Rebuild Plans

[dearmosd]

So as I have learned that street engine smarts do not really apply well to marine engine smarts, so i thought i would ask were can some benefits be applied to gain any performance while keeping reliability? Plans on taking older 5.7L boring 0.030 over and rods/piston upgrade at least, same compression ratio as stock. I have a friend who is an engine builder but i have know him to build only marine engines so as im waiting to hear back from him i thought i would ask the good people of iboats opinion.

I have a '98 Mercruiser 5.7L 2 barrel engine (unknown hours). I plan on slowly building a 355ci engine to replace the stock motor.

1) What 4 barrel carbs can I swap to? Do I have to use mercruiser 4 barrel carb or will a street carb work and if so is there a specific spec I have to look for?
2) Intake: Mercruiser intake matched for 4 barrel or any benefits to a street intake (better design for air flow ect)
3) Vortec heads: Any reliability issues with port/polish with new valves (either stock specs or slightly larger air flow)? Will upgraded roller rockers/springs be of any benefit (not sure if mercruiser has flat tappet or hydraulic)?
4) Camshaft I learned better stick with stock, but is there any options here?
5) Pistons/rods: Going stock specs just better quality rods/pistons/seals.

I can use all old mercruiser 350ci/5.7L parts (minus rods/pistons) and just start fresh or swap out an item or two for some performance benefit without compromising reliability. Wouldnt mind reaching for 300ish HP range since it has only a Alpha one outdrive although not sure what the Alpha One torque limits are.....?

 

[Bondo]

Re: Rebuild Plans

Ayuh,... Welcome Aboard,.... If yer motor actually Is a '98, it already has Vortec heads,...
Generally speakin', 'n what I read on the Hot Rod forums is,..
Don't port, nor polish 'em, you'll screw up, more than you'll fix...

For a Carb, the Edlebrock 1409 is an exact carbon copy of the Merc/ Weber used by Merc...

For the rest of yer questions, Think Truck motor,..
Ya want down, 'n dirty Torque, down low, up to 4800 rpms....

 

[dearmosd]

Re: Rebuild Plans

Sounds like there is little wiggle room as far as minor changes to squeeze out a couple more HP to near the 300HP marker, without making big changes and go over the 300HP marker. Now I found a used mercrusier that spun a rod bearing, but is still complete and the owner can not visual see any damage to the cylinders but I’m not too concerned as I would like to start fresh and bore it and get some quality pistons. He started with overheating issues and once solved (kinked hose) he ran the motor and lost oil pressure and when he noticed oil pressure and noise he shut it down and inspected and noticed spun bearing on #4 cylinders, he claims to give up and bought new motor.

So my new question would be is low/no oil pressure be simply bad oil pump or should I investigate a little deeper, or as I’m prepared to strip block down and bore 0.30 over and start fresh should I worry about the old oil pressure issue?

What passage ways does the oil take? Being a rod bearing the getting oil from the main sump should I think the lack of water through the block could have caused the bearing failure, possible age related?

Either way it a friend of a friend, willing to let me look it over nice guy.... the problem is I’m currently deployed and he is asking $300 for the whole setup minus the intake/carb and accessories. Should I keep looking or investigate more.

 

[RogersJetboat454]

Re: Rebuild Plans

So my new question would be is low/no oil pressure be simply bad oil pump or should I investigate a little deeper, or as I’m prepared to strip block down and bore 0.30 over and start fresh should I worry about the old oil pressure issue?

It may have been trashed gears in the pump. It may have been a pump pickup screen that was restricted, or the pickup fell off the pump all together. It may have been the relief valve in the pump stuck open. The drive shaft from the distributor to the pump could have broken. Might be a passage restriction. Might be low oil level. Might be bearings with clearances wide enough to drive a truck through. Lots of possibilities, and you won't know until you look. A proper rebuild should solve any block based issues. The pump, pump shaft, and bearings will all be replaced during the rebuild.

What passage ways does the oil take? Being a rod bearing the getting oil from the main sump should I think the lack of water through the block could have caused the bearing failure, possible age related?

