On v12 banks

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AndreyB
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On v12 banks

Post by AndreyB »

On v12 engines with two separate intake manifolds how unevenly would two banks run? Why?

Do we require throttle bodies synchronization to even out the banks or do we just adjust fuel/ignition trims?

How much of a big deal is that, how was it address back in the days of mechanical throttle bodies? I guess maybe a better question would be "when do you start caring" is that based on HP goal or annual mileage or your personal OCD or else?
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mck1117
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Re: On v12 banks

Post by mck1117 »

You start caring when the split is enough to "cause problems". All OEM applications EITHER have a crossover tube (to balance whatever small difference in flow exists), OR have sensors on both banks in order to balance them and also provide per-bank fueling.

We already have an issue for this: https://github.com/rusefi/rusefi/issues/3680
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Re: On v12 banks

Post by mk e »

AndreyB wrote:
Sat Jan 01, 2022 6:15 pm
On v12 engines with two separate intake manifolds how unevenly would two banks run? Why?

Do we require throttle bodies synchronization to even out the banks or do we just adjust fuel/ignition trims?

How much of a big deal is that, how was it address back in the days of mechanical throttle bodies? I guess maybe a better question would be "when do you start caring" is that based on HP goal or annual mileage or your personal OCD or else?
Starting at the bottom. but the short answer is just tell people to use a balance tube until you actually find a case where that doesn't work.

This isn't a HP thing generally. Air flow changes very little in the final few % of throttle motion so you are unlikely to notice or be able measure HP loss.

On mechanical systems the common setup was ITB and more importantly pretty much race only as most used a common shaft with no individual adjustment...."you get what you get and don't get upset" come to mind. They tend not to idle worth a damn, hence race only.

Multiple carb sets is much easier because they are individually adjustable and a carb by its nature is metering fuel to match the actual air flow so you really only need to get them close to matching and the engine runs pretty well. Most people adjust "by ear" and call it good enough, but a manometer or flow gauged is the preferred way to sync them. In the early 80s the 12cyl cars (at least Ferrari and Lamborghini) got 2 CIS units but 2 units means fuel is match the actual airflow of the bank so bank to bank flow errors are not a huge issue, just set them close and it runs fine...not sure if they had a small balance tube or not, I don't recall seeing one on the 400i I bought for my build but I may not have been paying attention or the salvage yard may have removed it....but it would screw up the bank to bank mixtures so I assume was not installed.

Multiple TBs are more of a challenge with EFI. Most OEM car stuff is multiple ECU based so like with multiple carbs or CIS setups, as long as they are close it takes cares or itself with each ECU managing its own bank meaning fuel and spark match the bank's actual airflow. On bikes they provide mechanical adjustment on the TBs and you need to adjust for matching air flow...but they have a little advantage over cars in the that the HP/weight ratio means there is WAY extra hp available and nobody really expects them to ride smooth much below 3k rpm so they get a pass down where car owners most want the engine smooth.

For 2 banks running speed-density, a 1/2" balance hose should be all that is needed to make it run pretty well. I did a setup like that before and it was fine, but it was mechanical TBs, cable operated so I could adjust them pretty close and the balance hose took care of the rest. I would assume this would also work on MAF setups as long as you are reading both MAFs and adding the flows....never tried it though and it does assume the TBS are at least close to the same flow so the hose can match them.

I posted this on my build thread, I have a mechanical adjustment on each TB so in theory I could adjust them all the same but in practice its quite difficult with 12 and functional but less than rigid linkage setup....so I am trimming each cylinder at low throttle. I have seem small like 1/4" balance tubes used and connected to a small plenum and IAC installed in front and that does sort of work when the TBS are closed but as soon as you start to crank them the balance tube becomes a huge vacuum leak TB to TB so far from ideal. Balance tubes work well on 2 plenums with relatively constant flow but are not so good with pulsatile flow like ITBs but this is an ITB issue though and not really what you asked about.
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Re: On v12 banks

Post by Simon@FutureProof »

It is also worth noting that most cross ram engines with dual plenums up until about 2010 were actually running 2 ECUs.

From the top of my head, the Ferrari stuff and BMW stuff was using 2x bosch controllers and the lambos used dual marelli ones.

No need to balance your banks if you treat each one as it's own engine. :lol:
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Re: On v12 banks

Post by nmstec »

Audi used Dual Bosch modules, and VW v10 touareg ditto on the MED bosch modules.
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Re: On v12 banks

Post by mck1117 »

We're actually very little code away from being able to run as "two ECUs", one for each bank.
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Re: On v12 banks

Post by mk e »

mck1117 wrote:
Sat Jan 15, 2022 8:31 pm
We're actually very little code away from being able to run as "two ECUs", one for each bank.
There is no reason in the world to do that if you have 12 fuel and spark outputs in 1 ecu. The OEMs did it for cost, it made no sense to develop an ecu for the small volume the V12s were....way easier to just use 2 for something they already had. Just add MAP/MAF bank trim and call it a day6 would be my advice, for what little its worth. I can tell you motec offered a CAN base solution to link 2 M800
ECUs they developed for an Aston Martin race team so it was 2 ecus, but the main was done in 1 to make it much easier. Then they release the M150 that has 12 channels of fuel/spark and the that was that and the M190 has 24 fuel/12 spark just in case someone wants a V12 with hi/low injection. 2 EECUs is what you do when you can't make it work with 1.
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Re: On v12 banks

Post by mck1117 »

mk e wrote:
Sat Jan 15, 2022 11:57 pm
There is no reason in the world to do that if you have 12 fuel and spark outputs in 1 ecu.
That's not what I mean - I just mean having two map/maf/tps and doing independent per-bank fueling on a split-manifold engine. There are two interesting cases, N=1 and N>1, and once it's N>1, N=2 and N=4 are very very similar in terms of complexity.
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Re: On v12 banks

