What's Torque Rise, and why do I care?

[SuperMag]

One thing I see mentioned a lot in talk about tractors and big trucks is torque rise, or the amount of torque increase (or percentage) from the amount of torque produced at rated speed and HP to the greater amount of torque obtained at torque peak speed. But why does this never come up in conversation about cars or pickup trucks?

And now the math problem:
Given: F-250 4X4, 300 powered, cruising speed 70mph, stock tire size.

What would be the best gearing to use, and what should the HP & Torque curves look like for maximum performance and economy for our truck loaded down with 1,500 lbs of tools, hunting gear, and construction debris?

 

[Anonymous]

What is stock on an F250? I know my old mans '80 F250 4WD ran some 235/85R16's but i've no idea if they were stock sized. Also best economy and best performace aren't related. If you want best performance, you would put your highest MPH and put that at your HP peak. If you want best economy, you put your most frequent mph at your torque peak. Clearly they aren't the same. 'Best compromise' is kind of a personal thing.

How's that for not answering a question


-=Whittey=-

 

[jwhoss76]

Vague, very vague

 

[StrangeRanger]

Torque rise isn't reallt relevant to cars and is not really practical for most light trucks with gasoline engines, the 300 is a possible exception because of the low torque peak. To make it work, your RPM at cruise needs to be slightly higher than your torque peak. With the F150's stock 29" tires and an OD automatic 3.55s put you ight at 2000 at 65, but with an M5OD it takes only 3.27s. With non-OD trannies, you just can't get there without taller tires

What size tires are you running and what tranny?

 

[Silver Shadow]

What about using taller gears? When my rearend was replaced by one thet is 20 percent faster it moved my RPM's at 65MPH to 2200, I realy like it there. The C-6 doesn't seem to have any trouble even mit trailer pulling. 3rd is like overdrive and if I need a lower gear there is always 2nd. But even in these hills in eastern KY I don't drop down very often.

 

[StrangeRanger]

I wasn't real clear. I posted before morning coffee, never a good idea.

With a non-OD tranny, no matter what rear end you run, you're going to be well above the torque peak of a 300 at 70 MPH unless you're running tall tires, then a 2.73 or even a 3.08 might give you a little slack. With the OD trannies, you can gear to take advantage of the torque rise. With 29" tires this occurs running any gears taller than a 3.55 with an auto or taller than a 3.27 with an M5OD.

The real problem may be that the 300 doesn't have much torque rise. It makes 260 ft-lbs @ 2000 but that only drops to around 230 @ 3500. 10 ft-lbs/500 RPM isn't much in the scheme of things.

 

[Fiorelli]

Torque rise is when an engine gains torque as the RPM's go down. Engines that have a high torque rise have a much longer and bigger power band, better fuel effencey and a tremendus amount more power. There is nothing better than an engine with a very high torque rise in the RPM range you run in. If you got into a pickup with 210HP with a torque rise verses a 300 hp pickup with out a torque rise you would wonder why the 300 hp pickup was so lame. There is a reasion anyone that pulls anything runs a Cummins or a powerstroke over a 454 or a 460. TORQUE RISE!!!! Torque rise increases horse power at the lower RPM's.

Torque rise is differne't for differen't engines some lose very little horse power some hold there horse power some gain a little some gain alot. It all depends on the % gain and the RPM's it's gained over.

Wouldn't it be great to put your pickup in overdrive and have more horse power than in drive and get better milage. Torque Rise!!!!! I wish I could get a torque rise out of my 300 like the new diesels get. The Gas engine are to bussy turnning those high RPM's to get some BS horse power figure to build a torque rise.

This graph is for the NEW HOlland 8870 Tractor or Buhler's 2180 tractor I took it off of there site so it is New Holland's not mine maybe its Buhler's. If you got to www.buhler.com and find the specifications for the Genesis tractor you should be able to find this graph.

Look how the HP increases as the Torque rises and how the fuel useage decreases. That is the best graph I found to show and explane torque rise. Also the most impressive engine I've ever been around with a 55% torque rise in 600 RPM's and a 22hp gain and a 20Hp/hr/gal effency at full power. That would make an unreal pickup engine. The powerstroke dosen't have any where near this much torque rise. Hear is the t444e truck engine aka powerstroke specks http://www.internationaldelivers.com/si ... detail.asp

<img src="http://us.f1.yahoofs.com/users/f490fb7f/bc/Yahoo!+Photo+Album/__hr_ptochart.jpg?bchEcw.ASd_SQpr4">

Impressive engine
Jeremy

 

[Anonymous]

Torque rise has nothing to do with the engine burning diesel or gasoline, and everything to do with it being equipped with a turbocharger. Anyone who has ever driven a non-turbo diesel will assure you they don't have any appreciable torque rise. :roll:

As we all know, a turbo is driven by a combination of the flow and heat of the exhaust from an engine. So long as the turbo is getting enough air flow (in other words isn't in the low-rpm "turbo lag" range), an engine can continue to make more torque as it slows down under load. That's because your right foot (or the cruise control) continues to press down on the pedal adding fuel and hence heat to the turbo. As the engine makes more heat, the exhaust continues to increase its total pressure against the turbo's turbine section blades, which in turn forces the compressor section to cram more air into the engine, adding more heat to the exhaust, etc., in what can only be called a virtuous circle.