Pump pushes oil through the filter up to the lifter/cam galleys. Oil travels through the galleys down to the main bearings. Holes in the main journals of the crank distribute the oil to the rod bearings. Rod bearings are last to get oiled. If there are any restrictions, OR if one of the other bearings in further up in the pecking order are too loose (allowing them to dump excess oil), it will wipe out the rod bearings.

Either way it a friend of a friend, willing to let me look it over nice guy.... the problem is I’m currently deployed and he is asking $300 for the whole setup minus the intake/carb and accessories. Should I keep looking or investigate more.

Up to you. You could probably pull a donor vortec truck engine that didn't have any oiling failures for the same price, and use it for your rebuild.

 

[dearmosd]

Re: Rebuild Plans

Up to you. You could probably pull a donor vortec truck engine that didn't have any oiling failures for the same price, and use it for your rebuild.

Thank you for your input Im having my friend look around local too.

Thank you Rodgersjetboat454, you helped confirm my thoughts on the used mercruiser. I havent messed with my engines to this degree since i rippped into my LT1 engine many years ago. All i really need is a good black, crank and heads. Now this guy his have his vortec heads disassembeled hottanked, valves resealed and new springs, which for $350 sounds good too

 

[RogersJetboat454]

Re: Rebuild Plans

All i really need is a good black, crank and heads.

What are you going to do for rods?
No need to get anything fancy. Correctly prepped factory rods from an unmolested engine are plenty strong, and should work just fine for your purposes.

 

[dearmosd]

Re: Rebuild Plans

I was thinking a general rod/piston kit rebuild kit. I was hoping to squeeze close to 300HP with maybe good intake/carb. Don’t know what the weight of stock rod/piston is didn’t know if spending a little extra on better quality metal would help save fractions of grams here and there to add up to free up a little HP with stronger/lighter push rods/RR arms/spring, just max out air flow with marine grade 4 barrel carb/intake.

I’m still waiting to here back from my friend who is a machinist. I’m hoping he has some simple ideas. That is cost effective and provide results. I could recoup some money from my engine also since there isn’t anything really wrong, I would feel better knowing I have a fresh engine pushing me and I can start the hours clock and maintenance procedures like and motor head nut

 

[dearmosd]

Re: Rebuild Plans

 

[dearmosd]

Re: Rebuild Plans

Shoot how much would a used fresh from the machine shop set of vortec heads cost?

 

[RogersJetboat454]

Re: Rebuild Plans

I was thinking a general rod/piston kit rebuild kit. I was hoping to squeeze close to 300HP with maybe good intake/carb. Don’t know what the weight of stock rod/piston is didn’t know if spending a little extra on better quality metal would help save fractions of grams here and there to add up to free up a little HP with stronger/lighter push rods/RR arms/spring, just max out air flow with marine grade 4 barrel carb/intake.

I’m still waiting to here back from my friend who is a machinist. I’m hoping he has some simple ideas. That is cost effective and provide results. I could recoup some money from my engine also since there isn’t anything really wrong, I would feel better knowing I have a fresh engine pushing me and I can start the hours clock and maintenance procedures like and motor head nut

300 horse is not a problem for stock rods. Shaving weight off the rotating assembly is primarily to help the engine stay together at higher RPMs. Not going to see HP big gains with expensive light weight parts. The drive limits the RPMs to what a factory bottom end is fine with. Hypereutectic D-dished pistons, and properly prepped factory rods with good hardware will be sufficient. Like Bond-o said, think truck engine. Low end grunt, built with the idea that the engine isn't going to be run past 5K RPMs.

 

[dearmosd]

Re: Rebuild Plans

all my knowledge is street cars, so.... thank you for helping me open my eyes. This build my just feature fresh intenal (nothing special) and spend the $ on the intake/carb.

 

[RogersJetboat454]

Re: Rebuild Plans

Shoot how much would a used fresh from the machine shop set of vortec heads cost?

