Todd157k

iTrader: (5)

Our club has an "economy run" coming up in a few months. I'm really only competing against a ZR1 guy that is going to kill 4 cylinders in hopes of more mpg. (although I doubt it will have any real effect on his mileage)
I've been playing with different things trying to squeeze a few more mpg's. I've tried "larger injector sizes" (low KPa only) figuring it would lean it out a little (yes, I watch the wideband to make sure it isn't killing the motor and NO, I don't hit the N2o) and I've tried putting the stoich at 15.2 (so far) but it's not really getting me any better mileage. Maybe 1 or 2 mpg. These tests are being performed at 50 mph or less with VERY slow accelerations. My temps haven't moved nor my w/b reading. What can I adjust (very temporary) to really squeeze 5-10 more mpg?

SSpdDmon

iTrader: (10)

Well, the larger injector sizes might have worked...but, not worked (if you know what I mean) for two reasons. If you made the changes to low kPa values, that would affect WOT. The injectors go off of manifold vacuum, not map. IIRC....MAP equals MANVAC minus atmospheric pressure. Also, if you're still in closed loop, the fuel trims will offset any changes you make to the injector tables during part throttle operation.

You could force your car into open loop and use the open loop fueling table (with the correct injector table) to lean it out during light throttle/low map kPa conditions. That way, you don't have to worry about the NBO2's trying to keep you in a certain spot. Then, just keep an eye on your WBO2 to make sure you stay close to the commanded AFR. Like you saw, I wouldn't expect more than 2-4mpg to be attained by doing that though.

The most control you'll have is really with your right foot. Put a block of wood under the gas pedal that won't allow you past a certain TP% if you need to , keep your speed close to 55~60mph, and try to hold your momentum once your moving. Most cars get the best mpg around 55~60mph and being on the gas when there's a red light 2000 feet ahead isn't going to help none either. On the other hand, most fuel economy goes to $h!t when starting from a dead stop. So, judgement is key...

That's all I can offer...g/l!

Billf6531

What he said, but I'd also turn on the STFT open loop, just to be on the safe side.

ChrisS@sdpc

The only way this going to work is for you to run OL (make sure all fuel trims adjustments are off). Then you will need to dial in your MAF and/or VE table to accurately predict/measure the airflow and provide a lean (leaner than stoich) AFR in OL target AFR table for the areas that you expect operate the engine. If the run is over an extended period, you will find that you can run the engine fairly lean (will need to add spark). You might be amazed at how lean it will run steady state with the right amount of spark. Keep an eye on ECT and oil temps as additional warning signs.

If you have starts and stops, you will find that going too lean will cause you to require more throttle (i.e. more airflow) to obtain the desired speed. As mentioned, this can really hurt your MPG.

Did you adjust for the larger injectors with tuning software?

Todd157k

iTrader: (5)

ok. I'll try some of these suggestions and see how it goes. Yes, I adjusted the "injector table" size through HPtuners. The automatic tranny and 342 gears are killin me. Best I could do (with above mods) was 30 mpg.
If all else fails... I'll go with the "technical" block under the pedal route!

SSpdDmon

iTrader: (10)

Oh....you could also make your torque converter lock-up tables a little more aggressive. You might be able to pick up a little more there if there's a significant amount of low-speed driving. Every little bit helps...

ringram

You can also alter your o2 switchpoints.
But I agree go open loop and tune to around 16:1 just dont hammer on it.
I also understand acceleration should be fair and not light for best economy. Afterall best VE is at higher MAP. Accelerate to cruise then be as light on the throttle as possible.

Bryan @ Speed Inc.

iTrader: (19)

2.73 gears and pull 500lbs out of the car.

you'll really see a difference! haha

Todd157k

iTrader: (5)

I'd have to put my old rear end back in... AND KEEP MY REAR END OUT OF THE CAR!!!

Blackbird

a trick I read about in sport compact car during a shootout was to actually acellerate slightly downhill instead of coasting, like most people logically think, to build up speed with very little cost gas wise and then coast as much as you can on the flat and uphill. the guy recorded a crazy 47mpg during the gas mileage loop using that method.

Killer_Bluebird

iTrader: (23)

I guess you can skip shift too, 1-3-5-6 works for me and I don't get bogged like when I had the original (1 to 4) skip shift enabled.

Formulated

iTrader: (16)

I agree that you should definately be able to run 16:1, maybe even a point leaner than that. Do address the ignition, though. The engine will begin to run poorly as it approaches the lean misfire limit. I would think the thing to do to try to make that go away is to close down the plug gap a bit, and/or go to some iridium plugs. Lean misfire is about the only thing that will limit enleanment. Multispark is another option, if you can get your hands on some MSD bits.

If you can cut cylinders, it does work.

2000Z28AUG

good luck!

RedWS6 00

OL would be the way to go, if you are in closed loop you car is going to use the fuel trims to get to 14.6:1.
One thng you could do, but it will only change you AFR a tiny amount is to change the threshold of the O2 sensors. Make the numbers 100mV lower and your fuel trims will adjust to a slightly leaner condition. I wouldn't expect you will be much leaner than 14.8-14.9...

I have got my car in OL all the time. Depending on the MAP I have a different Air Fuel Mixture. There is an OL table in HP Tuners. Cruising on the freeway on flat ground at 70mph its about 16:1 AFR. Getting about 30mpg when doing that, if I start going up hill, still with cruise control set to 70mph, the mixture gets ritcher depeding on hill gradient. Downhill its running leander than 17.3:1 AFR and getting over 50mpg. I suppose we can only really take note of figures on flat ground. Australia they implement 'lean cruise' in the PCM, this isn't enabled in US PCM's. So we cant get true 'lean cruise' but plainyg with the OL fueling table we can make it run leaner at lower MAP's. Can make it as lean as you like, but if you go too lean you loose power.

Steel Chicken

iTrader: (3)

use a pontiac GTO 04 OS and you can enable lean cruise. I get 30mpg hwy with it, even with a maggie and a cam, etc.

or like others have said, do a fake lean cruise with OL, more timing, less fuel, etc.

you prolly already know the rest, nice wax job, properly inflated tires, etc.

ringram

.. windows up, aircond off, thinner tyres..

Todd157k

iTrader: (5)

I'll start playing in OL and see where I can get. I have a couple months before "the day".
I'm not sure if cutting cylinders will work for me since the drag of the non-firing cylinders would cause more load. Pulling plugs would take care of that, but then there'd be codes coming out of my ears... and it would look like I'm cheating! LOL.
I'll have to spy on the ZR1 boards and see what kind of mileage they get w/ and w/o all 8 running.

thanks all.

horist

hidden 2 or 3 gallon fuel cell

Todd157k

iTrader: (5)

You are absolutely evil.

I like it!!!


off to ebay looking for fuel cells....

RedWS6 00

Also try to stay close to other cars on the motorway, the drag helps you get sucked along. I used to follow huge lorrys if you get the distance behind them right its very good on fuel. Obviously take care if they need to stop suddenly.