Post by mk e »

mck1117 wrote:
Sun Jan 16, 2022 9:32 am
mk e wrote:
Sat Jan 15, 2022 11:57 pm
There is no reason in the world to do that if you have 12 fuel and spark outputs in 1 ecu.
That's not what I mean - I just mean having two map/maf/tps and doing independent per-bank fueling on a split-manifold engine. There are two interesting cases, N=1 and N>1, and once it's N>1, N=2 and N=4 are very very similar in terms of complexity.
Still the question is why? The standard approach is to do a global calculation then just trim it which is a one line calculation (2 lines if you count converting the additional sensor reading) and uses the trim functionality you already have...now I might be biased as that is really the only approach the ecu I have will support (injector time calc is a low level thing I can't access, I just supply the inputs to the function and cyl trim is the only way I can vary from global) so I didn't give a lot of thought to other options but unless you are planning to to have independent tuning tables (which are a big pain in the ass to tune) then its also the most practical I think. I am doing the global calcs then N=12 cylinder MAP readings corrections this way and even when things are mechanically mismatched by 30+% the fueling ends up pretty close. The bank 1 & 2 WBO2 trim the 6 in each bank, I use the average as the global (I do the same with MAP readings) and reading/average type correction factor, multiply all the correction factors and its done.

If I had multiple throttle controllers I probably would invest a little time in trying to match them...but I'd be pretty tempted to do it with a simple pedal vs TB offset table on the throttle 2 rather than anything fancier that that would be controlling the throttle looking at anything but the pedal position and let the fuel trims sort out anything after that but On my engine the TBs can be 30+% mismatched and the trims fix it so I'm not sure this is needed, maybe nice but probably not needed.
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Re: On v12 banks

Post by blundar »

The Huracan and R8 both STILL use dual ECUs for the V10 configuration, and that's a LOT more recent than 2010. (ME17)
The best option here is to run the V12 as two independent I6 that share a common set of rotation speed sensors (cam, crank) IMHO. You can bandaid things some with individual cylinder fuel/ign trims but it's not ideal.
That is a humble opinion.
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Re: On v12 banks

Post by Zeiss »

Is it really worth so much that you have to discuss it forever instead of implementing it?

V12 have two banks, two throttle bodies and two MAF sensors. The intake manifolds are not connected at the factory. If you have two actuators for one quantity (in this case air mass), then they need to be synchronized. Yes, it is possible to connect the two intake manifolds so that all cylinders get the same air mass, but that is (my opinion!) absolute rubbish. Yes, it works, but it's not cool and is just a workaround for a missing feature. The more modern V12 engines even synchronize their throttle bodies in real time (starting with the M73).

To implement this feature you need:
-> independent throttle control: we have it!
-> independent TPS sensors: we have it!
-> input for second MAF/MAP sensor: Proteus has enough analog inputs. So only the identification that it is the second MAF/MAP is missing.
-> algorithm for synchronization: missing

So there are two small things we are missing to implement this (for V12 engines) important feature. When I started with the "alternative EFI", my rule was, I don't adjust anything on the engine (except COP, because that's what I want, an ignition without distributor), either the EFI can handle it or it's the wrong one. Proteus seemed to be the right one at first glance, meanwhile I'm not so sure unfortunately.

After a lot of text (sorry for that) again the question, do we really need to discuss it forever? What kind of effort are we talking about anyway? 10 hours? More? Less?
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Re: On v12 banks

Post by mck1117 »

Zeiss wrote:
Mon Feb 21, 2022 9:42 am
Is it really worth so much that you have to discuss it forever instead of implementing it?

After a lot of text (sorry for that) again the question, do we really need to discuss it forever? What kind of effort are we talking about anyway? 10 hours? More? Less?
All the humans who work on rusEFI do it mostly for fun, not as the thing that pays for our food and gas. It's on the (very) long todo list. Humans can always be persuaded to pluck something lower priority from the todo list with bribes of alcohol, racecar parts, and cash.
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Re: On v12 banks

Post by Zeiss »

I know it's a "just for fun" project. You have built a very cool board, for which my utmost respect. It should NOT come across as an attack, do not misunderstand. I would love to participate in the rusEFI project, but unfortunately I do not have the time :(

Therefore, the question, what effort are we talking about at all? How much cash do you want for it? :D
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Re: On v12 banks

Post by mk e »

I'm pretty certain the the factory 2 ECU solution was mostly to pull off the shelf parts where ever possible but it is a giant pain in the ass to tune, been there, done that. Having lived in ferrari performance land for almost 25 years now I can say that I have never met anyone who's ever installed 2 ECUs and ever wants to do it again. Its just SO much easier to tune 1 engine and trim the 2nd bank to match the 1st

When I started on my personal V12 build I owned a motec M800 which with a couple ignition expanders (they had a coded spark signal so 1 spark channel could fire 8 coils with an expander box to decode it) could to 12 fuel and 12 spark. At the time I was planning Hi/low injection so I was looking to control 24 injectors. In speaking to motec I leaned a team running Aston Martin V12s was doing hi/low and they (motec) has added code to CAN to M800s together to make it a little easier. Each ECU got connected to the crank and cam sensors but only the primary to everything else then those signals plus the main fuel and spark tables were sent to the secondary. It sounds clunky but it makes it WAY easier to tune. Then all that went away when the M150 (12fuel/12spar) and MA190(24fuel/12spark) cam out. This is the direction the aftermarket has gone because its just so much easier to deal with.

If whenever the day comes and you want to allow independence of the banks just please please please use common setup and main tuning tables.
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