[Mgs] Overdrive Numbers

[Charles & Peggy Robinson]

   Too many variables in your experiences to draw any solid conclusions. 
  My experience is a bit different:  I rebuilt the engine in a '70 B. 
All new innards but the crank and rods.  It got around 20 mpg during the 
breakin period (mixed driving) but I couldn't stand the sound of the 
engine howling at 4,000 + RPM at road speeds.  So I came by a top-fill 
LH overdrive tranny and installed it.  Soon after that we took a trip 
from TX to CA and OR.  Drove the coast highways in CA & OR, camped in 
Nat'l and state parks.  With two adults and our camping gear aboard, the 
B got 25 - 27 mpg for the trip.

   I have a '69 B now that has a fresh engine built to '67 specs and the 
same type OD as the '70 had.  It got about the same mileage as the  '70 
on a trip from Central TX to NoCal and back.  Same deal ; two adults and 
camping gear.  So at least the two cars compare well.

   I really have a tuff time believing 30 mpg from a B without OD at 70+ 
mph.  Shoot, it's a long stroke engine, with lots of internal friction. 
  Those piston speeds are waaay up there at 4K.

   Cheers,

    CR





Aaron Whiteman wrote:
> On Jan 15, 2008, at 2:32 PM, Charles & Peggy Robinson wrote:
> 
>>    Tell John Twist.  He thinks overdrives are strictly "feel good"  
>> add-ons.
> 
> That corresponds to my anecdotal experience.
> 
> Dads 1978 MGB got 28-31 MPG @ 70 mph on extended trips.  It had no  
> overdrive and ran all day at 4000 rpm (or more, I don't remember the  
> exact figure).
> 
> My 1975 MGB gets 26-30 MPG on the same trips.  It has overdrive and  
> runs at say 3500 rpm.
> 
> The '78 had a 25D distributor and a downdraft weber and was recently  
> rebuilt (less than 20K miles).  The '75 has a 45D with pertronix and  
> dual SUs, but is pretty tired.  I need to get over and buy dad's car,  
> if only for the engine.
> 
> My experience says the OD doesn't matter one bit regarding mileage,  
> but when my OD broke and would not engage, it was disquieting for me  
> to listen to the engine at the higher revs--even though I knew it was  
> just fine.