Air Fuel Ratios for supercharged applications

[07cobaltsupercharged]

Just curious what ranges you tuners are shooting for for AFR's at WOT...I know there are some variables involved but lets say for a safe tune with forged internals LS6 at 16 timing max with stock or close to stock cam/ stock heads stock fuel system with BAP. Seems to be 11.5 is a good safe bet but do you shoot for one AFR number for whole rpm range or go richer before peak torque and then drop a little leaner to redline?

Edited: Yes its a centrifugal blower

[RWTD]

If you're centrifugal, you can run leaner out of boost or low boost, and then taper it richer as boost comes in. PDBs (positive displacement blower setups) pretty much need a flat AFR at WOT.

[5_Liter_Eater]

I do 11.5:1 across the board but I realize I could lean it out in the lower RPM's. I've been debating going from 13:1 at atmospheric to 11.5:1 by ~5 PSI and flatline from there but I'd want to try it out on a dyno to see if there is much to be gained.

[RWTD]

Bill, honestly, there isn't a lot to be gained. I test this on many vehicles. However, the power can rise slightly, but it does make for a cleaner and more crisp power delivery, which you can see in the graph (maybe not feel tho, lol). Most of the time we race from, what, 3000 or higher rpms? By that time we're already well into boost.

[TXZ0603]

So what would you shoot for on a turbo application? I was going for 11.7 with meth @ 18deg.

[RWTD]

So what would you shoot for on a turbo application? I was going for 11.7 with meth @ 18deg.

It sounds as if you are tuning via PE table raping! You do realize that you must run richer on meth right (due to the lower stoich difference)? On top of making less power, you will potentially smoke your engine running that lean on meth under boost! Also, you tune off meth first to dial in your MAF, and then you spray the meth, and jet it properly. NEVER use the PCM to modify the fuel on meth!!! It is what it is when spraying.

[Ironmancan]

So what AFR should one aim for when spraying meth. I'm spraying a 50/50 mix.

[TXZ0603]

No PE raping here. No MAF either, 2barSD. Ive been using the afr%error only working with the VE table. The PE is set for 11.7 as well as the BE. So with meth I should shoot lower? Good to know!!! What would you suggest for AFR?? Oh and I am spraying 100% meth.

Not sure what you mean by jetting the meth?? Its an alky control unit that sprays under boost only.

[RWTD]

Well, meth kits have jets, right? Yes! So you only need so much meth to obtain the desired results (lower IATs and more spark and/or boost without knock).

As for AFR, in my professional opinion, once you get the amount of meth mix you want, you do NOT modify the Actual fueling that is obtained with it. You could experiment around with seeing if going richer or leaner will give you more power (0.1 tenths at a time!), but you MUST have a load-bearing dyno to do this. And, since you're using an SD OS, then use the Boost Enrichment table to change fueling for the meth. I'd still use the PE table for WOT/Boost, however.

[Ironmancan]

Allright I've been playing with my meth at the track trying to get the right AFR with the Meth. Changing the time it comes on vs the jets. I'm running about 10.1 at full boost 18 PSI Forged LS2. PE set at 11.7 but when the meth comes on it obviously changes my AFR. I've been looking at leaning out the mixture should I? Is there a target AFR I should be looking for when I'm spraying the meth. I'm sure there is.

[Ironmancan]

With Stoic on meth 7.0 vs 14.7 for pump gas.

From the Turbo buick forum. "Here in the states there is a lubriant called Klotz that is used.

(Meth) 5.0 should be like 11.3 (Gas)"

Since I am not running full Meth my 10.1 might be closer than what I think.

Edit: Looks like 10.5 is a safe starting point when I am spraying the meth. opinions?

[TXZ0603]

there are no jests in my meth kit. Its a progressive kit that operates off boost psi.

so you are saying boost it without the meth, set AFR then add meth and correct the BE to reflect the AFR I want??

[Ironmancan]

That exactly how I set mine up. Tuned for no meth (turned off meth kit) now I'm playing with the kit on to see if I can get more out of my setup. 13lbs of boost, 11.6 at 129. My posi unit craped out so no good 60's till i get that squared away.

It would make it quite a bit easier if I had a target AFR with the meth on vs running down the track and figuring it out. I'm going to head back out to the track and get it dialed in with meth on at 10.5 AFR and go from there. Adding timing, taking away fuel etc etc etc till I think I've reached a peak...

[blownbluez06]

RWTD, I have tons of respect for you and mean no disrespect, but wanted to post my experience and beliefs regarding this subject.

