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08-06-2021, 02:58 PM
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#57
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Senior Member
Join Date: Oct 2020
Posts: 499
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Quote:
Originally Posted by JMBXL37A
You sound like a nice guy....however, I'm not an Engineer BUT I am also a lifelong gearhead AND a subject matter expert at drag racing so you will appreciate Facts and Data to make this a CLOSED CASE and disprove your THEORY!
I took my 450/1250 ISL 9 and derated the TQ at 2200 RPM from 1074 to 1003 to give it 420 HP instead of 450 leaving the rest of the bottom end numbers the same (this could be accomplished VERY easily with VERY minor tuning). The reason I picked this 420 HP value because I now can compare it head to head against the new 2021 Cummins 6.7 Ram 420/1075 motor....420/1075 6.7L Cummins vs Cummins 420/1250 8.9L!
I took the Wallace Racing Calculator and loaded all data for both motors with TQ data by RPM (it obviously doesn't use TQ since HP is a function of TQ) and used my motorhomes' ~32K weight, 4.78 rear with 40.1" tall 275/80x22.5 tire, Allison 3000MH trans gears, etc and the bottom line is that the ISL ran an ET of 23.70 @ 55.21 MPH vs 24.41 @ 55.34 MPH! I consider the 0.71 seconds (almost 1 second) at the track a spanking! I shifted each motor at peak HP 2200 RPM for the 8.9L and 2800 RPM for the 6.7L.
I hope that this puts the HP vs. TQ debate to bed ONCE and for ALL! Cheers!
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You’re completely mistaken, I’m not nice at all! Glad we could clear that up.
No complaint with your simulation. However you’ve asked and answered a different question than the original discussion - it was terminal speed up a long grade. Acceleration through the gears from rest is a different exercise.
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08-06-2021, 05:48 PM
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#58
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Senior Member
Fleetwood Owners Club American Coach Owners Club
Join Date: Mar 2011
Posts: 6,767
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Quote:
Originally Posted by 2014Aspire
I now have a motorhome that weights approximately 40,000# and I tow an Expedition that weights approximately 5,700#. Our motorhome has 1,250 Ft Lb of torque and pulls the Expedition with no problems. In fact I averaged 8.4 miles per gallon on our trip from Florida to Illinois. We sold the motorhome and the Expedition and are looking at downsizing. We are looking at a smaller Diesel with a 340 Hp Cummins and 700 Ft Lb of torque. We are looking at towing either a Jeep Gladiator or another Expedition. So will the 700 Ft Lb of Torque be enough to tow the Gladiator 4,650#-5,050# or the Expedition 5,443#-5,692#. I want to be able to tow the best I can to what I have now. I know there are a lot of factors involved here. I just am interested in torque. Will 700 Ft Lb of torque tow 5,000# easily?
Thanks
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Many MHs do not give you a choice of engines. However, also most MHs can pull with ever their tow rating is. Determine how much you want to tow, and buy a coach with that tow rating.
__________________
2014 American Eagle 45T
DD 13, 500 HP
Pulling a Honda CRV
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08-06-2021, 08:46 PM
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#59
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Senior Member
Join Date: Dec 2013
Location: Chicago Area
Posts: 1,295
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Quote:
Originally Posted by tropical36
Not about to argue about all that math either, but what was so wrong about my 10hp/ft recommendation to the OP for putting it away and for being done with it in one sentence?
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Nothing wrong with that at all, although I would suggest that as a minimum. 11 might be more optimum.
__________________
2004 AllegroBay 34XB Nov 2017 Banks, Front & Rear Trac bars, Konis
Sold:'83 Revcon Prince 31' FWD GM Performance 502 w/Edelbrock MPFI, Thorley Tri-Ys & Magnaflows, 4L85E 4 spd. Tested to exceed 100 mph.
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08-06-2021, 09:29 PM
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#60
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Junior Member
Join Date: Mar 2021
Posts: 4
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is the Seina on a dolly and front wheel drive?
