SumKindaRanch
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What is this monster build I keep reading about that involves sleeving down the 7.3 to a 6.9?
Monster build info
- Thread starter SumKindaRanch
- Start date
There’s been a few IDIs built this way, but I think it’s a waste in a performance application for a couple reasons:
-The 7.3 cylinder walls have proven to be more than strong enough to outlive the na rods and even the better idit pistons. The idit engines have stronger rods and wrist pins, but with two kits of 300 hp of nitrous added on I found the piston to be the next weak link:
After tearing this engine down, I examined the cylinder walls and found no signs of scoring from the rings butting up which would break ring lands, it was physically just too much cylinder pressure and the piston failed. These are thick iron ring lands.
-So cylinder pressure seems to be the enemy here, with decreasing your displacement, you are increasing the amount of boost that is needed to be added on to make the same power as a 7.3, or 7.4 like what I’m building for the race truck. More boost is more cylinder pressure, which means less power potential before reaching a failure point.
-With 6.9 pistons, you are limiting yourself to the weakest connectingrod made for these engines, unless you cough up the money to modify a set of psd rods for over a grand, then you are looking into having to add weights to the crank to balance out the foreign, modified rods. More rotational weight is more power sucked out of the crankshaft, just like running a big supercharger.
The only reason I can see a benefit to spending all the money to sleeve to a 6.9, is for a mild build where you want the most protection from cavitation, but even then sleeves with a 4.11” standard 7.3 bore will never have issues with cavitation if some right, going down to a 6.9 is just restricting the amount of air the engine can move.
-The 7.3 cylinder walls have proven to be more than strong enough to outlive the na rods and even the better idit pistons. The idit engines have stronger rods and wrist pins, but with two kits of 300 hp of nitrous added on I found the piston to be the next weak link:
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After tearing this engine down, I examined the cylinder walls and found no signs of scoring from the rings butting up which would break ring lands, it was physically just too much cylinder pressure and the piston failed. These are thick iron ring lands.
-So cylinder pressure seems to be the enemy here, with decreasing your displacement, you are increasing the amount of boost that is needed to be added on to make the same power as a 7.3, or 7.4 like what I’m building for the race truck. More boost is more cylinder pressure, which means less power potential before reaching a failure point.
-With 6.9 pistons, you are limiting yourself to the weakest connectingrod made for these engines, unless you cough up the money to modify a set of psd rods for over a grand, then you are looking into having to add weights to the crank to balance out the foreign, modified rods. More rotational weight is more power sucked out of the crankshaft, just like running a big supercharger.
The only reason I can see a benefit to spending all the money to sleeve to a 6.9, is for a mild build where you want the most protection from cavitation, but even then sleeves with a 4.11” standard 7.3 bore will never have issues with cavitation if some right, going down to a 6.9 is just restricting the amount of air the engine can move.
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