landfish

Hello Crew,

What a great group of people on this site! Been using search function quite a bit.

I have to replace a 454 that has a couple cylinders full of coolant after overheating on the last trip.

We want to buy or build the perfect saltwater marine engine for fuel efficiency and torque in the 2000-3500RPM range, and durability. Currently running a Bravo3X drive, and closed cooling.

One option is a pre rebuilt 454HO with 385HP (forged, rollers, etc.). Problem is I can not find torque curve info on it compared to a 310-330 HP base model, so I can't make an educated decision. Sure, the internals are much better on the HO, but it has rectangle ports, and is that HP all in the top end, and of no benefit to my application? My guess is when on plane and cruising at our normal 3100-3200RPM, the rectangle ports (and more aggressive cam) will be less efficient than something with oval ports.

To make things worse, I have no clue as to if getting the 385HP HO and propping up a little, would actually be more efficient.

The boat we have is a fishing vessel. 24' Osprey, with a 26' extended cabin pilot house on top. Super thick glass, and stringers. Super heavy. Gets up on plane at 2900RPM. Holds there at 3100RPM.

So....question to the crew on the board, and engine build masters out there.

Is the 385HP HO model going to suck fuel compared to the base, and offer no additional performance since we don't go about 3600rpm ever?

AND...What are some thoughts on building an oval port torque focused 454, knowing our operating RPM will be between 3000 and 3500 assuming no prop changes. (sorry I don't have the prop pitch info at hand, but will repost it). Let's assume a budget of $6500 including exhaust, and intake manifold. I gave a JET products 750CFM Quadrajet to put on top. Also have an 800CFM we can put on and play with.

Thanks for your thoughts and input. Happy Friday Y'all!!

-Rich

Unlimited jd

iTrader: (5)

Is this a commercial fishing boat or recreational? If commercial I'd go with something readily available, in case in the future you need to replace again one can. Be ordered and in hand relatively quickly. Your budget is a bit on the light side though to start from scratch

JRider

iTrader: (1)

Buy a diesel

getrdunn

iTrader: (7)

Personally I'd find what ever has the least amount of hours and the cheapest. Both engines discussed run near forever at your desired running rpm's. Yes the forged internals are nice if you plan to build it up down the road but really a solid 330 is all you need and with the weight your pulling the smaller peanut ports on the 330 are much more efficient for your use. Many of the older 454/330's pre early 80's used the 049 castings which are a nice oval port head.

I'd place an ad in the wanted section for a fresh low hour take out. Years ago you could find new take outs for 3k complete engine. But things have changed and they're not put in many production offshore boats anymore. Regardless there still may be a few shoved aside in shops. Or a 365 mag but then you go back to the larger heads again. All depends on what you really want. Efficiency nor speed gonna change much either way.

SB

iTrader: (1)

Are you saying WOT is at 3100 ? Or you drive it at partial throttle at 3100 ?

landfish

I am saying that is where we are most efficient and on plane. It is our cruise RPM. Sometimes if in a hurry, we bump up to 3400, but that is occasionally. 31-3200 is our normal cruise. Would love to get that down to 2900 though, for efficiency.

MILD THUNDER

iTrader: (3)

It takes X amount of fuel, to make X amount of power. It takes X amount of power, to turn X prop, to X rpm.

There certainly are some efficiency gains to be had in engine design, that can improve fuel consumption numbers, or say , Brake Specific fuel consumption.

The stock L29 vortec engine used in GM trucks from 96-00, was the base engine for the Merc 7.4 LX in those years. Same heads, cam, compression, etc. I believe peak torque, was at 3200RPM. In truck form, it made 410ft lbs at 3200. And 290HP, at 4000RPM.

The 454 HO crate engine, makes 500FT lbs, at around 3500rpm, and 438HP at 5200rpm. Those numbers will shrink a bit, as the 454 HO, isnt' dynoed with accessories, or stock manifolds. Prob why the 454 MAG MPI marine engine , is rated at 385HP, and marine L29, was 310HP.

The 454 HO, used the big GM rectangle ports, the L29 used small oval port vortec heads. Even with the large rectangle ports, the 454HO, still cranks out 500 ft lbs, at a relatively low rpm. It also has quite a bit larger camshaft, than the L29 (204/209 vs 211/230).

Just about any factory boat that offered both the 310 and 385hp package, performed better all around, with the 385 "magnum" engine. Even single engine heavy boats.
I'd say from idle, to 2800ish, the L29 would be the engine to use. From anything over that, the 454 HO, pretty much does everything better.

MILD THUNDER

iTrader: (3)

454 HO power curve can be seen here. The mercruiser version of this engine, has a 224/224 115 LSA cam, the 454 HO, has a 211/230 112 LSA I believe.

http://www.chevrolet.com/performance...ck-454-ho.html

sutphen 30

small cam and a small supercharger,that will give you plenty of low end tq.

sutphen 30

hp and tq don't cross at 5252,,hummm.