Hello Barth Family,
First time posting here, but I need some advice. We have a 1993 Barth Breakaway 30 Foot. Cummins 6BT 190HP with the Allison AT542- 4 speed transmission. Love the coach, owned her since 2016. On the highway, flat ground, not towing, I'm doing 62-63mph, at 2600-2700 RPM. This is with the pedal to the floor. I've been told by our diesel mechanic this is pretty much the max power this coach will make.

I do understand this is an economical coach, I drive professionally for a living. I have driven school buses with this exact setup, and can easily hit 65-70 mph no issue.

Given the rpm you have you are probably topped out. This is the downside to the 4 speed trans. The rear axle ratio is the limiting factor also.

Good to see another Barth here.

Thank you Steve I was thinking the same.

Gives you an idea of the difference the drive train makes.

In DBarth I have a 5.9 at 268 hp, the Allison MD3060 6 speed, the beefier Eaton rearend. I have seen 85 with no problems with engine temp or exhaust temp. It is not something I do with regularity. I cruise at 70-75 often if in a hurry.

Have same drivetrain. At about 2300rpm @ 55mph. Believe providing a public service - admiration time. Appropriately have a SMV reflective triangle mounted on my ladder.

BTW, very economical - always 13+ mpg, except in mountains.

quote:

Originally posted by David Andrews Jr.:
On the highway, flat ground, not towing, I'm doing 62-63mph, at 2600-2700 RPM. This is with the pedal to the floor.

Most Breakaways of the late 80s early 90s 5.9L Cummins go into what is called "de-fueling" at 2400 RPM. This will lesson the HP the engine can produce. This combination is at best a marginal compromise between acceleration in 1st gear and top speed in 4th gear.

My 30' Breakaway has the 230 HP Cummins 6 speed Allison and Eaton rear diff identical to Dana's coach. Our rear diff ratio is 4.11 but the trans 6th gear ratio is 0.65:1 over drive. Both 5th and 6th are are overdrive ratios.

I drive routinely at 70-75 MPH, engine RPM from 1900 to 2100 and fuel mileage is right at 10.1-10.4 doesn't matter if I am towing or not.

There also appears to be a "sweet spot" around 2100 RPM where the engine will give a higher MPG, Steve and I are testing out this theory this summer.

Wordy but hopes this helps.

I can see it now, Ed and Steve running down the interstate, side by side, slide rules in hand.
jim

I appreciate the responses!
Thank you everyone!

quote:

I have driven school buses with this exact setup, and can easily hit 65-70 mph no issue.

I'm glad I don't have any kids using school buses any more.
Oh! Millville, N.J. .........never mind!!!

Being said, those speeds were done on highways like I95 with the school bus.

The school bus probably had 22" tires rather than 19.5. I had the same setup before changing transmissions. Overdrive and lockup torque converter allows about 70 mph at 1800 rpm.