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Old 09-26-2012, 10:50 AM   #1
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Max HP and Torque at RPM question

I have a 97' F350 with the 5.8L gas engine and manual 5 speed transmission.

The specs say that max HP is 210HP @ 3.600rpm and max torque is 310 foot pounds @ 2,800rpm, so seeing as how my truck has no red line on the tach and logic kicking in would you say staying in any gear past 3,600 RPMs would be a waste of gas and engine wear seeing as how there is nothing to gain past that rpm?
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Old 09-26-2012, 10:54 AM   #2
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In towing situations, you're generally going to find yourself working between the peak torque and peak BHP RPMs (2,800 to 3,600 RPM, in your case) on the grades and other high-load situations. It doesn't do much good (and is hard on the longevity of the equipment) to run above the BHP peak where the torque and BHP curves are both dropping - the more you rev up there, the less you get.

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Old 09-26-2012, 10:59 AM   #3
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Quote:
Originally Posted by RustyJC
In towing situations, you're generally going to find yourself working between the peak torque and peak BHP RPMs (2,800 to 3,600 RPM, in your case) on the grades and other high-load situations. It doesn't do much good (and is hard on the longevity of the equipment) to run above the BHP peak where the torque and BHP curves are both dropping - the more you rev up there, the less you get.

Rusty
Ok, that's what I thought but wasn't sure so I figured I'd ask before things start wearing out prematurely from revving too high with no results.
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Old 09-26-2012, 01:12 PM   #4
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Your most efficient RPM (best MPG) is as close to the torque peak as you can get and still have enough horses to pull the load without straining. But depending on gearing (axle ratio) you may not have enough horses hooked up at 2,800 RPM, so you have to give it some more gas to climb a mountain pass dragging a heavy trailer.

As Rusty noted, any RPM above the HP peak is usually just a lot of threashing for nothing. But you need to see a torque and HP curves for your exact engine. If the HP curve is fairly flat so you still have 200 HP a few hundred RPM past the peak, and if the torque curve is flat as a pancake so you still have almost 300 lb/ft at 3,600 RPM, then you can probably add some RPM above 3600 without much loss in efficiency. But where the HP and torque curves begin their nose dive, you don't want to go up there.
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Old 09-26-2012, 01:26 PM   #5
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Real world experience on my last gasser (a 1996 Dodge Ram 3500 dually with the 8.0L Dodge V-10 rated 300 BHP @ 4000 RPM and 450 lb-ft @ 2800 RPM) was that most 6% grades settled in about 3500 RPM as an engine speed that could be sustained on long climbs pulling a 13,500 lb GVWR 36' 5th wheel. As Smokey says, it really depends on the shape of your HP and torque curves - you want torque rise working for you, which it was in my case at 3500 RPM, a point between peak torque RPM and peak BHP RPM as I stated.

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Old 09-28-2012, 09:00 AM   #6
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Does anyone know where I can find the torque and HP curves charts for my truck? I tries searching google but don't think I'm entering the right search words.
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Old 09-28-2012, 12:12 PM   #7
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Quote:
Originally Posted by Corey9212 View Post
Does anyone know where I can find the torque and HP curves charts for my truck? I tries searching google but don't think I'm entering the right search words.
About the only place you're likely to find the power curves is in the '97 and earlier brochure for the F-250 and F-350 Heavy Duty pickups, and maybe in the brochure for the '97 and earlier "SuperDuty" regular cab chassis cab truck, but I seem to remember those came only with the diesel engine. My brother's '92 F-150 also had the 5.8L gas engine, but I suspect the HP and torque curves were different than the F-350. I have the '97 Ford Truck Source Book which includes all sorts of specs, but no graphic of the HP and torque curves. For those charts you need the sales pitch picture book brochure.

Dick Cutting bought a new '97 Heavy Duty pickup, and he still drives it. Maybe he has a '97 brochure? Contact him at
http://www.cutsoldtrucks.com/
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Old 09-30-2012, 02:54 PM   #8
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Hypertech has a rear wheel power/Torque curve developped for most trucks. They are real and well detailed to help you find the towing capacity and where to shift.

