ROE Owners... School Me on Air Fuel Ratio's

[eabrillon1978]

I guess this doesn't really pertain to just Roe's, but that's what I am running.

Not sure if you read my other thread on the Alley about my dyno results with the 8lbs pulley or not, managed to get 699rwhp with 700 lbs of torque with 91 octane and a 50/50 mix of ****/water. I jumped to the 10lbs pulley and the stock fuel pump cannot support it. I have a dual pump setup from Roe that I'll be installing this winter and will resort back to to trying the 10 pounder again, so I'm resorting back to the 8lbs for the time being.

I've been doing some research and it's not resulting into what I've read during my dyno session. I went into there with my air fuel ratio's 11.8 through the midrange and then leaned out to 12.0 from 5000 to 6000. and car made 560.

Gave it more fuel to 10.8 in the midrange and 11.5 at the top and car made 640. Then to 10.1 and top end at 11.2 car made 699. Using a Vec 3 this is all with retarding timing from 6.5 degree's from 2,000 then bring it up to 0 degrees from 3100 to 5000 then backing it down 2 degrees after that point.

I made 720 with same 10.1 curve but brought the timing up 2.4 degrees in the mid. Had some minor detonation issues, so brought it back down to 0.

I didn't get a chance to try giving it more fuel due to the shop closing for the day. My wideband gauge matched the dyno's ratio's.

From what I've read, it says and what I've been told. Your engine makes most horsepower around 11.8's to 12.1. I am just curious as to how many of you that went to dyno tried to give it more fuel below 11's and had an increase in your results as I did. Anyone running below 10's

I'm going to head to the dyno here again in a couple weeks to experiment with bringing the timing up, I'll post again with my results.


Please chime in..

 

[Red Snake]

Mine (10 pounds with w/m) is dialed in to 11.8-11.9 all the way thru the power band.

Didn't try to add/pull fuel or timing from there. I just wanted it flat where it is thru the rpms.

 

[EllowViper]

Posted on the Alley:
You need to also determine the amount of methanol that is being used as fuel in your final AFR computations...since stoiometric AFR for methanol is considerably lower. Your "actual" AFR is probably leaner than what your gauge is reading...thus your impression that adding more fuel is increasing power (10.1 indicated AFR). The indicated 10.1 AFR is not really 10.1 since you are mixing fuels with differing stoiometric values. You are probably actually quite lean and by bringing the indicated AFR down, you are actually moving closer to an optimized AFR. Further indicative of this is the amout of timing you are able to run. At that PSI and AFR, I would expect much more timing to be pulled. So if you are able to run that much timing, that means [to me] that you are using a lot of methanol injection (W/M should compute to about 18-25% of total fuel required) You can compute your total fuel useage at various RPMs/load based on fuel pressure, injector size, and pulsewidth. Take ~20% of that and compute it into the W/M volume required. If you are using a good amount of W/M, that will bring your indicated AFR down. I believe there are some W/M calculators out there on the WWW.
100% gas.......................14.7
90% gas, 10% ****.......13.87
80% gas, 20% ****.......13.04
70% gas, 30% ****.......12.21
60% gas, 40% ****.......11.38
50% gas, 50% ****.......10.55
40% gas, 60% ****.......9.72
30% gas, 70% ****.......8.89
20% gas, 80% ****.......8.06
10% gas, 90% ****.......7.23
100% ****.....................6.4

What I would do is tune first with using 100% water in your injection set-up seeking around a "true" 11.2 - 11.5 AFR. Once that is determined, you can start introducing an increased % of methanol in the water to see the effect on AFR and how you can manipulate timing. THis is the fun part of tuning and seeing where you can get it "just right" across all the variables. Takes time, buts you need to take the incremental steps.

 

[EllowViper]

One more thing...most gas today is not 100% gas...but a 90/10 mix of ethanol blend. So you can never actually tune to a set AFR that is predicated on 14.7 stoiometric values. It would be nice to be able to calibrate your wide band to the actual fuel composition, but the best we can do is estimate when we are forced to use "may include up to 10% ethanol." Throw that into a stout W/M injection mix and who know what your actual AFR really is....Just something to think about.

