It is true that gasoline has a small latent heat of vaporization, but there is something to be said for controlling burn rate with afr. I feel like there is something being overlooked by your philosophy.

 

Their is something to be said for shoving timing down a motors throat. You can alter your burn rate which indirectly "adjusts" the amount of ignition timing needed. Or you can run the *proper* AFR and adjust ignition timing directly as needed. The mere fact that you are suggesting slowing down the burn rate demonstrates that you don't understand the simple concept of mean brake efficiency and how to increase it.

I run mid 12's to redline. You should be mid 12's or richer during spool up due to AFR layering due to the poor atomization during boost transition. I don't care about dynos and HP numbers. I care about the fact that going from mid 10's to mid 12's netted me over 10mph in traps on a single T&T tune day. Honestly I don't care about any data you present to me because I've found a way to make nice power with awesome reliability in the real world not on a simulating machine.

 

I was trying to avoid semantics but you brought this point up.

At this point you may start arguing the definition of "efficiency" with me. For me efficiency is increasing the amount of energy we can get out of the fuel for each stroke. With that said you should look at Honda CVCC and honda civic VX lean burn technologies where they run leaner than stoich and increase efficiency.

If we had a perfect cylinder head we could run stoich in boost. However in the real world we have lean spots and layering to worry about. With that said we could not run leaner than stoich even with a perfect cylinder head because we would enter lean misfire territory where the mixture does not like to play nice anymore.

I live in the real world so as such I've done a lot of testing behind ALL my comments. I'm not trying to blow smoke up anyones ***, I've done a lot of racing with my comments. I like the real world, I like how things aren't so simple as in my physics and thermodynamic classes. I'm also still searching for that massless and frictionless pulley. I thought I found one on ebay but it sold before I could bid on it.

 

so essentially:

mid 11's for safety
mid 12's for power!

80/20 rule anyone?

 

If you set up your timing curve to run mid 12's and then richen it up to mid 11's then thats fine. If you shove timing down the motor and richen it up to mid 11's so that it doesn't detonate then, no. You have essentially eliminated the safety curve that way while reducing your peak power output. Some deem the difference insignificant and fast people deem it significant. Or you could run the proper AFR, richen it up half a point to account for "lean" fuel or a slight ecu miscalibration and back off the timing 1-2 degrees for safety all the while having another safety in the way of the active knock sensor.

 

You're wrong on that last statement. Its not a hard concept to grasp. What's more of a challenge is determining the optimum conditions for safety and power. You have your method which apparently works with great success for you. I'm curious about it, but I don't know if I believe it yet because my best results (combination of power and knock resistance) thus far have been with low or mid-10 afrs out at the higher rpms. And I'm not a fan of big timing numbers. I'm only running 10 deg at 7000 rpm. I've tried leaner afrs, and it starts knocking by the third pass.

 

Sounds like you guys have a lot more knowledge on the subject than I do. I only know what I've found through trial and error.

I've tried running 12.5:1 on my IX and it didnt care much for it on the mid to top end and it was causing knock even with considerable timing pulled, power was not up. However having 12:5:1 during spool up does work well for getting peak torque, it just seems like the engine can't handle that AFR for long after spoolup.

I've personally found that peak power on my car is attained by spooling lean starting out at 12.5:1 @ 3000 richening to 11.5:1 at full spool (max 2byte load) 4* timing, and then gradually richening to 11.1 at redline (7800 in my car) @ 15* timing. Any less fuel up top and power decreases and so does the knock threshhold. In fact I have a friend's car that seemed to make more power the richer it was up top.. like it made more power up top at 10.5:1 than it did at 11:1:1. We ended up leaving it 10.5:1. I wanted to get another wideband on his car to verify that his reading incorrectly.

 

Personally, my EVO8 likes 11.3-11.5 @ 24psi with as much timing as it will handle.

 

Dan l and MrFred,

I think that you are both on the right track.

As many of you have heard, an engine, regardless if it is FI or NA will make peak power with an AFR between 12.5-13.0. This is true for most gasoline fuels. The reason for this is that you are getting the fastest Flame Front Propagation near this AFR.

But.... and most of you will not beleive this unless you have seen it yourselves, and engine will make the same power with a wide window of AFRs. When I had my open wheel car's engine on an engine dyno, I could run 11.0 - 13.7 AFR and yeild the same amount of power. What this depends on is whether or not your fuel is knock limited.

In the case we are debating, pump gas with these cars at the boost levels they are running is Knock Limited. This means that we are not able to calibrate the engine to run MBT without the engine detonating.

