OK , I admit it. I have been stuck in the dark ages. Is this wideband Oxygen sensor thing something guys working on their own cars only can do and afford? Or does it take equipment that is only feasible to guys making a living at it ?
On a road trip to Texas and back I could count on 16 mpg with the 350 and turbo 400 and ? gears. Later with the 250 three speed and again ? gears the truck got 20 mpg on road trips. I got to where I could tell within about half a gallon as to how much gas it would take at a gas stop. Truck has never had a working gas gauge since I owned it by the way. I always went miles x expected mpg.
They are ***s! The price has come down a lot in the last ten years say. Have to have an O2 bung installed (welded) in the exhaust, maybe a foot or two past the manifold. That's it. Can't be any exhaust leaks. Have to have a good understanding of how carburetors work, their different circuits. Idle, transition, accelerator pump, power circuit, and cruise. The old timers knew how to read plugs, but that takes a lot of experience. Modern fuels don't "color" the way they used to is one problem. The other, one of the ways to get experience, is to burn valves or nuke a piston. The widebands take (most) of the guess out. I had a big Azz carb on my Y block and got 9 mpg. Put the stock carb back on it and thought it was tuned pretty well and got maybe 12 with a good tailwind. With wideband tuning I get 17, and I just "roughed it in", I am still tuning. The trick is ya can't just jet down five sizes and call it good, have to make sure the AFR doesn't ever go lean under load. So basically ya can jet it down till it squeeks on the highway at level cruise, and drill out the power circuit slightly to bring back the AFR into the safe range under acceleration. Each jet size flows about 2.5% difference. Steady highway cruise tuning is where range or economy gains is made. This circuit has little or nothing to do with power or performance, that's what's cool about tuning. Can have both a ride that smokes the tires AND gets respectable mileage, if you can keep your foot out of it anyway. A vacuum gauge is helpful for tuning. Plumb the hose into the dash so you can observe engine vacuum under different conditions. Get the distributor curve and ignition timing squared away with a good, HOT spark. Lean mixtures need good ignition and plenty of advance timing.
This CANNOT be emphasized enough, even if you are running ethanol-free gas. With E10, it is even worse. If you are tuning only by plug color, you are likely off by quite a bit.
I have been using this one for many years: http://www.zeitronix.com/Products/ZR-2/ZR-2.shtml It does not stay in the car once it has been tuned. The O2 sensor comes out, and a plug goes in its place.
Jim if it's a NV3500 don't take it apart it's not fun to put back together without a high dollar jig but you can change the pencil gear.
Actually got a chance a while back to put a couple hundred miles on the 40's now broke-in Pace Performance 350/350 - Holley 600 +/- 260 HP combo, power to the ground via ford 8" 3.00 ratio... it was about a 50/50 mixture of highway and rural stop n go roadway at 55 to 60 mph. Got a whooping 12.1 MPG. I was happy knowing straight highway can only be better for a future road trip, but then again I don't drive old hotrods for fuel mileage, I drive em cause I like em!
Near as I can determine from my "research" online a carbureted engine can usually steady level cruise up to around 16-1 AFR. Fuel injected engines can and do go a lot leaner. Have to keep in mind the O2 sensor indication of the AFR is an average, of one half the engine. The cylinders don't all receive the same charge. The old school way was to jet down till it surges or misfires, then jet back up two sizes. What I found so far was around 15.5 to 16 to 1 runs fine with no surging or misfire that I can tell. This tuning was done at around 45°F, need to hook wideband back up to see what's happening in normal summertime heat. Was able to jet down 5 steps, to #43 jets. Could maybe jet down more in the summer? Finding that hard to believe. Runs well though, so.. Holley jets only go down to #40! Hm. Had to drill out the PVCR with a pin vise bit to then get the full throttle AFR down to 12.5. Key is never, ever go lean on acceleration under load. Jetting down will also lean out the wide open throttle AFR. Am now running lots of vacuum advance connected to manifold, this should help keep temperatures down. Excessively lean cruise mixtures can run too hot, and even reduce fuel economy. If you have to run a catalyst btw, "lean cruise" tuning will probably nuke it. Wouldn't p*** smog either I'd expect. Saving money is nice but my consideration is range, I like to explore gravel roads and remote areas, two lane country roads &c and being able to p*** by a gas station once in a while is kinda nice. I know you just asked a simple question ha ha. Hope this helps.
