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

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 04-05-2020, 06:17 AM   #11 (permalink)
(:
 
Frank Lee's Avatar
 
Join Date: Jan 2008
Location: up north
Posts: 12,732

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: 1,571
Thanked 3,505 Times in 2,194 Posts
Right! It has me going too fast in the F150; there I pick a speed just above where the torque converter would unlock frequently due to slight grades and whatnot.

__________________


  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 04-05-2020, 08:10 AM   #12 (permalink)
Cyborg ECU
 
California98Civic's Avatar
 
Join Date: Mar 2011
Location: Coastal Southern California
Posts: 5,562

Black and Green - '98 Honda Civic DX Coupe
Team Honda
90 day: 59.47 mpg (US)

Black and Red - '00 Nashbar Custom built eBike
90 day: 3671.43 mpg (US)
Thanks: 2,043
Thanked 1,754 Times in 1,186 Posts
Quote:
Originally Posted by Frank Lee View Post
Get the stroke then online calculators can tell you the rpm range that 1000-1200 ft/mn piston speed is. ...
With my Honda Civic's 3.54 inch stroke, one of the online calculators suggests that my engine is in the ft/min range you talk about when the engine is turning 1700-2000 RPMs. Interestingly, as I pointed out in my earlier response in this thread, that's one of the ideal rev ranges that I use MUCH the time. Now I might begin to use it nearly ALL the time as an experiment.
__________________


See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

  Reply With Quote
The Following User Says Thank You to California98Civic For This Useful Post:
Frank Lee (04-05-2020)
Old 04-05-2020, 08:31 AM   #13 (permalink)
(:
 
Frank Lee's Avatar
 
Join Date: Jan 2008
Location: up north
Posts: 12,732

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: 1,571
Thanked 3,505 Times in 2,194 Posts
All signs point to that piston speed range as a good proxy for when you don't have a BSFC chart.

Years ago I inquired here about optimal piston speed and why wouldn't slower be better (because the calcs showed my F150 so different from the cars and bikes)? There is a sweet spot between too slow (excessive heat loss through head, piston, cylinder walls) and too fast (higher internal friction).

https://ecomodder.com/forum/showthre...peed-1477.html
__________________



Last edited by Frank Lee; 04-05-2020 at 08:36 AM..
  Reply With Quote
The Following User Says Thank You to Frank Lee For This Useful Post:
maczo (05-11-2020)
Old 04-05-2020, 09:57 AM   #14 (permalink)
EcoModding Lurker
 
Join Date: Mar 2019
Location: Russellville, KY
Posts: 84

Little Blue Fuel Sipper - '16 Nissan Versa SV Sedan
Team Nissan
90 day: 49.31 mpg (US)
Thanks: 3
Thanked 22 Times in 17 Posts
My Versa with CVT seems to get it's best mileage between 1400-1600 RPM and depending on terrain is usually 40-50 MPH.
__________________

  Reply With Quote
Old 04-05-2020, 11:44 AM   #15 (permalink)
Master EcoModder
 
Ecky's Avatar
 
Join Date: Dec 2011
Location: Vermont
Posts: 3,901

Gaptooth (retired) - '00 Honda Insight
Team Honda
Gen-1 Insights
90 day: 54.26 mpg (US)

Such Fit - '07 Honda Fit Sport
90 day: 41.27 mpg (US)

Connect - '15 Ford Transit Connect XL
90 day: 19.96 mpg (US)

K-sight - '00 Honda K-sight
90 day: 41.16 mpg (US)
Thanks: 1,650
Thanked 1,643 Times in 1,048 Posts
Using Frank's figure of 1100ft/min +/- 100, my engine would be most efficient at 1700rpm +/- 150, or 55mph +/- 5mph.


Something I wonder about, is how ignition timing plays into this.

Here is one of my ignition timing tables, which I built based on maintaining a roughly fixed peak cylinder pressure:




When spark ignited, a flame front spreads from the spark plug through the combustion chamber, and it's ideal to have peak cylinder pressure occur when the piston rod has the best mechanical angle to spin the crankshaft. Flame speed is pretty constant for a given fuel and air mixture, so as the piston moves faster (higher RPM), you need to start combustion a few degrees of rotation earlier to keep peak pressure at the same crank angle.

