Repower question:: Maestro?

[seef158]

I have been trying to send a pm to maestro but they seem to be stuck in my outbox, have tried 4 times.... So here is my question:

I have been considering a repower with a 383, 454 or 502 chev but I am curious if I will see much for performance gains.... I like the idea of easy parts availability of the chev engine. I am also concerned about economy since my 318 is pretty easy on gas, I can cruise at about 10 mph all day on less than half a tank, of course eats gas when opened up but I can get up to a max of 25-28 mph depending on load in the boat. I see that Maestro has a 440 in a 28 express and I am curious what input anyone has on having a single big block in a 28 express.

[collins69s]

@28mph? How fast do you want to go? What's the HP of the 318? 225? I would think that the extra lbs of a big block and the expense of changing everything wouldn't be made up in performance. What about your prop? Could you get more top end with a different prop? Maybe add some HP with aftermarket performance parts like a manifold and carb.. It would be cool if they made headers for marine engines.. Someone probably does or some marine equivalent. I'd try to jack up your 318s hp (without adding too much strain) and change your prop. Again how fast you tryin to go? It's all a trade off. If I was going to swap I'd do a crate marine power 350 FI. Or just go find another 28 with twins in it and sell yours.. You'd probably break even and get the speed you want. It'd be sweet to have a 28 with a 440 or 454 in it though, don't get me wrong.

[Fastjeff]

Don't put that 440 in there unless you have the 1.52:1 trans and larger driveshaft. Why? You'll pay hell trying to get a prop to work with it. The problem is excessive blade tip velocity.

Jeff

[Maestro]

First of all...love my 440, it's been a great engine so far.

Using a GPS for speed, she does about 26mph at 3000rpm. Fuel consumption of about 1.3 mpg at that speed.

I like to put around at 1000rpm or so, with a speed of about 7mph and fuel consumption of a hair over 3 mpg.

Disclaimer - I don't think I'm propped correctly at the moment. Prop is 14x12 and that's just what came with it when I bought the boat. At wide open throttle, my tach is only showing 3500rpm. It should be able to reach 4000. (Who knows how accurate my tach is, but I think it's pretty close). The original propeller size chart on John Althouse's website shows the Marinette sportsman available with a 440 paired with a 1:1 velvet drive and a 14x11 prop.

I contacted a guy at Michigan Wheel (major prop supplier) and he also determined that based on my current performance data I should be running a 14x11.

Going to try that next season and see what happens. Current top speed at wide open is about 28mph. My boat runs heavy for a 28 express. Weighed in at 7600 lbs at the CAT scale. Yes, I accounted for weight of trailer and truck. I have twin 50gal fuel tanks which were half full when we weighed.

[Fastjeff]

See what I mean? With that fast spinning prop, the tips are cavitating at high speed. That makes your propeller inefficient, which results in lower speed and excessive fuel usage. (In essence, your re frothing water like crazy down there.)

One of our members (John Hall) upgraded his 32 footer to 325 hp Chevies. He too had 1:1 drives and had to buy special ($$$) 4 bladed props from Australia to get it to work right. His trick props were smaller in diameter to reduce tip speeds, with those extra blades and pitch making up for the diameter reduction.

Another member (Diver Dan) put 454 big blocks in his 32 Express with 1:1 drives and never got it to perform correctly.

The ($$) solution is to go with a 1.52:1 drive and upgrade the driveshaft to 1 1/4 inch (for torque reasons).

Jeff

[seef158]

I appreciate the input guys. I am not necessarily looking for a lot more top end, just an easier cruising RPM which I would think the torque of a big block would give me as I should be able to spin a steeper pitch prop. That being said it sounds like the thing to do is just prep this extra 318 I have laying here or to sell it and find a small block chev that would be about the same weight and hp. The small block chev would gain the ease of parts availability I am looking for and open up some performance options. I do NOT want a 28 with twins, that I am sure of... I do all my own maintenance and they do not look fun to work on, plus I am an admitted cheapskate and I really like the economy of my single.

[Fastjeff]

..."I am an admitted cheapskate "

Are we related? Good decision with gas pricing soon to return to high levels again. (You don't think this low priced gas will last, do yah?)

Jeff

[Maestro]

The 440 does not have to work hard to make the boat go.

Boat will plane...barely...at about 2200rpms. 2500 is a decent cruising speed (about 20 mph)

Bow is high in the air at all cruising speeds, my trim tabs are not functional right now. Maybe tinker with those next year.

[Maestro]

Also, based on Jeff's comments about using a 4-blade prop to correct the tip velocity, I plugged my numbers into Michigan Wheel's "prop it now" calculator and set it to size me a 4 blade instead of a 3 blade. It said to use a 13x12 4 blade prop, which is smaller than my current 14x12 3 blade.

Now, this is just a quick calculator but it does account for your reduction gear or lack thereof. If I could score a used 4 blade prop I might try it someday. $800+ for a new one doesn't sound like any fun

[seef158]

I am still considering what to do and don't need to repower, just need new exhaust manifolds. I think if I do change from the 318 I will probably just go with a 350 as it sounds like performance with the 440 is fairly similar to mine. Since I have 2 running 318 motors and transmissions I figure I could sell both and pretty much pay for the 350. Right now I plan to swap the exhaust manifolds from my spare engine for next summer and keep running what I have as it runs great and burnt zero oil in about 65 hours this summer. I don't have anything against the mopars except parts availability. I'd like to build up the engine a little bit when I need to rebuild and I know that just changing to a nice aluminum exhaust manifold really helps, did that on a 454 in my old formula and gained about 400 rpm on the top end. I see nothing out there for exhaust for the 318 except the old cast iron style manifolds.