fastestonehere

I'm building a pair of 540 for a pleasure crusier that weighs about 20,000#
It cruses between 32-3800 Rpm rarely 4200

The build is keeping Mercrsier stock heads and exhaust manifolds. Light hone and a 4.25 stroke to a gen VI
Cam will be from Bob M., hyd roller lifters and roller rockers as well, Carb, Pro systems, duel plain air gap intake manifold, ignition a DUI unit,

Increasing torque in the low mid area I know RPM increases as well but not building a hi rpm or horse power engine

Can I use a GM Nodular crank ok or is there still a reason to use a forged. Options needed please
Thanks

Rookie

I would be afraid of the torque the 540 could produce and 20,000# load. I assume this is a semi-displacing hull so getting on plane and loosening up the hull is not an option. Forged...don't skimp now

Borgie

It will be interesting to see the opinions this generates. From everything I've gathered it seems like RPM is the main killer of the GM nodular cranks. Granted torque plays a role, but I'm really unsure as to how much that is. I'm not going to make a recommendation either way except ask a guy who you are already consulting for your cam. Good luck!

fastestonehere

I'm going to try and contact Bob today. The hall on this is a delta conic hall with a 15 ft. beam 2.5 draft

On another note: what will the mercrusier transmission hold. 1.51 ratio. The boat never has the sticks shoved to the wood just eased into.

motor

To be a Wet Blanket ....I think you are wasting money putting 540's in that hull........................my opinion

MILD THUNDER

Gm made 4.250 Nodular cranks? I don't think they even made 4.250 Forged cranks. I have never used a stroker cast crank, but I have heard by the time you buy them, the work to balance them correctly, the cost savings over a comparable 4340 Steel crank, isn't that much.

Keep in mind if you go to a internally balanced setup, you will need to change out flywheels and harmonic balancers, add that to the bill. For a setup like that, I d think about using a quadrajet carb. Most marine big block versions were 800CFM I believe. I don't think a pro systems double pumper carb would be the carb for a low rpm cruiser, especially if economy is a concern.

MER Performance

Do you already have a nodular crank that is 4.250 stroke? If not and you have to buy one; I'am not clear why; you would buy a nodular. I have no idea; who even sells them.
The 540 will definitely give you torque at the rpms you are stating. If you already have the nodular, maybe have it inspected for cracks, you could have it Omicron, this is done by a company I use Shaftech Ltd, Fostoria,Ohio. It is a media, polishing of surfaces and relieves, stress risers. To do a crank about $200.00. If they do this procedure, on a 4340 it's like a mirror.

You are in "Good Hands" with Marine Kinetics. Follow his recommendations and you will have a dependable piece of equipment.

MER Performance

I agree with Mild Thunder, on the crank issue. I was completing my post, when you posted.
You can external balance a 4,250 for your lower RPM set-up, I wouldn't recommend it for higher RPMs, although I have seen up to 4,625 balanced externally, that's to much counter-weight hanging on the ends. I would install new new balancer, anyways. You either spend $200 + for a new flywheel or put the flywheel in the lath and cut the counter weights out, and balance it neutral.

Rookie

I understand your point. If this was a straight 454 330hp build (which is in 1000's of cruisers) then I would have not said anything about forged.
But, I am assuming he is not building the 540 for 350HP.
JMO

bcfountain

I was told that eagle rates there cast steel crank @600hp max...