Reassurance question:Cylinder Heads

[Roman S]

HI,
I've done the homework and walked through the threads, especially Bondo's. Just want to make sure: I have a 1987 Mercruiser 5.7 liter 260HP S/B, Alpha One, Edelbrock 4bbl. If I have read previous posts correctly, would replacing the cylinder heads with Vortec heads yield more Horepower. I understand that the intake manifold would also have to be changed. If so, what Vortec head would someone recommend for my set-up. Thanks Roman If there is more to it than that. Let me know. Thanks!

 

[Bondo]

Re: Reassurance question:Cylinder Heads

Ayuh,...........
A set of factory Chevy Vortecs are capable of providing a Honest 25+hp............

But,...............
There's always the variables to consider as well.........

Is your 1987 Up to the task,..??.... A Compression test,+ Leak-down lately,..??....

There Used to be only 2 casting #s available from Chevy for Choices,.......
Now Edlebrock,+ All the Aftermarketers are building heads with the Heart shaped chamber of the Vortecs......

Maybe John,+ some others will chime in,...... I think he's been doing some more recent research........

 

[Roman S]

Re: Reassurance question:Cylinder Heads

Bondo, Thanks. Let me know if you need more info. If the motor ccan handle it,I would probably do the project. Also, I wonder how far I should go? Not far into the engine if I don't need to.
Thanks again
Roman

 

[John_S]

Re: Reassurance question:Cylinder Heads

I haven't done allot of research on that vintage of sbc, but think it will have flat-top pistons with valve reliefs. The mercruisers equiped with vortec heads have recessed "dish" type pistons, which have approx 12cc less compression. If your bottom end is good, and you don't have to rebuild, GM vortecs will give a compression ratio that is on the high side for a boat engine. If you are rebuilding the bottom end, then look into using "quench" "D" style pistons. If bottom end is good and flat-tops, you will probably have to look at aftermarket heads that have larger chambers than 64cc. Something in the low 70 cc. Try to stay with intake runners in the 170-180cc range.

You probably don't have center bolt type valve covers on current heads. Vortecs do require them.

 

[Roman S]

Re: Reassurance question:Cylinder Heads

Thanks for the reply John. Do the larger cambers relive some of the compression? Will they keep it within acceptable limits for a boat engine?
Thanks Roman

 

[Roman S]

Re: Reassurance question:Cylinder Heads

John, one more follow-up while I am here. I went on the Edlbrock site and loked at some of the heads they offer. Some are 70cc chamber. There are a few that claim that compression ratio would be 9:5:1 with stock heads. I don't know what it would be with 70cc chambers.
Roman

 

[John_S]

Re: Reassurance question:Cylinder Heads

Roman,

"Do the larger cambers relive some of the compression?"
Yes, if you have flat-top pistons, you probably have 72cc chamber heads. Unfortunatly, GM does not sell any 72cc vortecs. Standard GM vortec is 64cc and GMPP vortec heads are within a cc of that.

The best bet is to become familiar with one of the many static compression ratio calculators, like this one: "http://www.kb-silvolite.com/calc.php?action=comp"

Now, comes the tricky part. Even though merc advertises a static compression ratio of 9.4:1 on vortecs, anytime I have calculated it, it was just below 9:1. My advice is to target the range from 9:1 to 9.5:1. You should be able to adjust via pump gas octane then. Merc is set-up to run 87 octane.

For the calc listed, the data on my engine is:
64cc vortec head
12cc (this calculator does not require a neg value for recessed)
0.051 GM stainless comp gasket - supposidly the stock merc vortec gasket
4.005
4.000
0.025
3.48
which yields 8.8:1 comp ratio

Changing the piston 12cc to 4cc for the valve relief flat-tops gets you about 9.6:1

 

[Roman S]

Re: Reassurance question:Cylinder Heads

John,
Thaks for the reply again. Is 9:6:1 too high compression for a boat motor. Thanks Roman

 

[John_S]

Re: Reassurance question:Cylinder Heads

I am conservative, so wouldn't risk it. If this is a small, light, runabout, and you are not afraid of paying for 93 octane, maybe.

