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Old 10-16-2016, 10:30 PM   #1
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Default Mercruiser engine differences

Anyone smart on 7.4L generation differences? My boat has two gen V engines. I just picked up a gen VI long block to rebuild. I know it's a roller can instead of a flat tappet. Are there any other differences? I'm probably going have the heads on my engine rebuilt because these ones have a lot of broken bolts... But I'll buy bearings and rings in this short block for a quicker swap this winter.
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Old 10-17-2016, 01:50 AM   #2
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Instead of listing the differences I recommend you Google differences between 7.4 Gen V and Gen VI (?) IV.
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Old 10-17-2016, 06:09 PM   #3
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Ok.
Gen VI has a roller cam and my Gen Vs were flat tappet. No other meaningful differences.
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Old 10-17-2016, 09:47 PM   #4
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Ok.
Gen VI has a roller cam and my Gen Vs were flat tappet. No other meaningful differences.
Rocker ratios the same? Don't know but asking since its a roller cam.
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Old 10-17-2016, 10:02 PM   #5
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Pretty sure it's the same valve train after the pushrod. V and VI have rocker bolts unlike the studs on a IV.
The big changes were really between IV and V


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Old 10-17-2016, 10:09 PM   #6
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Pretty sure it's the same valve train after the pushrod. V and VI have rocker bolts unlike the studs on a IV.
The big changes were really between IV and V


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Ok thanks for the info.
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Old 02-22-2017, 01:07 AM   #7
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Ok.
Gen VI has a roller cam and my Gen Vs were flat tappet. No other meaningful differences.
creates a pretty big difference in cam profiles and power curves
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Old 02-22-2017, 01:17 AM   #8
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creates a pretty big difference in cam profiles and power curves
The cam profiles are different, but I'm not smart enough on cam timing and such to know how significant the difference is and if the roller lifters make up for it at all.
Now that my props are matched and both engines have the same intakes, I should be able to make a good comparison this spring.
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Old 02-23-2017, 03:17 PM   #9
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The cam profiles are different, but I'm not smart enough on cam timing and such to know how significant the difference is and if the roller lifters make up for it at all.
Now that my props are matched and both engines have the same intakes, I should be able to make a good comparison this spring.
The roller cam will have a flatter torque curve, makes more torque through more of the rpm range than a flat tappet cam.
Has to dowith the fact that with roller lifters they can usea more agressive lift ramp and a longer duration above .050 lift at the cam. This allows for more of an agressive profile without sacrificing idle or low rpm quality.
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