water reversion
 

I am rebuilding my 330 merc and have some questions about water reversion due to cam c/l. The cam I want to use is a hydrolic roller with 224/234 duration at .050, the lift on the cam is .527 int. and .544 on the exh. I'm running stock exhaust on the boat and I've heard there could be a problem with water reversion due to the 110 c/l. Does anyone out here have some good info on what the chances are of this type of problem exhisting?

First, reversion is due to overlap. Not lsa. The combination of duration and lobe separation angle will deterimine overlap.

On stock exhaust I wouldn't go with more than 3 - 4* of overlap @ .050 on the cam.

I'd have to see you valve timing numbers to tell you how much overlap you have. I'd suspect you're in the 8* range, however.

So, if that's true then yes, you are in danger of reversion with stock Merc exhaust.

DAVE

I'm not sure what the valve timeing is however the stated overlap on the cam is 82. this cam is a speed-pro series cam the number is cs1074r would you have any other suggestions on what to do? I am doing a basic overhaul and don't want to get anything big or radical, I'm just looking for good reliability and some added performance.

Look on the cam card. On the bottom part of the card it will tell you at what crank shaft degree the intake and exaust valves open and close.

Something like this for example, and I'm just pulling numbers out of the air:

IVOBTDC 6 IVCABDC 15

EVOBBDC 68 EVCATDC 3

DAVE

OOPS!
I meant EVCBTDC.

deffinetly gotta have at least 18" pipes for the 110 degree lobe seperation,or change the cam.....got the right exh valves?

I don't have the cam card for this cam, just the specs. I do have two different cam sizes that will probably work better; this is another hydraulic roller 216/[email protected] with a 112c/l 70* overlap, this would be my second choice the third is a hydraulic flat lifter cam at 222/[email protected] with a 115 c/l 88* overlap. These are all speed-pro cams and I can get a real good deal on themI really want to stay with the roller setup if I can. The heads I'm haveing ported and putting larger valves in them 219/188 I believe. The motor I had bored .030 and balanced the crank with the new pistons and rods. All I'm looking for is about 75 to100 hp gain with great reliability built in, hence I want to be sure of no reversion problems!!!

Ok. When I get home I can plug those numbers into the computer and depending on the icl I can tell you how much overlap you have.

You gave me 70 and 88 for overlap. That is a seat to seat measurement. I'll give you overlap at .050 because that's the only thing that has become "standard".
Some cam manufacturers measure seat to seat at .004 some at .006. So those numbers can change depending on manufacturer.

Again I would suggest no more than 3 - 4* @.050 on stock Merc exhaust.

I'll get back to you later tonite.

DAVE

thanks Dave, I'm sorry I don't have more info on these cams than what I have put in this forum but your help is appreciated greatly. The summer is getting short and I missed most of it with a broken engine, sure would like to get on the water a couple of times yet this year, I'll check to see what you figured in the morning.

Buck,

I haven't forgotten about you.

Got tied up and wasn't able to sit down at the computer last night. I'll plug in those numbers tonite when I get home from work.

DAVE