have SSTT and run sunoco 94 with 10% ethanol sometimes.. my regular fuel is shell 91. To be honest, I don't really feel much of a difference if any running the 94 octane. At first I thought I noticed a bit more power with the butt dyno, but now I think it just might be placebo effect. Although, I have been running the 94 for about 2 weeks now, so maybe I just got use to it, like everything else.

I'm going to go back to the shell 91 and see if I notice any changes.

[NYCe60ne90]

dont the PROCEDE and JB guys make power using high octane gas and no changes on dynos?

[S4to335]

Originally Posted by EastCoast335i

^ +1

just put in 100 octane and im think there's a difference but it could also be preceived and not a true gain.

My butt dyno definitely feels a difference. Why? I dunno. Trust us..power is definitely better with higher octane and SSTT.

[BmwFanFL]

Originally Posted by S4to335

My butt dyno definitely feels a difference. Why? I dunno. Trust us..power is definitely better with higher octane and SSTT.

I believe / accept SSTT users get more power with higher octane fuel. Too many reports to ignore. Have dynos shown this with SSTT?

Appreciate the comments -- I'm just trying to understand the mechanism.

The race gas overall quality comment seems plausible, though I would then expect the performance gains with race fuel in stock form as well.

[KWA VaTech]

Originally Posted by S4to335

My butt dyno definitely feels a difference. Why? I dunno. Trust us..power is definitely better with higher octane and SSTT.

now theirs a technologically sound argument worth taking to the bank. The OP was asking a very specific question and a good one at that. There are plenty of people that will have good input into this, the “trust us” really isn’t applicable here.

[NYCe60ne90]

i put in 100octane of sunoco with a 93 mix, i felt power on my JB2 compared to 91 octane? what exactly does this mean, i thought all turbo and SC cars gain HP from higher octane?

[StarrDlux]

with heatsoak the extra octane will allow the ecu to pull less timing. if you have ever programmed a "real" boosted ecu you will know it is a closed loop system where the conditions (octane,temp,yadda) require the ecu constantly keep "trims or regions" of timing pull per cylinder. Each region or trim area will be like a fuel trim so the car doesn't constantly pound itself if there's a problem that requires a specific cylinder to pull timing at a specific load X boost area. Usually the cars combat detonation or misfires by pulling timing and adding fuel (if appropriate). these adaptations are constantly changing to protect the $26K motor.

it's interesting how germans like to maintain boost but pull up to 40 degrees of timing to keep the cars smooth feeling where american manufacturers and some others will lower boost (and pull timing). the latter makes your car feel like butt as the boost changes giving it a less "all-motor" smooth feeling.

Anyways its closed loop like the air fuel and constantly changing. if you wanted to wreck your motor loosed the knock sensors or throw some aluminum washers in front of them to dampen the sensitivity. knock sensors are tuned piezoelectric micrphones essentially and do go deaf with old age (i always say 5/60K change them). The ecu does adjust for the knock voltage as they go deaf but like a mass air flow thats dying but not dead it can probably be fooled. This would be a quick way to destroy your motor. Some ebay tuners sell aluminum slugs but since the detonation that kills your motor quickest is subsonic you'd have to be superman to hear it.

SBD detonation. thank your knock sensors for doing their job. when you hear pinging you've obviously gone way past the point of the ecu's doing its job or the ecu's ability to do its job has been hampered (loose knock sensor, dampened knock sensor, dying knock sensor).

I thought the N54 had SAAB trionic technology though? Where it reads the resistance of the spark plug to determine if misfires are occuring? If so i wonder what happens if you use alternative plugs or modify the plugs?

anyone have more solid information on this ? I read it on the bmw website but it may be for another motor model. I was like SAAB ripoff!

saab has used the spark plug for detonation detection and lowered boost for a long time so when i saw this i was like SAAB!!

Interesting tidbit: The 1999-2002 LS1/LS6 (vette/camaro) motors use two knock sensors but can only pull timing on all 8 cylinders at once. The 1989-92 corrado G60 does cylinder selective knock sensing with fuel compensation and boost reduction (latter coming to europe years before the usa).

[BmwFanFL]

Starr,

Thanks for the real info. I know the general physics/chemistry, but have no experience of actual tuning (that won't prevent me from having strongly held opinions, though).

It sounds like controlled knock retard / advance is part of the answer. I'm still not sure why octane makes a difference with SSTT (supposition based on much input here) and stock cars don't.

