Community Forums

greatlakes · 02-21-2013, 05:47 AM

Quote:

Originally Posted by Mr_D

On our ISC with Banks it works out to 1,900 rpm
435*33,000 = 14,355
1200*6.283 = 7,539
14,355/7539 = 1,900 approx.
The published charts from Banks show approx 435 HP @ 2000 rpm.

Yes the published numbers are close. Typically when running an engine on a dyno the test will increment the engine up the rpm range in 250rpm increments. So they take a reading at 1500, 1750, 2000 2250 etc so you rarely see published numbers like peak tq at 2115. The exact rpm is something more common with a chassis dyno where you include the transmission and linkage to the wheels and it would be less than what the engine alone can produce.
Remember the published number your given is an engine on a stand without the loss of power due to transmission and not at the wheels.

topdownman · 02-21-2013, 06:33 AM

Ok, I'll be danged if I can figure out how you guys are calculating this. I never was good at new math

. What's the best RPM for a Cummins 300HP ISB and how do I find the torque numbers?

greatlakes · 02-21-2013, 06:40 AM

Quote:

Originally Posted by topdownman

Ok, I'll be danged if I can figure out how you guys are calculating this. I never was good at new math

. What's the best RPM for a Cummins 300HP ISB and how do I find the torque numbers?

I believe most everyone is just using the numbers that are typically published in your manual.

Coaster1 · 02-21-2013, 06:46 AM

Just my 2 cents. Having driven commercially for nearly 30 years I've been exposed to most any kind of diesel engine. Started in the 60s with a Detroit 671 @ 238 HP. Bear in mind the GVWR was 73,280 back then. Now of course it is 80,000 lbs. You had to work it hard keeping the RPMs between 2500 and 3000 just to maintain highway speeds. It required almost constant shifting in order to do this. In '69 I bought a new KW with a 12V71 rated at 330 HP with a 13 speed tranny. Less shifting but still crappy fuel mileage by today's standards, 5MPG but @.30/gal.. who cared? My last rig was a series 60 Detroit @550 HP. Automatic 6 speed Allison. 7 to 8 MPG at best. BTW, this was in a 42' Marathon. As you can see, while there there has been almost double the available HP the fuel mileage did not keep up. Owners are still striving for 10MPG and have resorted to all types of air management devices in the to attempt to get there. Those of us with coaches are restricted to what the MFG decides to use as a power plant. Cat and Cummins are the engines of choice in most MH while Detroit while is the accepted norm in larger specialty coaches. The reason being I think that Detroit does not build an engine in the 350/400 HP range. An interesting note is the the 60 series in the standard motor in Greyhound coaches. To the bottom line is if you want to get the best/efficient MPG you have to operate the vehicle not just drive it. Cruise control is perhaps the worst enemy of optimum fuel economy as it takes away control from the operator by increasing the RPM range that the vehicle will maintain the set speed. Having read this entire post in which many good points where made my observation is that if the operator does everything correctly, such as driving with an egg between your foot and the accelerator, the best improvement that can be made is maybe a 1.0 MPG advantage. If you calculate that over the life of ownership is it really worth the effort? Isn't Rv-ing supposed to be fun and relaxing? Sorry that my 2 cents turned into a dime.

speedpeddler · 02-21-2013, 07:06 AM

To answer the OP's question on HP......WAY TOO MUCH IS JUST RIGHT.

For me anyway, when it comes to cars, I always buy the model with the most HP and frequently find myself making modifications to get even more. Lol. Mileage isn't an issue for me. Just don't care and usually drive cars that only get 9 or 10 mpg on premium. Give me 500 HP any day over 30 mpg.

Same for a MH. I want the most power available and if it costs me a few MPG so be it. Don't have to use it all the time but, it sure is nice to have when you want it.

greatlakes · 02-21-2013, 07:51 AM

Quote:

Originally Posted by speedpeddler

To answer the OP's question on HP......WAY TOO MUCH IS JUST RIGHT.

For me anyway, when it comes to cars, I always buy the model with the most HP and frequently find myself making modifications to get even more. Lol. Mileage isn't an issue for me. Just don't care and usually drive cars that only get 9 or 10 mpg on premium. Give me 500 HP any day over 30 mpg.

Same for a MH. I want the most power available and if it costs me a few MPG so be it. Don't have to use it all the time but, it sure is nice to have when you want it.

I would have to agree with you as I have always been a HP junky also. Just sold my CTSV. loved it but was happy if I got 18mpg. With that said tho we typically only put about 5k miles a year on the RV and the difference from 8mpg and 10mpg equals $500 so for those folks that travel full time and on fixed income traveling 15k a year can save you $1500 a year if you can shave 2mpg. But when in comparison to buying a $300k mh $1500 is only like $125 more a month.

csrrsr · 02-21-2013, 10:48 PM

I like the hummm of a diesel engine at 60 mph. 9-10 mpg...running cool and in no hurry to go anywhere when I'm driving my house. I left my muscle cars/trucks for the RV life (R)etired and on (V)acation. If I need to get there early..I leave early. If I need to get there late...I leave early! I kinda like seeing all those people in a hurry passing me. It's a good reminder of what I used to be like and I'm glad I'm out of it!!

Mr_D · 02-21-2013, 11:04 PM

Quote:

Originally Posted by greatlakes

Yes the published numbers are close. Typically when running an engine on a dyno the test will increment the engine up the rpm range in 250rpm increments. So they take a reading at 1500, 1750, 2000 2250 etc so you rarely see published numbers like peak tq at 2115. The exact rpm is something more common with a chassis dyno where you include the transmission and linkage to the wheels and it would be less than what the engine alone can produce.
Remember the published number you're given is an engine on a stand without the loss of power due to transmission and not at the wheels.

As I understand it Banks figures are at the rear wheels as they use a chassis dyno, unless they're adjusting for trans, differential losses. I'll email them and see what they answer. I'm at work right now and don't have the brochures here.