If I were to get the 220 Alternator, should I expect it to have an impact on fuel economy?
RD for clarification,There may be another factor here. Alternators are notorious for producing almost no power at low speed and have to be belted up to an engine with a ratio that allows it to spin at a reasonable speed at idle and red line. Most are producing almost no amps at the 1800 rpm they run lots at. A larger one produces more output at these slow engine speeds. It is likely the 90 amp unit was turning faster so you got as much as the 220 amp one produces at those low rpms. This might explain the standard one being so much higher rated too. The cost is lifetime and a larger output slower turning alternator increases the likelyhood of long life. YMMV
Adrian, you may not be seeing a difference because it's smaller than typical variations between tanks, but I'm sure that running a 1200 watt heater or any other load has to decrease MPGs.Both PM I have owned, the previous gas PM andthe current diesel PM, have the 220amp alternators. I also typically run a 1,200 watt heater in the back of the van. With the heater on there is no affect on mpg! The wind on the other hand has an affect on mpg!
I was very pleased with mpg on the gas as I am on the current diesel!
Without the numbers I was saying that.... low output at low speed. What would the number be like for the 220 amp, about 30-35?RD for clarification,
The rpm is Alternator rpm not engine rpm the Alternator has a 2.5 to 1 or 3 to 1 pulley ratio so at 600 rpm engine idle the Alternator is turning at 1500 rpm and should put out 15amps for A 90amp alternator.
The Ford document, which is great in that it has a lot of details about a lot of things, lists the speed ratio at 2.7 for gasoline and 2.69 for Diesel engines. Difference may just be in rounding. The curves for Diesel engines show alternator spinning up to 15,000 RPM. Diesel engines can't even spin it that fast due to redline but it's good to know alternators can spin pretty fast.Re the curves in the 2 posts above: I assume the RPMs on the horizontal axis are alternator RPMs. A question is what are the pulley sizes so the RPMs can be related to engine speeds. In the old days alternators were generally driven at twice engine RPMs but I have no idea about modern vehicles.