There is an article in Hot Rod Mag's web archives at http://www.hotrod.com/featuredvehicles/98518/index.html that is well worth reading. Be sure to sroll down and click on the "Details" link. There you'll see that this guy uses 3.25 gears. He used to run 3.55's, but installed taller gears to add torque loading to the engine. When this article first came out it was substantially longer and had a lot more detail and discussion, but has been condensed for the archives. IIRC, he said he was looking to install 3.08s or even 2.92s to add even more torque loading.

I should think that a 300 I-6 would make an ideal candidate for making torque rise. It is already configured as a high-torque, low-rpm engine. All it needs is a turbo to make it a stump-pulling torque monster...

 

[SuperMag]

Stan, You da man...

So to make the most of this phenomenon it would not be necessary to turbocharge for some ungodly level of horsepower at 9 zillion RPM, but rather, just enough to 'load up' the motor to a boost level of a few psi up to the anticipated (realistic) operating range maximum. On the 300 that would probably be about 3500 RPM... correct?

On that note, if turbocharged in that manner, and if you're geared at say 3.08, you'd pull like popper...

 

[Anonymous]

http://www.isuzuengines.com/faqs.htm#c


-=Whittey=-

 

[Greywolf]

Supermag, the low-pressure turbo as used on Saab (also their asymetrical setup on some V-6 cars) is designed to take advantage of that. My dad's 9000 has a 2.3 LPT and it drives like a big V-6...my Zephyr had the same torque as his old 900 down low, but his 9000 has torque EVERYWHERE...I wonder why he won't let me drive it when I visit him... lol
Ben

 

[Fiorelli]

All engines gas, diesel, naturally asprated, turboed or turboed with a wastgate have a torque rise even if it isn't in there operational range even those High RPM low torque gas race horse engines. They give there peek torque at a lesser RPM than there peek horse but those engines gain is over a long RPM range and then the RPM's are so high unless your running in secound at 70 you aren' turning enough rpms to utilize the torque rise. When it comes to the tractor and truck diesel and even the spark ignition engines they are rated at the top of there operational RPM range, there torque rise normaly is in that Rpm range.

This is the way I see it: right, wrong, or indefferent!
A turbo won't creat a torque rise with or with out a wast gate. It just shoves more air into the engine increasing the torque over the RPM range a non wastgated may accually hurt torque rise. As you lose rpm's you lose boost takeing torque away with it. Torque rise isn't taken buy haveing the engine running at an RPM with the throttle bearly open then opening the throttle up and seeing how much more it produces. Torque rise is messered buy haveing the throttle wide open under full load and seeing how that changes the torque curve over the RPM range.

A waste gated turbo changes the engine differently than a non waste gated one. A non wastgate builds more bost as the RPM's go up and wastegated turbo builds the same bost over more of the RPM range.

Look at it this way if you take the two turboed engines both build 30psi boost at 2600 RPm's they have the same horse power. AT 1400 one builds 15psi boost and the other one builds 30psi which engine has more torque at 1400 which engine has more horse? The one that is still building 30psi. Which is why you use a waste gated turbo! That engine may hold it's horse and torque better but it still may not have it's torque rise in that rpm range. If you take those two engines again and run them at 3000 Rpm the non wastgated may have 35 psi boost but the wastegated will only have 30 making the non wastgated turboed engine have more horse. But come to a big hill and start losing RPM's the non waste gated turbo is going to loose horse power faster than the other one.

I'm sure there is more to torque rise than just a good waste gated turbo.

I think the 300 is a good canadate for a waste gated turbo. I don't see any reasion you could get a good torque rise out of it. Find a turbo that will build the maxium bost you want at 1200 RPm or where ever and set the wast gate for that much boost so you build that amount of bost from 1200 on up!

I'll have to check out your sites.

Jeremy

 

[Anonymous]

Fiorelli is absolutely correct that all engines experience some torque rise as they slow under load at WOT from above their peak torque rpm. However, the original question was about turbocharged heavy-duty diesel engines, and my point was that with the engines in question it is the turbo that produces so much additional torque as they back into torque rise, not the fact that the engine is a diesel.

Fiorelli is also correct that a wastegated turbo produces its peak numbers across a much broader rpm range than a nongated turbo. These are the only turbos that should be considered for a vehicle. Nongated turbos are appropriate only for constant load applications, and have no place in our projects.

And therein lies the answer to your question, SuperMag. A mildly turbocharged 300 should make peak torque from 1500 all the way to 3500. As you're towing a load of lumber up the hills in Idaho, the turbo will take you from 150 lbs/ft to 400+ lbs/ft instead of the 250 lbs/ft of a non-turbo version of the same setup... 8)

Thanks for the great link, Whittey.