<VV> Mo MPG

[NicolCS at aol.com]

There's been a lot of traffic regarding EFI over the last couple of days  and 
I like to add a few comments.
1) 3.1 GM TBI: While the published horsepower for the 3.1 TBI is similar to  
the 2.8 horsepower rating, I'd be more inclined to select the 2.8  TBI.   The 
base fuel map for the 2.8 should be much closer to correct  for our 2.7 
Corvair engine. The 3.1's low and mid-range torque is greater than  the 2.8 and will 
likely overfuel our 2.7 engines.  Cold start, warm-up,  WOT, operation after 
battery disconnect, and operation during certain fault  codes all rely on the 
base fuel map.  There's no reason to select a donor  system that's farther 
away from correct.  Note that my 2.8 MFI system is  already slightly overfueled 
on the base map.
 
2) There seems to be a perception that TBI is much easier to install than  
MFI.  While it is easier, it's only slightly easier.  A WAG?   Let's say MFI is 
a 40 hour job where TBI is a 30 hour job.  Cost?   Both require all the same 
sensors and a junkyard system is likely to be the same  price.  The only real 
difference is that MFI will require milling of the  heads and purchasing of 
fuel rail and bungs.  
 
3) Performance.  Similar GM engines from 1991 show about 20 more  horsepower 
in the MFI configuration.  Also TBI motors are less fuel  efficient (like 
maybe 5 mpg) due to fuel condensation in their "wet"  manifolds.
 
If you are going to do all this work, why select the less efficient, lower  
power TBI?  FWIW, the 280ZX system is simpler to install than a TBI system  and 
is 100% proven.  
Craig Nicol
66 140 with Fiero MFI
65 140 with 280ZX MFI