1991 mercruiser 4.3 roller cam specs.

[bluewater19]

When I was swapping the intake manifold on my mercruiser Was suprised to see roller lifters in the lifter valley. My repair manual says they were flat tappets until 1992. Anyway I am experincing "Valve float" above 4200 rpm and I am putting in rebuilt heads with heavyduty springs and Comp cams self aligning roller rockers. I also purchased a comp cams marine roller cam and I have no Idea what the stock cam specs are.I was told this cam is a mild upgrade from stock and am wondering what to expect performance wise. The roller rockers are stock ratio 1.5/1. the intake is a GM Marine cast iron 4bbl with a holley 4160 marine carb. these came off a volvo 4.3. The drive is a alfa 1.84/1 ratio turning a quciksilver mirage 14 5/8 /21 pitch prop. wot is 44 mph at 4400 rpm.I am also replacing the manifolds and risers with the perfomance pieces from www.mooreperformance.com the boat is a 1991 bluewater 19'cuddy.<br />Thanks<br />John

 

[tylerin]

Re: 1991 mercruiser 4.3 roller cam specs.

Bluewater, I couldn't tell you what you should expect performance wise, but it does seem to have a large pitch (21) prop for that motor. I have read posts here about problems w/ cams that have big overlaps. Bondo talks about a Lobe seperation angle and how water can be sucked into the exhaust, especially on aftermarket roller cams. Do some prior searches

 

[Bondo]

Re: 1991 mercruiser 4.3 roller cam specs.

The OEM Should be about 197/207dur. .430/.450 lift 109LSA.....<br /><br />If your Valves are Floating at 4200rpms... How are you making 4400rpms WOT ?????<br /><br />You'll see a 25/35hp increase with all you mention...

 

[bluewater19]

Re: 1991 mercruiser 4.3 roller cam specs.

I am not seeing 4400 rpm anymore. I noticed little while back that when I was running a WOT for more than a minute or 2 that the motor started making a rattling noise from the prt side head. I brought my father(GM factory trained master tech) on the boat because I thought my motor was about to go south and he said my valves were starting to float. He suggested just changing the valve springs with a springs that will handle more lift. So I took it from there and started collecting parts.I told him of my plans for the new cam and rebuilding the heads after rolling his eyes he laughed and said he would help me. The comp cams marine cam isn't to much bigger it has nearly the same duration and valve lift around .480 on both sides I don't know the specs right off but will post them when I get home. thanks.

 

[bluewater19]

Re: 1991 mercruiser 4.3 roller cam specs.

Ok the specs on the roller cam are duration<br />intake 210 deg, exhaust 214 deg. lift<br />intake .479, exhaust .388 lobe seperation is 112 deg. Is this cam to wild? I looked at a gm performance parts marine cam and it was almost identical to this one.

 

[Bondo]

Re: 1991 mercruiser 4.3 roller cam specs.

Either that cam, or the original will work just fine......<br /><br />The Most Important # on Marine cams is the LSA # Must be within 109*, to 112* to prevent Reversion....<br /><br />I Agree with your Dad..... Valve Springs Would have Cured your Problems..... But, Hey, More is Better.... Your overall plan doesn't sound tooo bad.... I'm not all that in love with the Holley carb, But, It depends More on what You're comfortable with....

 

[akriverrat]

Re: 1991 mercruiser 4.3 roller cam specs.

bluewater19, i have a 1991 4.3 with roller cam. problem i ran into was the metric screw in rocker studs. the adjusting nuts were lock tighted in place. have been unable to locate locking adjuster nuts in 8mm. have you checked yours and are they 8mm?