Okay so after reading a lot of posts on here and a few on other forums I have came up with a few different concepts. Some have stuck throughout all of them.

Okay so as we all know we shoot for peak pressure to occur at around 12-20 atdc right? Peak power occurs at an afr of about 12.5. Most run richer on pump gas because of it is knock limited or more prone to detonation. So using the fuel to cool the combustion makes a safety net to avoid detonation. At higher Rpms we need the ignition to occur very quickly since it has less time burn all the fuel.

That is where that I am coming up with an issue. I have read in some places that the absolute best AFR for the fastest flame speed is an 11.1. Then I have read that it is actually still around the 12.5 AFR. In one other internet source it stated that to increase flame speed you increase turbulence slightly to increase atomization. My issue is that almost all of those sound legit.

I know that it cant be argued that peak pressure should occur between 12-20 degrees atdc. I just am wondering where the fastest flame speed occurs.

Also is it good to tune cylinder to cylinder since one cylinder could be different than another and maybe require more spark advance or a richer mixture? Would it net any gains I have heard its worth it. But i haven't seen it mentioned on here. What EMS will do this?


Sorry for the long post and all the questions. I hope that someone can help. Thanks in advance.

 

no one will or answer you on this. Every car is different, you got to find out and fine tune what work for your evo. But i can tell you on 91 octane 11.3-1.09.

 

You can set up a few standalones to enrich or lean based on EGT (or timing for that matter) but it requires individual EGT probes to be done properly. Realistically the time you'd spend is only going to find limited results.

91- 11.0 to 11.3 seems to be the best depending on the turbo (larger will run leaner)
92- 11.5-12.0
93- Havent done one in a while but I am assuming the same basic range as 92
E85- 12.0 on a gas wideband. You can make more on a lean tune but if its run at that level for an extended period of time it will raise combustion chamber temps high enough to lead to piston damage.

Hope that helps a little, some of it is versus RPM as well. Changes to enhance VE will affect how tolerant or intolerant a motor is as well.

aaron

 

I am asking mostly for what people have tried and found to work on their cars. But one question that I do want answered is what afr does the fastest flame speed occur? And is it worth it to tune cylinder to cylinder since not every cylinder is the same?

I am sorry if the first post seems misleading but i am not asking for an absolute sound fact on each car because they are all different just other people theories and what they have used and what works for them.

 

According to the greg banish advanced tuning guide the fastest flame front is at ~ 12.5 AFR.

 

Arron would you also say the A/F ratio that you can "get away with" on E85 also would depend on how efficient your setup is.... As in stock turbo at 30psi Vs 35R at 30psi?

 

Why would you only run it to a 12 afr on e85? I am not an expert by any means so i am not trying to knock anyone but i was told that stoich was a 10 at idle is that true?

 

Aaron's suggested AFR reading for E85 was for a GAS calibrated wideband, the AFR would be different if the wideband was calibrated for E85.

 

11.5 afr

 

air/fuel mixture and characteristics

AFR Comment
6.0 rich burn limit (fully warm engine)
9.0 black smoke/low power
11.5 approx rich best torque at wide-open throttle
12.2 safe best power at wide-open throttle
13.3 approx lean best torque
14.6 stoichiometric AFR (chemically ideal) <-- mean just enough fuel and air
15.5 lean cruise
16.5 usual best economy
18.0 carbureted lean burn limit
22.+ EEC / EFI lean burn limit


hope this helps

 

I'm so far from an expert in this area......but, It seems to me you are making this more complicated then it needs to be. If you start looking at tuning on a cylinder to cylinder basis would gains justify the time and effort involved with trying to get the best tune.

The way its looked to me through research here and on other sources (please correct me if I'm wrong) is that since there are so many variables that make it infinitely impossible to tune each the car the same you want to mainly pay attention to your knock count (if you are using something like ECUFlash. Just because your friend can advance his timing to a certain point on his car doesn't mean you will have the same/similar knock count.


Ok re-reading that it seems like maybe I'm over simplying.

Ok nevermind me.....carry on. lol.

 

Ha ha its okay if you over simplified. I have been told that you could net a gain that was substantial tuning cylinder to cylinder. But I didn't quite think about the fact that you would most likely need an egt and most likely a wideband for each cylinder. Lol not worth an additional 30 hp if you even obtain that.


Thanks for all the replies everyone that helped a lot. I just heard about max power occurring 12.5 but almost every tune i see says tuned in the 11.4 range.

Thanks for clarifying.