Air/fuel ratio question

Haggisbash

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Joined
Dec 10, 2013
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7
Location
Dunedin
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).
 
Thanks Bullshark, just the info I needed:thumbs: Maybe I have a slight induction leak somewhere that allows the range to get so lean.
 
General guideline.

1748863e3143499.jpg

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:
 
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.
 
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:
 
Gene, I do remember Norval. He was a pretty sharp Mechanical Engineer/ Instructor I believe. Didn't like to debate much though. :D :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:
 
Gene, I do remember Norval. He was a pretty sharp Mechanical Engineer/ Instructor I believe. Didn't like to debate much though. :D :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.....:(
 
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.
 
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:
 
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