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Home > A-Series EFI / Injection > AFR Distribution with TBI setup

gcos93

17 Posts
Member #: 11040
Member

Portsmouth (South East)

Hi All,

I've been considering converting my Mini to fuel injection. Largely for convenience of tuning, easy starting, avoidance of vapor lock etc.

I was hoping to use a wet manifold / throttle body injection approach similar to the Specialist Components kit just to keep things as simple as possible for my first EFI conversion.

I was originally discouraged after reading a lot of concerns that AFR distribution could be significantly worse with TBI than with a carb.

I then saw Paul S's response in this thread:http://www.turbominis.co.uk/forums/index.php?p=vt&tid=611550

"Yes, ignore that earlier thread. We now know that the risks were over-stated."

Based on that comment, I was just wondering if any AFR distribution data exists for a TBI setup and what is actually considered acceptable AFR variation on a boosted application?

The car in question is running 15psi boost and about 140 "bananas" with a 5600rpm rev limit. If I do an EFI conversion, I'd like it to work with the above specs as I obviously don't want to turn down the boost *happy*

Any pointers you guys can provide would be greatly appreciated :)

Thanks


Turbo Phil

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4619 Posts
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My sister is so fit I won't show anyone her picture

Lake District

I’m not sure if anyone has fitted dual wideband sensors with a wet manifold setup, or a least not anybody that’s shared the results on here.
This is something that has been discussed many times but I don’t remember seeing any genuine data.
I’d be interested to know as it’s something I plan to do myself as I’ve all the parts sitting here.

Phil.

WWW.TURBO-MINI.COM


gcos93

17 Posts
Member #: 11040
Member

Portsmouth (South East)

Cheers Phil. I figured there was a reason I couldn't find anything!

Has anyone even run TBI with >15psi boost before? I saw a post from wil_h saying that he ran 12psi with the SC TBI kit but I couldn't find anything else.

I could start by doing some trials with TBI on my brother's NA mini using twin widebands. Not sure how representative it will be for a turbo setup but I'm not keen to fit dual widebands to my turbo due to needing sample chambers.

I suppose data from an NA motor would be better than no data at all...

Grant

Edited by gcos93 on 23rd Sep, 2020.


Rod S

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5988 Posts
Member #: 2024
Formally Retired

Rural Suffolk

As Phil says, no genuine data on this forum (there may be elsewhere but I doubt it).
Someone did try to use EGT data to do the comparison but it was proved worthless because the centre exhaust runs hotter anyway because it's siamesed.

Whilst it's easy enough to put dual widebands on a N/A engine, the main problem with dual widebands before a turbo is their pressure dependency - if you don't run them at consistent and equal pressures, the results will be meaningless. And they may also be killed by the temperature.
There has been some talk, both on here and other forums, about the latest generation from Bosch being less pressure dependent but, again, no real user data.

But, as far as I can see, using the sample chamber technique is the only safe way on a turbo.

Otherwise, on a throttle body/wet manifold, just put a single wideband after the turbo and use other signs - spark plug colours or holes in your pistons, to gauge the offset.....

Schrödinger's cat - so which one am I ???


gcos93

17 Posts
Member #: 11040
Member

Portsmouth (South East)

Thanks Rod!

Yes, I've seen some pictures of Graham T's sample chamber setup. Makes sense but does add some complexity.

I'll have a think about ways of making it a temporary fit as I'd rather not have all that pipework hanging around permanently.

On 23rd Sep, 2020 Rod S said:
Otherwise, on a throttle body/wet manifold, just put a single wideband after the turbo and use other signs - spark plug colours or holes in your pistons, to gauge the offset.....


Hmmm well yes. Holes in pistons indeed... best avoided! *happy*


jbelanger

1267 Posts
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Montreal, Canada

One thing you will need to do is to have 4 injection pulses per engine cycle. That's the only way you can have an AFR distribution that's close to correct.

And you will want to use more than one injector to cover the entire rpm/load range. How you do this will depend on your physical setup and what your ECU can do (same size injectors or one big one small, set in alternating mode or staged,...)

http://www.jbperf.com/


gcos93

17 Posts
Member #: 11040
Member

Portsmouth (South East)

Thanks Jean :)

I was thinking along the lines of 2x 440cc injectors mounted side by side in alternating mode.
I'm planning to run 4 squirts/cycle as you suggest so it's good to hear that this is a sensible approach (for TBI).

Regarding ECUs, Speeduino looks promising but I still need to add MS3 to my spreadsheet.