 

[rw99]

VERY interesting points above regarding the effect of MeOH spray on apparent AFR post-combustion. I need to meditate on that.

Logging knock retard would give you an idea of whether increasing fuel has moved you into your optimum combustion AFR, regardless of what the widebands are telling you... BTW, it was wise to track both your wideband and the tailpipe wideband from the dyno.

 

[EllowViper]

Well, I might have been off on the AFR discussions a bit after doing a bit of backtracking. The logic holds, but WBs don't actually report AFR, but calculate AFR based on Lamda. If you are logging or viewing straight Lamda values, 1 Lamda is 1 Lamda regardless of the fuel used. Its simply measuring free oxygen. We are not used to viewing or thinking about Lamda and instead, looking at a gauge converting Lamda into an AFR. You really need to look at the actual Lamda value to compute your AFR.

 

[eabrillon1978]

Posted on the Alley:
You need to also determine the amount of methanol that is being used as fuel in your final AFR computations...since stoiometric AFR for methanol is considerably lower. Your "actual" AFR is probably leaner than what your gauge is reading...thus your impression that adding more fuel is increasing power (10.1 indicated AFR). The indicated 10.1 AFR is not really 10.1 since you are mixing fuels with differing stoiometric values. You are probably actually quite lean and by bringing the indicated AFR down, you are actually moving closer to an optimized AFR. Further indicative of this is the amout of timing you are able to run. At that PSI and AFR, I would expect much more timing to be pulled. So if you are able to run that much timing, that means [to me] that you are using a lot of methanol injection (W/M should compute to about 18-25% of total fuel required) You can compute your total fuel useage at various RPMs/load based on fuel pressure, injector size, and pulsewidth. Take ~20% of that and compute it into the W/M volume required. If you are using a good amount of W/M, that will bring your indicated AFR down. I believe there are some W/M calculators out there on the WWW.
100% gas.......................14.7
90% gas, 10% ****.......13.87
80% gas, 20% ****.......13.04
70% gas, 30% ****.......12.21
60% gas, 40% ****.......11.38
50% gas, 50% ****.......10.55
40% gas, 60% ****.......9.72
30% gas, 70% ****.......8.89
20% gas, 80% ****.......8.06
10% gas, 90% ****.......7.23
100% ****.....................6.4

What I would do is tune first with using 100% water in your injection set-up seeking around a "true" 11.2 - 11.5 AFR. Once that is determined, you can start introducing an increased % of methanol in the water to see the effect on AFR and how you can manipulate timing. THis is the fun part of tuning and seeing where you can get it "just right" across all the variables. Takes time, buts you need to take the incremental steps.

That's what I was looking for right there!!! Very well put. I will try just that. As far as the nozzle size, I"m running the stock nozzles from Roe. I believe Mike said they were 7gallons and hour. Mix is 50/50. I stepped it up to a 60 ****/ 40 water mix to work on that detonation issue I was having when I was trying to advance the timing further.

I have been doing some reviewing of my dyno runs. On my second run I had a strait and level curve of 12.1 from 2,000 all the way to 6000 and I put out a low 610-620. I started to experiment by keeping a strait curve and bringing is down to 11.8. gained another 20. Then I decided to richen up the midrange a little heavy and and leaning out on the top end to end up at 11.8 and the result was torque/horsepower increased. If you haven't tried already you should experiment with this as well and see if you get a huge increase as I did. I didn't touch the timing at all until the very last pull.

 

[FastMatt]

Well, I might have been off on the AFR discussions a bit after doing a bit of backtracking. The logic holds, but WBs don't actually report AFR, but calculate AFR based on Lamda. If you are logging or viewing straight Lamda values, 1 Lamda is 1 Lamda regardless of the fuel used. Its simply measuring free oxygen. We are not used to viewing or thinking about Lamda and instead, looking at a gauge converting Lamda into an AFR. You really need to look at the actual Lamda value to compute your AFR.

This is Correct