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1949 Ford Coupe RESURRECTION
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1,046 Posts
Discussion Starter · #1 ·
How much fuel should a 383 stroker burn at light loads and 1500 RPM? I can't seem to find a calculator that gives that particular answer they all seem to be simply RPM related with tire size and transmission ratio in overdrive and rear end ratio but I found a nothing that could give me theoretical gas mileage.
 

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Hates: Liver. Loves: Diesel
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6,303 Posts
WAY too many variables. You can use BSFC and power/torque to get what the engine itself will require, but a few millions factors are involved with how much it actually consumes. A short list:

A/F ratio
thermal efficiency (as in BMEP, VE, and IMEP)
chamber design
piston crown design
cam timing events, specifically IVO, IVC, and STS overlap
ignition tuning
ignition health
tire rolling resistance
wind resistance
vehicle weight
bearing resistance
brake drag
transmission parasitic losses
prevailing winds
fuel properties
and mostly... driving style.

The reason there are no calculators is because it's not something you can really estimate at all. If it were possible, the EPA would have come up with it, but you know how they come up with their (often way-off) numbers? By running it and calculating MPG by how much fuel it consumes.

At best, one could say "well mine got 14mpg in a 69 pickup with 3.42 gears" but yours might get 9 or 18.

Also, when picking a target cruise RPM, lower is not always better. Shoot for about 75-80% of your peak torque RPM. If your RPM peaks at 2500, I wouldn't cruise below 2000. You'll be too far below peak VE which is "lugging." and MPG can suffer greatly. You won't save any fuel because you'll have to use more throttle to get the oomph you need to overcome wind and rolling resistance and end up using more fuel than if you spun it a bit faster.
 

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1949 Ford Coupe RESURRECTION
Joined
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1,046 Posts
Discussion Starter · #5 ·
Thanks, I fully agree...but not only that, since I think we all understand the compressability of air (and vapor phase fuel) nonetheless, a theoretical calculation of "nominal" steady state, constant speed and loading could be reasonably be calculated...hard to accept "well, you just can't do it...it's too complicated"....
 
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