[NYCe60ne90]

higher octane made more HP on my stock car and on my JB2!!!

[Craigito]

Originally Posted by StarrDlux

with heatsoak the extra octane will allow the ecu to pull less timing. if you have ever programmed a "real" boosted ecu you will know it is a closed loop system where the conditions (octane,temp,yadda) require the ecu constantly keep "trims or regions" of timing pull per cylinder. Each region or trim area will be like a fuel trim so the car doesn't constantly pound itself if there's a problem that requires a specific cylinder to pull timing at a specific load X boost area. Usually the cars combat detonation or misfires by pulling timing and adding fuel (if appropriate). these adaptations are constantly changing to protect the $26K motor.

it's interesting how germans like to maintain boost but pull up to 40 degrees of timing to keep the cars smooth feeling where american manufacturers and some others will lower boost (and pull timing). the latter makes your car feel like butt as the boost changes giving it a less "all-motor" smooth feeling.

Anyways its closed loop like the air fuel and constantly changing. if you wanted to wreck your motor loosed the knock sensors or throw some aluminum washers in front of them to dampen the sensitivity. knock sensors are tuned piezoelectric micrphones essentially and do go deaf with old age (i always say 5/60K change them). The ecu does adjust for the knock voltage as they go deaf but like a mass air flow thats dying but not dead it can probably be fooled. This would be a quick way to destroy your motor. Some ebay tuners sell aluminum slugs but since the detonation that kills your motor quickest is subsonic you'd have to be superman to hear it.

SBD detonation. thank your knock sensors for doing their job. when you hear pinging you've obviously gone way past the point of the ecu's doing its job or the ecu's ability to do its job has been hampered (loose knock sensor, dampened knock sensor, dying knock sensor).

I thought the N54 had SAAB trionic technology though? Where it reads the resistance of the spark plug to determine if misfires are occuring? If so i wonder what happens if you use alternative plugs or modify the plugs?

anyone have more solid information on this ? I read it on the bmw website but it may be for another motor model. I was like SAAB ripoff!

saab has used the spark plug for detonation detection and lowered boost for a long time so when i saw this i was like SAAB!!

Interesting tidbit: The 1999-2002 LS1/LS6 (vette/camaro) motors use two knock sensors but can only pull timing on all 8 cylinders at once. The 1989-92 corrado G60 does cylinder selective knock sensing with fuel compensation and boost reduction (latter coming to europe years before the usa).

I love reading posts from real gearheads who know their stuff. I'm an expert at my job but the in's and out's of the engine and engine management systems is mostly beyond me. Thanks for posting.

[BMdblU]

Originally Posted by Craigito

I love reading posts from real gearheads who know their stuff. I'm an expert at my job but the in's and out's of the engine and engine management systems is mostly beyond me. Thanks for posting.

+1

Very informative post

[BmwFanFL]

Thanks for the helpful posts.... (really)

To summarize, it seems likely that the closed loop trim process yields more power with SSTT at various octanes (likely JBx as well and maybe others - but OT).

I'm still unsure why this effect would occur only when the TMAP (temperature - manifold pressure sensor I believe) values are modified and not with a stock car.

I can speculate that the control system's trim logic is designed to maintain a specific performance envelope, and when parameters (e.g., boost via temperature and/or pressure input values) is modified, the stable output goal is also rendered ineffective. I'm not referring to the general power boost, obviously due to higher boost / air mass and compensating fuel trim, but to the variation based on fuel octane. In other words, the computer attempts to keep total power within a defined curve, based on all inputs and controls its managing. When tmap values are modified, it still obviously "thinks" its doing that, but actual values differ and allow variables such as octane to have a different effect...

It could be the effect is a benign translation of the parameter space, exploiting normal areas of the ECUs management range.

However, if it suggests that regular premium octane is too low (e.g., 91) for the SSTT and higher octane avoids knock retard and yields "normal" power (for the SSTT), this would be very important for SSTT users. In this case, the higher octane fuel is essentially mandatory for SSTT owners, IMO.

[do not really try this] Maybe someone should try 86/87 octane in their car and see if it REDUCES power dramatically after a few days of heavy driving and adaptation. If so, this might shed light on the SSTT effects. (do not really try this -- but please let us know the results if you do ;-)

I'd really like to further perspective and from those with deeper experience and data on this. A friend (with a 535i) is considering the SSTT and asked me for advice. generally, I'd say go, but always use the higher octane (e.g., 93-94), which is readily available in our area.

