Question about torque - Page 3 - Fuelly Forums
Go Back   Fuelly Forums > Fuel Talk > General Fuel Topics
Search Today's Posts Mark Forums Read
Thread Tools Display Modes
Old 07-29-2008, 05:23 AM   #21
Registered Member
theholycow's Avatar
Join Date: Apr 2008
Posts: 6,624
Country: United States
Send a message via ICQ to theholycow Send a message via AIM to theholycow Send a message via MSN to theholycow Send a message via Yahoo to theholycow
Pardon the tangent for a moment...

Originally Posted by R.I.D.E. View Post
Assuming your car is air cooled, low speed high load (sometimes called lugging)
Sometimes called lugging, but in modern fuel injected vehicles, that term is usually incorrect. Perhaps not incorrect in such an old vehicle as the OP's 1979 model. Either way it sounds like one should be careful when trying new strategies on an air-cooled engine.

This sig may return, some day.
theholycow is offline   Reply With Quote
Old 07-29-2008, 07:15 AM   #22
Registered Member
Join Date: Nov 2007
Posts: 1,111
Country: United States
Send a message via AIM to dkjones96
Originally Posted by Loserkidwac View Post
Any thoughs one accelerate at the point where HP and TQ cross over? Correct me if I'm wrong don't TQ and Hp always cross over at the same point on a dyno graph around 5200rpms? Wouldn't this be the more efficient even though HP is falling the TQ is still climbing...just a thought on my part...please discuss I'd love to here from some knowledgeably people!
They always cross at the point for a reason. You can't measure horsepower because it is a mathematical calculation of torque versus engine speed. Large V8 engines like the Vortec 8100 won't even rev to the 5250 cross over rpm. Diesels don't either. On the opposite side, the Civic Si revs way past it. That's why they can make 139 pounds of torque and make close to 200 hp. It's a numbers game.

Torque is what you want to look at, lets take my car for example. The solid line is normal engine output the others are acetone testing results.

I have two peaks to work with in my engine's power band (the first one is the intake and exhaust manifold tuned rpm and the second peak is the cams, no fancy cam switching on this 4 banger). I usually stick with having the engine rev up to 2900 and drop to 2100 at the next gear. But, if I need a little more power I can have the engine hover around 4200-5500. The engine makes over 110 pounds of rear wheel torque anywhere between 2500 and 6000 so I have pretty much the entire rev range to work with if I need it.

Brings up another question though. In my particular case, with two peaks, which one is more efficient? My logic is to get to the highest efficiency before a drop and stay there. Since it starts to fall at 3000 before it goes up again at 3750 it makes sense to me to avoid that rpm range.

- Kyle
dkjones96 is offline   Reply With Quote
Old 07-29-2008, 09:30 AM   #23
Site Team
Join Date: Dec 2006
Posts: 652
Country: United States
Personally, I still fail to see the connection between WOT torque curve characteristics and low-throttle efficiency.

There is an "internet rumor" (never substantiated, as far as I know) that your best gas mileage occurs at the same RPM as your WOT torque peak. If anyone can provide substantiation (logic, quoted sources, etc.), I'd be intrigued to know about them.

-Bob C.
Think you are saving gas? Prove it by starting a Gas Log, then conduct a proper experiment.
bobc455 is offline   Reply With Quote
Old 07-29-2008, 09:43 AM   #24
Registered Member
Join Date: Oct 2006
Posts: 557
Country: United States
The 5252 constant is for units of ft*lb of torque and horsepower. Newton meters and kilowatts use a different constant and will have a different value when the two numbers happen to be equal.
Originally Posted by dkjones96 View Post
Brings up another question though. In my particular case, with two peaks, which one is more efficient?
Maybe both, maybe neither. These charts don't show what is needed to make that determination. What is needed is a fuel consumption chart showing grams of fuel consumed, power produced, engine rpm, and at several different percentages of load. Then add gearing charts to indicate when shift points should be to minimize fuel use.
Interesting to know, but impractical to put in practice.

Here's a link to a thread discussing the BSFC for the 1Z engine in my white wagon. The BMEP is cylinder pressure, think of it as the amount of torque being produced. Also note that half the torque requires more than half the fuel. One more comment: Constant speed operation does not require maximum torque. 1900 rpm and 150 lb*ft at full load, makes nearly 55 hp. 1900 rpm in 5th is 55 mph. Steady 55 mph in 5th requires about 11 hp or 20% of load.

Have you looked at the chart and digested it a bit?
At full load (14 bar pressure, making about 150 lb*ft of torque) at 1900 rpm the fuel needed is right around 200 grams per kilowatt each hour. 200 grams times 41 kW is a 8200 grams per hour consumption rate.
Requiring less power, say only 1/5 of full load, means the pressure is 2.8 bar and torque is 30 lb*ft. At 1900 rpm that's 8.2 kW. Notice the fuel use is less efficient per kW at this load with 280 grams required per kW. Nearly 40% more fuel per kW is needed, but since the number of kW is 80% less the result is a 2300 grams per hour consumption rate.
Full load is more efficient, but the lower load produces more distance per volume of fuel.
Lug_Nut is offline   Reply With Quote
Old 07-29-2008, 01:31 PM   #25
Registered Member
Join Date: May 2008
Posts: 140
Country: United States
torque x rpm divided by 5252 = h.p. torque will always be more than horsepower below 5252 rpm, the same at 5252 rpm, and lower over 5252. maximum torque has less to do with optimum fuel mileage than gearing does. for example, my bike makes maximum torque at 4700 rpm, and runs 55mph at 2500 rpm. , 4700 rpm would guzzle fuel. however, if you were pulling a heavy load with a truck that makes maximum torque at 1800 rpm, and gearing allows you to operate at that speed, optimum fuel mileage under load might be at 1800 rpm. the gearing is what made it possible. if however, I was able to gear my motorcycle to operate at 4700 rpm, gas mileage would still suffer. maximum torque does not always guarantee optimum fuel mileage.

mikehallbackhoe is offline   Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Adding this to my forum site signature JonnyZero Fuelly Web Support and Community News 6 04-10-2009 07:53 AM
New Chevrolet Aveo to Debut in Frankfurt MetroMPG Automotive News, Articles and Products 12 08-15-2007 05:31 PM
How does Automatic Tranny choose? GeekGuyAndy Transmissions and Running Gear 5 08-13-2007 04:05 AM
Honda 2005 1.8L i-VTEC 88HF General Fuel Topics 4 07-09-2007 05:40 PM

Powered by vBadvanced CMPS v3.2.3

All times are GMT -8. The time now is 12:50 PM.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.