The additional oxygen released in the burn of Methanol slightly skews the true AFR#'s. It does take more alcohol ( Ethanol or Methanol) to reach a good boosted mixture, however the UEGO's don't know what kind of fuel we're using. They're only measuring oxygen. If you run gasoline in a car and tune it and then run E85, you would still tune it for the same #'s. It will take much more E85 to achieve those #'s though. It must be understood that the sensors are simply converting a Lambda value to an AFR, but that isn't necessarily your true AFR. If you programmed it to convert the Lambda to a proper AFR for a different fuel, it would read differently. One more example. If max power, WOT true AFR should be 9.0:1 on a pure Meth car but you had it programmed for gasoline and you set it up to run 9.0:1, you would be running way too rich because of the conversion of Lambda to gasoline AFR.

Take a look at this and it may clear up any confusion I may have caused by not wording something properly. Notice the chart has a lambda value, and then the true AFR for gasoline (petrol), natural gas, methanol and then diesel. The lambda is the same, but the true AFR's are not.
http://www.techedge.com.au/vehicle/wbo2/wblambda.htm

I had a short discussion with an engineer from Innovate regarding this very thing.

I tune with meth for my ending desired AFR. On my 9.5:1 403, I have my PE and BE set for desired and when under boost on my 2-bar tune, It looks like a professional skiiers dream. A huge down slope, lowering VE values with increasing boost to compensate for the meth.

The question people ask me is "what happens if you lose your methanol for any reason?"
The answer is that I use the IAT vs. Spark and remove tons of timing in the area which I will only hit in the event I lose the meth for any reason. I have made 2 full quarter mile passes with no knock, running a very lean, 13.x:1 AFR to prove it works.

[blownbluez06]

there are no jests in my meth kit. Its a progressive kit that operates off boost psi.

so you are saying boost it without the meth, set AFR then add meth and correct the BE to reflect the AFR I want??

Who's kit do you have Jerry?
The "jets" in the Alky Control system are defined by the nozzle size. i.e. I have a size 15 nozzle. Then there's a dial to determine the pump speed relative to boost.

[Ironmancan]

The question people ask me is "what happens if you lose your methanol for any reason?"

The answer is that I use the IAT vs. Spark and remove tons of timing in the area which I will only hit in the event I lose the meth for any reason. I have made 2 full quarter mile passes with no knock, running a very lean, 13.x:1 AFR to prove it works.

So under boost running meth your registered AFR is 13.x:1? Really?

[RWTD]

RWTD, I have tons of respect for you and mean no disrespect, but wanted to post my experience and beliefs regarding this subject.

Thanks!

Hey, we both agree on the fact that using meth requires a richer stoich/AFR. That is what so many do not realize or care to understand.

I could work to point you all to a few in-depth writeups on determining proper stoich values (more on who made those in a few). For those only running one form of fuel enrichment, all one needs to do is determine this and then modify their Stoich AFR parameter within their pcm calibration, and everything else falls into place. Now, for meth, this is a different story, as one is not on meth 99% of the time, therefore they have to allow the meth to add the fuel for the most part. Yes, some tweaking can be done with the PE and/or Boost Enrichment table to add even more fuel (or even richen it up). As know, I do not recommend skewing the Load/VE calculations of the pcm. However, everyone will be different in this area, and it's hard to say which is "less wrong" or "more right", since meth takes away the perfection of proper tuning via pcm only control.

Stoich of pure gas is approx. 14.6x, as we know, 50% ethanol is approx. 11.8x, and 100% pure ethonal is approx. 8.9x, and 100% pure meth is approx. 6.47. A 50/50 of pure gas with meth would produce a stoich of approx. 10.4. On ModularFords.com, my good friend Eric (black2003cobra), who is a brilliant engineer, I believe has an article on how to determine stoich in the combustion process based on % of meth injecting. On a meth kit, naturally it's not going to be 100% perfect, as there isn't any logical means of determining the exact mixture within the combustion chamber, due to variances in meth kits and how they release the fuel. However, if I'm right in remembering that Eric did make such an article, then his data would help you get it VERY close.

All in all, as we both agree upon, one must always run richer when using alcohol based fuels, and this goes for injecting meth. The stoich is what it's all about!

So under boost running meth your registered AFR is 13.x:1? Really?

No, what he's saying is that he adjusted his IAT vs. Spark table OFF meth to see if he would register any knock, and even ran it up very lean.

No, I would NEVER recommend anyone doing that under boost, but all he's saying is that obviously IATs skyrocketed at his boost levels when meth was off, and he used the IAT vs. Spark table to yank out a buttload of spark to remain safe.

[5_Liter_Eater]

Got a link to that article James?

[TXZ0603]

Who's kit do you have Jerry?
The "jets" in the Alky Control system are defined by the nozzle size. i.e. I have a size 15 nozzle. Then there's a dial to determine the pump speed relative to boost.

I got Julios kit. Running it on #6 I didnt know there were diferent nozzle sizes for these ( got it used ) Just trying to wrap my head around it all so I tune it right.

[Ironmancan]

RWTD thank you, I understand. I've learned more reading on this forum about tuning my car the right way and its greatly appreciated.

Rick