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cvd · 01-30-2022, 10:11 AM

I have a 1999, single slide, 34 ft Itasca with a 275 HP ISB. Power is very adequate to move 27,000 lbs (21,000 loaded coach and 6,000 trailer).

Now thinking about newer coach, Eg. Tiffin Red 37PA (360 Hp version). Of course the newer, larger, 4 slide coach weights quite a bit more (I'm thinking 31000 lb fully loaded, plus 6000 lb trailer). The weight/power ratios will be close, slightly worse w the new coach (calculations below)

Question - is is reasonable to expect the newer coach to pull grades similarly to my old coach?

≈≈============================
Old coach-5.9 ISB, 275 HP, 600 Tq
27000 lb/275 Hp = 98 lb/hp
27000lb/ 600 Tq = 45 lb/ ft lb Tq

RED 37PA- 6.7 ISB, 360 Hp, 800 Tq
37000/360 =103 lb/hp
37000/800 = 46 lb/Ft lb
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MrMark52 · 01-30-2022, 10:50 AM

While Hp is important, so are gear ratios - particularly the rear end but tranny as well (not to forget the # of shift gears of the transmission).

If the rear end gear ratios between the two coaches is the same with the same transmission, then it is likely all is good. If there are differences, then you’ll need the power curves for the two engines and then overlay the transmission speed shift points and rear end to come to somewhat of a conclusion.

Skip426 · 01-30-2022, 11:05 AM

I roll at 107 lbs/hp and although I slow down on hills I have no problem passing loaded semis.

I would hope the 360 hp/ 800 ft.lbs ISB is equipped with the 3000 series Allison and not the 2500 .

As MrMark has mentioned , the entire drive train has to be considered as well as tire size.

Unplanned Tourist · 01-30-2022, 12:10 PM

Quote:

Originally Posted by cvd

I

Question - is is reasonable to expect the newer coach to pull grades similarly to my old coach?

==

Yes. HP and Torque have never changed since they were first measured.

Gearing can make a difference, either good or bad.

Then there's torque curves, and other variables, but just forget all that and drive it.

cvd · 01-30-2022, 12:14 PM

Good point on transmission and gearing - 6 speed M3000 on a new coach, 4 speed MT643 in the old. More grears means better chance of matching rpm to situation.

BigEvi · 01-30-2022, 01:01 PM

Simplifying it of course...Torque gets you up to speed and HP determines how fast the top speed is. So you should feel the exact same acceleration between the 2...maybe slightly better with the 6 speed tyranny. As far as top speed goes...who gives a crap what that is on level ground. But it's the same on hills...so the newer rig might be a little slower on steep grades. It's a push if you ask me.

If I were buying new I would get the most HP/TQ I could afford. 600hp sounds about right to me.