The only potential issue with Speeduino is lack of siamese code in case I can't get any results with TBI.
To be honest it might be a fun challenge to add the siamese functionality to the Speeduino as I've got some embedded programming experience... although not on AVRs!


jbelanger

1267 Posts
Member #: 831
Post Whore

Montreal, Canada

The MS3 also doesn't have a siamese code option. You need to use sequential injection and single pulse setup (not an MS3 option but the way to wire injectors and how you tune the injection timing); you also lose 2 injector channels. So if the Speeduino has sequential injection, you have the same option. The only ECU that has a complete siamese-port option is the MS2.

http://www.jbperf.com/


gcos93

17 Posts
Member #: 11040
Member

Portsmouth (South East)

Ah ok, interesting. I'll do some more digging around here on the siamese code to better understand what I might be missing out on. Speeduino does seem to support sequential up to four cylinders.

Probably a silly question but I've been playing around in tuner studio again and notice there's a mappable fuel trim for each cylinder if using sequential injection: Is there a reason why this can't be used to help reduce charge robbing?
Obviously it would be necessary to use a cam sensor and run twin widebands to tune the fuel trim so I'm not really intending to use it this way if I go TBI... just curious.


jbelanger

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Montreal, Canada

Nothing preventing you from using the fuel trim tables but you might also need to tune injection timing to get a perfect AFR distribution. But if you start tuning the injection timing, you might be able to simply use that with the main VE table to get the same result which would be much less work than playing with timing, VE and trim.

There are potentially many different ways to get to good fueling and the best will depend on your actual setup and which one makes the most sense to you (which way to tackle the problem is more comfortable to you and how that relates to analysis of the datalogs). But there are also other correction and calibration factors that need to be correctly set which will affect fueling differently depending on which tuning method you use (injector parameters, voltage corrections, baro corrections, ...). So it gets a bit complicated to predict all the potential interactions.

http://www.jbperf.com/


Rod S

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5988 Posts
Member #: 2024
Formally Retired

Rural Suffolk

If you go for a rear mounted (ie, more conventional) turbo setup the sample chambers can be quite unobtrusive.
All my original build photos went from this forum when photobucket committed commercial suicide but I still have them all on my server.

Mine's a rather crude Metro T3 turbo and cast manifold.
It's not ideal as the small bore sample tubes both have a dip in them which means they can collect condensation so I have to delay the power-up of the LSU heaters until the engine is running but the physical setup is very un-obtrusive because I run port injection so there is a large plenum chamber above that location.
Re. the MS2 siamese code it was really only intended for port injection with timed pulses to co-incide with the individual inlet valve openings so the injectors have to be as close to the valves as possible.
I might be wrong but I don't think it would work very well with a TBI setup because (a) the injectors would be a lot further away and (b) they wouldn't be physically associated with only one runner each.

Re, Speeduino, I had a play with it a couple of years ago. It appealed to me because of the TunerStudio interface. It is fully sequential (or batch if you want). At the time I would have said it was half way between an MS2 and an MS3 and although I never pursued it (just built one on their own board and played with it on a JimStim) but I still occasionally look in on their forum and it seems to have advanced quite a bit since i had a play.

Schrödinger's cat - so which one am I ???


Paul S

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Formerly Axel

Podland

The problem with TBI with sequential, timed injection as I see it is that the injectors are sitting at the end of a manifold and port that is greater volume than the cylinder. So, theoretically you need to start injecting before the cylinder starts filling. Even then some or all of the fuel will be left sitting in the port.

But, at the point you want to inject, the TB is feeding the other port so is going to go the wrong way.

It's a can of worms that I dont want to start to get my head around.

I did port injection using an Mpi manifold and an MS3 kit for less than the cost of an off-the-shelf kit, so that would always be my first choice.

Edited by Paul S on 24th Sep, 2020.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."


Steve220

238 Posts
Member #: 11017
Senior Member

Shropshire




On 23rd Sep, 2020 gcos93 said:
Cheers Phil. I figured there was a reason I couldn't find anything!

Has anyone even run TBI with >15psi boost before? I saw a post from wil_h saying that he ran 12psi with the SC TBI kit but I couldn't find anything else.

I could start by doing some trials with TBI on my brother's NA mini using twin widebands. Not sure how representative it will be for a turbo setup but I'm not keen to fit dual widebands to my turbo due to needing sample chambers.

I suppose data from an NA motor would be better than no data at all...

Grant


I run 18psi on an SC set up with 2x 630cc injectors. I regularly check the sparks and boroscope the cylinders for any potential signs of det, I also used a phormula KS3 as a sanity checker. WOT AFRs are around 11.8-12, taking into account that the WB is at the bottom of the downpipe.


gcos93

17 Posts
Member #: 11040
Member

Portsmouth (South East)

Thanks everyone for the helpful responses!

Jean: Interesting. Fair point that it may not be the best way to achieve even AFRs if other parameters are available (e.g. if using the siamese code).

Rod: Your sample chambers look very tidy! What sort of fittings have you used to connect the pipes to the sample chambers & manifold? Some sort of compression fittings? Flared pipes?

