how and how much can a engine be safely detuned? Scenario: a well build 427 engine in a well built chassis car. not so well of a driver. how can we go about detuning the engine without replacing any parts or causing any major damage to slow the car down as much as possible until the driver is up to par.?
Retarding the timing is one way. Installing a throttle-stop is another. I'm sure there are more ways. Exactly what magnitudes are you talking about (example: you want to go from a potential 9 second car to a 12 second car?)?
Disconnect the rear throttle plates on the carb. Go down one step on spark plug heat range. Rev limiter. Run a higher gear ratio. Restrict the exhaust flow. Adjust the throttle blades from opening all the way. Use smaller squirters in the carb. *carb suggestions are assuming Holley... Use a less aggressive pump cam on the carb. Jet up 2 sizes. Be careful not to do any mods that lean the engine out and you can slow it down without any ill effects. Dave
run on 2 barrels instead of 4. shift earlier. put a block under the gas pedal, that was an old throttle stop trick, make sure you run an air filter that will slow you a little.
Changing rear gears With a 427, changing to higher rear gears may make it more difficult to handle if the 'student' happened to break the tires. Think about it. Let's say you have a redline of 7,000-easy with a 427. 'Student' slips the clutch or just nails it, car is moving at about 10 mph. At redline with a 4.11 rear, wheelspeed will be lower than with a 3.00 rear. What would you rather try and keep between the lines, a car moving 10 mph while the wheels are travelling at 40 mph or 70 mph? In general lower gear ratios can eliminate wheelspin in high horsepower engines for this reason. I would look at a MSD/Mallory type ignition box with a rev limiter. Perhaps one is made that can restrict RPM's to 3K or so. Are you referring to on a track or driver? Driver I assume. If ignition box won't work, I would retard the timing, depends on the ignition setup. Change/restrict the carb. Wish I had this problem!
Yep. I wouldn't mess with the timing too much. They only thing you're going to do there is get everything all carboned up, and burn an exhaust valve or two while you chase a flame out into the manifold. It'll burn tons of gas and smoke like a freight train. The throttle stop is the best way to "de-tune" the engine without taking it apart. If you really really wanted to detune it, it'll need a 2 barrell carb and a peanut cam and cast iron garbage truck intake. That'll make it so anemic you'll be praying it can get out of it's own way.
Msd Al I just checked the book. With an MSD spark box featuring the Adjustable Limiter-chips can be bought that restrict RPM's to 3000. I'd go that route. Seth
