Different gas to adjust AF ratio?

[69 GTX]

So where I live the corrected altitude can be anywhere from 0 to 4000 ft depending on weather and time of year. So I was wondering if I tuned the car with straight gas for spring and good air, could I run 10, 15 or 20% ethanol blend to lean it up a touch as the DA rises? I have installed a wide bans O2 sensor on both sides to help tune & monitor the AF. Just wasn't sure if this was feasible or not. All input welcome. This will be a street/strip car. 440+6

 

[Yatzee]

So where I live the corrected altitude can be anywhere from 0 to 4000 ft depending on weather and time of year. So I was wondering if I tuned the car with straight gas for spring and good air, could I run 10, 15 or 20% ethanol blend to lean it up a touch as the DA rises? I have installed a wide bans O2 sensor on both sides to help tune & monitor the AF. Just wasn't sure if this was feasible or not. All input welcome. This will be a street/strip car. 440+6

First off you'll have to find what altitude your operating the car at. Iowa is pretty flat and near sea level with slight rolling hills and farm land. Don't know what "spring and good air" means because I'm certain you're not the only driver in Iowa and I'm sure they run regular gas year round. What A/F ratios are you trying to reach because a value of say 13.9:1 at idle will change infinitely as you accelerate or decelerate. Carbs are not good at maintaining fuel to air ratios because they operate on vacuum to draw fuel with timing changes that occur mechanically. Unlike TB or MPI you can never have fuel tables for different operating conditions. I would think a 440+6 at the strip would require fuel with no ethanol so that's the fuel type I'd use consistently. If you need to lean it out, carbuerator work is required. Just what is straight gas these days anyway?

 

[69 GTX]

I'm referring to gas without ethanol as straight gas. We also have blends of 10% 15% 20% & 85% blends. Spring temps 50-60 & humidity 20-40% usually equate to 0-2000 ft corrected alt. As summer comes in, like now, we see 90 degrees with 60-80% humidity and 2000-4000 ft correct alt. I know that when running alcohol you need to run bigger jets, so I was wondering if running blended fuel it would lean up the AF ratio.

 

[67 coronet]

give it a try and let us know if it makes a dif. i could see maybe on a full blown race only vehicle,but seems like it would be hard to swap all the gas in a street/strip car.

 

[66Satellite47]

IMHO, I'd avoid the ethanol blends. Run the highest octane non ethanol you can get. Air density (density altitude) will effect your jetting a bit. If you have the carb in the "ball park", the air changes won't matter that much. I bracket raced from BIR Mn, Rock Falls Wisc, Cedar Falls Iw, Byron IL, Stanton Mich. Keep your jetting in the middle. If you need to go for Max power/performance OK. That may lead you astray.

 

[68 HEMI GTS]

Your gonna have to find what the motor likes. The six pack carbs don't have adjustable air bleeds (unless you drill and tap them) so you are somewhat limited on your levers for adjustment. Generally a larger cammed engine will need to be in the 13's at idle. Example the roadrunner idles around 13.5 in neutral, in gear the vacuum drops and it goes 14.0. It then becomes a balancing act between idle and cruise. Get the idle fattened up to work good at low vacuum but under cruise you have high vacuum and the motor pulls like crazy an the idle circuit and is fat. Generally if you can get the motor into the low/mid 13's under cruise it'll be happy. Your plugs will stay clean and your mileage will be decent. Without adjustable bleeds you'll have to tweak your IFR's on the center carb and idle screws on all 3 carbs to find the happy medium. Under WOT its best to target fat then go to the strip and make adjustments from there. My 511 is fastest around 12.0. Also having the timing curve right will play a big part on your idle and cruise. I run premium pump gas. I'd have to check the ethanol content though.

I though I seen you had an adjustable metering block in the center. That's good, I had to go down to .032 on my IFR's to get that balance between idle and cruise. My motor only wants to pull 5.5 inches of vacuum at idle though so that adds to the complications.

 

[Cranky]

Is your fuel system ethanol compatible? When they went to 10% here, my mileage went down some on the EFI cars and it played havoc on the older carbed cars....

 

[69 GTX]

Yes it's compatible. Yes a blend will give you less mpg, but usually the cost per mile is usually the same.

 

[69 GTX]

Thanks for the input 68. My combo has about 10lbs of vacation at idle. Yes to IFRs. It was tuned on dyno and idled & pulled at WOT perfectly. But that was at 5000 ft. I guess I'll just have to wait till it's on the road.