Walt T
Lieutenant
- Joined
- Mar 16, 2002
- Messages
- 1,369
Re: Mercruiser 6.2L Info
I would like to interject if I may, the reason there is pull in the exhaust at idle. That is caused by 'cam overlap'. Cam overlap is the period of time the intake and exhaust valves are open at the same time. This creates a scavenging effect in the cylinder to help rid it of outgoing exhaust gases. This is why you cannot put wild automotive cams in marine engines. That 'whump whumpity whump' idle you hear on wild cammed engines WILL suck water in your engine at idle. The reason roller cam engines need more static line is because they have a longer overlap period. <br />You can see this at this link:<br /> Camshaft overlap <br /><br /> On a boat that has been built with the static line at exactly the minimum distance from the risers, the risk of ingestion becomes greater with every item you store on the boat, especially in the back. I should note that static line should be checked with the total weight that is usually in the boat. If the owner goes boating with his brother 'Bubba' who weighs 400 lbs, it wont do you any good to check static line with just yourself in the boat. It's not that the manufacturers build defective boats, it's just that weight adds up, and in some boats will put a boat in danger of ingestion. Water weight in the hull, transom, floor and stringers will also add up. Static line is easily overlooked since a lot of boat repair joints only work on boats on trailers and are loathe to put a boat in the water for a test run because of the time it takes. The problem is, the static line doesnt get checked until the customer has bought a 2nd or third set of engines.
I would like to interject if I may, the reason there is pull in the exhaust at idle. That is caused by 'cam overlap'. Cam overlap is the period of time the intake and exhaust valves are open at the same time. This creates a scavenging effect in the cylinder to help rid it of outgoing exhaust gases. This is why you cannot put wild automotive cams in marine engines. That 'whump whumpity whump' idle you hear on wild cammed engines WILL suck water in your engine at idle. The reason roller cam engines need more static line is because they have a longer overlap period. <br />You can see this at this link:<br /> Camshaft overlap <br /><br /> On a boat that has been built with the static line at exactly the minimum distance from the risers, the risk of ingestion becomes greater with every item you store on the boat, especially in the back. I should note that static line should be checked with the total weight that is usually in the boat. If the owner goes boating with his brother 'Bubba' who weighs 400 lbs, it wont do you any good to check static line with just yourself in the boat. It's not that the manufacturers build defective boats, it's just that weight adds up, and in some boats will put a boat in danger of ingestion. Water weight in the hull, transom, floor and stringers will also add up. Static line is easily overlooked since a lot of boat repair joints only work on boats on trailers and are loathe to put a boat in the water for a test run because of the time it takes. The problem is, the static line doesnt get checked until the customer has bought a 2nd or third set of engines.
