Looking for info on a "best fuel to air ratio" on a hooded door car with a flat fuel ratio-current is 5.3 start to stripe-small block with carbs-any help would be great

I use the gas scale and run 12.9 to 13.1 which translates to 5.66-5.76 on Methanol scale.
I take my measurements before the finish line full throttle.

Hey thanks for the reply thats what Im lookin for -other folks with a small blocks ratios. Just changed hood scoops and old forward facing scoop was 5.3 on starting line but went to 5.7 at finish line new hood is modified cowl with rearward facing scoop showed 5.3 end to end and wanted to know how lean to make it at a flat fuel ratio-sorry for long winded post

quote:

Originally posted by vetman:
Hey thanks for the reply thats what Im lookin for -other folks with a small blocks ratios. Just changed hood scoops and old forward facing scoop was 5.3 on starting line but went to 5.7 at finish line new hood is modified cowl with rearward facing scoop showed 5.3 end to end and wanted to know how lean to make it at a flat fuel ratio-sorry for long winded post

Curly is leaving out one detail, he runs 8 O2 sensors and tunes each cylinder. If you are looking at the average of 4 cylinders, I would be real careful about running at 5.7. I would let the MPH and the plugs tell me what average a/f to run.


Joe

X2

I think 5.3 is a good start but read plugs...

Agree with others that 5.3 is a safe number to start with. Along with O2, I find using an EGT sensor data with methanol to be a help.

Never intended to go 5.7 flat but was thinking maybe 5.4-5.5 for a good middle ground set-up will start at 5.3 but check on MPH from old curve. Thanks again for replies

This is a carbed small block car running 5.60 on this pass. 5.5-5.7 varying throughout the pass.

quote:

Originally posted by vetman:
Hey thanks for the reply thats what Im lookin for -other folks with a small blocks ratios. Just changed hood scoops and old forward facing scoop was 5.3 on starting line but went to 5.7 at finish line new hood is modified cowl with rearward facing scoop showed 5.3 end to end and wanted to know how lean to make it at a flat fuel ratio-sorry for long winded post

You may want to take a good look at the scoop and carb deal. If the scoop causes turbulent air to enter the carb it will cause issues. Try an air filter or even a velocity stack, both will smooth the air entry into the carb. The carb should/will see the added pressure from a sealed scoop and will deliver more fuel.

Also I would NOT chase any specific O2 reading until you verify want works best in your combo, period! Let the time slip tell you what it should be! Values that you read on here are just ballpark numbers for you!

Add fuel until engine doesn't like it.
Take fuel away until engine happy again.
Read o2 data and plugs.
Use o2 data for reference only.
Use plugs to tell you what to tune..

Add more fuel and enjoy......

I don't think they are accurate enough on alcohol. I have an O2 in each header (had them in the collectors and moved them to 1/2 way between header flange and merge). They vary .30 in their readings.

4.9-5.3
5.2-5.5

I have switched them side to side and the variance stayed with the O2.

I use it only as a reference and tune it old school using water temp at the head and mph.

My water temperature never changes from start to finish line. I have leaned it until it fell off and whatever you leave the line at is what it will be when you lift. Large radiator in my car I guess is why.

Tom are you saying the 2 different sensors vary or that they varied from collector to tube location?

quote:

Originally posted by Tom Reyer:
I don't think they are accurate enough on alcohol. I have an O2 in each header (had them in the collectors and moved them to 1/2 way between header flange and merge). They vary .30 in their readings.
4.9-5.3
5.2-5.5
I have switched them side to side and the variance stayed with the O2.
I use it only as a reference and tune it old school using water temp at the head and mph.

When I switched from MFI to Holley EFI I had to use only their recommended O2 sensor made for methanol to be used with their ECU. This O2 sensor is calibrated and expensive ($300).

Prior to installing the EFI injectors, I ran the MFI with the Holley ECU to collect data to be used for initial EFI tuning.

With either system (efi/mfi), the water temp (170- 175) stays the exact same from start to finish (fan Not On during run) in the 1/8 mile. I have a small radiator with 11.5 qt cooling system.

Ok guys when I switch to alky I put in a inovate motorsports o2 setup sensor in collector at number5 car has made hundereds of passes with no issues at 5.3-5.7 all I was lookin for was a number for new hood scoop setup it was 5.3 end to end same as number at about 60ft. mark before not gona buy more stuff as what I have has been very succesful

I just posted up that pic to show the shape of mine. Everyone's numbers vary slightly.

quote:

Originally posted by CURTIS REED:
My water temperature never changes from start to finish line. I have leaned it until it fell off and whatever you leave the line at is what it will be when you lift. Large radiator in my car I guess is why.

Tom are you saying the 2 different sensors vary or that they varied from collector to tube location?

I have 2 Grid O2's on the car. The sensors read different side to side. I switched sides and the difference followed the sensor.

As far as water temp. I make a run with the pump and fan off and my temp sensor is in the head. In the 1/8 in cool weather, temp doesn't change. In the summer, I gain 10-15 degrees going down track with everything off.

I rarely change jets now and only play with air bleeds.

What's everyone's idle O2 readings with methanol? I know gas likes 13.5-14.0 or so, does that equate to about 6.2-6.5 on methanol scale? Just curious.

quote:

Originally posted by NC3x58:
What's everyone's idle O2 readings with methanol?

With MFI my idle was 4.0. With EFI now my target idle AFR is 4.6

With my carbs I set it at 4.9 5.1 stays clean and no stumble