Making an AFC work? And other fuel questions.

[Mekkahfire]

Well, some of us dont really have the money to blow 1500 bucks on an EMS... So we make do with an AFC.

But how do you tune it?

From what i understand, when you use the AFC to restrict fuel from large injectors, the ECU advances timing to compensate.

I remember talking to ATS Aaron a while back. I cannot remember the full extent of the conversation, but if i remember correctly he told me to get some adjustable camgears, retard the timing two degrees, Then restrict fuel with the AFC so that when you put the engine under load, it resets to Zero.

Also, why cant you just restrict the fuel flow to the 550's with a Fuel Pressure Regulator?

[jerzefigga]

you use the AFC in conjunction with an adjustable FPR.

[Weasy2k]

you can use the FPR to change the FP so that you have to ADD fuel with the S-AFC vs remove fuel...thus in turn tricking the ecu there is MORE air then there really is...MORE air = MORE load = less timing according to the ecu.

if you have a decent sized turbo and 550's this is easy. If you have a CT27 and 880's then this isnt a smart idea.


Or you can scrap both and get a smt6 :P

[Mekkahfire]

Originally Posted by Weasy2k

you can use the FPR to change the FP so that you have to ADD fuel with the S-AFC vs remove fuel...thus in turn tricking the ecu there is MORE air then there really is...MORE air = MORE load = less timing according to the ecu.

if you have a decent sized turbo and 550's this is easy. If you have a CT27 and 880's then this isnt a smart idea.


Or you can scrap both and get a smt6 :P

See, thats what i asked and i got shot down.. Hmm.

Anyway, what do you think about CT27, 550's, Apex-i AFC?

[Weasy2k]

Get a FPR.

strongly recommended.

This method wont unlock the MOST power potential and will be finicky. I prefer to be able to tune the timing as well, but it has worked in the past.

[Enthalpy]

I'm going to disagree, respectfully.

When you bring down the fuel pressure, you turn 550s into 440s. If you have to add fuel, then you have gone further than that.

When you do this, you also hurt atomization, which is required for good fuel economy and a responsive engine.

Given you can't do it right with an EMS, I suppose the 2nd-best idea is Aaron's. You should retard the base timing and pull fuel with the SAFC where needed. This will accomplish two things:

-Pulling fuel where needed (probably across the board)
-Avoids adding overall timing.

However, there are side-effects:
-The AFC is a horrible estimator of what the engine needs, especially with our AFM system! You will approximate what the engine needs in some places and be grossly off in others. I can get into the reasons if you would like.

-The 2nd side effect is reduced timing off-boost, which will lead to reduced fuel mileage and reduced response. However, your engine will survive just fine.

If you add cams, you make things WORSE. Cams require MORE timing off-boost, and LESS timing on-boost! Because you are forced to choose one or the other, your mileage will wind up being worse.

[Mekkahfire]

Arg, there has to be a way to make a decent tune with an AFC! I dont see EVERYONE running EMS's! Theyre like 1500+ bucks man..

Grr..

[Enthalpy]

I know, believe me. You have to pay to be fast AND have great drivability.

It depends on your definition of "decent." You can get it to run acceptably well, but you will probably notice a rough idle, more fuel consumption and a reduction in off-boost engine response.

It's sort of like the difference between a carb and fuel injection. Carbs do the job adequately well, but fuel injection does everything better, faster and more reliably.

[Weasy2k]

Well i got pwn3d by enthalpy

I agree tho its a shitty way of doing it...i like to try to give other options even tho sometimes they suck and wont do to much and run pig rich :P

Enthalpy I read all over the place that is what has been done in the past, even from some of rickyb and noshoes posts.

The base timing idea is a good one too I did that with the last AFC FPR tune i did.



As far as ems's go...take a closer look on how much they cost...

[Mekkahfire]

Okay well take this from a broke-ass kid that is trying to do things right standpoint.

Yes, im a nazi about not half-assing things and doing things right. But that can only go so far due to my income level. :/

I just hope my local tuning shop can do something with it.. I doubt theyl already have the knowledge of the ECU's effect of advancing timing with an AFC.

[Enthalpy]

Originally Posted by Weasy2k

Well i got pwn3d by enthalpy

How did I pwn you? It's a respectful disagreement, that's all. It doesn't make me right. My opinions are based on my training, my research and my experiences.

Enthalpy I read all over another board that is what has been done in the past, even from some of rickyb and noshoes posts.

