Air/fuel ratio question

[Haggisbash]

Hi guys, this is my first post, I have had my 70 Vette for 12 months or so and this is my first American car, first V8 etc. I have some experience with European cars but primarily with motorcycles. I've been trying to get the engine running better and mostly succeeding but I have a question regarding the above. I'm using a wideband 02 sensor and gauge to check the mixture settings of the carb (this is a new tool for me) I notice that when descending a long hill on a closed throttle that the A/F ratio leans out to 17:1 is this normal/harmful? Before the descent the ratio is approx 14:1.
Info: car came with an old Holley 1850 carb and Torker 1 single plane manifold, I have changed the manifold to a Perfomer EPS dual plane, changed the secondary vac spring to the third lightest avail (it came with the black spring fitted which is the heaviest and I could not get full opening of the secondaries).

 

[Bullshark]

General guideline.

 

[Haggisbash]

Thanks Bullshark, just the info I needed:thumbs: Maybe I have a slight induction leak somewhere that allows the range to get so lean.

 

[mrvette]

General guideline.

Bullshark, remember that engineer named Norval, from the other forum, years ago he got his QJ to cruise at 17-1, with a wide band O2 sensor??

anyone else ever do that?? and how much are wide band O2 sensors these days, would be nice to tune my injection for that....

:smash::stirpot:

 

[Haggisbash]

My understanding is that there are only two wideband O2 sensor manufacturers - NGK and Bosch, everything else is badge engineered. Cost to you would be under $60 for the sensor alone. I'm using an Innovate Motorsports unit.
With fuel costs in the region of $7 + per US gallon here a 17:1 cruise A/F ratio sounds like a good idea. I don't know whether it would be attainable on this particular engine. People say why buy a car like the Vette if you are worried about fuel economy but I like to use the car regularly and tuning that will improve the economy but not kill the performance is my aim. A 200R4 trans is sitting in my garage awaiting fitting for that reason but also because of the better "cruise ability".
Looking at the carb I often wonder if an accelerator pump with a variable delivery would have been workable, ie slow acceleration gives a smaller pump shot than normal for city stop start driving.

 

[mrvette]

My understanding is that there are only two wideband O2 sensor manufacturers - NGK and Bosch, everything else is badge engineered. Cost to you would be under $60 for the sensor alone. I'm using an Innovate Motorsports unit.
With fuel costs in the region of $7 + per US gallon here a 17:1 cruise A/F ratio sounds like a good idea. I don't know whether it would be attainable on this particular engine. People say why buy a car like the Vette if you are worried about fuel economy but I like to use the car regularly and tuning that will improve the economy but not kill the performance is my aim. A 200R4 trans is sitting in my garage awaiting fitting for that reason but also because of the better "cruise ability".
Looking at the carb I often wonder if an accelerator pump with a variable delivery would have been workable, ie slow acceleration gives a smaller pump shot than normal for city stop start driving.

Jeez, wide band O2 for a silly 60 bux?? I be ON that one....years ago it was 200 bux, and with dubious possibilities, given I have FI on the car....BUT, looks like this is worth another glance.....thanks....

:yahoo::clap:

 

[Bullshark]

Gene, I do remember Norval. He was a pretty sharp Mechanical Engineer/ Instructor I believe. Didn't like to debate much though. :smash: I seem to remember he did some detailed studies on combustion temperatures or something like that. A/F ratio of 17:1 on a carbureted engine running pump gas {10% ethanol) is a crap shoot IMHO even though he used his LC-1 wideband o2 to tune it. Today's Lean Burn engines employee technology like direct injection/ variable valve timing with aluminum block and heads, sophisticated knock control etc. They can realize up to 23:1 A/F ratio.

The Innovative LC-1 is the most economical way to go. I think you can get one for around $175 including sensor these days. Remember, your junk yard GM computer uses narrow band o2. You could reprogram it to run a wideband O2 but thats a bubba rig IMO. I think Marck is the expert doing all that.
Whoops, I didn't mean to call you a Bubba TT :lol:

 

[mrvette]

Gene, I do remember Norval. He was a pretty sharp Mechanical Engineer/ Instructor I believe. Didn't like to debate much though. :smash: I seem to remember he did some detailed studies on combustion temperatures or something like that. A/F ratio of 17:1 on a carbureted engine running pump gas {10% ethanol) is a crap shoot IMHO even though he used his LC-1 wideband o2 to tune it. Today's Lean Burn engines employee technology like direct injection/ variable valve timing with aluminum block and heads, sophisticated knock control etc. They can realize up to 23:1 A/F ratio.

The Innovative LC-1 is the most economical way to go. I think you can get one for around $175 including sensor these days. Remember, your junk yard GM computer uses narrow band o2. You could reprogram it to run a wideband O2 but thats a bubba rig IMO. I think Marck is the expert doing all that.
Whoops, I didn't mean to call you a Bubba TT :lol:

:devil: maybe that will bring him outta hiding, not been heard from in a long time.....

 

[Haggisbash]

Yes, it is the Innovate kit that I have, but you can run a wideband sensor and read off it with a multimeter if you want to have an cheap metering system You have to be careful though, if you have an O2 sensor with a heater in it you will need to power this or the sensor will be destroyed within minutes.

 

[mrvette]

Yes, it is the Innovate kit that I have, but you can run a wideband sensor and read off it with a multimeter if you want to have an cheap metering system You have to be careful though, if you have an O2 sensor with a heater in it you will need to power this or the sensor will be destroyed within minutes.

:shocking: Yeh, mine is a heated stock narrow band switch in the header collector on right side....but it's only a 3 wire unit, I could convert to 4 wire in a few minits effort....just run a sensor ground to the computer directly, I suppose it gives better accuracy.....like the wide band would do....

MY problem is that back in '95 I installed the 1227730 speed density computer and have never changed it, had a few chips in it, but never messed with the computer, have had maybe5 of them over the years, still have 3 as one got destroyed due to stock wiring, long story....

:ill::shocking: