[DeTomaso] MSD Fuel Injection

Stephen steve at snclocks.com
Fri Jul 24 15:33:25 EDT 2015


Just got back from a 20 mile drive going to the post office that is a couple
of miles away.  Lovely excuse to take the long way both ways.  The drive
reminded me how nicely the MSD fuel injection is working, now that I have
gotten the system where it is happy.  The challenge was deciding what cam
setting to use with the MSD system.

 

Here are the cam spec’s for the engine (original 351C block bored 0.040
over) that is in 5332:


 

Intake

Exhaust

lobe separation

Overlap


Duration @ 0.05

224

230

114

56.5

 

The MSD manual has the following table to describe the cam setting options:

 


CAM

Duration @ 0.05


Stock

Stock Less than 210°


Medium

211° - 230°


Large

Greater than 231°-250°

 

When we built the engine we intentionally went with a bit more lobe
separation to make the engine more receptive to fuel injection.

 

When setting up the MSD system one has to decide if one has a stock, medium
or large cam.  The engine builder and the MSD tech both recommended “large”.
So, tried the large setting – car had a heck of a time idling and in
deceleration the car huffed and puffed.  And farted a lot.

 

Next tried the medium setting.  The car idled better, but had problems
idling when cold, and still huffed and puffed on decel, just not as bad.

 

So, finally went to stock.  While there is nothing to suggest it should be
better, it is significantly better.  Car decel’s smoothly, farts less, and
is much better on idle.  In fact, the car now runs like I hoped it would
when I went with MSD.

 

My impression, from the control theory class I took 40 years ago, is that
the medium and large settings crank some delay, or capacitance, into the
system.  And that the system is then hunting for the right setting.  On the
large setting the idle would cycle up and down, and, funnily enough, it got
worse as the system tried to “self tune”.  Perhaps one of the folks on this
forum can comment on why there should be different settings for larger cams
– besides the obvious, a higher idle


 

Next I need to set up the distributor so the MSD computer controls the
timing.  I suspect (hope) this will make the system even better, especially
in that I can dial in a vacuum advance to improve gas mileage when cruising
down the road.

 

If you decide to go with an MSD system – hopefully my experience will help
at least a little. 

 

 

Stephen Nelson

 

-------------- next part --------------
   Just got back from a 20 mile drive going to the post office that is a
   couple of miles away.  Lovely excuse to take the long way both ways.
   The drive reminded me how nicely the MSD fuel injection is working, now
   that I have gotten the system where it is happy.  The challenge was
   deciding what cam setting to use with the MSD system.


   Here are the cam spec's for the engine (original 351C block bored 0.040
   over) that is in 5332:


   Intake

                                   Exhaust

                               lobe separation

                                   Overlap

   Duration @ 0.05

                                     224

                                     230

                                     114

                                    56.5


   The MSD manual has the following table to describe the cam setting
   options:


   CAM

                               Duration @ 0.05

   Stock

                           Stock Less than 210DEG

   Medium

                               211DEG - 230DEG

   Large

                         Greater than 231DEG-250DEG


   When we built the engine we intentionally went with a bit more lobe
   separation to make the engine more receptive to fuel injection.


   When setting up the MSD system one has to decide if one has a stock,
   medium or large cam.  The engine builder and the MSD tech both
   recommended "large".  So, tried the large setting - car had a heck of a
   time idling and in deceleration the car huffed and puffed.  And farted
   a lot.


   Next tried the medium setting.  The car idled better, but had problems
   idling when cold, and still huffed and puffed on decel, just not as
   bad.


   So, finally went to stock.  While there is nothing to suggest it should
   be better, it is significantly better.  Car decel's smoothly, farts
   less, and is much better on idle.  In fact, the car now runs like I
   hoped it would when I went with MSD.


   My impression, from the control theory class I took 40 years ago, is
   that the medium and large settings crank some delay, or capacitance,
   into the system.  And that the system is then hunting for the right
   setting.  On the large setting the idle would cycle up and down, and,
   funnily enough, it got worse as the system tried to "self tune".
   Perhaps one of the folks on this forum can comment on why there should
   be different settings for larger cams - besides the obvious, a higher
   idle...


   Next I need to set up the distributor so the MSD computer controls the
   timing.  I suspect (hope) this will make the system even better,
   especially in that I can dial in a vacuum advance to improve gas
   mileage when cruising down the road.


   If you decide to go with an MSD system - hopefully my experience will
   help at least a little.



   Stephen Nelson


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