San_Diego_SeaRay
Petty Officer 1st Class
- Joined
- Nov 9, 2014
- Messages
- 337
So I have two boats: A 1993 Chaparral 270 cabin cruiser and a 1998 Reinell Bowrider. Both have run of the mill non-MAG carb'd Bravo 7.4s. I believe the 1993 is Gen 5 while the 1998 is Gen 6.
I'm just finding out about this issue that 7.4s have where they have "cam overlap" or maybe it's called "valve overlap". Basically it means that while one cylinder is causing positive exhaust pressure, there's another cylinder that causes negative exhaust pressure at the very same time. This causes the water being blown out the riser to circle back into the "negative" cylinder.
But the thing is that most of the threads I see discussing this seem to be high performance forums, which makes me wonder if this problem is more likely in certain 7.4s than others? Are there certain years or models that were worse? Thx in advance.
I'm just finding out about this issue that 7.4s have where they have "cam overlap" or maybe it's called "valve overlap". Basically it means that while one cylinder is causing positive exhaust pressure, there's another cylinder that causes negative exhaust pressure at the very same time. This causes the water being blown out the riser to circle back into the "negative" cylinder.
But the thing is that most of the threads I see discussing this seem to be high performance forums, which makes me wonder if this problem is more likely in certain 7.4s than others? Are there certain years or models that were worse? Thx in advance.
