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This is another one of those situations where "more" is not always better, even though the customer may think it is. After a certain point, you don't still gain magical amounts of mpg with a super steep gear. The mds + 2300-ish rpms is really not a bad pairing.
If you are running the full 8-cylinders, then you have no choice but to run the tallest gear you can tolerate to maintain good mpg. It's not like you get a 66% mpg benefit out of a 66% change in overdrive gear. Putting the same gear on an mds auto be pretty well pointless. The mds wouldn't pull it worth a damn, and it would just end up in v8 mode at the slightest provocation beyond level ground and a stiff tailwind.
I'm not even sure super low rpm is all that optimal for these "high-strung" hemi's, anyway, as far as getting the most out of a partially-filled cylinder. It's waaaay out of the range where good scavenging is going on, so some of that fuel is just sneaking from the intake valve right out through the exhaust valve during overlap, at such low speeds, since the timing/momentum is all wrong. On a wedge-head Chevy that is cam'd to better favor low rpm work, the tall overdrives make more sense. The same doesn't automatically hold true for the "free-flow through" design of the hemi that is cam'd to sing through the 4k-5k rpm range.
If you are running the full 8-cylinders, then you have no choice but to run the tallest gear you can tolerate to maintain good mpg. It's not like you get a 66% mpg benefit out of a 66% change in overdrive gear. Putting the same gear on an mds auto be pretty well pointless. The mds wouldn't pull it worth a damn, and it would just end up in v8 mode at the slightest provocation beyond level ground and a stiff tailwind.
I'm not even sure super low rpm is all that optimal for these "high-strung" hemi's, anyway, as far as getting the most out of a partially-filled cylinder. It's waaaay out of the range where good scavenging is going on, so some of that fuel is just sneaking from the intake valve right out through the exhaust valve during overlap, at such low speeds, since the timing/momentum is all wrong. On a wedge-head Chevy that is cam'd to better favor low rpm work, the tall overdrives make more sense. The same doesn't automatically hold true for the "free-flow through" design of the hemi that is cam'd to sing through the 4k-5k rpm range.