All depends on what the heads needed for work. Minimum would be cleaned, magnafluxed, check guides, check springs, resurface, grind valves/seats. Depending on the shop rate, and how fancy the shop is, probably around $300-$400.

When the guides are trashed, or the valves are burnt, or the seats need to be replaced is when the cost starts going up.

 

[dearmosd]

Re: Rebuild Plans

i figured for $350 im getting at least a fresh set of factory spec heads, new water pump, new push rods.

Possible block probably good cylinder maybe damaged but if so then boring may solve that issue. Crank may be good depending on bearing issuing, but a used crank reconditioned wouldnt be much, so worst case the block is not usable, the heads would be worth the gamble i think....

 

[RogersJetboat454]

Re: Rebuild Plans

all my knowledge is street cars, so.... thank you for helping me open my eyes. This build my just feature fresh intenal (nothing special) and spend the $ on the intake/carb.

If we were in a different forum, and you were building this engine as a high winding animal, with a manual transmission and slicks for the drag strip, that's when you need to worry about the strength of the bottom end.

There's allot of constant load placed on these parts in a boat. But at 300hp with low RPMs, the factory GM parts are all up to the task. Just keep her out of detonation, and water reversion, and she will live to a ripe old age.

 

[RogersJetboat454]

Re: Rebuild Plans

i figured for $350 im getting at least a fresh set of factory spec heads, new water pump, new push rods.

Possible block probably good cylinder maybe damaged but if so then boring may solve that issue. Crank may be good depending on bearing issuing, but a used crank reconditioned wouldnt be much, so worst case the block is not usable, the heads would be worth the gamble i think....

Yep..

 

[dearmosd]

Re: Rebuild Plans

whe i first thought of this i have always wanted to build a 400sb with a 350 crank (destroking) and let her rev high.... till all my info is not going to work.... or all my old LT1 parts i have left over....


Now another question.....this is a one piece rear main seal",block #10243880.... should this fit upto my current outdrive configuration?

 

[Bondo]

Re: Rebuild Plans

whe i first thought of this i have always wanted to build a 400sb with a 350 crank (destroking) and let her rev high.... till all my info is not going to work.... or all my old LT1 parts i have left over....


Now another question.....this is a one piece rear main seal",block #10243880.... should this fit upto my current outdrive configuration?

Ayuh,... That's an easily adaptable point, regardless which way yer goin'...

Ya just need the starter, flywheel, coupler combo that'll work...

I'm gonna move this over to the I/O Non-repair forum, seein's this is a plannin' stage thread,...

 

[RogersJetboat454]

Re: Rebuild Plans

whe i first thought of this i have always wanted to build a 400sb with a 350 crank (destroking) and let her rev high.... till all my info is not going to work.... or all my old LT1 parts i have left over....

Yep...
Like we said, you want to go for low end torque, rather than high RPMs.
A 383 Stroker (350 W/ 400 stroke) would be a better choice over a 377. Plus... you really don't want to use a GM cast 400 that's being raw water cooled (if that's what you have for a cooling system).

LT1 is a different animal. Some things are interchangeable with normal SBC's, some things aren't.

 

[Tail_Gunner]

Re: Rebuild Plans

Well food for thought... factroy cam room for improvement absolutely. Time and time again you will hear build for low tourqe and with some solid reasoning..but have anyone ever watched where a boat engine need's tourqe...there not like a car they slip heavliy until about 1800 rpm that is where thing's begin to happen..below is a pic of speed and rpm. lower left thats a nav screen notice the 6mph and 1600 rpm. At that rpm the boat hasnt even begun to create or climb the pressure wave (hole)

Here's a shot of cam profiles and rpm band

And another shot of a well know marine cam that is succesful in marine build's xm 270 hr @112 lsa

Hmm i will get some dynoed cam results showing cams with no overlap with less tourqe down low than that 270 or even the 276...It would be intresting to see a factory marine cam on the dyno..

 

[dearmosd]

Re: Rebuild Plans

is the blue bar the power range for that type for cam spec?