Personally, I think that supercharging is an excellent way to get more
horsepower out of older engines. A little pressure in the manifold makes
up for a multitude of sins in head design! As I said befor, intake charge
pressure is the single most important variable in engine performance.
When building a supercharged engine, the first thing to take care of is
lower end reliability. Find someone who knows your particular engine and
get suggestions an improvement. This is expecially important for old 3
bearing engines. Good machine work and careful preparation will make your
life better for years to come. Have everything magnafluxed. I have heard
that some treatments such as nitriding can increas crank toughness.
Breaking sharp edges on the crank can eliminate sources for crack
propogation. Rods can be shot peened. Forged, low compression (8.0:1 or
less) pistons may be fitted but I am not aware that MG's have a weakness
here.
Concerning increases in compression ratio- DON'T! Most supercharging
effectively increases the compression ratio and further mechanical
increases are undesirable. You are better off making sure that there are
no hot spots in the combustion chamber be carefully breaking all sharp
edges such as the "widows peak" between the valves on MGA's. You might
want to consider polishing the chambers, also. Use the best head gasket
you can find. If a set is available, buy new, high strength head, main,
and rod fasteners. Make sure that the block and head are perfectly true
while removing the minimum possible material.
With camshafts, you do not want too much overlap since the supercharger
will take care of the scavenging. If lift and duration are increased, it
usually help more with the exhaust valve since the supercharger is already
helping the intake. Valve springs and such probably wouldn't help either
since superchargers tend to work best at low to middle RPM so you won't be
reving the engine that much faster. If someone made really good valves or
sodium filled exhaust valves to handle the heat, this would help. I would
suggest hardened valve seats- at least on the exhaust.
In the exhaust, freer is better. Use big tubes and big mufflers. Ceramic
coating the manifold will help keep heat out of the engine compartment.
Speaking of heat, superchargers produce lots of it. When you compress air,
you make it hotter. Pay a lot of attention getting cold air to the
carburator. Many new installations use an air to air intercooler mounted
in front of the radiator but that would look "interesting" on a T series.
Get a bigger radiator. Fit an oil cooler. Ad auxilliary fans. Do
whatever it takes to keep the temperatures down. Use water wetter?
Finally, remember that a lean mixture and incorrect timing will kill an
engine. Start rich and retarded (this also helps when it comes time to pay
for all of this) and work your way towards optimum. Remember, lots of
cold air to the carburator. Denser mixtures are also harder to ignite, so
more power and larger gap to the sparkplugs (which should be of a colder
heat range) will also help.
This probably isn't in the spirit of what you are looking for, but there
are a lot of really trick new electronic devices designed to help with this
type of installation all the way from retard on boost controllers to
competed electronic injection / ignition / boost control. You might want
to look into this stuff.
Good Luck
Bill Eastman
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