What are some of you guys seeing for a/f ratio on MFI set ups. After many struggles I have got my car to finally 60’ consistent, but now i’m seeing a good bit of inconsistency down track. I’m thinking its tune up related at this point. 23 degree 434 with Ron’s Toilet. I know those numbers vary, but i’m trying to make sure i’m in the ballpark. O2 in collector shows 5.6-5.4, with the 5.4 being at the highest rpm. In my experience, a little lean will tend to just around on the et and fat will not. That being said, based on other factors, water temp, fuel consumption etc, I’m resisting what the experience is telling me about it being lean. Water gains a couple degrees max going down track, and burns a gallon or maybe a hair less, driving up on primer plus, driving back on alky, with shut off pulled to lean it out.

I use the gas scale on my data logger and it runs best 12.9 to 13.1. It does not have to be that close car will run good and run number probably 12.3 to 13.7 but I like to keep it close to ideal number. Do not remember exactly what that comes out to on the alcohol scale but there are charts out there.

Also with MFI not every cylinder is not the same. I run 8 O2 and have learned some interesting information. You can private message me and call and I will go into more detail.

typically they are faster when they are 5.2-5.4

quote:

Originally posted by 329L:
typically they are faster when they are 5.2-5.4

So looking back at my 598 runs, I typically run it in the 5.3-5.1 range. I guess that answered my question right there.

I have the O2 in the collector, but on my dragster I put bungs in the back two cylinders on each side and collector. I move the sensor around to see if there is a difference and it’s usually nothing noticeable.

My 388 on Rons (toilet) is fastest and most consistent using 5.1- 5.3 afr wot. I like it richer. It’d idle at 4.0

I just switched to my EFI intake and used 5.2 for the entire target afr map.

quote:

Originally posted by markemark:
My 388 on Rons (toilet) is fastest and most consistent using 5.1- 5.3 afr wot. I like it richer. It’d idle at 4.0

I just switched to my EFI intake and used 5.2 for the entire target afr map.

Thanks for the response! Looks like i’m a bit lean then and i’ll make a pill change before the next outing.

All 4 of my O2s are reading 4.8 for the car to be consistent. It’s a 421 running 0 pump with kinsler nozzles flowed to what my 33 Ron’s are and 92 kinsler main pill. I do have to run a high speed leanout to get the 330 and backhalf numbers consistent

JMO 02s are like an EGT. Depends on where you have them what there going to read. Racepak says 12” from the head. My car 2 pills lean or 2 pills rich the car isn’t consistent

quote:

Originally posted by C Hodge:
JMO 02s are like an EGT. Depends on where you have them what there going to read. Racepak says 12” from the head. My car 2 pills lean or 2 pills rich the car isn’t consistent

I am going to disagree with that. EGT temps will change depending on how far from the head the probe is.

With O2 it is reading Oxygen (or lack of)and that does not change for most part through out the pipe unless there is a gasket leak or too close to exhaust drawing in air.

Yes I would prefer if all my O2 sensors were close to same location and distance but I do not think it is critical like it is with EGT.

quote:

Originally posted by markemark:
My 388 on Rons (toilet) is fastest and most consistent using 5.1- 5.3 afr wot. I like it richer. It’d idle at 4.0

I just switched to my EFI intake and used 5.2 for the entire target afr map.

I am going to say this. I do not really care what the O2 or EGT numbers are do not tune to those numbers. Tune to best ET and then see what your O2 is and then you can use it as a reference. Your O2 may read quite different than mine and your motor may like more or less fuel than my combination. Your calibration may be different.
Tune to time ticket and then you have good O2 numbers to shoot for.

quote:

I do not really care what the O2 or EGT numbers are do not tune to those numbers. Tune to best ET and then see what your O2 is and then you can use it as a reference. Your O2 may read quite different than mine and your motor may like more or less fuel than my combination. Your calibration may be different.
Tune to time ticket and then you have good O2 numbers to shoot for.

I agree with that statement.

My Rons MFI has been tuned for best MPH for years. I prefer to be on the rich side of the tune and have done well with it this way. I’ve never owned an EGT or O2 sensor so I had no idea what my reading were nor did I care. You’ve seen my 500+ runs spark plug pics.