Just to clarify: If I go TBI, I'm not intending to use the siamese code. I was just thinking that if I start off with an MS2 then I have the possibility to upgrade to port injection at a later date depending on my success with TBI.

Paul:

On 24th Sep, 2020 Paul S said:
The problem with TBI with sequential, timed injection as I see it is that the injectors are sitting at the end of a manifold and port that is greater volume than the cylinder. So, theoretically you need to start injecting before the cylinder starts filling. Even then some or all of the fuel will be left sitting in the port.


This is an interesting point. I'll do some thinking on this as it does seem possible to get it "working" to some extent. I suppose as the duty increases, the situation becomes closer to that of a carb where there is a more continuous fuel distribution in the manifold? The effect you describe must have a bigger impact at low duty I would think?

I guess there must still be a point where the airflow "switches" from one manifold branch to the other and I guess that point in time would be close to the optimum injection start point...?

Steve:
On 24th Sep, 2020 Steve220 said:
I run 18psi on an SC set up with 2x 630cc injectors. I regularly check the sparks and boroscope the cylinders for any potential signs of det, I also used a phormula KS3 as a sanity checker. WOT AFRs are around 11.8-12, taking into account that the WB is at the bottom of the downpipe.

Very interesting. Thank you for this. So it might be possible to achieve what I want with SPI...

Everyone:
So currently, I'm thinking that I'll aim to bodge together a quick and dirty SPI setup to test with dual widebands on an NA motor. Just to satisfy the collective craving for knowledge!

Depending on the results I may then transfer to the turbo or have a rethink.


jbelanger

1267 Posts
Member #: 831
Post Whore

Montreal, Canada

Thanks for confirming that you were talking about port injection when you mentioned sequential. That's what I read in your previous message and what I considered when I replied. I also don't see the point in using timed injection when using a TBI setup and that's not what I was advocating, if that was not obvious.

http://www.jbperf.com/


gcos93

17 Posts
Member #: 11040
Member

Portsmouth (South East)

Ah sorry Jean. Were you responding to this comment from my previous post?

On 24th Sep, 2020 gcos93 said:
Just to clarify: If I go TBI, I'm not intending to use the siamese code. I was just thinking that if I start off with an MS2 then I have the possibility to upgrade to port injection at a later date depending on my success with TBI.


If so, that comment was addressed to Rod to cover this comment:
On 24th Sep, 2020 Rod S said:

Re. the MS2 siamese code it was really only intended for port injection with timed pulses to co-incide with the individual inlet valve openings so the injectors have to be as close to the valves as possible.
I might be wrong but I don't think it would work very well with a TBI setup because (a) the injectors would be a lot further away and (b) they wouldn't be physically associated with only one runner each.


Sorry for the confusion... there were so many posts I figured I'd try to reply to all of them in one go but I didn't do a good enough job of breaking them up.

Thanks for all of your input *smiley*


jbelanger

1267 Posts
Member #: 831
Post Whore

Montreal, Canada

No I was responding to Rod and Paul who both mentioned that TBI and sequential don't mix well which neither you nor I were proposing. I just wanted to make that clear to both and that I agree with them.

Edited by jbelanger on 24th Sep, 2020.

http://www.jbperf.com/


Rod S

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Member #: 2024
Formally Retired

Rural Suffolk

On 24th Sep, 2020 gcos93 said:

Rod: Your sample chambers look very tidy! What sort of fittings have you used to connect the pipes to the sample chambers & manifold? Some sort of compression fittings? Flared pipes?

Stainless steel compression fittings.
6mm OD stainless tube for the compression bit and either 1/8 NPST or BSPT for the threaded bit (can't remember which, I've got some of both and both taps). The important bit is the "T", tapered thread so no sealant needed.
The 6mm tube is either 0.5mm wall or 1.0mm wall (again, can't remember, I bought a bit of both and did toy with the idea of making the longer tube the larger diameter so the gas flow would be quicker and get there at the same time as the shorter tube but decided against it because the centre sample is hotter anyway - the small green wires you see in the photo are thermocouples, Paul, Graham and myself have used them at various times to check various things hence why we know there is little or no correlation between EGT and AFR).
The tube out of the chambers down to the downpipe just below the turbo flange is 16mm bore (can't remember the OD, but it's either 1.6 or 2mm wall thickness just for rigidity whilst still being able to bend it around a former without kinking).
The 14point7 controllers I use, in conjunction with Jean's T-IOX code, read the LSU temperatures and they are rock steady at 750C+/-1 whatever the engine load and the AFRs respond very quickly to changes so I think the tube size ratio must be pretty much spot on.

and Jean, sorry about the confusion, I didn't read carefully enough, I just saw TBI in some parts of the thread and MS-2 siamese in other bits.

Schrödinger's cat - so which one am I ???

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