Yes, I know. I must respectfully disagree with them. I think this was a position they advocated early-on. They might be softer on these positions now. I can point you to posts by both of them that say cams are the impetus for traveling to EMS land.

Every tuner should always be learning. An example is Aaron, who had posts that indicated he had zero knowledge of the physics involved. That has undoubtedly changed by now. The two that come to mind were Aaron's arguements with Ricky involving calculating Volumetric Efficiency and calculating the AIT's (air temp sensor) impact on fueling.

Once again, this comes down to what is acceptable to the user. I tuned a car a few weeks ago that was cammed, had big injectors and an SAFC. I got it to work, and the owner accepted the results because they were cheap.

[Enthalpy]

Originally Posted by Kiddquikk

Okay well take this from a broke-ass kid that is trying to do things right standpoint.

Yes, im a nazi about not half-assing things and doing things right. But that can only go so far due to my income level. :/

I just hope my local tuning shop can do something with it.. I doubt theyl already have the knowledge of the ECU's effect of advancing timing with an AFC.

You know, you could always try it and if you don't like it, then get rid of it. Start by pulling at least 5 degrees from the base timing. Set the fueling with the SAFC on the dyno. Then, add the timing back in, find the limit of detonation, and back off ~3-4 degrees for safety.

[Weasy2k]

Originally Posted by Enthalpy

How did I pwn you? It's a respectful disagreement, that's all. It doesn't make me right. My opinions are based on my training, my research and my experiences.

No no not in a negative way I never take it as offence twas more of a joke

And I too am learning (always will be) so thank you for being here and adding all this info its great to see another tuner in this forum helping out (one much more experienced then me which ROCKS!)

I should have just stuck with my original saying...once you open it up you need to change engine control.
I am using cams on my 5vz tacoma using the SMT6 with no problems, but with that unit i can tune to a finer degree then the afc (i hate that thing with a passion!)

[Mekkahfire]

Okay maybe i need to reinstate my goals.

Im looking for 300hp, or a 12.5 quarter mile time.

Can i do it with an AFC and my listed setup?

[Enthalpy]

If your goal is speed, then yes. If your goal is speed, fantastic drivability, off-boost response and fuel economy, the answer is no.

[Mekkahfire]

Then i already knew the answer this entire time.

Thanks lol.

[karl]

Originally Posted by Enthalpy

I'm going to disagree, respectfully.

When you bring down the fuel pressure, you turn 550s into 440s. If you have to add fuel, then you have gone further than that.

When you do this, you also hurt atomization, which is required for good fuel economy and a responsive engine.

i don't think people understand the extent to which fuel pressure makes a difference in atomization. the other day i had an injector set up at 35psi and it emitted a steady, almost straight stream of fuel. with the pressure up to 45psi the fuel coming out was a nice misty cloud. dropping the pressure on 550's to make them run like 440's is akin to turning the nozzle on a spray bottle from "spray" to "stream." just my 2c.

[Enthalpy]

Originally Posted by karl

i don't think people understand the extent to which fuel pressure makes a difference in atomization. the other day i had an injector set up at 35psi and it emitted a steady, almost straight stream of fuel. with the pressure up to 45psi the fuel coming out was a nice misty cloud. dropping the pressure on 550's to make them run like 440's is akin to turning the nozzle on a spray bottle from "spray" to "stream." just my 2c.

I knew with low pressure it turned into an open garden hose type of a stream, but I didn't realize it did so at 35 psi! Great information!

[the2ndr]

my 440's@43psi base fuel pressure with 16psi of boost= leaner than my

my 550's@29psi base fuel pressure with 16psi of boost.

The 440's a/f ratio is 12.2-12.5 from 6500-7200 rpms.

The 550's af ratio is 11.5-11.9 from 6500-7200 rpms.

I use an safc and haven't blown up my mr2 in the 5 years Ive owned it.

Do what you want to do, not what some else tells you to do. You may have mave some consequences or you may not. Its up to you. I do not have a ct26, ct20, or ct 27.

[Enthalpy]

I have personally seen 3 blown up 3S engines on that stupid SAFC. I didn't blow them up, but I helped the owners deal with the aftermath. The SAFC brings you closer to the edge. Your car is clearly further from the edge than most.

AFR measurement is a tricky thing. It can get quite noisy, especially if you have atomization issues like you would with 550s at a logic-defying 29 psi. Aside from that, the pintle dynamics will change things.

Like 2ndR pointed out, it's your car. Do what you want. The tuners on the board have recommended against this course of action, and provided very good reasons for it. If you still want to do it, then Mazel Tov.