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08-07-2021, 04:19 PM
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#61
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Senior Member
Join Date: Oct 2016
Posts: 277
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I certainly agree with those saying it is horsepower that counts. My experience is real life experience, not theoretical. I had a 32000 lb GVWR motorhome powered by a 400 hp engine with 1000 lb-ft of torque. I now have a 31000 lb. GVWR motorhome powered by a 340 hp engine with 660 lb-ft of torque. I can tell you I can clear the same hill in the new motorhome at just about the same speed as I did with the one with 400 hp. The difference, of course, is the rpm of the engines, as many have explained in great detail. The 400 hp engine was turning over 2200 rpm, while my 340 hp engine is turning over about 2750 rpm (4th gear).
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08-07-2021, 08:04 PM
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#62
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Senior Member
Tiffin Owners Club
Join Date: Oct 2010
Location: Granger, TX
Posts: 595
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I think you will not be a happy camper. Max Torque comes at the low end of the RPM range, and that is great for starting from a dead stop, but not great for towing a large toad up hill. That takes HP and comes at the upper end of the RPM range.
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08-08-2021, 10:52 AM
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#63
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Senior Member
Join Date: Aug 2001
Location: North America somewhere
Posts: 30,878
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Quote:
Originally Posted by tropical36
Not about to argue about all that math either, but what was so wrong about my 10hp/ft recommendation to the OP for putting it away and for being done with it in one sentence?
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Weight is the factor in this discussion not how long the vehicle. HP is rated by moving a specified amount of weight and time elapsed.
reference: Power and Torque: Understanding the Relationship Between the Two, by EPI Inc.
1 HP = 33,000 lb/ft. per minute. ref: https://en.wikipedia.org/wiki/Horsepower
__________________
2000 Winnebago Ultimate Freedom USQ40JD , ISC 8.3 Cummins 350, Spartan MM Chassis. USA IN 1SG 11B5MX,Infantry retired;Good Sam Life member,FMCA. " My fellow Americans, ask not what your country can do for you, ask what you can do for your country. John F. Kennedy
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08-08-2021, 11:23 AM
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#64
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Senior Member
Join Date: Jun 2016
Location: Ontario, CANADA
Posts: 318
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I agree with most that torque is the governing factor over HP. I have a CTA-8.3 Cummins that pulls really good at 325 HP; which is considered under powered as we are 40,000 gross when towing our Jeep. I would say that the gear ratio also comes into play with it. Our coach runs at 70 mph while at 1800 rpm. I would guess that going from 1200 Ft/lbs to 700 would be a big change unless the gear ratio and rpm of the engine can make a difference.
I know I do like more Torque/ HP when I need it (grades). I am fortunate to have an older coach where it can be easily increase in Torque/ Hp; which is on the list of modifications; so long as DW is in agreement.
__________________
Mike and Family
98 American Eagle EVS, Cummins C8.3
2022 Jeep Wrangler Sahara ECO, Blue Ox
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08-08-2021, 01:01 PM
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#65
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Senior Member
Join Date: Dec 2013
Location: Chicago Area
Posts: 1,295
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The problem with empirical judgement in the HP/torque discussion is the two tend to follow each other. So when you get a 340 HP, the torque is 6 or 700 ft-lbs. When you are talking 450 HP, the torque is usually 1200 ft'-lbs. So there is the temptation to compare the 700 vs 1200 and view torque as the governing factor in performance. Ignoring the reason you have 1200 ft-lbs is because you have a 450 HP engine. Where is gets interesting is when you compare gas engines to diesel. As it turns out, many of these gassers will pull hills faster than the lower HP diesels even though the diesel has almost twice the torque. While the gasser is a lighter coach, its not half the weight of the smaller diesels, yet the gasser will be faster on the hills. Yes, the engine screams running higher RPM, but its faster.
A sad reality is that I think some of the reason we all fall for those big torque numbers is because who wants to brag about 400 HP, when they can brag about 1000 ft-lbs of torque? The bigger number just sounds better.
__________________
2004 AllegroBay 34XB Nov 2017 Banks, Front & Rear Trac bars, Konis
Sold:'83 Revcon Prince 31' FWD GM Performance 502 w/Edelbrock MPFI, Thorley Tri-Ys & Magnaflows, 4L85E 4 spd. Tested to exceed 100 mph.
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08-08-2021, 04:41 PM
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#66
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Senior Member
Join Date: Jun 2015
Posts: 1,077
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Love it when the Gasser guys tell us we don't know what real power is.... Paul
__________________
2017 Ventana 4369
towing a 2013 Honda CRV
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08-08-2021, 09:22 PM
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#67
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Senior Member
Join Date: Dec 2013
Location: Chicago Area
Posts: 1,295
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Quote:
Originally Posted by PandS
Love it when the Gasser guys tell us we don't know what real power is.... Paul
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Don't think he looked at my signature.
