I have a question about mileage and airfuel ratio. Can I assume that the relationship is near linear for afr near 14.7 . Driving Home tonight I decided to put the innovate wideband on the car and see exactly what the afr is. The trip home is 1.5 hours and has every type of terrain from freeway to 8 percent grades. Down the freeway I pulled 11.5-12 When the powervalve comes in (holley 750 VS) the afr drops to 10 . Over the hills the car ran at 11-11.5 . This was in fith or sixth gear. Dropping off a 8 percent grade for 3 miles the afr was 13. The way I see it the difference between 12 and 15 is 25 percent. Would I see a 25 percent increase in mileage if I could get the afr up where it should be? I am going to fuel injection in the next couple of months So I want to get a good background of tunning fuel injection. Does anybody know of some good books that would show me how to dial in a fuel injection. I know Grumpy has mastered tunning fuel injection and has increased the mileage of stock fuel injection systems.
Thanks
Dan

 

It is hard to say whether you will see a set 25% increase in milage. Although it may even be more then that. On one particular vehicle I found a highway driving increase of 16% by going from 14.7 AFR to 16.1 AFR (26.5 MPG to 31 MPG).

I don't know of any books on tuning EFI systems. However, Holley's 950 Commander manual (found on their website, pdf file) is actually pretty good. It covers a lot of material in an organized straight foreword style. Well worth reading it.

RBob.

 

Thanks RBob,

You mentioned you went to a 16.1 afr. When does the afr become to lean? Can I run a extremly lean mixture down the freeway as long as the WOT mixture is rich? Also , does the ecm turn off the injectors when you decend a hill? How does it know that it would need to completley turn off the injectors or go to an idle?

 

A lean mixture is harder to ignite. Once it becomes too lean misfires will occur. I never attemted to see how lean I could get the engine to run. There is a bunch of research available that will give one an idea of what to use for AFR's.

Yes, decel fuel cutoff (DFCO) is in every GM ECM that I've played with so far. Typically for DFCO to occur the engine speed needs to be above 1200-1400 RPM, vehicle speed above 15-20 MPH, TPS below 2%-3%, and MAP below 30-40 KPA. Don't need to be descending a hill for this to happen.

Just lifting to exit a freeway will cause it.

Idle is basically 0 MPH, and TPS less then 2%-3%.

RBob.

 

Besides a misfire, are there any other concerns at running an engine lean while cruising? I know Wot the engine needs more fuel to keep cool but is this an issue at cuise. Just curious becuase I know there is a substantial number of patents for better mileage. Most of the patents vaporize the fuel before it is introduced in the cylinder.
If I wanted to experiement with lean burn , how could I know that I was not hurting the engine?
Also something neat I came across last night, Patent how to convert a 4 stroke into a 2 stroke

 

Everything that can go wrong from lean at WOT can happen at cruise. Just takes a little longer.

AND
Running too high of chamber temps., makes detonation and tip-in preignition all the more likely.
Plus elevated oil temps, and the corresponding increase in oil in the PCV system and that being inhaled into the engine.

Life is full of compromises. If you want great MPG, it'll cost you something else.

 

Grumpy,

How can I know if A lean mixture is ruinning my engine before anything happens. Cylinder head temp guage? Egt? This is just something that really intrests me because of the numerous patents for better mileage. I found another patent that leaned the motor down to 30-1 afr and used some sort of microwave to ignite the combustion. If you would like to see some of these patents go to the Us patent site and type in gasoline vaporizer in the search. It should bring up a couple thousand patents for better mileage.

 

I would only run lean on the highway,more or less durring a steady state. An EGT gauge would clue you in if you are going too lean(OVER TIME). I would imagine that the greatest damage would occur jumping from lean cruise to WOT. The chambers would need cooled off before WOT IF cruising lean,IMO. An engine can handle lean mixtues up to 17.x or higher, for short periods of time. How long do you want to run lean. I think that'll determine what a/f your engine can handle.

 

BTW, the name of the game is mileage vs afr vs engine life .

 

If you have a good oil temp guage or eve oil pressure guage you can see when your putting too much heat into the motor. The coolant temp is a very rough average, whereas oil temp can tell you a bit mroe accurately some things. Going from lean cruise and alot of timing, to slightly rich and much less timing made a 5 PSI change in oil pressure on my car. Lots of testing to get repeatible results in doing something like this. Going from 44d @ 15.6 AFR to 32d @ 14.2 AFR made about a 3 MPG difference. For me having 5 PSI more oil pressure and sacrificing 3 MPG was an easy choice.

A Plasma ignition system looks like the Ultimate, but even a CNP gets you close. The thing with coils is as the temp goes up so does the resistance, so you want to run the coil(s) as cool as possible which means firing them less often, so DIS or CNP helps in that reguard.

Getting MPG is large part is about rolling resistance, and weight. The newer large rims let the sidewalls flex alot less so are another reason to use them, and weight is weight. Shedding weight is always a good thing.

 

Thanks everbody for the help.
Grumpy thanks for the example it helps me relate to hear real world examples.
I will have to find another motor to experiment on, Im not going to get greedy with the zz430, No sense ruinning a 5000 dollar motor while im in the learing curve.
Really Im not doing that bad. I datalogged the AFr again 100 miles. Most of the time the Afr was 12 when the powervalve opened it drops to 10. The car is still getting 23-25 mpg.
After digging up a graph of mileage vs afr I can see the curve is not linear I should see a good increase just getting the afr up where it needs to be.


Just in case your curious here is the link for the Us patent office
www.uspto.gov
go to search and type in "Gasoline AND vaporizer" It is amazing the number of patents that come up. Most of them work off of the simple truth that only vaporized will burn

 

I've spent alot of time hunting around thur there.
That and the NACA site are priceless.

 

Most of them work off of the simple truth that only vaporized will burn

Not true. The ideal state of fuel is ATOMIZATION. This state is where the fuel is still actually a liquid. Vaporization is when it is nothing but fumes. Physics= it requires energy to convert to a gas from a liquid.

 

Atomization it the mechaical changing of a liquid into a gaseous state.
Vaporization is using heat to convert a liquid into a gaseous state.

You want the fuel in the chamber to be in a gaseous state. While some might be still liquid as it enters the cylinder, by the time the reaction starts, it's gas. Talking 3rd Gen Specific engines.

Thou, you can miss tune an engine, and have it rich enough, that the added fuel acts to *artificially* raise the CR.