Go Back   EcoModder Forum > EcoModding > EcoModding Central
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 11-15-2011, 06:57 PM   #61 (permalink)
(:
 
Frank Lee's Avatar
 
Join Date: Jan 2008
Location: up north
Posts: 12,651

Blue - '93 Ford Tempo
Last 3: 27.29 mpg (US)

F150 - '94 Ford F150 XLT 4x4
90 day: 18.5 mpg (US)

Sport Coupe - '92 Ford Tempo GL
Last 3: 69.62 mpg (US)

ShWing! - '82 honda gold wing Interstate
90 day: 33.65 mpg (US)

Moon Unit - '98 Mercury Sable LX Wagon
90 day: 21.24 mpg (US)
Thanks: 1,551
Thanked 3,428 Times in 2,153 Posts
FYI I went up TWO sizes and the suspension remains stock. It ain't no monster mudder.

__________________



Last edited by Frank Lee; 11-15-2011 at 07:03 PM..
  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 11-17-2011, 08:16 PM   #62 (permalink)
EcoModding Lurker
 
Join Date: Jan 2011
Location: Hamilton, New Zealand
Posts: 74
Thanks: 1
Thanked 3 Times in 3 Posts
Quote:
Originally Posted by Duffman View Post
My old Thermodynamics professor use to say heat transfer is a slow process. I dont think its why.
think of a model airplain engine, if you turn it over fairly slowly while holding the prop, you feel a pulse as it fires, but that pulse is done in about 1/5th of a second, all the heat has been absorbed by the head , piston and cylinder in that time.
  Reply With Quote
Old 11-17-2011, 08:28 PM   #63 (permalink)
EcoModding Lurker
 
Join Date: Jan 2011
Location: Hamilton, New Zealand
Posts: 74
Thanks: 1
Thanked 3 Times in 3 Posts
remember that those efficiency figues will be with wide open throttle, I don't think any of us would be running at 1000 RPM and wide open throttle for long, and this will change everything.
  Reply With Quote
Old 11-17-2011, 11:02 PM   #64 (permalink)
Master EcoModder
 
Join Date: Mar 2008
Location: Edmonton, AB, Canada
Posts: 531
Thanks: 11
Thanked 12 Times in 11 Posts
Quote:
Originally Posted by Frank Lee View Post
VE is nice and all, but I was after the bsfc peak... the reason for an optimal piston speed has been mentioned earlier in the thread (thanks guys ) but I resurrected it just cuz I found this:

Quote:
Sfc measures how efficiently an engine is converting fuel into work. The graph of an engine's sfc plotted against engine RPM will be "U" shaped. At high speeds the sfc increases due to increased friction, while at lower speeds the sfc also increases due to higher heat losses from the combusted gas to the cylinder and piston wall because of the increased time the hot gases remain in the cylinder. This is also the reason why air cooled engines are usually less fuel efficient than water cooled engines.
Wow its been a long time since I posted in this thread. Frank I think your explanation of the U shape is oversimplified at least with respect to the lower RPM. The curve is U shaped in part because the torque curves in general are inverse U shaped. Its been over a decade since I learned the term "mechanical efficiency" wrt to engines but... The maximum torque is like the engines maximum potential, when the engine is operating below that it still carries the frictional losses associated with that RPM but its out put is less so it is mechanically less efficient.
  Reply With Quote
Old 11-17-2011, 11:20 PM   #65 (permalink)
(:
 
Frank Lee's Avatar
 
Join Date: Jan 2008
Location: up north
Posts: 12,651

Blue - '93 Ford Tempo
Last 3: 27.29 mpg (US)

F150 - '94 Ford F150 XLT 4x4
90 day: 18.5 mpg (US)

Sport Coupe - '92 Ford Tempo GL
Last 3: 69.62 mpg (US)

ShWing! - '82 honda gold wing Interstate
90 day: 33.65 mpg (US)

Moon Unit - '98 Mercury Sable LX Wagon
90 day: 21.24 mpg (US)
Thanks: 1,551
Thanked 3,428 Times in 2,153 Posts
That's not my explanation but I've bought into it. They are saying why it's an inverse u.

