Creating a fuel map from scratch

[hawkwind]

There are many ways to skin a cat so im interested in ways to caculate a fuel map from scratch.....is there a caculator or programme on the market that can do this ?....I have done one in the past and need to again.... very interested in how others have done it    .......thanks in advance.
 

[hotrod]

Give us a bit more info on the engine involved.

Is it NA or blown or turbocharged?
Does it have near stock cam, heads and compression ratio?
Do you have a sample of the OEM stock fuel map as a starting point (assuming the engine is not heavily modified)?

Those factors could impact how you go about building a ball park fuel air map.

One rule of thumb would be to combine known fuel air mixtures (for example 12.5:1 for gasoline) with the engine airflow.

Air flow (by mass) will pretty much follow the engines torque curve. At peak torque the engine will have maximum volumetric effeciency (which is why the torque peaks at that point.

Combine that with RPM and displacement info and you can figure out a rough airflow rate for the engine.

(Displacement/2 * rpm ) * estimated volumetric efficiency would get you in the ball park.

Then multiply the calculated engine airflow demand by the target fuel air ratio at each rpm.

Some electronic fuel air systems perform essentially that calculation to compute approximate fuel required at a given rpm and load.


If you have mass flow information for the engine in another configuration you can do the same directly from the grams/min, or lbs/min airflow at various rpm.

If you have a horsepower and torque curve for the same type engine with similar modifications you can also guesstimate fuel/air requirements.

In a NA engine it takes about .5 lb of gasoline per hour to make one horsepower for an hour.

If you know that the engine makes 350 hp at a certain rpm you can multiply that by .5 lb fuel/ hr and know you need to feed it about 175 lbs of gasoline per hour at that rpm (probably near 12.5:1 fuel air ratio).

Try a couple different methods and use them to cross check each other for a starting map, then make it a bit richer for safety and get some real test numbers to refine the map after you get the engine to start and run.

Larry

[hawkwind]

Thanks Larry......ok the engine is a DOHC 4 cylinder of 1000cc....has a ported head with oversize valves...no idea

 what it flows.... cams are stock  ...lsa of 102.5....74X58 mm bore /stroke...10.5:1 static CR forged pistons.....its

 turbo charged using a to4E hybrid ......fuel is 70% methanol 30% nitro .... is running  2 X 750cc low imp

 injectors  per cylinder which are staged  using boost to turn on the second.....there is no starting map all needs to

 be done from scratch.....I have put together a starting map but not sure if it’s in the ball park due to the fuel I’m

 using  and I have no way of knowing what the VE is only that its low at idle and maybe over 100% on boost ?I

calculated the specific gravity of the fuel to be 0.8951 @ 20C I used a bsfc of 1.3 and the fuel pressure is set at

 43.5psig......I have O2 and egt to refine when it starts  and then dyno ........ But I was after several ways to calculate a base map to cross check my method.



Cheers Gary.

[NathanStewart]

Gary, are you using a VE-based engine management system?  The system I use is a simple load vs engine speed look up type system and I knew that I was limited to 60% duty at 6000 rpm because of injector timing restraints so I made a rough fuel map based on injector duty values.  I knew I'd need 60% duty at max load and max rpm and then figuring 1-2% duty at idle, I just interpolated between the two points in both axes.  Keep in mind that the 60% duty number comes from my planned turbocharged setup and I was starting out naturally aspirated and figured I'd be making about 50% less power n/a versus boosted.  When all was said and done, with my fuel map fully tuned and optimized my max duty cycle was 30% so that validated my calcs.

My quicky fuel map was good enough to have the engine start, run, and free rev fairly easily however once I started doing loaded tuning the fuel map changed significantly but it was still a good place to start.

I also used throttle position as my load input with a manifold pressure correction multiplier going on in the background (+100% more fuel for every 100kpa over zero manifold pressure).  One assumption I wound up being wrong about was that my throttle body would no longer restrict air flow at about half throttle.  In most cases where an over-sized TB is used and basing load on throttle, you generally see a fuel map flatten out above the point where the throttle is no longer a restriction and figuring this would happen around 50%, I flattened my fuel map out between 50% and 100%.  Once on the dyno and under load, I found that my throttle never actually "saturated" or reached a point where more throttle position meant no throttle restriction.  If anything, I still had a slight amount of vaccum at WOT indicating that my TB wasn't quite big enough (70mm Ford 5.0L TB on a 3.6L four cylinder). 

[FoundSoul]

My quicky fuel map was good enough to have the engine start, run, and free rev fairly easily however once I started doing loaded tuning the fuel map changed significantly but it was still a good place to start.

All of the above advice is good- I narrowed it down to this line though, regardless of the 'guesstimate' you'll want to dial it in on the dyno, and then if barometric correction is setup and tuned properly you shouldn't have any major adjustments on the salt, and if you do they should be pretty linear (meaning move the whole curve up or down a little) which keeps it simple. 

I usually advise people to get it idling and free revving cleanly, and at that point your tuner (or yourself if you are the tuner) can build a map on the dyno.  You can pretty quickly get an idea of how the map is going to take shape once on the dyno, and pre-guesstimation honestly doesn't save a lot of time as the tuner is going to go over it all anyways more than likely. 

[robfrey]

I use Engine Analyzer Pro 3.9 to get a rough start on my maps. It shows where peak VE will be at different boost levels. It is also very handy for developing timing curves although they recommend that you don't rely on them for that.
Can't say enough about the product, it has saved me big dollars.