What makes a marine engine a MARINE engine

[270win]

Re: What makes a marine engine a MARINE engine

My truck has 108,792 miles on it right now. The hour meter says 3,848.8 hours.

JMO- I wouldn't run a car/truck motor in a boat...but that's just me.

 

[John_S]

Re: What makes a marine engine a MARINE engine

I was thinkin 5.7 with vortec heads. Shouldn't that make a pretty substantial difference? Wont that be a good 50 hp increase. Mine's a 228 hp.

That 228HP number has to be at the crank. At the prop, you are probably talking 200hp. Compare that to a stock 350 vortec w/4brl (not MPI) of 280HP at prop. You WILL notice the difference.

 

[Bondo]

Re: What makes a marine engine a MARINE engine

My truck has 108,792 miles on it right now. The hour meter says 3,848.8 hours.

JMO- I wouldn't run a car/truck motor in a boat...but that's just me.

Ayuh,.... Why not,..?? What are your Precieved differences,..??

 

[BigBoatinOkie]

Re: What makes a marine engine a MARINE engine

you can get an easy 260-300 out of the 305 with a head/cam swap using your same ignition and carb.

Could anyone tell me specifically what cam and head combo might yeild that kind of hp. I'd be pretty interested in beefing up the 305 if it can be done without sacrificing reliability and cheaper than rebuilding a 350.

 

[mylesm260]

Re: What makes a marine engine a MARINE engine

270win sounds like he has lots of auto experience and very little boat experience.


Sure you can get that kind of HP from a 305. No question about it.

But. In order to do that, you would have to go with a "hotter" cam.

This is bad in a boat for 2 reasons.

#1. boats don't have transmission. Therefore, above all else they NEED bottom end torque. Otherwise they just won't plane. Especially loaded.

#2. Hotter cams have more over-lap. This increases volumetric efficiency at higher rpms. BUT at lower RPMS, this creates little vacuum pulses in you're exhaust system. These pulses can (and do) cause water to get sucked into the exhaust and hydro-lock you're motor.


Caming a 305 in a camero for more HP? sure.

doing it in a boat is just going to create more problems than it's worth. Not to mention worse mileage @ cursing RPMS.

You're best bet is a vortec 5700. Straight up. Either low mileage or rebuilt.

 

[Alpheus]

Re: What makes a marine engine a MARINE engine

People always are making the misconception that a huge cam will add so much more HP (the bigger the better) and its all wrong. Yes they sound cool when they are sittin there idling, and add some HP but there is only so much flow that those little low performance valves will allow through. A well degreed, proper sized cam will beat an oversized cool sounding cam any day... You need to just save your pennies and dimes and get a professionally built long block...

 

[Isaacm1986]

Re: What makes a marine engine a MARINE engine

If you are looking for reliability do the 350 swap. In my opinion those 305 are junk motors, they have thin cylinder walls, and i have seen too many of them throw rods through the pan.

350's are just a better motor, they are bullet proof beyond all hell, and they will provide a much more reliable boat ride for you.

Go on craigslist for your area, find a rebuilt 350 in the auto parts section that is ready to go. I see them online all the time for $500-$700. Just make sure the seller has the paperwork on the rebuild.

That is just my opinion though.

 

[Alpheus]

Re: What makes a marine engine a MARINE engine

Yep 305 cranks are junk. Yes they are the same stroke as a 350 but with the extra weight shaved off the counter balancers to compensate for the lighter pistons of the 305 make for a very unbalanced and undependable crank. IMHO the 305 is just a bad platform to sink money into rebuilding...

 

[Isaacm1986]

Re: What makes a marine engine a MARINE engine

here you go, 1984 350 crate motor with 75k on it, $450 Oklahoma city. it is complete with a carb. ready to drop into the boat. you can't beat a price like that.

http://oklahomacity.craigslist.org/pts/1547571373.html

 

[270win]

Re: What makes a marine engine a MARINE engine

The first thing you'll want to do is diagnose the bottom end of your 305. If the rings and bores are still in good shape, I'd be comfortable with proceeding with power upgrades.

In pricing the upgrades, it's still cheaper to just get the 5.7 and have new everything...

 

[BigBoatinOkie]

Re: What makes a marine engine a MARINE engine

Dang, how did I miss that. I've spent hours staring at craigslist. Prolly cause I keep looking for vortec.

