Vortec Head 5.0 vs 5.7 question

[staintx]

Can someone help me understand an issue Im having with cylinder head options.
My boat is listed as having a 97 5.7LX which has vortec cylinder heads. Last year I bought this boat with a blown engine. Removed the cylinder heads and they looked clean and in good shape with casting numbers 12558059, which I found out later on that they are 5.0 vortec heads. Original engine block was bad so I had to search and find a good block which wasn't easy even though Im in Houston.
I found a 2 bolt main 350 block with electric fuel pump it was from a 98 truck. I had the shop bored them .040 over, slapped the existing heads after machine shop checked them. But 2 hours of running and both side heads are either cracked or gaskets are toasted.

Did mercruiser 5.7's came with 5.0 heads in 1997 or did the engine I pulled out was a 5.0?

I will be removing the heads tomorrow morning and I was wondering if I should order 5.0 or 5.7 heads? Ebay has brand new 5.7s for a fairly low price.

Any info or help is appreciated as I don't want to go through this one more time.

 

[Scott Danforth]

No, 5.7's would not have come with 5.0 heads. the valves on a 5.0 head are smaller for the smaller bore, and the combustion chamber is 57cc's vs 64cc's which would put the compression ratio way too high

just like you dont want to put 5.7 heads on a 5.0 because the cylinder wall would shroud the valves, and the larger combustion chamber would lower the compression way too much.

if you have a 5.7, order heads for a 5.7. if you have a 5.0, order heads for a 5.0.

your GM dealer probably has lower pricing than ebay.

stay away from the chinese knock-off heads.

 

[staintx]

Thank you Scott, I can't believe I made this mistake, old owner must have downsized the engine to 5.0 and busted it and sold the boat to me. It ran good while it was running : ), it just never stopped overheating. Im going to order 906 heads for 96 and up 350.

 

[Scott Danforth]

it was probably pinging like crazy as well.

 

[staintx]

It's not pinging at all, now Im worried about the crankshaft because it turns out cranks shafts are same but they are balanced different and I used the crank from the old engine, so now Im debating on pulling the block and puting a new crankshaft or just put new heads.

 

[Scott Danforth]

5.0 and 5.7 use same crank. they are balanced exactly the same.

however a new crank is about same money as reconditioning a crank. in some cases its less.

if you are building a motor from scratch, I would build a stroker. the cost difference to build a 355 and a 383 is about $30.

 

[staintx]

I'm trying to avoid pulling the complete engine out of the boat. I will remove the heads in the morning. If block looks damaged, I will probably yank it out of there and build stroker. When I got the boat I was debating on building a stroker but at the same time I wanted to get this thing in the water so I rushed and ordered over sized pistons and used the good crankshaft and the heads. This time if I can't get away with only two heads i will call it the season and start building a stroker and enjoy it next summer.

 

[NHGuy]

There are loads of good small block heads out there. Make sure you calculate for a tidy compression ratio. Like 9.4:1. And try for a good quench too. Quench isn't as big a deal because the pistons in those engines are dished.
Get 185 or 195 cc intake runners, that will give you some wide open throttle kick without going all the way to the 215's which give a lazy bottom end.
You gotta take the power that's there and those things matter.

 

[Scott Danforth]

I would stick with 170 cc intake runners for low end torque. that is what is on both the 906 and 062 heads.

185 or 195 cc intake runners would be what I would run on a hot-rod motor in a car.