AFR Tuning and Knock on E85
 

So I have made the switch to e85, the VDR has me at about 620hp/433ft. I am currently in the process of turning up the boost, right now I am at 25psi, and I started with some pretty rich AFR's and the car pulled good and clean. Once I turned the boost up to 25psi, the car really did not like the rich AFR's anymore. So I have been leaning out the car to try to get the engine noise down. There are a lot of people saying that the AFR's need to be in the 12.5-13.0 range.

So here is what I am shooting for.

Spool Up - 12.8-12.9
Peek Torque - 12.7-12.9
Peek RPM - 12.4-12.6

So on my quest to get to those numbers I am seeing some very strange stuff showing up as knock. I was wondering if anyone has any advice on this.

Do you have a good COP setup?

Have you tried tighter plug gap?

AFR's should be good, assuming your W/B is correct?

I'm guessing ignition...

:mitsu:

I'm guessing too much timing or something making noise :D

I have a COP, AEM TwinFire.

I was running BPR7ES gapped at .020.

I switched to BR8ES gapped at .020. Now I have a massive missfire around 8400 rpm, so I will tighten up the gap a little more. I also go the AFR to be pretty consistant.

Peek Boost = 12.47
Peek Torque = 12.65
Peek RPM = 12.50

So it is pretty much 12.50 across the board. I am not sure why it would missfire up top except gap. It was only at 15 degrees of timing. Is it possible to have to little timing?

So my car goes from

Peek Boost = 5*
Peed RPM = 15.5*

I'd suggest dialing back the peak trq timing a bit.

Your red-line timing should be OK, but the peak trq timing might be a little high. If you are getting some knock at trq peak it can easily cascade into an even bigger event.

I think you will find that zero timing at peak trq is common on E85, but each car is different.

I think it is much safer to pull a bunch of timing and then add it back in small increments. Work the timing up rather than down, if that makes sense.

:mitsu:

does your car make more power this much leaner? that is the question..... if it gains a significant amount of power going from 11.8 to your current then its probably ok, but the leaner you run the hotter egt's get remember that.

The numbers in my sig i ran with just 11.0-11.2 a/f when i go to 11.8 i gain nothing more then i do at 11.0-11.2 ---------------- now if i go from 11.8 to 12.2 i gain some more power. the question is do you trust running this lean? if you beat the **** out of your vehicle on a daily basis then running slightly richer would be the smarter decision. Most guys will say 11.8 is what E85 likes. From my experience 12.2 seems to be the best for it.


also e85 will not knock if you run it to lean. keep that in mind. with all the above said i dont recommend going over 11.8-12 a/f for a daily driven vehicle that is beat on a daily basis.

ya good advice. start low and work your way up. and use something such as vdr to make sure you can atleast somewhat monitor the changes the timing is doing to the vehicle.

The tricky part is getting the mid section 5-6k setup for best timing, hard to do this not on a dyno.

btw what you said makes absolutely no sense at all. turning the boost up requires more fuel in return the afr will go leaner by default. It should have ran better regardless. The cars probably pulling timing without you realizing it. read the bottom stuff mentioned about timing.

I will re explain.

At 10-22psi, my base tune was at 11.8-12.2 afr's. When I turned the boost up to 25psi, the car no longer liked 11.2-12.2 afr's.

This could have been plugs, afr's, or timing. This could have also been related to me having a little q16 left in the tank when I first made the switch to q16. I just finised tuning the car at about 700whp on q16. I was tired of paying 15 bucks a gallon for Q so I made the switch to E85.

Now that I am 100% sure that there is no Q16 in the car, the E85 could be telling me what it wants.

Also I am on an AEM EMS, and in my log files I can see when it pulls timing related to knock.

Here is a screen shot of a pull I did recently.

http://carphotos.cardomain.com/ride_...0016_large.jpg

where is the timing graph on that log? i dont see it. be careful, e85 isnt like q16. knock your peak torque/load area down to 1* and go from there. once you get close to where mbt is you will gain crap tons of torque. dont push it past 20* uptop with e85.

also i wouldnt go past 12.2 on gasoline wideband. see how much power different you get from 11.5 to 11.8 and 11.8 to 12 and 12 to 12.2 and base your decision on a/f off the results. the richer you can get away with the better.. colder egt's = safer.

Awesome, good info.

The next big steps for me are gapping down my BR8ES to .018.

Pull even more timing out of my map. I am going to pull it all the way down to 1* and have it ramp to about 15*

The stoich for E85 we use here in Oz is way lower than 98RON Gas we run... Have you tried converting your AFR to Lambda, then checking with your E85 data...

As said by others.. plug gap at high boost is critical because captured mixture has higher density, timing ditto.

Hi all, bringing an old thread back from the dead here - but it raises some interesting points.

What are people tuning their E85 setups to? Like on 18psi, 25psi, 30+psi?

It seems generally accepted that around .82lambda is a good place, but there are documents lurking around which suggest max power rich is ~.7 lambda and max power lean is ~.86lambda (10.3 - 12.6 with gas scale AFRs) for E85.

Fortunately the low .8s are right in the middle of that range, so no matter what it should be good - however I have heard of people trying 11.0 or richer and getting power gains, and I have also heard of people running 11.0 or richer and measuring knock which I find interesting. When tuning E85 does "lean is mean" become "rich or lean is mean"?

Does anyone have ideas why E85 would get "rich knock"? I've not found a proper explanation for why this might happen, though have started constructing theories.

Any discussion would be appreciated :)

My assumption for "rich knock" would be to it being a thicker fuel per sue. I may be wrong though.