__________________
2004 AllegroBay 34XB Nov 2017 Banks, Front & Rear Trac bars, Konis
Sold:'83 Revcon Prince 31' FWD GM Performance 502 w/Edelbrock MPFI, Thorley Tri-Ys & Magnaflows, 4L85E 4 spd. Tested to exceed 100 mph.
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08-08-2021, 11:20 PM
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#68
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Senior Member
Join Date: Jan 2021
Posts: 281
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Quote:
Originally Posted by Maik
I agree with most that torque is the governing factor over HP...
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No it is not. The only way to know how a coach will perform is to compare HORSEPOWER numbers, NOT torque numbers. A little Cummins 5.9 or 6.7 just has to spin faster than the 8.9 to develop its horsepower, that’s all.
And…contrary to what another poster way up higher in this thread posted, HORSEPOWER IS HORSEPOWER no matter what kind of engine produces it. A 350 HP gas engine will pull a hill just as well as a 350 HP diesel. The difference is RPM, which no one talks about. The gas engine will have to spin around 4,000 RPM to make that power, where the big diesel will only have to turn over at 1,800 to 2,000 RPM to make the same power. The gas coach will be geared differently than the diesel coach, but they will ultimately perform the same.
Horsepower is horsepower…period.
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08-09-2021, 05:58 AM
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#69
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Senior Member
Join Date: Oct 2020
Posts: 499
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Quote:
Originally Posted by JMBXL37A
You sound like a nice guy....however, I'm not an Engineer BUT I am also a lifelong gearhead AND a subject matter expert at drag racing so you will appreciate Facts and Data to make this a CLOSED CASE and disprove your THEORY!
I took my 450/1250 ISL 9 and derated the TQ at 2200 RPM from 1074 to 1003 to give it 420 HP instead of 450 leaving the rest of the bottom end numbers the same (this could be accomplished VERY easily with VERY minor tuning). The reason I picked this 420 HP value because I now can compare it head to head against the new 2021 Cummins 6.7 Ram 420/1075 motor....420/1075 6.7L Cummins vs Cummins 420/1250 8.9L!
I took the Wallace Racing Calculator and loaded all data for both motors with TQ data by RPM (it obviously doesn't use TQ since HP is a function of TQ) and used my motorhomes' ~32K weight, 4.78 rear with 40.1" tall 275/80x22.5 tire, Allison 3000MH trans gears, etc and the bottom line is that the ISL ran an ET of 23.70 @ 55.21 MPH vs 24.41 @ 55.34 MPH! I consider the 0.71 seconds (almost 1 second) at the track a spanking! I shifted each motor at peak HP 2200 RPM for the 8.9L and 2800 RPM for the 6.7L.
I hope that this puts the HP vs. TQ debate to bed ONCE and for ALL! Cheers!
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You know what’s interesting about these simulation numbers? The smaller 6.7 is assigned a higher terminal speed. So while several tenths of a second do indeed represent a spanking at the strip, on the street maybe not so much. Accelerating down a hypothetical 1320 foot freeway merge ramp, both coaches are traveling the exact same speed at the end of the ramp when they need to merge into traffic. Perhaps there is some advantage getting there sooner, but I’m thinking that in street driving the ability to reach merge speed before the end of the ramp is the more important factor. In a way, you have actually proved the point of the horsepower is horsepower camp here.
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08-09-2021, 06:12 AM
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#70
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Senior Member
Join Date: Jul 2021
Posts: 833
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I drive the shortest diesel pusher out there today, 32 Tiffin Breeze. I have roughly 220hp and 600ftlb. I tow a Honda CRV regularly. My tow capacity is 5k. Flat roads and small inclines you don’t even know the car is back there. Once you get into steep 9-12% grades and some extremely steep switch backs in the back country you notice the lack of power. It’s a trade off I knew going into my purchase. I wanted small, but liveable and the coach delivers. Sometimes I end up doing 55mph going up long inclines as well, but I have plenty of company in the right lane with both trucks and 40ft pushers towing Yukon’s and the like.
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