Cruising speed?

[inflt]

Entering here, for lack of a better place, since question is fairly specific to my type of bird (PT, 5 speed, 8v92).

What is a "good" cruising speed? Good in this sense referring to "good for the engine". I have been trying to keep it about 60, which, according to my tach seems to average about 1750 rpm. Having the aerodynamics of a brick, my goal is to get as good a fuel mileage as is possible. Time, I have, money, less so. But I have no idea where the "sweet spot" should be, for best performance. Also, I don't want to "lug" the engine, and contribute to reduced engine life, in what might be a false economy.

I guess what I am asking is, since it is staying in 5th and not hunting between gears, is this a good speed? I seem to have plenty of power to burn.

All advice welcomed, whether or not acted upon.

[irmagoo]

hi lee
i don't know the right answer don't know if there is one... i run 1700rpm (most of the time) on my tack and thats about 62 my my speedo and gps...mike

[rwoody]

MY 8v92 40 footers sweet spots are around 76-78 mph

they like to run!

62mph? west texas? run good tires and ride

[tiger38117]

My mechanic has always told me the best way to drive a 2-stroke DD is with both feet planted firmly on the floor . You are not "saving" your engine by running slower.

Drive as fast as you feel comfortable. In both my 86 PT and my current bus, I run with the cruise on 72 on the open road and have no worries running up through the 70's if I need to get past traffic or whatever. I'd run 80 if I didn't think it was an unnecessary risk on tires. These busses are built to run.

Find your own comfort level and run there, the well-maintained bus doesn't care.

[sfedeli]

Our 6V92 with a 3.42 rear seems to like around 72 MPH. Tach is at 2100.

[Don Meyer]

Like Mike and the sugarland express, I like to run about 62 to 63. This keeps me at 1700 to 1750 RPM's. While cruising at 1900 to 2000 RPM and 70+ MPH is certainly comfortable on these coaches, I do it for the dramatic increase in fuel mileage. (well...dramatic for a Bird anyway) I'm now in our 11th year with this coach. I've driven in nearly every state, on and off interstates, on and off US highways and smaller roads when needed. We've monitored our fuel mileage under all possible conditions, temperatures, speeds, towing a Hummer, towing a Jeep Wrangler, towing a 24 ft enclosed trailer and running with no tow. We have found the above mentioned 62-63 MPH to give the best results under all conditions. If we maintain those speeds, it really does not matter whether or not we tow. Once we get in motion and maintain the speed and RPM's we get 5.5 to approaching 6 MPG. BUT, once we get over those speeds and RPM's we drop to 4 to 4.5 (especially at 2000 RPM). We all know the 92's will run all day at those speeds, but the fuel usage becomes a BIG issue. especially when you're full timing like we are. I've never heard of any damage being done to these engines running in the 1700 to 1800 RPM range. So bottom line, why waste the liquid gold we pump into these beasts on a regular basis. And then we can talk about what happens when a steer tire blows out at 70+ MPH. But that is a topic for another discussion. So just sit back, slow down, save some fuel. enjoy the scenery and perhaps even live a little longer.

[Rob Robinson]

Keeping the engine rpm sweet spot in mind for your particular coach I would add that anyone who drives ten mph slower than their tyre rated speed is wise.

[tiger38117]

I echo Don's fuel consumption comments, I just choose not to make that my deciding factor in how fast I go.

My 86 PT38 8v92 would get about 5 mph at 70-72 mph. The DDEC computer in my current Series 60 shows 5.75 mpg at those speeds. Any time that I am "forced" to slow down for traffic, construction, etc, the mpg will start to creep up if Im running in the 60's.

Fuel consumption is a very real variable to consider when choosing your personal comfort speed. The difference between 5 and 6 mpg may not sound like much on the face of it, but it's a 20% increase . But from a standpoint of durability, which seemed to be the original poster's topic, turn her up and let her go.

[rrueckwald]

Any comments on a sweet spot for the S-60?

[bubblerboy64]

My bus runs good between 65 and 70 too hard stop to run faster much faster but out west on good open straight roads 75 is no problem. Fuel use IS the difference between 55 and 75 might be 2 1/2 mpg . Hard to drive 55 but on the average 62 is the best compromise