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Old 01-14-2008, 12:28 AM   #8 (permalink)
EcoModding Apprentice
Join Date: Jan 2008
Location: SF Bay Area
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Silver Bullet - '02 VW Golf TDi
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Originally Posted by MetroMPG View Post
That said, running a vehicle off its battery alone is a pretty extreme mod. Yes it will save fuel.
I don't mean to be rude...but no, it won't.

A study done more than 10 years ago and written up in Circle Track magazine showed that the typical carb'd 350 CID V-8 engine loses about 1 hp per minute with the alternator's field switch turned off (in other words...running on pure battery). That directly translates to modern EFI engines losing power with the alternator cut off...and hence, decreased FE.

So don't do it. The best way to maximize your engine's performance is to ensure the electrical circuit is operating at full capacity. Trying to increase FE by shutting off the alternator is false economy...just let it run. When the battery is full the alternator pulls just whatever the pulley and bearings require, and nothing more, so IMO this is one area that one needn't bother with. There are too many areas on any car where bigger gains are to be made to bother with this one...
Best tank ever: 72.1 mpg in February 2005, Seattle to S.F.
New personnal best 'all-city' tank June '08 ... 61.9 mpg!
Thanks to 'pulse-n-glide' technique.
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