I think EFI is a large part of it. I have a 5spd, but I put a shortened gearset in it so it turns 3000 at 75mph or so. I have tuned it so that under light cruise my AFR is 15.2-15.7 and 38 degrees of timing. The engine uses less fuel at those areas than it does at idle. You could not do this without EFI. Steady light throttle such as highway cruise the car sips fuel.

Before anyone says "No Way!" let me say that this is exactly what your normal production car is programmed to do. Run lean with appropriate timing to reduce emissions and increase fuel mileage.

 

8 mpg, day in, day out.

Daily Driver in Boston.

 

Geoffrey:

I surely have no right to question IF. So I'm just more curious how it is done. What type of temperatures are you running? head, oil or EGT

Lean and advanced with a turbo sounds like a dangerous recipe....how long did it take you to find a safe lean mixture? I will look up old threads of yours, but I imagine dual plug, fully mapped timing and coil packs, and monitoring systems. What do you run for monitoring on the road or track? How do you "trim" it for conditions, gas or altitude changes...cockpit dial?

I find this MPG issue almost as impressive as your HP numbers. I would think that the short gears allows the AFR to be possible not not over tax the engine, but the trade off is outstanding. TIA for any insight.

Luke

 

Luke,

You are very correct that lean and advanced under HIGH LOADS with any engine are an issue. However, the requirements of an engine vary depending on load and RPM. The area I am speaking of is light throttle cruise where the cylinder filling is inefficient. It is virtually impossible to have detonation here, the cylinder will simply just misfire and no damage occurs. I can lean the car out to 16.5-17:1 afr before the engine begins to misfire because it does not have enough fuel. A lean engine always requires more advance so here the timing is increased. EGT, oil, and cylinder head temps are well below the maximum under boost temps the car sees. As the load increases, the engine is richened and timing retarded to a point where full boost is 12.2-12.5afr and an appropriate amount of timing.

I have a MoTeC ECU installed with on board wide band data logging. I initially set the car up on a chassis dyno, then tuned it on the street and track for the last 10%. The car has no cockpit adjustability, I basically set it with the laptop and forget about it. The ECU has ability to compensate for altitude, barometric pressure, air temp, engine temp, cylinder head temp, boost pressure, etc. which allows the engine to maintain the same afr under a wide operating range. The engine was tuned for 93 octane fuel and is not adjustable for race or basic fuel.

My first engine lasted 6 years of track miles and was in near perfect condition when dissassembeled last year. As I've said before, fuel injection is a very misunderstood topic.

 

Geoffrey,

It seems the dyno is a bigger load where I'm seeing a significant difference at full power vs. the street. I'm running a wideband unit...solo of course since I still have CIS. My A/F is richer on the street than on the dyno but not at idle or just reving the motor. I even had the wide band checked by the guy who makes them and it checked out. What kind of differences are you seeing between the two? In any case tunning can really affect your gas mileage.

Brent

 

It depends on the dyno you are using and its ability to load and hold a car for sufficient enough time to get an accurate reading. I try to use only Dynapack dynos and load and hold the cells (rpm/map) for adjustment. I then make swept runs with the dyno allowing a maximum change of 300rpm per second which allows the wideband sensor to get a fairly accurate reading. Street/track testing will always show small amounts of variance, especially in a turbo car where the intercooler is more efficient at speed.

The Bosch LSU-4 has a 300ms refresh time. The NTK is faster at 100ms, but does not last very long and does not like leaded race fuel.

Also, if you are comparing your wide band to the dynos wide band, you could run into issues. As the sensors go bad, they are slower to read and generally read lean. Many shops aren't that careful with the sensors either. I always bring my own because I know where its been used and how much time is on it and what type of fuel it has been used with.

 

Is this largely due to a typical turbo charged engine or is the characteristics of the high performance engine? Thanks.

 

Just my 0.02 worth I get 10mpg in the city and 15 on the highway. DE event more like 6.