Hey need technical input - strange idea inside

[BBR]

While diagnosing my latest problem. I pulled the plugs and noticed that the 4 center cylinders seemed to be running leaner that the 4 outboard cylinders.

Uneven flow is a trait of this particular intake manifold. Edelbrock Victor.

Typically in a carb'd application, the outside 4 run lean.

In a efi application, the fuel is going to be a constant for all 8, so the air flow differences effect the afr differently than a carb. You will have an inversed effect. Given the same volume of fuel for each cylinder, the end cylinders are getting less air, thus running richer than the center 4. With a carb, you will have a direct relationship between flow and afr since the fuel is atomized in the airstream.

Now for the idea:

Since MS is bank to bank, can I rewire injectors so that the outside 4 are a 'bank' and the inside 4 are a 'bank' and run them off separate fuel tables?

Or is there a better way to vary fuel flow bank to bank?

Discuss!

[TheSilverBuick]

Re: Hey need technical input - strange idea inside

From what I know that's how you'd want to do it. Run the lean ones on one bank and the rich ones off the other. I "think" you can run separate VE tables for each bank..... Like staged injection only the parameters are set so both stages are running all the time.

[BBR]

Re: Hey need technical input - strange idea inside

Holy crap. Just found it.

Dual Table.

Dang, they think of everything.

My ms1-extra supports this very function. Wow.

Now I just gotta figure out how to set it up.

[TheSilverBuick]

Re: Hey need technical input - strange idea inside

I've looked a bit into it for shutting down 4 injectors. I'll experiment to see if I net any gains (not expecting any noticable gains due to pumping losses), or to possibly experiment down the road with a Caddy 4-6-8 engine and Multi-port injection.

[dieselgeek]

Re: Hey need technical input - strange idea inside

We run dual table for staged, dual fuel setups.


It's ballsy, you probably just want to take your primary VE table, and subtract or add just a few percent of fuel to balance it out. You'll be stuck with the same percentage on the inboard 4 cylinders though, and the problem is - they won't be the same amount of flow difference at all RPMs/loads. Which is OK, you can tune for that, but you want to start with just the WOT cells at 100kpa.

The other thing you NEED to do at this point: get those injectors flowed, rated, and matched. It's common to have a 5-7% variance between them (even the ones that claim they are matched, aren't that great, unless they come from RC IMO)

Anyways, I'd get them matched, know which injectors are a little lower quantity than the others, and factor that into your tuning.


For dual table, make sure you configure it to fire both banks of injectors during cranking. Holler if you need help.


One cool thing about Dual Table: it's a feature NO ONE ELSE has, not even MoTec. It's 100x better than staging.
-scott

[Dynoroom]

Re: Hey need technical input - strange idea inside

The only thing I would add to this conversation is that "dry air" flow is different than wet flow. So the end cylinders might not be lean at all in a direct port injection application. Test first.

[BBR]

Re: Hey need technical input - strange idea inside

The outside ones are certainly richer in this application. It is very obvious when looking at the plugs.

I am gonna read up on the dual table stuff and decide what I want to do. It's too bad there's not just a bank-to-bank fuel bias adjustment you could make. Something that just uses one VE table but adds or subtracts a percentage to fine tune it.

[dieselgeek]

Re: Hey need technical input - strange idea inside

I am gonna read up on the dual table stuff and decide what I want to do. It's too bad there's not just a bank-to-bank fuel bias adjustment you could make. Something that just uses one VE table but adds or subtracts a percentage to fine tune it.

Negative!

That's how most of the systems out there do it already. BigStuff3, FAST, Gen7 DFI. My testing showed that, there is almost NEVER a "fixed percentage" of airflow difference. Barometric changes, airflow volumes, etc. are going to cause the variance among cylinders to be different, and frankly it pisses me off that someone would put that kind of adjustability into an EFI system and sell it as "individual cylinder tuning" - the way to handle that properly, is to monitor what the AFR, EGTs are doing at all loads and at different barometric conditions so you can map out what each cylinder needs at all those different points...

the absolute right way to do it, is to have a VE table and Baro corrections for each cylinder.

And the only box you and I can get our hands on that does it this way, is a MoTec. keith Turk's Rodeck motor was tuned this way by Dave Dahlgren. It adds about 20x the complexity and time required to nail down the tune, but you can at least be sure that the engine is going to run right and not kill itself at ALL possible loads, weather conditions, density altitudes, etc.


-scott

[CTX-SLPR]

Re: Hey need technical input - strange idea inside

I dream of MoTec......

[dieselgeek]

Re: Hey need technical input - strange idea inside

I dream of MoTec......

buy one! they're not even that expensive anymore.

[shaun callaway]

Re: Hey need technical input - strange idea inside

I dream of MoTec......

Why

just to say you have a motec lol

[BBR]

Re: Hey need technical input - strange idea inside

It's ballsy, you probably just want to take your primary VE table, and subtract or add just a few percent of fuel to balance it out. You'll be stuck with the same percentage on the inboard 4 cylinders though, and the problem is - they won't be the same amount of flow difference at all RPMs/loads. Which is OK, you can tune for that, but you want to start with just the WOT cells at 100kpa.

For dual table, make sure you configure it to fire both banks of injectors during cranking. Holler if you need help.

So do I use the reg_fuel and ve table values I have now for both tables? or does req_fuel need to be cut in half?

[dieselgeek]

Re: Hey need technical input - strange idea inside

Should be the same req_fuel since it's a per cylinder number.

[BBR]

Re: Hey need technical input - strange idea inside

Aaaaaah yes. I knew that. doh! :P

[CTX-SLPR]

Re: Hey need technical input - strange idea inside

Nope.... because the MoTec gives me the capabilities that I like of the OEM systems without the restrictions on being able to only access certain tables. Its also Aircraft certified so I know its going to be hardned and survivable. It includes traction control and some other provisions if I can remember correctly. And its got cool stuff like individual cylinder skewing and such. Oh and I can say I have a MoTec M900 or such running my ride.