WRT friction, I would think internal friction has more variables than just plain ol' rpm; I suspect as loading gets higher on the piston it slams harder onto the cylinder on the thrust side thus having more friction, plus the higher chamber pressures are going to drive the rings onto the cylinder walls harder.
__________________


  Reply With Quote
Old 11-17-2011, 11:28 PM   #66 (permalink)
Master EcoModder
 
Join Date: Mar 2008
Location: Edmonton, AB, Canada
Posts: 531
Thanks: 11
Thanked 12 Times in 11 Posts
I agree with your last comment on friction too but bearing friction is small compared to ring friction and valvetrain friction is independent of engine load. Until recently though it was typical that the bsfc curve tended to correlate well with the torque curve. Newer engines with VVT have changed that somewhat.
  Reply With Quote
Old 11-17-2011, 11:55 PM   #67 (permalink)
...beats walking...
 
Join Date: Jul 2009
Location: .
Posts: 6,191
Thanks: 179
Thanked 1,521 Times in 1,122 Posts
Quote:
Originally Posted by Duffman View Post
...Until recently though it was typical that the bsfc curve tended to correlate well with the torque curve. Newer engines with VVT have changed that somewhat.
...agreed; VVT changes (pun intended) how the engine both BREATHES and EXHAUSTS in respect to both load and speed.
  Reply With Quote
Old 11-18-2011, 01:16 AM   #68 (permalink)
EcoModding Lurker
 
Join Date: Jan 2011
Location: Hamilton, New Zealand
Posts: 74
Thanks: 1
Thanked 3 Times in 3 Posts
Quote:
Originally Posted by Duffman View Post
Wow its been a long time since I posted in this thread. Frank I think your explanation of the U shape is oversimplified at least with respect to the lower RPM. The curve is U shaped in part because the torque curves in general are inverse U shaped. Its been over a decade since I learned the term "mechanical efficiency" wrt to engines but... The maximum torque is like the engines maximum potential, when the engine is operating below that it still carries the frictional losses associated with that RPM but its out put is less so it is mechanically less efficient.
yes, true, and your consumption does not relate to this as you only open the throttle to get the torue you need, so that chops the top off the U.
  Reply With Quote
Old 11-18-2011, 09:05 PM   #69 (permalink)
Master EcoModder
 
Join Date: Mar 2008
Location: Edmonton, AB, Canada
Posts: 531
Thanks: 11
Thanked 12 Times in 11 Posts
Yeah but if you made torque curves at 75%, 50% and 25% throttles the shapes would be similar to WOT, Obviously though less throttle would taper off faster at high RPM.

Talking about BSFC curves becomes pointless at low throttle openings, if your throttle is nearly closed then you are geared wrong and barking up the wrong tree to begin with.
  Reply With Quote
Old 11-18-2011, 09:09 PM   #70 (permalink)
(:
 
Frank Lee's Avatar
 
Join Date: Jan 2008
Location: up north
Posts: 12,651

Blue - '93 Ford Tempo
Last 3: 27.29 mpg (US)

F150 - '94 Ford F150 XLT 4x4
90 day: 18.5 mpg (US)

Sport Coupe - '92 Ford Tempo GL
Last 3: 69.62 mpg (US)

ShWing! - '82 honda gold wing Interstate
90 day: 33.65 mpg (US)

Moon Unit - '98 Mercury Sable LX Wagon
90 day: 21.24 mpg (US)
Thanks: 1,551
Thanked 3,428 Times in 2,153 Posts
I wonder how much throttle opening those 30mpg Vettes are running?

__________________


  Reply With Quote
Reply  Post New Thread


Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
News: Utah Considers Joining 80 MPH Speed Limit Club MetroMPG General Efficiency Discussion 68 11-04-2009 08:25 PM
News: Switzerland cutting speed limits to reduce emissions MetroMPG General Efficiency Discussion 7 09-18-2008 01:02 PM
Field Weakening Experiment for Speed Increase TomEV Fossil Fuel Free 12 04-10-2008 04:53 PM
Series Motor - Speed vs Torque TomEV Fossil Fuel Free 3 03-02-2008 01:27 PM
Basic EcoDriving Techniques and Instrumentation SVOboy Instrumentation 2 11-17-2007 12:38 PM



Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2020, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com