Out of sheer curiosity and a fascination for increasing volumetric efficiency, what are you guys averaging for MPG in your turbo cars? Preferably assuming the answer as daily driver figures, not for a track rat.
For clarification, please also list engine management and final drive ratios.
I would also be interested in the figures if you have another turboed car of the M5x/S5x variety.
Damn, that sounds like a lot to ask now that I read it back...
City mpg = 13.6 Beaucoup stop & go.
Hwy/fwy mpg = 20.1 Driving the snot out of it.
This over ~11,000 miles.
Engine Management: Electromotive TEC-3r; firmware 3.5.5 with proprietary modifications.
Final drive = 3.64 Quaife.
HTH
Turbo M20 with Megasquirt gets 22 in town and high 20's on the freeway. I've never gotten through a tank without spooling it up at least a few times. Diff is usually a 3.25.
I just tested for what I could get out of a tank of gas, and it was very painfull, not the results, but the way I had to drive to maximize them.
I used an entire tank of gas without once going over 2500rpms and got 335 miles out of a tank full before the red gas light came on.
Suprisingly that was about 65% city driving.
BUT, when I drive it the way I want, I've seen as low as 208 miles out of a tank.
That of course was a tank of gas that saw boost every time it had a chance.
Living outside of Durham NC, the back country roads allow for plenty of opportunites for a heavy right foot.
Duke wrote:Completely dependent on right foot. Gets the same mileage as a NA M30 until you hear the turbine spool............then it drops a lot.
No turbo noise ='s good mileage
Turbo noise ='s bad mileage
It's not that cut and dry, although it may not be noticeable in an overall MPG standpoint, but volumetric efficency is effected by the turbo. Even when you haven't made 1psi of boost, on a standalone system you would find the volumetic efficency is still changed. It's always still there moving.
Scott, if you are doodling with changes to FI and looking at Ve, keep in mind that the other two major components here will be Brake Specific Fuel Consumption (BSFC) and the A/F ratios.
Generally speaking, there will be a need to run slightly richer at higher boost levels. Usually this gets done out of an abundance of caution to avoid having a "lean-burn" condition when under boost. The lower numeric A/F # will help to avoid possibly burnt exhaust valves. How much additionbal "rich" needs to be programmed in needs to be determined by pulls on a chassis dyno., but moving from 12.5 to 11.5 A/F isn't unusual.
BSFC is a calculated value. To derive that number, it is necessary to have accurate flow gauges measuring the amount of fuel in and out of the fuel rail. The difference between the recorded values on the gauges gives fuel consumption. These readings, when correlated to horsepower, yield the BSFC. This arrangement obviously speaks to needing to datalog the fuel flow rates along with recording the hp outputs.
Typically, FI engines show BSFC around .55 to .65 pounds of fuel burned per hour per horsepower at the flywheel. Lower is better, insofar as it indicates a more efficient burn. But don't expect to see numbers in the .40's with any kind of boost.
Ve, as you undoubtedly know, is a reflection of how much charge is getting into the cylinder. While a great deal of effort and attention gets paid to cramming the charge into the cylinder, relatively lirttle goes into looking at the exhaust side. To the extent that the cam configuration and the exhaust plumbing restrict removal of the spent charge, the benefits of a healthy incoming charge are reduced.
Another way of looking at this is to have a highly efficient scavenge segment of the cycle; if this is present, a much smaller incoming charge is needed for a given level of combustion efficiency.
So, build a really good tubular exhaust manifold that spools the turbine across a broad rpm range and you can use a somewhat smaller compressor. That smaller compressor will spool more quickly and you get less lag.
Back to Ve for a moment. The only way to get an accurate determination of this vital number is to have it measured on a flow bench. With that figure in hand, you can proceed to make some definitive steps towards cam configurations, injector sizing, pulse widths and duty cycles. The flow bench numbers, in turn, will prove essential in working thru the appropriate compressor sizing.
Key point here is Ve is a derived number and is a function of design of not only the head, but efficiencies of piston and stroke design.
If you know all this, sorry for preaching to the converted. But lots of people think that the way to more power with FI is simply to jack up the boost or install a larger compressor. Were that it were that simple. But it ain't.
HiNick wrote:Thank god we got 98 and 99 on all stations around where I live
Yea, but your 98/99 is the equivalent of our 93/94 due to the fact that they're rated differently. Europe uses RON, North America uses AKI. If you can consistently get 99 RON, that's just one octane point better than our 93 AKI gasoline (which is commonplace except in California).
I know it's not under boost, but for what it's worth I just squeezed 28 MPG out of my last tank. I only adjusted my style; kept my foot out of it more, coasted longer, tried to keep off the brake, etc.
Normally I see 23~25, pushing the car every now and then.
super eta bottom end, 325i head, intake manifold, throttle body, 325i Motronic EMS (173 ECU)
on my supercharged stroked 2.8 m20 e30 when sucking down gas it likes it'll get 19.5-20.7 in normal mixed driving with a fair amount of stomping, but when i get a load of something it doesn't like16 is about all it gets in the same driving, its real sensitive and i think it hates ethanol
You can calculate ve from a hp curve. Ve changes with rpm.
Here are the relevant forumula. The trick here you must put SI units into these equation not funny imperial units.
Power = mass air flow rate * FAR/BSFC
FAR is fuel to air ratio = 0.08 BSFC = 8.333e-8 kg/J = 0.49 lbs/hr/hp
BSFC = 1.015e-7 kg/J = 0.6 lbs/hr/hp
An engine is an air pump and therefore obey's the ideal gas law quite well in fact. It can be shown that.
Mass air flow into the engine = (P*N*Vd*Ve*Mair)/(R*T*(1+FAR))
Where P is pressure in Pa!
N = rpm/120 (engine speed/2 per second).
Vd engine capacity in m^3
Ve volumetric efficiency
R ideal gas constant = 8.314 (it has units but I cannot remember what they air)
Mair = molar mass of air = 0,029 kg/mol
T temperature of air in Kelvin!
FAR fuel to air ratio
You can therefore determine the Ve of other poeples engines and compare that to a standard engine which will give you an idea of how it changes under boost. These formula also allow you to make predictions about what the air flow through a boosted engine should be which allows you pick the right compressor.
To pick the right turbine and waste gate then use this:
W = 0.55((Dex(AR)^1/2)-7)
where:
W is value of mass-air-flow through the turbine at which the turbine chokes in units of lbs/minute,
AR is the A/R value of the turbine housing (0.48, 0.64, 0.82 etc..), and
Dex is the exducer dimension of the turbine wheel in mm.
M30B35 running MS2, 3.25 diff and I average around 22mpg. This is probably 75%hwy/25% city, with an occasional foray into boost. It definitely isn't that good under boost though.
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