Sorry my mistake the curve is not available for the 5.8L just the 5.4L in the F150. Check older model but no curves for 95 5.8L

When I towed with the last gas truck I replaced the exhaust and installed dynomax kit and I could rev the truck engine all day almost at the red line. It was the only way to keep from over heating by reving the engine fast enough to cool the rad. It was a standard also and 5600 RPM uphill was never a problem with an open exhaust.

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Old 10-05-2012, 01:44 AM   #9
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Don't forget to take into consideration the drop in rpms when you upshift. RPM's too low at upshift and you'll fall off the curve.
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Old 10-06-2012, 12:51 AM   #10
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Quote:
Originally Posted by caissiel
Hypertech has a rear wheel power/Torque curve developped for most trucks. They are real and well detailed to help you find the towing capacity and where to shift.

Sorry my mistake the curve is not available for the 5.8L just the 5.4L in the F150. Check older model but no curves for 95 5.8L

When I towed with the last gas truck I replaced the exhaust and installed dynomax kit and I could rev the truck engine all day almost at the red line. It was the only way to keep from over heating by reving the engine fast enough to cool the rad. It was a standard also and 5600 RPM uphill was never a problem with an open exhaust.

Performance is our Passion - Hypertech
I keep putting off getting my exhaust and air intake upgraded for better performance, will check out the site and see what I can find.

Quote:
Originally Posted by Mr_D
Don't forget to take into consideration the drop in rpms when you upshift. RPM's too low at upshift and you'll fall off the curve.
I found that out the hard way, going up a hill and the truck is at 5400 RPMs, I shift up and release clutch to find my RPMs are now too low to keep going so shifting down two gears now to get back up to speed, lol.
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Old 10-10-2012, 09:10 PM   #11
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Quote:
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Hypertech has a rear wheel power/Torque curve developped for most trucks. They are real and well detailed to help you find the towing capacity and where to shift.
OK, dumb question:
Why do these after market programmers give you better performance and mpg than the stock programming? Why wouldn't the mfgr provide the better program? What are the negatives to using these after market devices?
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Old 10-11-2012, 01:03 AM   #12
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OK, dumb question:
Why do these after market programmers give you better performance and mpg than the stock programming? Why wouldn't the mfgr provide the better program? What are the negatives to using these after market devices?
I think it's cause the manufacturer has to build the vehicle for all types of drivers so they have to balance HP and fuel economy, you can have lots of HP but burn more fuel getting it or you can burn less fuel but have less HP.

The programmers allow the end user to pick when they are towing to have all the HP the engine can put out or when they are casual driving to have better mileage usually with just the push of a button.

That is my thoughts, I'm sure others will ring in that know more about it.
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Old 10-11-2012, 01:20 AM   #13
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Banks worked with Cummins and Allison when testing their diesel kits so as not to overly stress either the engine or trans.

As to why Cummins doesn't do it? Warranty costs come to mind. I waited to install the Banks kit till my warranty was almost gone before I installed it.

When we had a CAT 3126 300/860 CAT wanted over $2,000 to uprate it to 330/860. Almost all the cost was the warranty upgrade to cover the increased HP. If I didn't want a warranty it was only a few hundred $'s for the program and tech's time.
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Old 10-11-2012, 01:26 AM   #14
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Quote:
Originally Posted by SmokeyWren View Post
Your most efficient RPM (best MPG) is as close to the torque peak as you can get and still have enough horses to pull the load without straining. But depending on gearing (axle ratio) you may not have enough horses hooked up at 2,800 RPM, so you have to give it some more gas to climb a mountain pass dragging a heavy trailer.

As Rusty noted, any RPM above the HP peak is usually just a lot of threashing for nothing. But you need to see a torque and HP curves for your exact engine. If the HP curve is fairly flat so you still have 200 HP a few hundred RPM past the peak, and if the torque curve is flat as a pancake so you still have almost 300 lb/ft at 3,600 RPM, then you can probably add some RPM above 3600 without much loss in efficiency. But where the HP and torque curves begin their nose dive, you don't want to go up there.
Cummins and CAT usually say the best economy is at about 200 rpm over peak torque rpm.
Not sure how that works with a Banks kit on though as my peak torque is 1200 ft lbs from 1400 to past 1700 and only drops to 1050 (stock max) when past 2,100 rpm and red line is 2,200 rpm. I try to run around 1650 rpm which is just about 60 mph in 6th.
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