When I installed Holley HP control with the existing MFI this spring, I was able to get the data (O2, EGT, MAP, Fuel pressure) I needed prior to making the switch to EFI. I now knew what the MFI fuel map looked like and tried to make the first EFI map very close to the same based on my engine HP.

quote:

Originally posted by C Hodge:
All 4 of my O2s are reading 4.8 for the car to be consistent. It’s a 421 running 0 pump with kinsler nozzles flowed to what my 33 Ron’s are and 92 kinsler main pill. I do have to run a high speed leanout to get the 330 and backhalf numbers consistent

I’ve been debating on adding a high speed leanout also to flatten the fuel curve a bit.

From my experience the High Speed Leanout is not much help in 1/8 mile racing and in fact just adds another potential problem with the tune up. I run one but mine has a small bypass and really is not doing much. For 1/4 mile I would probably want it coming in 1000 to 1100 feet just to fine tune top end. We rarely ever get to race 1/4 mile here.......

If you go with high speed get a electric triggered on. That way you can time it to be same place every time rather its timer or rpm. IMO RPM would be best for working with fuel curve since pump flow should is controlled by rpm.
The old pressure poppets work but any change in jetting will effect when it comes in.

As for 02 vs egt. Both are just a tool and when used correctly are great benefit.

quote:

Originally posted by markemark:

quote:

I do not really care what the O2 or EGT numbers are do not tune to those numbers. Tune to best ET and then see what your O2 is and then you can use it as a reference. Your O2 may read quite different than mine and your motor may like more or less fuel than my combination. Your calibration may be different.
Tune to time ticket and then you have good O2 numbers to shoot for.

I agree with that statement.

My Rons MFI has been tuned for best MPH for years. I prefer to be on the rich side of the tune and have done well with it this way. I’ve never owned an EGT or O2 sensor so I had no idea what my reading were nor did I care. You’ve seen my 500+ runs spark plug pics

I have 2 o2 sensors for my grid and use them only when there is a problem. They give me a number range and I look for anomalies if the car does something stupid.

You certainly can't tune an alcohol carb with them. One reads .2 lower than the other. I even switched them side to side to see if it followed and it did.

When I tried my Ron's fuel injection, I adjusted the idle with an egt gauge.

quote:

Originally posted by Tom Reyer:

You certainly can't tune an alcohol carb with them. One reads .2 lower than the other.

Would you mind explaining that a little further? I have had zero problems tuning my alcohol carb with my o2s. What did I do wrong?

I run 8 O2 sensors on both my cars and tune each cylinder as needed. I am a firm believer on O2 and have no faith in EGT's in fact I removed them on my car.

This Holley EFI I installed uses a $287 calibrated NTK O2 sensors for methanol. Holley HP control only uses one O2 sensor for closed loop. I don’t see the need for more than one O2 and believe an average of one side of the engine could possibly the best.

Richen it with the pill till it slows down and starts to blubber at the gear shift, then lean out in steps of 5 to get to optimum ET/MPH, back up 5 numbers richer on the pill and leave it. Read the A/F at that point see where you are, tune to get back to that if racing in crazy weather that the ET is way off from historical. Targeting a specific ratio is about like targeting a specific EGT it don't make sense due to variations in probes and engine combinations.

The o2 sensors to me are a lot like thermocouple probes. Everyone elses data means jack nothing compared to your combo. You can try to get to a number that makes sense for someone else, and still be lost and with a car that runs like crap. Once you find a happy place, sure the o2's can be helpful to watch and compare to weather conditions. Very dangerous, particularly when you get to forced induction to rely on the o2's and ignore the plugs. Plugs do not lie. When you get to a happy place with your tune, even on efi, you can use the o2 to make corrections to help with weather changes. IMO, I don't like to let the o2 have control under most conditions. If you get a wiring issue or a sensor that's going south, you can be unwittingly be led down a bad path. I prefer to get a tune that works for particular weather, and if needed use the o2 data to get a tune that works for today's weather, and then set it in stone for the day.