Big Tires and Magnum Engine Damage
Using oversize tires on computer controlled vehicles such as our popular trucks will send the wrong speed (mph) signal to the computer. The speed the computer “sees” coming from the tires controls the air-fuel mixture and spark timing.
With taller than stock tires, the computer “sees” the vehicle speed/load as less than it actually is and alters the fuel/spark timing accordingly. This causes engine to lug, creating extremely high combustion chamber temperature, resulting in burned valves and guides and possibly cracked heads. The speedometer driven gear in the transmission must be changed when the tire size is changed to correct the speed the computer sees.
What most people will miss in this article is that the Sensors were sending the wrong information to the computer which in turn incorrectly changed the ignition timing and the air/fuel mixture. This caused extremely high temperatures in the combustion chamber. Temperatures high enough to burn/ melt valve guides and valves. Don't blame the machine shop that did the work! Who checked the sensors?
For more information on this problem, check out the May 2018 issue of HotRod Magazine at HotRod.com - “HotRod Rescue”. Click here for the article.
Check with these folks for speedometer corrections.
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