How many of you try to get more hp out of your motors?

[Timmy!]

Marine motors are pretty maxed out when they come from the factory.

Sans a supercharger!

[rensink]

Along with modding motors when in marine application which I understand if you're doing the motor work yourself you'll probably never bring your boat to a dealer for work but they technically can't work on it if it contains automotive parts.

[skippabcool]

but they technically can't work on it if it contains automotive parts.

Interesting, is this a law or manufacturer rule? I didn't know this.

[Wickedcummins]

The 343 engines have stamped steel rockers and by swapping them out with a roller rockers and with added ratio you will see gains. Also I believe the 340+ engines have a 1.6 ratio. I do believe you could upgrade to a 1.7 ratio and gain a little.

[Timmy!]

The 343 engines have stamped steel rockers and by swapping them out with a roller rockers and with added ratio you will see gains. Also I believe the 340+ engines have a 1.6 ratio. I do believe you could upgrade to a 1.7 ratio and gain a little.

Heck, I figured they were using the good stuff for how much they charge! At least they have a 1.6 in them. Any idea what heads they are using? Are they custom for marine or based off of the vortec heads or?

[dom w. forte]

Marine Powers 340 had rail rockers and the 360 had rollers, you couldnt notice much difference, because the torque was very little changed.
A lot of the marine engine companys like to one up each other with a HP claim but a 350 chevy can only achieve so much torque so thats why you saw Indmar come out with the Hammer Head 6.2l stroker which worked very well pulling more ballast.

[IDBoating]

Dom, that raises a question. Using PCM's engines as examples, their EX343 provides 343 HP from 5.7L displacement. Their 6.0L EX409 has only 5% more displacement yet gets 19% more horsepower out of it. What's happening there? How are they able to get a greater percentage increase in HP than the percentage increase in displacement?

[Timmy!]

Dom, that raises a question. Using PCM's engines as examples, their EX343 provides 343 HP from 5.7L displacement. Their 6.0L EX409 has only 5% more displacement yet gets 19% more horsepower out of it. What's happening there? How are they able to get a greater percentage increase in HP than the percentage increase in displacement?

Longer stroke, more aggressive cam, different heads, roller rockers, etc. Displacement isn't linear to power output necessarily.

[Wickedcummins]

Heck, I figured they were using the good stuff for how much they charge! At least they have a 1.6 in them. Any idea what heads they are using? Are they custom for marine or based off of the vortec heads or?

Not sure.. I didnt dig that deep. But when talking to someone at pcm he said all there engines have roller cams Only difference was rockers and some tunning.

[dom w. forte]

Dom, that raises a question. Using PCM's engines as examples, their EX343 provides 343 HP from 5.7L displacement. Their 6.0L EX409 has only 5% more displacement yet gets 19% more horsepower out of it. What's happening there? How are they able to get a greater percentage increase in HP than the percentage increase in displacement?

I dont want to get too technicle, but engines breck down to 3 catagories, oversquare bore larger than stroke, square bore and stroke equal, and undersquare, bore smaller than stroke, that being said as stroke increases torque goes up and HP doesnt increase as much, so if you look at a 350 chevy its bore is 4.05 with a 3.48 stroke, the 364 6.0l bore is 4.05 with a 3.62 stroke, the numbers that should be looked at is the torque, thats what gets the boat on plane with heavy load.
If you look at a vintage 427 vs 428 ford motor you would think they have to run relatively close, but they had 2 different purposes and there cubic inches were derived 2 different ways, 427, 4.23 bore x 3.78 stroke, lower torque to propel ford gt at high speeds and rpm, 428, 4.130 bore x 3.98 stroke , tons of low end torque to propel drag race car , gets the mass moving from a dead start.
hope this helps

[IDBoating]

hope this helps

Indeed it does. I knew about under/over "square" but didn't realize it was stroke that affected torque. I thought it was exactly the opposite. I based this on high RPM racing engines often having larger numbers of smaller diameter pistons (lower piston mass, easier to move faster), whereas diesel engines meant for lots of torque generally have fewer cylinders of larger diameter (higher piston mass, lower max RPM's). Guess I'll have to rethink that relationship.

Thanks for the data!

[dom w. forte]

With the newer varable valve motors they have been able to keep the torque curves more liniar with smaller displacement.