 

[Isaacm1986]

Re: What makes a marine engine a MARINE engine

I don't know if the vortec will work honestly. you need to know what kind of rear main seal (1 piece or 2 piece) is on the 305. When i did the 350 swap on my 1986 bayliner capri, i wanted the vortec also but it has a 1 piece rear main seal, and I needed a two piece rear main seal. beside those 350 crate motors are pushing 280hp, a lot more than the 200-220 that the 305 is putting out, i don't know that the vortec is necessary in my opinion.

 

[270win]

Re: What makes a marine engine a MARINE engine

Who said anything about big cams with lots of overlap??? My last 355 was built with 906 heads and a HR cam 224/224@.050 and .492/.492 with a 110LSA. No lopey idle, plenty of vacuum, almost completely smooth idle. Made 375hp/400ft.lbs. on the dyno and ran 12.30's in a full body 72 Nova show car...

Lots of people think the only way to make hp and torque is to put WAY too much cam in. That's only part of the equation...

Anyway, my advice all along has been to go with a long block 5.7...but if the O.P. wants to do it with a 5.0 then there is a way to do it...it doesn't make sense and won't save money, but it can be done...without using a huge cam. We're only talking 300hp here.

 

[ckgreenman]

Re: What makes a marine engine a MARINE engine

Dang, how did I miss that. I've spent hours staring at craigslist. Prolly cause I keep looking for vortec.

I've been just searching for chevy 350 or gm 350 and looking for ones that come close. From what I've learned on here you can get away with a truck block with roller RV/Marine cam and kit. If you want the EXACT cam specs they're in the Mercruiser Service Manual from the "Adults Only" thread in this forum. I think you want Chapter 17.

 

[270win]

Re: What makes a marine engine a MARINE engine

Are you guys really suggesting a USED car or truck 5.7 for marine use? If your main criteria is cheap...that'll get a 5.7 between the stringers for sure.

Again, I wouldn't recommend a car motor for a boat...but what do I know?

 

[270win]

Re: What makes a marine engine a MARINE engine

I've been just searching for chevy 350 or gm 350 and looking for ones that come close. From what I've learned on here you can get away with a truck block with roller RV/Marine cam and kit. If you want the EXACT cam specs they're in the Mercruiser Service Manual from the "Adults Only" thread in this forum. I think you want Chapter 17.

a roller cam kit will run over $400 with lifters...and that's if the block is an OEM roller block, if it's not the retro roller kit is more money because of the different lifters required, they need a tie bar. Also wanna make sure the valve springs match the cam.

IF you do all of this and it only costs you $450 for a good motor and $500 for the cam setup you're still almost $1000 deep in a used motor with no warranty.

 

[Isaacm1986]

Re: What makes a marine engine a MARINE engine

Are you guys really suggesting a USED car or truck 5.7 for marine use? If your main criteria is cheap...that'll get a 5.7 between the stringers for sure.

Again, I wouldn't recommend a car motor for a boat...but what do I know?

I have a 87 Chevrolet motor out of a truck in my bayliner and it works just fine. Can you tell me what the difference is? And why you won't use a truck motor in a boat? There is not a big difference.

 

[mtnrat]

Re: What makes a marine engine a MARINE engine

A car motor will not have enough torque. A truck or RV motor will.

 

[BigBoatinOkie]

Re: What makes a marine engine a MARINE engine

marineenginesales.com seems to have cheaper long block prices than rapido.

Marine Engine Sales
$1369 for 5.7 vortec, roller, 2 bolt main
$1289 for 5.7 vortec, flat tappet, 2 or 4 bolt main
$180 shipping
$145 core price
Free one year warranty unlimited hours

Rapido
$1550 for 5.7 roller
$1450 for 5.7 flat tappet
$150 shipping
Free one year warranty unlimited hours
$299 2-year warranty unlimited hours

Information is from their websites.

 

[270win]

Re: What makes a marine engine a MARINE engine

I have a 87 Chevrolet motor out of a truck in my bayliner and it works just fine. Can you tell me what the difference is? And why you won't use a truck motor in a boat? There is not a big difference.

did you decide to use a used truck motor in your boat because it was the best possible option for your boat, or because it was cheaper?

The engineers at GM and MerCruiser don't just come up with specific application motors just to charge more money. Every engine has a specific design and application.

This is why I always have a survey done on any boat I buy. If I were looking at two identical boats for sale and all things were equal but one had a truck motor in it I would buy the one with the marine engine...my logic behind that would be, what else did they cut corners on...but that's just me.