 

[Mkos1980]

Re: Reassurance question:Cylinder Heads

What are the current casting numbers on your heads now? If they are the 217 083's or 193's those are already 64cc. Moving to another 64cc will keep the compression the same. If they are something else, check them out on Mortec.com and it'll tell you what size heads you have.

 

[Bondo]

Re: Reassurance question:Cylinder Heads

Ayuh,........

While I agree with most of what's being said,......

The design of the Vortec combustion chamber will allow you to run up to 10:1 compression,.....
Without worry of Detonation...................

Usually,.......
The combination of the distance the piston is Down into the cylinder at TDC,+ the thickness of the Head Gasket,.....
Will give you an acceptable Compression Ratio.........Even with the 64cc chambers......

 

[Roman S]

Re: Reassurance question:Cylinder Heads

Thanks for the reply's. I will check on the casting numbers, If I can find them. Thanks Roman

 

[Mkos1980]

Re: Reassurance question:Cylinder Heads

Thanks for the reply's. I will check on the casting numbers, If I can find them. Thanks Roman

Just pop the valve cover off and the part number is right there on the head.

 

[Roman S]

Re: Reassurance question:Cylinder Heads

Thanks for the replies once again. I will pop the valve cover early next week and find out what type of head I have. Whether its 64cc or much more. Bondo, Am I correct in assumming that that compression ratio without detonation will be OK on my motor. I emailed Edelbrock and they said their E-tec 170 would work in my application, with a new intake manifold, of course.
Thanks Roman

 

[Bondo]

Re: Reassurance question:Cylinder Heads

Bondo, Am I correct in assumming that that compression ratio without detonation will be OK on my motor. I emailed Edelbrock and they said their E-tec 170 would work in my application, with a new intake manifold, of course.

Ayuh,.........

With the information you've provided,...... I Completely Agree with the people at Edlebrock.........

As you get deeper into it,.......
We'll gladly help you verify that you Do in fact have All the Right pieces...........

 

[Flukinicehole]

Re: Reassurance question:Cylinder Heads

I`v used the summit racing vortec heads and there great. They are much cheaper (there steel the etec is aluminum) and have a little bigger combustion chamber 67cc compaired to the 64cc on the etec. There much cheaper $650 a pair and go by p/n sum-151124. Go to summitracing.com and look up this p/n. They also have the etec heads but there $579 each. I would stay with the steel for what your looking for but thats just me. Either head will give you more power. Good luck with your project, just for the record I use Darts on my boat.

 

[Roman S]

Re: Reassurance question:Cylinder Heads

Hi everyone, Thanks for replies so far. I poped the Valve cover this morning to pull the casting numbers off the cylinde head. 462642. Went to Mortec .com to look up the number. From what I could gather the heads on the mercriuser right now are 76cc heads. They were built from 1976 through 86. Now, would dropping Vortec heads on this engine push the compression ratio out the door and is it still worth considering? Bondo, what would be the next step to decide whether I should contineu with this project.
Thanks Roman

 

[Bondo]

Re: Reassurance question:Cylinder Heads

Bondo, what would be the next step to decide whether I should contineu with this project.

'ell,....... I've already decided,..........

Let's Rock'n Roll.................

As I said before,...... Vortecs will handle 10:1, without Problems........
And,.....
I Truely Doubt you could get much more than 9:1/ 9.5:1 with a stock motor,... Without machine work,......
Probably not even that high........

 

[John_S]

Re: Reassurance question:Cylinder Heads

Given those 76cc heads, I highly suspect you do have the flat-top pistons, w/valve reliefs. My calculation of 9:6:1 was based on the thick 0.051 stock head gasket, and that the engine has not been bored or decked from a prior rebuild. I still think you are borderline based on what I have found of actual compression ratios vs advertised. FWIW, my calculated 8.8:1 engine had consistant 165-170psi compression test readings. That was warm engine, dry test. My reservations come from all the searching and reading prior to and during my head change. Bondo probably has "real" experience with flat-top piston/vortec head engines in boats. That trumps my hand! I do think it is probably close enough, that higher octane and/or reduced timing curve could get you out of trouble. Please keep us posted on your project.

More compression ratio info:
"http://www.kb-silvolite.com/article.php?action=read&A_id=36"

 

[Roman S]

Re: Reassurance question:Cylinder Heads

Thanks again for the replies. Just one question remains. