QUIKDECISION

I have a question about Camshafts. Likely, someone has already addressed this but I would like to ask anyway.... I intend to freshen up our 454's , they are 365 hp magnums. I have purchased 1 set of roller rockers and lifters. I am looking for another set, I have been watchful to Ebay, lookin for deals... Anyway, I will eventually obtain the 2nd set, and I was wondering if anyone could recommend an appropriate marine roller camshaft. Our boat is a F311, and I am not looking for anything too wild, but would like something with some snot. I am hoping ( likely a fantasy) that I can just re-ring and put new bearings in. I will tear it all down and have the blocks boiled and new cam bearings and frost plugs installed. Freshen the heads and all that... I am still curious about what the difference between the merc 365hp is, vs. the 420hp. I read in another article that the 420's seem to have all the same "goodies", per se... I.E. forged crank and pistons.
Also, they have the rectangular port heads. So is it just the camshaft that makes the difference in horsepower? Any thoughts that anyone has would be most appreciated.
Thanks, Quikdecision.....

Griff

The differences between the 365 and 420 are cam, intake manifold, carb and exhaust.
The 420 cam is the same as the 525SC cam. Crane # 132561. 228/236 duration and .530/.551 lift on a 114 lob sep. The intake is a single plane (dart, i think) and carb is an 800cfm Holley. Gil exhaust. Possibly roller rockers, not sure.

Depending on your budget, you may just want use a better flat tappet cam. The conversion to a roller cam will run about a $1100 for about a 20hp gain. You need new pushrods and a different timing set and the springs/retainers are more $$$.

A good flat tappet Crane #134241(kit # 134242)--226/236, .534/.553 on a 112 lobe sep.
A good roller cam would be a Crane #139731--226/234, .587/.610 on a 112 lob sep.

Also, if you upgrade the cam, you'll need to upgrade the exhaust from stock merc to prevent reversion.

KAAMA

iTrader: (1)

The Merc 365hp engine has a 4-bolt main block, rectangle port heads, and all forged internal parts as does the Merc 420hp engine, however, the 420 comes with Crane gold roller rocker arms where as the 365mag does not. The 365mag has a smaller flat tappet hydraulic cam, dual plane aluminum high rise intake manifold, and a Rochester spread-bore carb and comes with Merc's very crude cast iron exhaust manifold system. The Merc 420hp engine had a better breathing exhaust system on it, a Holley carb, and I have seen the dual plane hi-rise intake on the 420 as well, but have also seen some Wieand X-cellerator single/open plane intake manifolds on them as well----kind of a gray area there. I would prefer a dual plane intake on a 454cid engine anyway. I would also do a little bowl/pocket clean up on the heads and pay attention to the short side radius. A flat tappet hydraulic cam can be used with about 222*/230* on 112* lobes. "rmbuilder" (Bob) would be at least one good guy to consult on a camshaft. Griff is right though----a hydraulic roller cam would add a lot of expense to the rebuild. With these mods a better breathing aftermarket cast aluminum exhaust system would bennifit your engines in performance over the stock Merc exhaust system as well. They would be much lighter than the cast iron Merc system, look MUCH nicer and sound a little healthier.

Also, the more hi-perf mods you do to an engine on the intake or induction side the more it will need to be able to breath out the exhaust, otherwise you will choke it and no real performance gains may be noticed. There is a lot of controversy in how much you will bennefit in performance from an aftermarket exhaust system. To try and put it in a nutshell I will try and simplify it with this concept/statment;--------- the thing that you must keep in mind is that the more performance mods you ADD or DO to your engine(s), the more an aftermarket exhaust system is going to bennefit you in performance. I honestly cannot think of any way that would be easier or more simple way to say it than that! Hope this has helped. Have fun.

QUIKDECISION

KAAMA,
I very much appreciate your answer. I have purchased a set
of revolution aluminum marine exhaust manifolds. I did this out of necessity, the merc's ( Osco's) had a leak and kept filling my crankcase with water. I could not imagine that a leaking exhaust could result in this situation. I suspected heads and did a top end rebuild, pulling heads etc. I did get some great excercise. You are so right about the expense of the roller cams... Geez, I have thus far purchased one set of roller rockers and lifters. Have not yet obtained a cam. It may not be worth it all. Since the engines are to be rebuilt. Anyway, I still entertain the idea of the roller set up. Again I thank you for your time in answering.

Quikdecision...

QUIKDECISION

Griff,
Thankyou very much for responding. My experience with engine building ( re-building ) has always been in the automotive arena. Though things are not all that different, with boats, they certainly present some unique situations... I am learning... Just too darn slow though.
Again, Thankyou..

blue thunder

I agree with above posts concerning flat vs roller, unless money is no object. I have had good luck with flat tappet cam 11-239-3 comp cam. 226/234 @.050, .544/.564 lift 111lsa. I believe the revs incorporate a anti reversion dam so you should be ok with exhaust. Overlap is 52* if memory serves me. Add 924-16 springs, two sets of roller rockers and engines should come alive quite a bit. You should also consider oil temp collection and control methods to prevent heat related problems due to more snot.

BT

Payton

One thing to consider is that is that the spring seats will need to be machined for for roller lifters. At least that's what I was told.

Also do a searcg on "Bore Notching" the block. If you have the engine out and the heads off, it seems pretty easy to do. It's an easy way to unshroud the valves a little more.