% Over EPA Frequency Distribution

[imzjustplayin]

Originally Posted by RoadWarrior

Ummm so when I swap the 3.0V6 that's in Marvin for the rebuilt spare 3.0V6 that happened to come out of a (junked) Dodge Shadow rather than a minivan, I should go by the car's EPA figures?

Naw you can go by the original EPA MPG rating since they're the same engine in two different vehicles and you've already got the EPA ratings for that vehicle. For example if you take a VW Rabbit '02 Diesel engine with the vehicle getting an EPA rating of 50mpg, you put that engine into a car that has an EPA rating of 40mpg, then you should use the 50mpg rating as your baseline, not the 40mpg. If you put that VW diesel engine into a car with an EPA rating of 60mpg, then you'd use the 60mpg rating as your baseline, not the 50mpg rating that the engine came from.

The same rules apply if you take a transmission from a more efficient vehicle and put it into your less efficient vehicle, you should be calculating % of EPA rating from the more efficient vehicle, not what your vehicle was by default. Reasoning behind this is that you haven't actually created anything, you've just shifted it around and therefore we're not overall better off.

However! If you take your stock transmission, replace the final drive with a machined part that was not taken from an existing transmission, then I'd say you can use your old EPA MPG rating, even if the final drive ratio matches that of another transmission (Civic CX/VX vs DX/LX,EX).

[GasSavers_RoadWarrior]

Ah, but what if I steal parts off a less efficient vehicle to equal the configuration of a newer more efficient model of the same vehicle.... Like later Escorts have different TB and injectors, but I could steal equivalent ones from a couple of other Ford products that get worse than the older model Escort MPG...

[GasSavers_maximilian]

Simple enough to divide the absolute economy numbers by the % over EPA ones to get the EPA ratings in the garage.

[imzjustplayin]

Originally Posted by RoadWarrior

Ah, but what if I steal parts off a less efficient vehicle to equal the configuration of a newer more efficient model of the same vehicle.... Like later Escorts have different TB and injectors, but I could steal equivalent ones from a couple of other Ford products that get worse than the older model Escort MPG...

Can these parts you're taking off a vehicle, while may have come from one vehicle, can also come from another? Ala Civic CX vs VX? (In Respect to the transmission) If so, assuming is a true fuel economy booster, then you should use the higher rating vehicle. So if you put a CX/VX tranny into your DX Hatch civic, I'd probably go with the CX Fuel economy rating assuming it actually came from a CX not only because your DX engine doesn't have lean burn and Vtec like the VX does, but because you're not "depriving" (so to speak) a VX of its fuel economy. However if you swap in a CX tranny into a VX because your VX tranny went bad, I'd still stick with your VX fuel economy rating since you're theoretically trying to keep a VX on the road opposed to taking one off the road when you put it into a completely different trim altogether.

Just try to figure out why you're doing these modifications, is it for a performance boost or fuel economy boost. Can and is this part found in a more fuel efficient trim as well? Some cars the only difference is the gearing of the transmission like the Cobalt XFE and in that case, if you're putting a Cobalt Engine from an XFE into your Vanilla Cobalt, then your fuel economy numbers shouldn't change and you're probably doing it because your engine went bad, not because you're trying to get a fuel economy boost/get ahead of your EPA numbers. But if you put the XFE tranny into your Vanilla Cobalt, then you should be using the XFE EPA numbers as your baseline, NOT your Vanilla Cobalt's.