Tuning Your Austin-Healey for High Altitudes
by Norman Nock
Originally published in the Austin-Healey Magazine
Driving to Snowmass “2” will involve traveling over high mountain passes. To give you an idea of some of the highest roads in Colorado - Pikes Peak 14,000 feet. Trail Ridge Road 4 miles at over 12,000 feet, while Europe's highest "Col-de-restefond" is 9,113 feet.
Traveling up and down these passes can show any weak link in your Healey from brakes, radiator, clutch to engine condition.
Cooling system was covered in the July81 issue of Healey-Highlights. Full engine power will be necessary to climb in the high altitudes.
IGNITION TIMING STATIC
Assuming engine and all its ancillary equipment is in good order. Set ignition point gap to .015", turn rotor in direction of rotation, it should spring back when released indicating mechanical advance is not frozen (if stiff or frozen - INVESTIGATE).
Align pointer to front pulley T.D.C. Mark by pushing car with 3rd gear engaged. Connect a low wattage test light from distributor low tension wire to ground, turn on ignition, push car backwards until light goes out, push forwards VERY! slowly until light comes on, the difference between pointer & pulley mark is your ignition timing. (Approximate timing ½" B.T.D.C.) Check more than once to be sure. Check your service manual for correct timing.
The circumference of the crank pulley will give you an idea of what is equal to 10 degrees in inches.
With engine idling, very carefully lift up the side of the distributor cap, to expose the points plates inside, with a slight opening of the throttle you should be able to see the plates move caused by the vacuum applied to the distributor vacuum unit. If no movement you will need to investigate further.
If you have an extra distributor cap & wires a good idea would be to cut windows in the side of the cap observe the plate movement thru the window.
EFFECT OF ALTITUDE AND CLIMATIC EXTREMES ON STANDARD TUNING
The standard needle is suitable from sea level up to 6,000 feet, above this altitude it may be necessary to use the recommended weak needle, experimenting with alternative needles until one which is satisfactory is found. If you will only be at these altitudes for a short period, it would be practical to only adjust mixture via the jet adjusting screw or mixture screw (ref. your model service manual) using the standard needle. When you have climbed to 5,000 feet since you last adjusted your mixture recheck your mixture by lifting the carb-piston 1/32" (NO MORE!) There should now be an increase in RPM indicating a richer mixture. Adj. mixture by turning the jet adj. screw or mixture screw that will lean out the mixture until there is no appreciable change in RPM by raising the piston 1/32" this should give you the correct mixture for this altitude (readjust when returning to lower altitudes).
Manifold vacuum goes from approx. 1" per 1,000 feet.
Power decreases 3% per 1,000 feet, at the top of Pikes Peak you have lost 42% of your power.
Air weight decreases 1% with each 10 oF temp. rise above 59 degrees F.
Engine produces less power breathing the hot air from under the hood (a cold air box draws ambient temp.)
50/50 coolant with a 7 lb. rad. cap will boil at 235 degrees F at 15,000 feet with the same coolant it will boil at 215 degrees F.
Manifold depression and lack of power changes at various altitudes due to lessened weight (pressure) of air at the higher altitudes
What you need is a super charger!
Ignition timing is always "In accordance with factory specification" Do Not Experiment. Excessive spark advance resulting in detonation and overheating of the spark plugs to the point of preignition can also cause badly burnt pistons common to Austin-Healey.
Not what you were looking for? Don't forget you can check our back issues using the AHCUSA Magazine Index.