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hlagooty · 12-19-2019, 06:57 AM

I'm looking at a beaver motor coach that has a 7.2 L cat in it my question is am I going to be disappointed with this on hills and it be a dog. I'd like to cruise at the speed limit or near it and not drag along up hills but I don't need to go 80 miles per hour. the unit is a 99 so unsure if mechanical or electronic. I realize it can pull the coach because it was put there by the manufacturer but I've been in some underpowered Vehicles before

**Spdracr39** · 12-19-2019, 07:25 AM

The 3126 engine is rated for between 330 and 360 hp and up to 925 ftlbs of torque. The towing and climbing ability will be more about the transmission. I suspect it will pull fine but won't be a racecar. My 8.3 cummins in my 32,000 lb rig for example has 350 and 1020. It gets up to speed and pulls well on the highway with a 3500 lb toad but climbing 8-10% grades are slowing going. I don't mind as I'm not in a hurry.

Gary RVRoamer · 12-19-2019, 08:11 AM

The benchmark horsepower-to-weight ratio for motorhomes is 1:100 lbs. That yields adequate performance but compared to any car or pick-up it's a dog on hills and standing starts. Your car is probably in the range of 1:15 or 1:20, so at least 5x better at acceleration. You won't find any motorhomes in that bracket, so be prepared for performance that might best be called "majestic".

A 1999 version would be a 3126B and horsepower is probably in the 300-330 range. It's likely the 330 hp version in a 32,000 lb coach, so right at the benchmark ratio. I would expect it to be fairly slow on any grade exceeding about 3%, climbing at somewhere around 30-40 mph on a 5% grade. Some people find that frustrating, while others just relax and know the top of the hill will soon be reached.

crb478 · 12-19-2019, 08:40 AM

I have the 3126 in a 30K coach. Mine is the 330 hp model and it will pull grades just fine if you downshift the transmission and keep the rpm's in the upper range. What it will not do is pull up a steep grade from a stop or near stop and max out your speed at the top. In other words you will need to be at speed before you hit the grade. The 3126 is a HUEI system so it is electronic.

Even pulling a car most grades can be handled at 45 to 55 mph. If you want faster than that, go for big torque numbers in another MH.

Skip426 · 12-20-2019, 08:08 AM

The 3126B has electronically controlled fuel injection.
In nine years of travelling with my mini van in tow , rolling weight 32k, it’s gotten me everywhere I want to go.

For decent fuel economy, with the gearing and tires on my coach, keeping the RPM in the 1700 range works best. 62/65 mph.
Some will try to warn you off the engine because of issues with the HEUI fuel system, but Cummins engines of the same vintage have fuel system problems too. In the case of the ISB engines with a VP-44 injection pump , I’d consider them worse. JMHO, of course.
Good luck with your search for a coach and safe travels.

gpounder · 12-20-2019, 08:28 AM

There are a lot of vehicles with that same configuration. It is all in the numbers

The Cat 3126 is 925 ft lbs torque

The C9 400 hp is the next bigger at 1100 ft lbs torque

Consider what that means to power on the ground when using these numbers an an example.

3rd gear transmission is 1.41:1 and differential ratio 4.11:1

925x1.41=1304x4.11=5360 ft lbs torque
1100x1.41=1551x4.11=6374 ft lbs torque

This is what moves your 32,000 lb beast up that hill.

jcussen · 12-20-2019, 09:01 AM

Had the 300/860 version in a 40 ft coach with a toad, about 32000 lbs combined, Up a long 6% grade, 2nd or 3rd gear at 35 to 45 mph.

hlagooty · 12-20-2019, 10:39 AM

i knew this would be a matter of opinion and in the end it would be my impression of driving it that would be the determining factor. So I test drove a 5.9 supposedly 315hp 38 footer. It was a dog, yes it could do 65 on the flat but a speed bump slowed it down. I need next to run a 3126 powered unit I will post when this happens. Would love to try a thunder or something with c12 power but not finding them.

Cincy Steve · 12-20-2019, 11:17 AM

Quote:

Originally Posted by hlagooty

i knew this would be a matter of opinion and in the end it would be my impression of driving it that would be the determining factor.

This is brilliant logic on your part!

I drove a Peterbilt, w/330 Cat, for several years. Pulled serious weight, sometimes bumping 80,000#, all over OH, IN, & KY. Ran 65 on the flat stuff & made it up every hill w/o any drama....but I would've preferred the Pete, w/400 Cummins, that had previously taken me to 48 states & Canada. Have since driven other rigs in the 450-500 HP range.

Our (1st) MoHo is a 450 HP, tag axle, & I have a hard time imagining putting enough weight in/on it to want any more motor.