Read: http://www.oldsmobility.com/old/carlife_apr67.htm Apparently, RPM is the most important thing when it comes to mpg? More important than cubes, weight, aerodynamics etc.....?
Gearing, definitely. Ignition timing. The distributor curve for example on a V8 is typically 34° to 38° degrees "total", but this is based on RPM. High compression engines will tolerate less total advance. But this is usually around 2500 or 3000 RPM or so? When cruising at a steady speed in high gear, a street motor won't have all that RPM or the full ignition advance. That's where vacuum advance comes in to take up the slack, and pulls in more timing, that the mechanical can't. Somewhere around 50° BTDC for later V8 is right in there, and will give the best efficiency, because the lean fuel mixtures at level cruise need the fire lit a lot earlier.
1940 Ford 2dr sedan, stock 305HO Camaro with a Holley 600cfm, 700R4, 2.79 gears.....21mpg at both 75 & 85....checked it on 500 mi trips last summer
Something shaped like a C.O.E could get mileage in the mid teens with a progressive 3 pack overdrive transmission and gearing in the mid 3's. Wide band o2 sensors are worth every penny when tuning. Followed by oil temperature(s), fuel pressure, and Manifold pressure will let you know of issues right away. I hate the ones that "dance" all the time though. I prefer just a digital readout especially with a tach letting me tune at 700rpm and know it is at 700 instead of somewhere between 500 and 1000. It also is nice for motors that only rev to 4000rpm. Some of you will say something about a timing light. But If I am at a light and see the thing idling at 450 when it should be running 650 look over and see my MAP is lower then normal I can stop right away and find/fix that leak. Worth every penny and of course affects mileage.
my MPG,depens more on how many times I rev it up just to hear the cool sound,then gear,carbs or tune. I get about 10mpg,but if I drove like a little old guy,it may make 12mpg.
I'm running 13.6 to 1 set on a smog machine sniffer, a little for the mileage and a little get up and go when required.
Thanks! I always thought anything over 14.7 was too lean. 16 to 1 is much leaner. I will need to lean mine down.
Well you'll have to experiment. Spent a lot of time getting a hot ignition with a good spark, and then when I finally got around to carb tuning, that really paid off. Lean mixtures need a hot spark to reliably fire. Make sure the distributor curve is optimized, with plenty of advance and no sticky plates or worn out parts, leaky vac diaphragm etc. What surprised me is how well an engine runs both before and after tuning with a wideband. The main difference is before, all that fuel wasted going out the tailpipe. The instructions themselves don't have a whole lot to go on in terms of actual numbers. Here's a chart that helped me: What do all the numbers mean? AFR Values & Characteristics 6.0 AFR - Rich Burn Limit (engine fully warm) 9.0 AFR - Black Smoke / Low Power 11.5 AFR - Best Rich Torque at Wide Open Throttle 12.2 AFR - Safe Best Power at Wide Open Throttle 13.3 AFR - Lean Best Torque 14.6 AFR - Stoichiometric AFR (Stoich) 15.5 AFR - Lean Cruise 16.5 AFR - Usual Best Economy 18.0 AFR - Carbureted Lean Burn Limit 22.0+ AFR - EEC / EFI Lean Burn Limit Lean Conditions - Common Side Affects Hotter Engine Temperatures Detonation / Pinging Hesitation in Throttle Response Rich Conditions - Common Side Affects Engine Flooding Decel Pop / Backfiring Lethargic Throttle Response Excess Carbon Build-up (sooty pipes) Fuel Smell from the Exhaust http://v8sseries.com/install-wideband-o2-gauge/
The Jalopy Journal
