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Old 05-14-2019, 11:46 PM   #1
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Cruising Speed with 454 and 3-Speed Transmission

My class A rig is built on a 1989 Chevy P30 chassis with a carbureted 454 and 3-speed automatic transmission. I don't know what the rear end gear ratio is. I've been spoiled by newer vehicles with 4+ speed overdrive transmissions for so long that I could use a refresher course on older vehicles built during the national 55 MPH speed limit days.

Should I expect my rig to cruise comfortably at 65 MPH without pieces flying off?

And even if it can, is that a good cruising speed for this glorious fuel-guzzling old beast, or does it want to putter along at 55 MPH?
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Old 05-15-2019, 01:38 AM   #2
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If I remember right on my 1974 Shasta Class A with the 454 3 speed turbo 400, it was around 3000 rpm's at 60 MPH! It would cruse faster, but you could watch the fuel gauge drop!
It will be whatever speed you will feel comfortable at when you are up to speed! Remember, you are going some where to relax and have fun! Enjoy the drive, Too! Rail!
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Old 05-15-2019, 06:57 AM   #3
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Our 1983 Winnebago Chieftain had the same engine/transmission as your rig. My memory is that is was happier at 60-65 than 55 MPH. It didn't have a tachometer but I think the higher vehicle speed had the engine running closer to the it's torque peak. It would stay out of the carburetor secondaries at higher speed but you could hear these open when on a highway overpass at the lower speed. Because of this, it "may" have had better mileage at 65 than at 55 (or not... memories are not always accurate). Our class A Winnie was 27 ft. long, and we usually towed a car trailer. 115,000 happy miles, then we saw a Safari Trek.

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My class A rig is built on a 1989 Chevy P30 chassis with a carbureted 454 and 3-speed automatic transmission. I don't know what the rear end gear ratio is. I've been spoiled by newer vehicles with 4+ speed overdrive transmissions for so long that I could use a refresher course on older vehicles built during the national 55 MPH speed limit days.

Should I expect my rig to cruise comfortably at 65 MPH without pieces flying off?

And even if it can, is that a good cruising speed for this glorious fuel-guzzling old beast, or does it want to putter along at 55 MPH?
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Old 05-15-2019, 08:11 AM   #4
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As an engineer, this is all leading me to think about instrumenting the fuel line and speedometer so I can monitor MPG in real time.
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Old 05-15-2019, 10:36 AM   #5
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lol, I'm a fire protection engineer and this idea is dangerous for my OCD and spare time.
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Old 05-15-2019, 11:11 AM   #6
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I’m an electrical engineer. I’m looking for gasoline-safe flow sensors in the one liter per hour range that aren’t lab-grade expensive...

Hey, if I add a mass air flow sensor, then I can also monitor my fuel/air mixture!
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Old 05-15-2019, 12:58 PM   #7
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My kid had a 89 3500 dually with the same 454/400 combo but with a Gear Vendor overdrive kit which had him cruising at ~2200 rpm at 70 and over 12 mpg to boot.
Its a great unit if you love your RV and don't mind putting ~$4000 into it.
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Old 05-15-2019, 07:53 PM   #8
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With the 3 speed tranny, you will get better mileage under 60 mph. A tach would be a nice option .
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Old 05-15-2019, 07:58 PM   #9
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Thank you! I have a tach strapped to the steering column, and I may replace it with an in-dash one layer that will be easier to see. I don’t know what RPM is good for cruising, what redline is, etc. yet.
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Old 05-16-2019, 01:09 PM   #10
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60-62 in that area.
Same engine, trans, But with headers and recurved distributor
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Old 05-18-2019, 07:55 PM   #11
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Fuel Monitoring

Quote:
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Iím an electrical engineer. Iím looking for gasoline-safe flow sensors in the one liter per hour range that arenít lab-grade expensive...
A few of us are adding a vintage mpg monitor called a Zemco ZT4. Search iRV2 for Zemco computers for more info.
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Old 05-18-2019, 08:52 PM   #12
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Oh, I'd roll my own electronics and firmware, of course. It's the only way to get what I want.
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Old 05-19-2019, 06:57 PM   #13
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Have a 82 Pace Arrow p30 with same set up. I did 65 pulling a 09 Genesis on a car caddie from Yuma to mpls Got bettrr mileage than i did at 60 on way down. Tac sat at 2900. Had a tail wind also
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Old 05-19-2019, 10:56 PM   #14
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On my 89 Fleetwood I had originally a Ford EFI 460 and it would cruise all day on flat ground at 70 mph while pulling my Rodeo with 2 mountain bikes and a 17' kayak on it's roof. I normally got 7.5 mph if I didn't run the generator to run the roof ac's. Got 6 mpg with the generator going too. Crossed a lot of deserts in the summer.

Your carbed motor will not do that as easy, but should be able to run 65 to 70 as long as your not climbing hills


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