Mercruiser 454 mag re-power!
 

I am in the middle of a 454 mag rebuild to reporter my 98 model 25 outlaw. It is .030 over the cam specs are below. The cylinder heads are aluminum with 119 cc chambers and by the compression ratio calculators I have found on the net say it will make 10.33 to 1 compression ratio. It will have a Holley 715 cfm carb on it I am looking for recommendations for how many rpm this engine can safety handle reliably, and a recommendation on an intake manifold for this engine I am currently looking into a world Merlin intake unless someone can reasonably recommend something better. If more info on the engine is needed please ask I will tell all that I know. Also I have bought total seal gap less rings for this engine, also I have bought rocker stud girdles because I have never had many encounters with aluminum ears and figured they could only help. Any recommendations are greatly appreciated!
Intake Duration at 050 inch Lift 218
Exhaust Duration at 050 inch Lift 228
Duration at 050 inch Lift 218 int./228 exh.
Advertised Intake Duration 276
Advertised Exhaust Duration 286
Advertised Duration 276 int./286 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.500 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.500 in.
Valve Lift with Factory Rocker Arm Ratio 0.500 int./0.500 exh.
Lobe Separation (degrees) 114
Thanks
WO1 Bradley Weaver

never had good results with total seal rings in harley engines...the gaps eventually line up and stay there...maybe someone can chime in....

....and that cam seems a bit mild for the compression you are running

I have had great luck with those rings in racing engines when I was in my late teens and early twenties they typically have a leak down percentage of only about 2% or so, but that is my opinion and those are already purchased. I can still exchange the cam what would you recommend if you think that is not enough? I am looking for decent power but also reliability ease of tuning and longevity of components. I know I am asking a lot!

you need a cam with more duration to cut down that compression....a bit high for a marine engine....crane 741 is a proven design and is just an example of what you can run...i've never done any business with bob madera,but i heard only good things about his expertise on cams....call him

I would recommend an Edelbrock RPM Air Gap intake and a 800 or 850 Holley.
Crane 168731 camshaft, 288/298 duration,587/610 lift, 112 LS
Scorpion Roller Rockers

What are the pistons that you are running? Something with a little dome to them. That seems like a lot of compression.
What kind of exhaust are you going to run with this?
As for RPM I would think to prop it for 54-5600rpm.

The pistons are speed pro forged with. -23.1 cc dome. As for that camshaft I was told to avoid any cam with less than 114 LS because of the chance for sucking water back into tthe engine . I. Was planning on just stock manifolds as the rebuild has already exceeded my budget by over $1000 and quickly eating away at more than that. Big performance exhaust will probaly not happen until next winter.

Oh yeah is theat edelbrock made with the brass water passages? I already have harland sharp roller rockers.

You need to upgrade your exhaust or you are throwing money away. You always start with the exhaust system for any good marine build.
Also unless you plan on running expensive gas, I would lower the compresssion or risk the chance of a melt down.

You definately want to be sure you are running Manley inconel exh valves as well. You will be running some heat on the exhayst for sure. Severe duty won't cut it in a marine environment

Cam is basically the same as a stock cam
Carb is too small
Compression is too high
You need better exhaust to see any real gains in performance.

From what you have posted, you will most likely not see any gains over a stock engine.

like he said...the only thing you're going to gain is detonation...

That Crane cam is also availiable with a 114 LS as part #168791.
Not sure on the manifold being availiable with the brass water passage. You running in salt?
Agree with other posters you deffinately need Inconel exhaust valves especially running that compression and an exhaust up grade. Their good insurance. Stock exhaust valves will never withstand the heat with that compression and especially if you try running it through stock exhaust. Losing an exhaust valve gets real expensive. May want to concider different pistons to keep the compression around 9.5-9.75:1. If you already have those pistons you may want to concider having some of the dome milled off, if they can.

It may sound like bashing, but believe me, what is being said here isn't. It will save you $$ and headache later on.

I have not considered any of the replies bashing this is exactly what I was looking for, just more opinions on my current rebuild. The rebuild is due to a 7.4 mpi with way low compression and in ability to get the boat on plane effectively. The compression check was all over the place from 100 psi on two cylinders to 135 at best on three others. And the cylinder walls after teardrop were scored to he!! And back. What I have posted as initial specs is the parts I already have and was planning on using but am making adjustments as I find more information on what I need to do. The compression is an estimate from an online calculator I found. Once again thanks for all previous advice and advice to follow!