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Old 11-19-2010, 11:34 PM   #1
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Monitoring Engine RPMS when accellerating

Hi
When entering the freeway, going up hills, ect. I try to limit the engine RPM on my Chev 454 to 3000 rpm. I have a 30 ft. MH with a 4sp auto. The MH weights about 18K.
I know the dash guage shows a higher rpm limit. I don't want to over rev the engine as it is pulling alot of weight.
Now I really put my foot in the floor on my 74 Merc. 460 but I'm only pulling 5000 K. not 18,000 K
Your thoughts, please.

Fred from Pasco, Wa.
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Old 11-20-2010, 12:41 AM   #2
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I would like to add to the above that I like to keep my speed at 60 MPH at 2000 rpm in overdrive whenever possible.
Fred from Pasco, Wa.
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Old 11-20-2010, 12:56 AM   #3
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A good RPM range for my paticular set up is 2200/2500, and try not to exceed 3000/3500 when going up steep grades. JMHO, safely follow the yellow brick road.
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Old 11-20-2010, 05:49 AM   #4
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I got a 2000 Pace on a Ford chassis with a V10 ''Triton'' engine. I try to hold the max rpm on the motor to 3500. This usually occurs when I pull into inner state traffic as she upshifts to about 62 mph. Between 62 and 65 I am turning 2200 to 2400 rpm in overdrive. I usually set the cruise at about 62 or 2200 rpm and let the traffic pass me. Two reasons for this.

One. The traffic is in a ''going away'' pattern in that there usually is a ''space'' in front of me that is empty because all the traffic is pulling away from me. I have actually made some really long days on the road and never pass a vehicle. They all passed me. I stay out of the ''speed'' lanes and when the highway is four lanes going my way I usually run in the second lane from the right.
Two. This speed is my economy notch and I can get fairly good m.p.g. out of the old hoss. On two lane roads I try to run with the traffic so to speak and if I see several behind me I will find a spot and pull over and let them zipp by me. I stopped being in a hurry back in 95 when I retired...

nuff said .....

Thank you Vets for keeping me safe......
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Old 11-20-2010, 04:56 PM   #5
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You really can't compare the older big-block engines, Ford or GM, with the later gasser engines - the later engines are "winders", that largely rely upon higher RPM operation to keep the load moving down the road and up the grades - they seem to get the job done, while maintaining decent fuel MPG - but that constant down shifting when driving into head winds and at the slightest upgrade drives me NUTS! My brother in law has a Minnie Winnie on a Ford chassis, with the V10 engine - and if you SNEEZE in it's direction, it has to downshift...

The GM 454 in our Winnie with the older 3-speed automatic and no OD, seems happiest down at 2600 RPM or so at just under 60 MPH - and the Oregon speed limit is 55 MPH anyway - so no problem. Like the OP, in the grades, when downshifting IS required, I too prefer to limit RPM at the 3000 mark.
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Old 11-20-2010, 06:27 PM   #6
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I don't understand your reasoning to limit acceleration RPM. What you are doing is forcing the transmission/torque converter to work much harder and in turn possibly 'lugging' the engine down. You end up accelerating very slowly and potentially creating problems with oncoming freeway traffic. Additionally, with many more transmission changes, you are increasing wear and tear on the clutch packs and bands. You can also be defeating your gas mileage too. While I don't advocate 5000 plus rpm while getting going, for sure 3500-4000 is economical, put your engine into a good power band and will allow you to slip into traffic more easily. Now, as far as steady highway driving, that will depend on where you like your speedometer to read. Most of us it appears, like 62-68mph on a highway. Personally with my V10 Ford hauling my 11-12,000# 5er(total truck and trailer of ~20,000#), I like to see 2-2200 rpm in overdrive. When I had a 460 hauling a 5er, the rpm was somewhat higher as I didn't have OD, but 2800rpm all day never hurt a thing
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Old 11-20-2010, 08:18 PM   #7
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The GM engine design engineers are actually quite smart. They designed their engines to safely operate within their RPM specifications, whether it be low or high RPM's. Nearly all gasoline engines produce their most HP above 3,000 RPM.The GM 454 HO engine for instance produces a maximum of 425 HP @ 5250 RPM and maximum torque of 500 TQ @ 3250 RPM( GM Engines :: Performance Engines :: My Crate Motor - High Performance Engines ) You are correct thinking that it is not wise to maintain maxmum HP while climbing grades, but normal interstate ramp entry speeds are not detrimental when the engine is properly maintained.
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Old 11-21-2010, 04:35 PM   #8
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Quote:
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The GM engine design engineers are actually quite smart. They designed their engines to safely operate within their RPM specifications, whether it be low or high RPM's. Nearly all gasoline engines produce their most HP above 3,000 RPM.The GM 454 HO engine for instance produces a maximum of 425 HP @ 5250 RPM and maximum torque of 500 TQ @ 3250 RPM( GM Engines :: Performance Engines :: My Crate Motor - High Performance Engines ) You are correct thinking that it is not wise to maintain maxmum HP while climbing grades, but normal interstate ramp entry speeds are not detrimental when the engine is properly maintained.
AH, but Ray - you have TOTALLY overlooked the FACT that the 454 BB engine as used in our motorhomes is NOT the "performance" version - but a VASTLY strangled and detuned version that doesn't even come CLOSE to the HP and torque figures you mention, OR the RPM range capability.

