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you (and tuomo, and everybody else) should look into VEMS ECU.
for about $1300 you can get a plug-and-play (uses stock wiring harness) standalone ECU, MAP-based, that allows trimming both fuel an spark for each individual cylinder.
i've been running it for about 2 years, super user-friendly software, tune it from your laptop via bluetooth (no cables running around the car)..
Originally Posted by FredR
Some interesting comments there. I found that 6 and 2 control the amount of advance that can be applied at higher rpms. I also assumed that those cylinders were flowing more air thus running leaner so your comment is interesting. What I did find through experimentation with the patch that Ken wrote for me was that 6 and 2 need to be pulled by about 3 degrees to get similar knock characteristics in the higher rpm range but then the patch was an across the board type of thing, not cell specific. This led me to wonder whether one can increase the timing across the board and rely on the knock sensors to pull timing on the "noisy cylinders" as needed. This also told me that the motor needs 98 RON and that 95 RON is a bit limiting. That I had to pull a bit of timing compared to stock was a bit disappointing thus but then I later learned that having a faster exhaust compared to stock also suggests less advance needed.
I also found that AFR did not impact advance in the value range 12 to 13.5. I was also advise dthat the 928 inlet manifold is quite efficient and that best power is typically made in the low 13's.
Hopefully Marti will advise what he finds when Sharktuning.
you (and tuomo, and everybody else) should look into VEMS ECU.
for about $1300 you can get a plug-and-play (uses stock wiring harness) standalone ECU, MAP-based, that allows trimming both fuel an spark for each individual cylinder.
i've been running it for about 2 years, super user-friendly software, tune it from your laptop via bluetooth (no cables running around the car)..
How do you plan on getting sequential fuel injection using the stock harness which is wired for batch fire?
How do you plan on properly tuning sequential fuel injection without knowing the air / fuel of every cylinder?
got me there with the wiring - didn't think that all the way thru.
would be pretty straightforward to de-pin the stock injector wiring and add new circuits, but i'd leave that to the VEMS-seller to build.
but VEMS has multiple WB02 inputs and the ability to "VE auto tune" fuel trim to get WB reading closer to AFR target.
but rather than buying 8 WB's and bungs you could probably get close by plug-chopping and playing with the individual injector settings.
In my opinion, for what you’re building and the long exhaust duration that you’ll have, it’s more important to have small enough primaries off the head than creating a step. What exhaust can duration will you run again? If it’s what I think it is, you don’t want to go larger than the port for the first part of the primaries. Just an opinion.
Greg and Åke can more intelligently comment on how much can be shaved off the heads. I’m on the turbo track so I don’t know much about that. The amount coming off my heads is the absolute bare minimum to clean them up.
If it's 228 degrees at 0.05", then that's a lot of duration given the exhaust port flow, displacement, and realistic rpm for the stock bottom end. I'd open the exhaust valve later (and keep the same overlap), but that's just me. If you run that exhaust cam, then in my opinion you want a small header primary. Nothing larger than the port. Goes without saying, these are just my opinions. Others may disagree.
I see little point is attempting such a project with a goal to only "get it close". Either do it right or stick with what we already have, which is "close" already. Contrary to what most people assume, it's not a case of X cylinder being Y lean or rich throughout the rev range, it changes for each cylinder through the rev range, with and without the flappy.
Individual cylinder tuning has been done on 928's before and it was not as straight forward, inexpensive, or simple as you make it out to be - at least to do it right.
Even installing a WBO2 into each cylinder isn't as "easy" as most think since your typical Bosch WBO2 sensor will not be very happy that close to the exhaust port. There are also issues with extreme back pressure (see turbo applications) for WBO2's installed before the turbo.
Properly tuning such a setup is not for the amateur behind the laptop.
I see little point is attempting such a project with a goal to only "get it close". Either do it right or stick with what we already have, which is "close" already. Contrary to what most people assume, it's not a case of X cylinder being Y lean or rich throughout the rev range, it changes for each cylinder through the rev range, with and without the flappy.
Individual cylinder tuning has been done on 928's before and it was not as straight forward, inexpensive, or simple as you make it out to be - at least to do it right.
Even installing a WBO2 into each cylinder isn't as "easy" as most think since your typical Bosch WBO2 sensor will not be very happy that close to the exhaust port. There are also issues with extreme back pressure (see turbo applications) for WBO2's installed before the turbo.
Properly tuning such a setup is not for the amateur behind the laptop.
It's also the case that you'll get very different results on individual cylinder fueling and ignition timing requirements for cars with exhaust manifolds vs. cars with headers. Furthermore, with stock exhaust manifolds, cylinders that require less fuel may also require less timing, so it's very counter intuitive until one realizes that the imbalance issues come from the exhaust manifold and not from the intake manifold.
In my opinion, for pump-gas cars that have long-tube headers, stock S4 intake manifold, and streetable cams that run ok with the stock intake manifold, the indvidual cylinder fueling is not a big issue. As long as the fueling is at low 13's on average, there's not a huge amount of power left on the table. And I think the new, experimental JDS ST version will allow individual cylinder ignition tuning. That can be just tuned to be at the knock limit for each cylinder, as it's almost certain that the engine is knock limited on pump gas.
As always, let's be clear that these are opinions.
I am working on the theory that with the increased airflow now being sought by the engine that this may be worth doing especially since I have the parts off the car at present.
With your 5.0 motor, the stock intake will flow more than enough air for your relatively minor mods.
