<VV> Rookie Corvair Driver (now lugging)

[NicolCS at aol.com]

Frank  DuVal:
Ok, I'll  bite.
What dire consequences will happen when I drive around the city in 4th  with 
the engine running below 1800 rpm? In my Spyder that would be about   35 mph.

_M_ (mailto:TimogensTurbo at aol.com) att Nall  wrote:
NEVER let the engine go below  1800 rpm in any gear, unless coasting....shift 
down!
 


 
JR Wrote:
He did say OK  when "coasting".  I think the point would be not to attempt 
more than  very gradual acceleration in 4th.  3rd would be way better.  
Acceleration from around 1800 at about 1/2 throttle or more will generally  
(depends on the set up of the car what the speed would be) provide an  
unpleasant (and probably not good for the engine) temporary bucking  
sensation - sometimes referred to as "lugging" the engine.  But then,  you 
already knew that - but a "rookie" may not.
Later,  JR

 
Craig  sez:  IMHO the "minimum" engine speed depends on the camshaft.  With  
the most 110s and 140s, torque stability (smoothness) deteriorates below 1500  
rpm and the engine starts bucking.    I believe this effect is  due to 
confusion in the carb caused by unstable manifold vacuum and pulsing  airflow. With 
milder cam grinds, torque is smooth at 1200 rpm and operating the  engine 
there is OK. My 67 has the 889 cam, and PG140 crank combo. This was  GM's solution 
for making high-torque at low rpm.  This engine  pulls smoothly from 1200 
rpm.  Both of my EFI 140s have the hotter 304 cam  but since they are immune to 
airflow issues, they also pull easily from  1200 rpm.  The effects you'll see 
from driving at lower  rpm are improved fuel economy and lower noise.  Why is 
economy  better?: Engine friction is reduced and you aren't wasting engine 
power by  running a 164 cubic inch vacuum pump. (The throttle is more open so less 
vacuum  is created).  Do you want to use your fuel to go down the road or to 
suck  on the throttle plates - you pick.  Having said all that, JR and Matt 
are  right: If the engine isn't pulling smoothly (bucking, growling, or 
spitting)  (sounds like a mad dog, eh?) it shouldn't be asked to pull at low rpm or 
engine  damage (mostly rod bearings) could occur.
Craig