Does anyone have any good reference data points to start from to build a AFR vs Boost curve? I don't think going right to 11.3:1 at 2000rpm at 1psi is the best thing to do. Figure an AFR of 12.5:1 once in PE and ramping in fuel with boost enrichment is the way to go but at what point is 11.3:1 really needed? 6psi? 8? 4? The dyno will help fine tune this but i'd like to get in the ball park. The car does see a lot of part throttle boost (road course, autocross and mostly fun on the street)

YSI peak around 16psi, 12:1, 408ci, E85

 

MAF or SD? What fuel system parts do you have? How are you controlling enrichment right now? Boost referenced Regulator? Fuel pump booster? Tune? have you pulled the plugs after a boosted pull? What did they look like? What's your plug gap? What plug do you run? How are you tuning? HP, SCT, Diablo? How are you measuring AFR? Dyno only, or do you have a wideband in the car?

A lot of questions I know, but you're asking a vague question within a complex system of parts that require functioning a certain way to achieve your goal. All the questions are relevant to one another. Also, the stoich points of E85 are totally different than pump. So 12:1 sounds all wrong as it is if you're running E85 100% of the time. If you start mixing fuel (E85 and pump) tuning will because MUCH more difficult without a flex fuel sensor equipped.

 

MAF based.
ID1000 and plenty of pumps. I know the injectors should be bumped to at-least 1300's, but they are making due
2BAR OS. PE set to 12.5 @ 15% and I've just started playing with BE and it seems to be working fine. Targeting 11.3
Fore 2i regulator with base idle pressure of 72PSI with MAP @ 8.8-9.0psi and boost referenced 1:1. (decent sized cam)
No fuel pump booster, just a couple holley's hobbs switched at 4 and 6psi
Plugs aways looked good as far as I can tell, no I don't pull them after a pull, this isn't a drag car, it's a street car. gapped to 26 and are NKG BR7EF
How am I tuning? By luck I suppose. Rods are still in the block! HPTuners.
AEM AFR analog output wired to HP Tuners pro data logging box. So all the data is in HPTuners.
Wish I had a dyno to do this one. :/

So with regard to AFR, the previous tuner did things on the gas scale, I kept it. I do have a flexfuel sensor to monitor the content on the dashlogic/hptuners, but I have no plans to switch to allow for pump just yet.


So again. if Stoich is 14.62:1 and getting into the power around 0psi is 12.5 and that's decent. how quickly would one ramp into the fuel to what boost level to get int he ball park? I've started out with 12.0:1 at 110kpa and at 11:3:1 by 124kpa. to keep things close to how they were working just fine before.

 

That's the thing...stoich for GAS is 14.7ish, but it's 8.8-9.0 for E85. The gauge only cares about Lambda though. That being said stoich for E85 at boost should be around 7.0 - 8.0. You may be really lean if you're tuning only with your wideband gauge, which is why I said check the plugs. If they're white (or crusty white) you're lean. The car maybe pulling timing to prevent going pop. You really should take it to a tuner that specializes (or is at least familiar with) in E85. Tuning by luck is playing with fire man...especially, if YOU don't understand the variations between the two.

 

It's just a number that i've stayed consistent with. Things can be converted back and forth and mean the identical thing.

11.3 = 0.77 = 7.51.... which is exactly where you said I should be. WEIRD HOW THAT WORKED OUT.....

If you haven't a clue what you're talking about I suggest you stop suggesting.

thanks for not answering my question a second time, it's probably for the best.

 

Okay man...you never said your trims were anything of the sort, but more power to you. If you know everything, you shouldn't need forum help. I'll duck out and hope your engine stays together. Good luck.

 

Part of tuning and finding what works, but your thinking is on the right path. I run 23-24psi peak boost, at ~11.2-11.3 afr. At 5-6psi I'm around 12.5:1 and don't get into the 11s until over 10psi, but you just have to see what the car likes. See where it picks up torque/power, and how sensitive it is to knock.

As far as when it is needed, really depends on your compression, cam, etc etc etc. Put it on a dyno, and spend a few hours finding out.

 

Thank you Unreal. I'm going to keep ramp from 12.5 (base for PE) to 11.3 at 6psi for now see how things drive and what not. Dyno time is coming one of these days to confirm I can run a little leaner than 11.3. motor is a 12:1cr so I'd rather be on the rich side.

 

 

Generally, it's easier and safer to just run on the richer side under most boosted conditions and use the spark to find best torque at each point. I typically aim for Lambda=0.78 across the board for my first guess and then find the knock limited spark advance for each load (g/cyl varies with boost) and RPM point. Slightly richer AFR mixtures will help with knock resistance on pump gas as well as help keep exhaust components cooler.