4.7? 5.2 (318)? 5.7?

684 Views 12 Replies 4 Participants Last post by GeorgiaMoparMan, 5 mo ago

andyvh1959

Discussion Starter · 5 mo ago

I am planning a build for my 56 Dodge C3 pickup, going onto the chassis from my 2001 Dakota. My SLT Dak has the 4.7V8 with a 5-spd manual, 3:55 RWD, and if I drive it at 60 mph the revs are just under 2,000 rpm. When drove steady at that speed I have gotten around 20mpg. I found that by noting the gas used per 100 miles, not as indicated by the way-off overhead console. My plan for the 56 is to use a remanufactured 4.7HO with a 545RFE tranny, which the 6th gear ratio will get me 70 mph at near 2,000 rpm, the sweet spot for decent highway fuel mileage.

I've read that the 4.7 is not known for fuel mileage. So, is the 5.2/318 or 5.7 Hemi really any better or worse? If I can get around 300 hp from the 4.7HO with the 545RFE behind it, it seems the best choice to get good power and reasonable economy for daily driving. I doubt the 5.2 or 5.7 with the 545RFE trans would produce any better economy.

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immattj

· #2 · 5 mo ago

Not an answer to your question, but I can tell you from experience that the 5.9 gets horrible mileage.

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immattj

· #6 · 5 mo ago

Zaan said:
I'm also running 80mph (yes that's the speed limit) out here in Montana

You gotta love that.
However, the last time I was there (2016), somewhere between Great Falls and Shelby a MHP in a Charger with backwards facing radar pulled me over and told me that 80 means 80. Five over doesn't cut it. Maybe it was because of my out of state plates. He asked me where I was going and when I told him he said, "you're almost home; slow down," and he gave me a warning ticket.

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immattj

· #8 · 5 mo ago

andyvh1959 said:
Heh, my last time driving through Montana was back in 92, dad's V6 Camry back home with my brother. I got on the highway and set the cruise at 85 and got blasted by everyone else doing well over 90.

In '92 wasn't the day time limit on the interstate in Montana (once again, after the 55 mph hiatus) "reasonable & proper"? Meaning at the discretion of the MHP who clocked you? After that I remember it going back down to 75 mph, & one of my Dad's friends told me it was because of "the out of staters coming here & driving like they were on The Autobahn." The MHP who pulled me over back in '16 didn't sound as if he was crazy about the 80 mhp limit. He said that "fatals were up."

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immattj

· #9 · 5 mo ago

andyvh1959 said:
30 years ago it was standard that any speedo was showing at least 10% higher than actual speed. These days most speedos are electronic and much more accurate. That officer must have been having a bad day.

Well, I remember coming up on him as I came over a rise somewhere south of The Marias River Hill; he was actually doddling along pretty slow, & I think that was a strategy he was using. I got on the brakes pretty hard, but as I flew past him, his lights went on immediately. He seemed friendly about everything. As I typed, he didn't seem to be a big fan of the 80 mph sped limit.

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immattj

· #11 · 5 mo ago (Edited)

Zaan said:
" Reasonable and prudent" was the exact term used but no it wasn't imposed to 75 mph because of crazy out of staters. It was the fed government overstepping its bounds saying they would not fund any highway projects unless a speed limit was enforced.

I am just saying that was what my Dad's buddy seemed to think. In '92 they would have been in their 70s and pretty set in their ways, and their thinking, and they weren't all that crazy about "out of staters", which would have, at the time, included me, if I wasn't my Dad's kid. I was, under the impression, back then, that the locals (AND law enforcement) generally didn't care for "reasonable & prudent." But back then I was only getting out there about once a year. In '00 I quit flying out there & started driving out (a couple of times a year) because I finally broke down & got a decent car; I used to especially love driving across SD.

Anyway, I remember the year I got my Montana driver's license, I think it was '75 and the same year that the 55 mph speed limit (the "double nickel") went into effect nation wide. "It was the fed government overstepping its bounds saying they would not fund any highway projects unless a speed limit was enforced " was what they said about it back then as well. I had the impression that the $5 ticket for daytime speeding, and NO moving violation, was Montana's version of thumbing their nose at it. I remember getting a few fast night times, however, & those did cost me a few bucks back then.

(I remember those $5 day times for going over 55 mph used to say something about being for violating the energy conservation law, or something like that.)

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immattj

· #12 · 5 mo ago (Edited)

Zaan said:
" Reasonable and prudent" was the exact term used but no it wasn't imposed to 75 mph because of crazy out of staters. It was the fed government overstepping its bounds saying they would not fund any highway projects unless a speed limit was enforced.

Hmmm . . . well, according to this, not exactly. Looks like it was the Montana Supreme Court. However, I do remember that being said in the 70s when the 55 mph limit was first imposed.
(1974 "President Richard Nixon signs the Emergency Energy Highway Conservation Act into law.")

And actually, it appears as if in '95 the fed was the reason Montana went back to "Reasonable & Prudent" and did away with the threat of cutting off federal funding of Montana highways.
("President Clinton signs the National Highway System Designation Act of 1995 into law, repealing Nixon’s speed limit and eliminating the highway funding penalty. Montana reverts to its original law, which states that drivers shall operate vehicles “ . . . at a rate of speed no greater than is reasonable and prudent.” Violations are issued at officers’ discretion.")

Montana Was Once the Last Bastion of Hot, Nasty, Bad-Ass Speed

Call it the autobahn of America, only now it's gone. Read more about why Montana imposed posted speed limits.

www.caranddriver.com

https://missoulian.com/news/state-and-regional/remember-reasonable-and-prudent-speed-limits-long-controversial-in-montana/article_06be4f06-f083-571d-a359-dd1698b56b77.html

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