The 454 engine in my '88 vintage Winnie is rated about HALF what you mention - and while later versions of the 454 might be a little more refined, I doubt it's a night-and-day difference or improvement as to peak HP, torque, or RPM...

I'll stick with my 3000 RPM or so limit for hill-climbing and such - and if you have any version of the GM 454 or Ford 460 that you plan to rev up at the 5K+ RPM range in passing or climbing situations, be sure to give us a warning blast on the horn before you pass, so we can move wayyyyyy over to avoid flying pieces...
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Old 11-22-2010, 11:16 AM   #9
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The GM engine used since 2002 in a MH has been the.
8 .1L 496 cu in
HP may vary but usually the 325 HP@4,000 RPM
450 lb ft torque @2,800 RPM

At 3,000 RPM the HP is around 250
The 450 lb ft torque will last from 2,800 to around 3,800 RPM before it drops off.

The older(80's) 454 carb engines had a cam that required much higher RPM for the peak torque.
A vacuum gauge was good to use on them.

The cam was then changed to use lower RPM with TBI and 4 speed transmissions.

So it depends on what engine is in your MH as to how it should driven by RPM. Low RPM can hurt in some.
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Old 11-22-2010, 07:23 PM   #10
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You probably have a redline of 5000 or slightly more. You could easily run to 3500 RPMs when accelerating and I wouldn't be alarmed if once in while you ran it to 4000 to get up a steep grade. Your engine will make a lot of noise, but it is just doing what it is designed to do. And the weight of the rig doesn't really have any effect on the engine. It does on the transmission and drive shafts, but it has to deal with that weight all the time, regardless of gear or RPM.
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Old 11-23-2010, 10:37 PM   #11
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Gary that is why I said "for instance", it is an example only. True, the only way to know about your particular engine is to obtain its HP/Torque graph. Even a diesel engine produces its maximum HP in the upper half of its RPM operating range. That is the beauty of a automatic transmission, they make lugging an engine impossible by forcing the engine to run in its power band/ at a higher RPM.

Fred's driving style is fine. It would also be considered economy driving. I was just pointing out that higher RPM's do not harm an otherwise healthy engine.
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Old 11-24-2010, 11:33 AM   #12
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It makes a difference which Ford 460 you have. There is the auto and the industrial (truck) versions. Among possibly other things, they have different cam and crank. Also Ford had a 390 series that had 389, 390, and 391. All used pretty much the same block but other wise different. You could rebuild a 390 block to 389 or 391 by boring out the disributor hole.
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Old 11-28-2010, 03:18 PM   #13
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Fredrick,

You say you don't want to "overrev" your motor. Do you have any idea what RPM GM rates the horsepower for your engine? If you don't how do you what RPM is "overreving"

If you put your transmission in drive and start out from a stop on flat ground with your foot to the floor the transmission known what rpm to upshift at. The transmission will not let you overrev your engine. If you are for example going down a hill in second gear and the speed keeps getting faster the transmission will upshift by itself to prevent overreving the motor. Don't worry about overreving your motor it is almost impossible to do it. The transmission governor won't let you.

Jim
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Old 11-28-2010, 07:41 PM   #14
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Fredrick,

You say you don't want to "overrev" your motor. Do you have any idea what RPM GM rates the horsepower for your engine? If you don't how do you what RPM is "overreving"

If you put your transmission in drive and start out from a stop on flat ground with your foot to the floor the transmission known what rpm to upshift at. The transmission will not let you overrev your engine. If you are for example going down a hill in second gear and the speed keeps getting faster the transmission will upshift by itself to prevent overreving the motor. Don't worry about overreving your motor it is almost impossible to do it. The transmission governor won't let you.

Jim
You may be giving some bad info. I don't know how long the 454 was used in the MHs, but that would suggest to me that it might be an older MH. The older auto trannies would not automatically shift up if they are manually shifted to a lower range (our 03 Honda is this way). Obviously a manual tranny doesn't shift unless you do it. If the MH has an OE Tac, it should show the "red line RPM". If not a speed for each gear can be determined.
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