[StarrDlux]

^^ what you describe in the VAG and GM world it called torque management. it is designed to do stupid stuff (both MT and AT) in different amounts. AT6 is most affected and you can simply test this by hitting the gas in M1 letting it burnout then bump up a gear. on an LS6 Auto thats been programmed to not reduce torque the car would keep smoking tire probably up to 5th gear if such GM had 5 gears. with the brakes mashed

torque management may be even be considered part of the system that does good things too. (Please feel free to correct me, i am learning too) such as blipping the throttle and RPM matching, and shutting down the DBW when you try to brake stand.

In the MT6 world this still exists and the ECT will exist just as well. they do not want you to throw down 450wft/lb on a tranny that can't take it. so its easier to turn down the volume (power) when necessary. All behind the woodworks and the best of tuners will know its there because EVERYONE uses it. manual ECT AT6 they've got it.

I thought it was funny some a-hole brought his car in for a check engine at the bmw dealer 535i and they charged him $90 to empty his tank and put premium in; sorry not covered under warranty quite being a dumbass charge.

which means they probably threw a few gallons of 100 octane in and sent him on his way lol.

keep in mind they do sell 85 octane up in colorado as the low octane because of the altitude so when you are telling your car its on mount everest it is computing certain values of elevation to compensate for the lack of REAL mass air flow meters. If you are using speed density you have to assume some things:

P(V/n)=RT P=absolute pressure, V=volume, n=moles of gas, R=universal gas constant, T=absolute temperature. V/n is the inverse of the density.

P=VrT is more common in car forums.


Typically cars with speed density use the foundation of a VE TABLE (RPM * Pressure) then throw every sensor and tons of tables to compensate.

The main problem i see with piggy's is that every sensor is used to complete both timing and fuel calculations so when you tweak one sensor you thus have the ability to change the timing map and fueling map (Along with many other items).

That is my concern (of piggbacks) instead of just changing the tables such as "requested boost" and "desired air fuel ratio" and "desired coolant temp" in the chip. there is ALWAYS collateral damage when 'effing with signals that were not meant to be.

[BmwFanFL]

Starr,

Great perspective. I think you've hit what I suspected and feared a bit.

Simple piggys (e.g., SSTT) have an advantage of simplicity and if mild, work quite well the vast majority of the time. However, some ECU safety measures, especially around boundary conditions, lose some amount of effectiveness (as these features are based on mappings or algorithms that assume real data values).

Complex piggys have the advantage of balanced control of inputs and outputs, but put the engine in a virtual reality "matrix" that leaves more of the boundary condition safety up to the piggy. If the engine thinks its at 8 psi boost with particular temperatures, pressures, wastegate duty cycle, fuel pressure, etc., and the real values are ALL different, many subtleties of the engine control unit could be lost or undermined.

I was mainly exploring whether, IMO as a result of this input, the SSTT is a simple/focused piggy that is harmless enough to recommend to a friend who bought a car near his cost limit already. Frankly, still undecided in the long run, though probably a relatively safe choice (I'd add only 93+ octane though).

On the high end piggys, its how much you trust the engineering and testing and systems knowledge. Obviously, the players are very good, the main questions a buyer has to ask is are they "good enough" to trust with your engine and do you (the buyer) feel lucky.

[Driver72]

I've dyno tested STOCK cars on 91 Octane and then poured in 100 Octane gas to make around 93-94 Octane mix. Ran the car on the dyno rollers for 2-3 minutes revving it up to 5500 rpm (for some adaptation time) then let the car cool for 5-6 minutes and re dynoed.

In each instance of dynoing with higher octane (vs. 91 Octane) the stock car showed power gains of 3-4 rwhp (again with VERY little adaptation time).

On STOCK cars it's safe to say a car on 93 Octane will see 3-4 rwhp more than cars on 91 Octane.
On pure 100 Octane gas, I wouldn't be surprised to see 10 rwhp gains over 91 Octane on a STOCK car.

[BmwFanFL]

Driver,

Thanks - that's great info and real data. This suggests at least the basic behavior seen with SSTT/higher octane occurs on stock cars (though maybe smaller gains). This makes me more confident the SSTT isn't getting the ecu too far from its baseline mapping.