Do not get sidetracked by the real issues faced by the turbo crowd since you are running normally aspirated, and with headers. Also, there is no need whatsoever to swap-out the ECU and all the headaches that entails...
Instead, keep your eye on the real target, and that is doing your best to equalize the mixture distribution amongst the cylinders with an inherently crappy stock intake. The end-result will allow you a much better tune, more hp, reliably.
Since you have the intake off, go ahead any eyeball runners 2 and 6, and it should become readily apparent why they flow so well, thus why they run LEAN with batch fire, especially compared to convoluted-cylinders 5 and 8, the richest.
To go along with the 'eyeball data', there's plenty of real, empirical data showing that 2 and 6 does run lean, and why while Shark Tuning, timing must be pulled. And the latest mention of that fact is within this very thread.
If you really and sincerely want to improve the stock intake's performance, that would be by improving its mixture distribution, versus just trying to flow more air thru it.
As stated earlier, it is impossible to improve the flow on 5-8 to match 2-6 with the stock intake. IMPOSSIBLE.
Therefore, the logical alternative using the stock intake is to reduce the flow on the highest flowing runners/cylinders, 2-6, which will bring them closer to the poorest flowing, 5-8.
As I mentioned in my earlier post, cutting the bellmouths off of 2-6 will reduce their flow, thus bringing them more in-line with 5-8. This is a super-easy mod and a win-win, and will improve mixture distribution for any configuration 32v 928 using the stock intake from 5.0L to 7.0L engines - I'm surprised no one has thought of this idea prior to now.
I like the idea so much, I have 3 spare intakes and will take one and do it myself in the spring and put it on the GT racecar with a fresh tune.
As a final data point, I personally know the guy who installed 8 O2 sensors on his 28 psi supercharged S4 and logged all kinds of data. To make a long story short, his conclusion was that if he used the stock intake for his (..then) upcoming twin-turbo 928 build, he would essentially be committing mechanical suicide, and would never be able to achieve his goals. As a result of his empirical data gathering and analysis, the first thing he did was to build a new intake, specifically to equalize mixture distribution to all cylinders, and whose end-result has been a resounding success. That car dyno'd at 941 rwhp and has been running trouble-free for years now.
In Todd Tremel's data which was produced with stock exhaust manifolds, at high rpms cylinder #6 is running rich, not lean, with batch fueling and needs fuel pulled with individual cylinder fuel trim. Cylinder #6 gets less fresh air at high rpms than the average cylinder, not more. Cylinder #6 needs both fuel and timing pulled because the hot exhaust does not evacuate from the combustion chamber during the overlap and the fresh charge doesn't get going when the intake valve opens. The combustion chamber evacuation and overlap flow of #6 is screwed up with stock exhaust manifolds because the distance between cylinders #5 and #6 is such that the exhaust blowdown pressure pulse from cylinder #5 arrives at the cylinder #6's exhaust port during cylinder #6's overlap. I'm talking about the 6000rpm and 7200rpm columns in Todd Tremel's data.
Phrases like "improve mixture distribution" and "equalize mixture distribution" I take to mean simply "air distribution" since that is all the the intake manifold does, at least down to the point of the fuel injectors. In that regard it brings to mind thoughts about what the flappy actually does and what my own manifold design will be like without one. I am also wondering about something I think I saw in one of these threads, that suggests that the S4 TB feeds the manifold with a bias for one side or the other, rather than equally on each side. Does anyone have any further thought about either of these concerns of mine.
Phrases like "improve mixture distribution" and "equalize mixture distribution" I take to mean simply "air distribution" since that is all the the intake manifold does, at least down to the point of the fuel injectors. In that regard it brings to mind thoughts about what the flappy actually does and what my own manifold design will be like without one. I am also wondering about something I think I saw in one of these threads, that suggests that the S4 TB feeds the manifold with a bias for one side or the other, rather than equally on each side. Does anyone have any further thought about either of these concerns of mine.
Air distribution.
I think it's self evident when looking at the S4 throttle body that one side has to make a tighter turn. It would be an interesting experiment to measure exactly how much less does that side flow.
On intentionally reducing the flow to some intake runners: I think someone has done that, maybe nic Simos? Maybe ask him what the dyno said? Here's the photo that I found:
Since someone has already tried that, I'd want to know what the dyno results were before replicating this effort exactly. Then maybe tweak the idea if necessary.
Personally, I'd just install headers, make every runner flow as much as they can with the prescribed cross-sectional area, let fueling be a little unequal, and use the cylinder-specific ignition timing map.
On intentionally reducing the flow to some intake runners: I think someone has done that, maybe nic Simos? Maybe ask him what the dyno said? Here's the photo that I found:
Since someone has already tried that, I'd want to know what the dyno results were before replicating this effort exactly. Then maybe tweak the idea if necessary.
Agreed. And that is a nice find and looks exactly like what I have in mind. Nice job, Tuomo.
I think it's self evident when looking at the S4 throttle body that one side has to make a tighter turn. It would be an interesting experiment to measure exactly how much less does that side flow.
On intentionally reducing the flow to some intake runners: I think someone has done that, maybe nic Simos? Maybe ask him what the dyno said? Here's the photo that I found:
Since someone has already tried that, I'd want to know what the dyno results were before replicating this effort exactly. Then maybe tweak the idea if necessary.
Personally, I'd just install headers, make every runner flow as much as they can with the prescribed cross-sectional area, let fueling be a little unequal, and use the cylinder-specific ignition timing map.
I would like the user name of this member as I am keen to reach out to find out more.
01-10-2018, 11:25 AM