At higher engine speeds, there's a larger percent of of high pressure before the piston even reaches the top (trying to spin the engine backward) and also too late in combustion, where the angle isn't very good. At least, to a certain point. My understanding is that, although the piston moves faster as RPM increases, after a certain point one does not need to ignite it any earlier, and indeed my ignition timing tables suggest this is true. I don't have a firm grasp yet on why this is so.
  Reply With Quote
The Following User Says Thank You to Ecky For This Useful Post:
California98Civic (04-08-2020)
Old 04-05-2020, 12:51 PM   #16 (permalink)
Somewhat crazed
 
Piotrsko's Avatar
 
Join Date: Sep 2013
Location: 1826 miles WSW of Normal
Posts: 1,063
Thanks: 71
Thanked 276 Times in 234 Posts
I recall 1100 fpm as a magic number, but it was related more to a structural limit, either you couldn't aspirate faster, or perhaps fatigue on the rod ends. Been 40 years too long since I was a hot rodder. You may be correct on the ignition limit as I recall there was no point going beyond a certain amount of advance.
  Reply With Quote
Old 04-05-2020, 01:15 PM   #17 (permalink)
EcoModding Apprentice
 
Join Date: Jul 2015
Location: Louisiana
Posts: 204
Thanks: 101
Thanked 66 Times in 54 Posts
I have always figured that after achieving high gear in any car, the lowest RPM value will yield the highest fuel economy.
__________________
  Reply With Quote
Old 04-05-2020, 01:54 PM   #18 (permalink)
Master EcoModder
 
Ecky's Avatar
 
Join Date: Dec 2011
Location: Vermont
Posts: 3,901

Gaptooth (retired) - '00 Honda Insight
Team Honda
Gen-1 Insights
90 day: 54.26 mpg (US)

Such Fit - '07 Honda Fit Sport
90 day: 41.27 mpg (US)

Connect - '15 Ford Transit Connect XL
90 day: 19.96 mpg (US)

K-sight - '00 Honda K-sight
90 day: 41.16 mpg (US)
Thanks: 1,650
Thanked 1,643 Times in 1,048 Posts
Quote:
Originally Posted by MeteorGray View Post
I have always figured that after achieving high gear in any car, the lowest RPM value will yield the highest fuel economy.
That's probably true with fixed gearing, because load is *probably* more important than piston speed in the vast majority of cases.

But, let's say you have a hybrid vehicle, which can spin the engine at whatever RPM, and toggle it on and off whenever. Is it going to be more efficient to spin the engine at, say, 3000rpm 90% load for 30 seconds out of every minute, or to spin it at 1500rpm 90% load and leave it running all the time?
  Reply With Quote
Old 04-05-2020, 07:02 PM   #19 (permalink)
Master EcoModder
 
Join Date: Feb 2014
Location: Missoula, MT
Posts: 2,079

Dark Egg - '12 VW Touareg TDI Sport AWD
90 day: 25.81 mpg (US)
Thanks: 174
Thanked 865 Times in 593 Posts
Quote:
Originally Posted by MeteorGray View Post
I have always figured that after achieving high gear in any car, the lowest RPM value will yield the highest fuel economy.
I used to think that as well but with direct injection, a turbos, and an 8 to 10 speed transmissions I'm not so sure about that anymore. They are building in lower, and lower highway cruise RPMs all the time looking for better economy at 65 mph. With the turbo and direct injection they can get a good BSFC over a big range, but with 2 or more overdrive ratios the spped can get pretty high before you reach "top gear". Then maybe one of the lower gears would have less aero drag while still being at peak efficiency.
__________________

  Reply With Quote
Old 04-06-2020, 01:09 AM   #20 (permalink)
Master EcoModder
 
Join Date: Jan 2012
Location: United States
Posts: 1,407

spyder2 - '00 Toyota MR2 Spyder
Thanks: 87
Thanked 259 Times in 196 Posts
Newer engines with high EGR dilution can run better at slow speeds since the diluted mix burns cooler and loses less heat to coolant.

  Reply With Quote
Reply  Post New Thread


Thread Tools




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