" Grumpy?
I have a 400 ci small block bored out to 408 ci, dynoed at the flywheel at 525 hp 505 torque. I'm using a Holley model 4150 hp 830 cfm 0-80511-1 on it. The oil is always dirty shortly after an oil change, could this be due to over carburation? The motor is in a 57 chevy that's used for the street only in the summer. I was thinking of down sizing to 750 double pumper. Any advice would be appreciated. "
most modern oil has detergent additives , most modern oil is designed to trap and transport micro ash and debris to the oil filter, most oil filters trap much of the larger debris but can not trap the fine ash that will eventually build up and make the oil darker in color, so oil must be changed to remove abrasive particulates. in a well maintained engine the color change after an oil change takes several hundred mikes, but all oil changes color over time, and ALL oil needs to be changed eventually due to soot and acid build up.
its VERY VERY UN-likely to be the size of the carburetor , a 830 should work fine! a 750 cfm is about perfect for a hot 408 sbc engine, either carb will work,it could be a PCV valve thats defective,,it could be the fuel/air mix ratio is far too rich, allowing the fuel to wash the bore surface, BUT its far more likely that the engines ring to bore seal is allowing enough cylinder pressure to get past the rings, minor detonation damage to piston ring lands causes this frequently or worn rings can cause the issue, or it can be that contaminates like micro ash from combustion are getting into the oil. a leak down test is a good place to start checking, blocks honed without use of a deck plate to simulate the block bore distortion with the head bolts tightened are much more likely to have this issue simply because the upper bore walls are pulled away from the bore center line when the bolts are tight, making ring seal far less effective.
running fairly tight piston to bore clearances tends to reduce this tendency but obviously you can,t run under detonation conditions or parts break.
DETONATION DAMAGE , CAUSING RING SEAL TO FAIL
DETONATION DAMAGE , CAUSING RING SEAL TO FAIL, if run a bit longer
RELATED INFO and LINKS you really should read thru
viewtopic.php?f=53&t=3897
viewtopic.php?f=87&t=332&p=14269&hilit=leak+down#p14269
viewtopic.php?f=51&t=125&p=10972&hilit=hone+plates#p10972
viewtopic.php?f=53&t=5454
viewtopic.php?f=53&t=4630
viewtopic.php?f=53&t=509
I have a 400 ci small block bored out to 408 ci, dynoed at the flywheel at 525 hp 505 torque. I'm using a Holley model 4150 hp 830 cfm 0-80511-1 on it. The oil is always dirty shortly after an oil change, could this be due to over carburation? The motor is in a 57 chevy that's used for the street only in the summer. I was thinking of down sizing to 750 double pumper. Any advice would be appreciated. "
most modern oil has detergent additives , most modern oil is designed to trap and transport micro ash and debris to the oil filter, most oil filters trap much of the larger debris but can not trap the fine ash that will eventually build up and make the oil darker in color, so oil must be changed to remove abrasive particulates. in a well maintained engine the color change after an oil change takes several hundred mikes, but all oil changes color over time, and ALL oil needs to be changed eventually due to soot and acid build up.
its VERY VERY UN-likely to be the size of the carburetor , a 830 should work fine! a 750 cfm is about perfect for a hot 408 sbc engine, either carb will work,it could be a PCV valve thats defective,,it could be the fuel/air mix ratio is far too rich, allowing the fuel to wash the bore surface, BUT its far more likely that the engines ring to bore seal is allowing enough cylinder pressure to get past the rings, minor detonation damage to piston ring lands causes this frequently or worn rings can cause the issue, or it can be that contaminates like micro ash from combustion are getting into the oil. a leak down test is a good place to start checking, blocks honed without use of a deck plate to simulate the block bore distortion with the head bolts tightened are much more likely to have this issue simply because the upper bore walls are pulled away from the bore center line when the bolts are tight, making ring seal far less effective.
running fairly tight piston to bore clearances tends to reduce this tendency but obviously you can,t run under detonation conditions or parts break.
DETONATION DAMAGE , CAUSING RING SEAL TO FAIL
DETONATION DAMAGE , CAUSING RING SEAL TO FAIL, if run a bit longer
RELATED INFO and LINKS you really should read thru
viewtopic.php?f=53&t=3897
viewtopic.php?f=87&t=332&p=14269&hilit=leak+down#p14269
viewtopic.php?f=51&t=125&p=10972&hilit=hone+plates#p10972
viewtopic.php?f=53&t=5454
viewtopic.php?f=53&t=4630
viewtopic.php?f=53&t=509