It is important to understand that MBT (minimum best torque) which is the smallest amount of timing advance to create the best torque at a given load and RPM, is pretty much completly independent of AFR. Most people will argue this, but as I said before, if your fuel is not knock limited, you can run a wide range of AFRs and create the same amount of power and torque.

If you are running inside of the engines "window" which is usually between 11.0 and 14.0, MBT is MBT. Anywhere outside of this window, power drops off significantly.

Purley hypothetical....Lets say that 20degrees advance, 11.0:1 AFR at 20psi and 4000rpm, puts peak cylinder pressure between 12-20degrees ATDC. This would be the roughly the same amount of advance needed at this load and RPM to produce MBT for the window of AFRs I have been talking about. So for 4000rpm and 20psi, as long as the fuel is not knock limited, and the engines temperature is under control, 20degrees advance is MBT. If you change the afr from 11.0:1 to 13.0:1, remembering that you are not knock limited, you will not see much of an increase in power due to the fact that your fuel is not knock limited, and you are able to run MBT.

I have seen cars on dynos countless time make the same amount of torque at 11.0:1 to almost 14.0:1. The percentage difference throuought the range was roughly 2%, which interestingly enough is about the same percentage change you see in the rate of flame from propagation. Since there is only roughly a 2% difference in flame speed in this window, with the proper fuel, you can run MBT and make the same power. With pump gas, we can not run this lean without detonation, so we must run richer.

I dont agree with cramming timing down the engines throat and just adding fuel to compesate. But, what is needed is to find the window of AFRs where the car will make the same power, and get timing as close to MBT as possible inside of that window. This will yeild the most power safely.

So on a knock limited fuel, such as pump 93, I would figure out what window the engine will make the same power, run it to just about the richest it can be within this window so that you can run timing advance as close to MBT as possible.

Customers in my area typically run 93-94 octane, and I have found the low end of the window to be right around 11.2:1 depending on where the fuel is from. My preference is sunoco 94 for pump gas, evos and dsms love it!

Good Luck

 

Finally a post I can fully follow and agree with. It's really all about that ~15* ATDC point. The AFR you use get there is pretty much irrelevant as long as you aren't super rich or lean.

Thank you Dei.

 

Reason everyone likes more timing and overfueling is due to lousy source of fuel. Once water/methanol is introduced and if the ignition system is healthy, if you have 12.1 or more across the rpm and timing is reasonable - it would be difficult to go back especially when 4000 - 6000 rpm 3rd gear times have been as low as 1.96 seconds. Compared to 2.4 seconds with more timing

After getting encouraged to boost timing a couple degrees from the recent E98 post I decided to go ahead. The result was no gain in power, in fact a little less, still no knock from being supressed with W/M but no gain in power. Why is that? Perhaps because the power was allready optimised -no more to tap, I don't know so I pulled the timing back where it belongs.

 

Yes, you are very much correct. Using very precise pressure transducers inside of the combustion chamber, I have seen the peak cylinder pressure window narrowed down to about 14-16degrees ATDC. I used 12-20 since it is a bit larger, and was use by a previous poster as a reference.

It pays to be an engineer! Thanks for the compliment. You would be amazed how many "tuners" do not understand the above!

 

Well, many people know what to aim for, they just don't understand why.

C6 is also correct in the above post. I'm not 100% on how meth injection works, but my understanding is that it's main purpose is to raise the knock threshold of lower octane fuel. This goes right back to Dei's post.

If your timing was already at the MBT point, then more advance will do no good. It is really difficult to find this point by road tuning though ... I'm not sure if you're referencing dyno numbers or a road dyno calculation.

 

Post 24 marks the point in this thread that I no longer understand and is basically for engineers only, I understand a little chem, but physics I'm lost.

I do feel smarter already just being here though

 

Honestly, it is pretty simple ...

You get the most torque from the combustion stroke when the cylinder reaches peak pressure at ~15º After TDC. Your goal as a tuner is to reach this mark for peak power. Hitting this mark involves many variables, such as:

Engine RPM
Ignition Timing
Flame Front Propagation

My understanding is that the sort of "rough tune" is the ignition timing @ a given RPM, and the "fine tune" is the fuel mix and plug choice that defines the flame front propagation. The faster the engine spins, more ignition advance is needed to reach the 15º ATDC mark.

With fuel that is infinitely knock resistant it is as simple as setting the minimum timing for the most torque (MBT) and then fine tuning to that 15º mark by adjusting the AFR within .85 to .9 lamda. It becomes more complicated when knock is involved which is why all of these debates start.

In the most basic sense, hitting dead on the 15º ATDC mark with the greatest cylinder pressure possible will make the most power. This is honestly undebatable.