View Single Post
Old 12-21-2016, 05:14 PM   #10 (permalink)
JohnAh
EcoModding Apprentice
 
Join Date: May 2012
Location: Vallentuna, Sweden
Posts: 129

Phantom Blot (Spökplumpen in swedish) - '75 Saab 96 V4
90 day: 52.77 mpg (US)
Thanks: 17
Thanked 55 Times in 30 Posts
Quote:
Originally Posted by Frank Lee View Post
The idea is to use the stock drivetrain to get up to cruise speed then throw it in neutral and shut it down, then activate the little cruising engine. Makes for low HP requirements and low torque transfer requirements via friction drive.
Exactly! By adding a second engine, barely powerful enough to keep a steady cruising speed, I can run THAT engine at the BSFC sweet-spot most of the time, without having to work engine and transmission as a madman, as I have done now for two years. (with great result but to an awful lot of work)

Any kind of transmission has some friction losses, some more than others. A standard gearbox designed for 4x the power usually needed to keep a steady speed, with all gears rotating soaked in oil, will probably give more losses than just a simple chain-drive or belt with a single fixed gear ratio. When designed for high speed/low torque i also THINK that a simple friction drive with one tyre pressing against another without too much deformation, may have quite low friction. If such a drivetrain should be used from stand-still with multiple gears I don't think it would work very well.

A huge benefit of the friction drive compared to making a more "normal" transmission is that almost nothing needs to be changed at the car itself. The extra engine is attached as "cargo" and it's wheels are never touching the ground so the attachment cannot be called a trailer either.
__________________
1975 Saab 96 V4, carburetted stock engine. Usually below 4,5 L100 = above 53 mpg (us) by Burn & Glide with engine shut-off. http://ecomodder.com/forum/em-fuel-l...vehicleid=8470
  Reply With Quote