|
Newbie: Marine Motor Questions
Hi All, I have some basic and technical questions about building sport boat/race motors.
What are the traits preferred in a motor for, say a 27' +/- sport boat. High torque High HP, low torque Hi HP, hi torque low hp? Strong bottom? midrange? top end? I've never built a boat motor but I've built a few Chevy race motors. The curent motor in my full road race Vette is a stroked 415 SBC w 600 hp/tq ++/- . It seems pretty straight forward to build a 600 hp sbc or 750 hp bbc. Are there specific marine application cams. what are stock grinds for mercruiser bbcs, what would be a good high power grind for say a 496ci bbc? Do aluminum block or heads work on boat motors (corrosion isues?) what are god RPM ranges to work with? can the out drives handle 7500 rpms? Thanks for the advice Evan |
Re: Newbie: Marine Motor Questions
I am sure you will gets lots of input from the engine guys here. Heres my info.
Marine Engines, you want a flat torque curve from 3000 to 5000 rpm. You would usually prop the boat 1000 rpm over its peak torque. So, if peak tq is 4200, wide open you should be around 5200. I think most guys running hydraulic roller cam engines are spinnning up to 5500-5700. 7500rpm is probably not a good idea because parts wont hold up well spinning 7500 rpm for long periods of time. I have found that in marine engines, bigger cubes, smaller head runners is key. I currently have a 540 with merlin 345cc runners and a crane 610/632lift cam, and a 1050 dominator. I make about 585hp. There are guys here running 310-315 cc intae runners and 850 carb on 540's, and make 600 plus hp all day. My points is, you want to make the tq and hp earlier in a i/o boat, which is hard with giant cams and huge heads. The big cams and heads are good for drag cars, not boats. The cool thing is you will find tons of engine combo's with results, to give you an idea. Lots of guys run aluminum heads in the fresh water. Salt no good for the aluminum. The key to building a reliable, hi-po marine engine is good parts, and good machine work. Marine engines take way more abuse than a car, so for it to last, you have to use quality stuff. Heavy duty rods, pistons, crank, pushrods, rockers, etc. And to answer your question, yes, they do make special marine cams. This is important because if the cam you choose is to big, or not the right size, you will get water reversion. This happens when water from the exhaust system gets sucked back into the engine because the exhaust valves are staying open to long. You will gets lots of better info from the engine guys here, they know their s!@t! |
Re: Newbie: Marine Motor Questions
Originally Posted by MILD THUNDER
I am sure you will gets lots of input from the engine guys here. Heres my info.
Marine Engines, you want a flat torque curve from 3000 to 5000 rpm. You would usually prop the boat 1000 rpm over its peak torque. So, if peak tq is 4200, wide open you should be around 5200. I think most guys running hydraulic roller cam engines are spinnning up to 5500-5700. 7500rpm is probably not a good idea because parts wont hold up well spinning 7500 rpm for long periods of time. :fish: Are we talking engine parts or drive parts, It may be unnecssesary in a pleasure boat but 7500rpm isn't really high for a motor, even a small block, but the bottom end starts to get lost in the cam when the torque curve gets moved much farther up on the motor. I have found that in marine engines, bigger cubes, smaller head runners is key. I currently have a 540 with merlin 345cc runners and a crane 610/632lift cam, and a 1050 dominator. I make about 585hp. There are guys here running 310-315 cc intae runners and 850 carb on 540's, and make 600 plus hp all day. My points is, you want to make the tq and hp earlier in a i/o boat, which is hard with giant cams and huge heads. The big cams and heads are good for drag cars, not boats. :fish: THis is the kind of info I was looking for The cool thing is you will find tons of engine combo's with results, to give you an idea. Lots of guys run aluminum heads in the fresh water. Salt no good for the aluminum. The key to building a reliable, hi-po marine engine is good parts, and good machine work. Marine engines take way more abuse than a car, so for it to last, you have to use quality stuff. Heavy duty rods, pistons, crank, pushrods, rockers, etc. And to answer your question, yes, they do make special marine cams. This is important because if the cam you choose is to big, or not the right size, you will get water reversion. This happens when water from the exhaust system gets sucked back into the engine because the exhaust valves are staying open to long. You will gets lots of better info from the engine guys here, they know their s!@t! It really moves the conversation forward. Evan |
Re: Newbie: Marine Motor Questions
Dregsz, I will be posting the progress of my rebuild shortly.
Maybe give you some more ideas... or not. |
Re: Newbie: Marine Motor Questions
So does the Mercruiser 1075 hp motor make all its power below 6 grand?
|
| All times are GMT -5. The time now is 04:56 AM. |
Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.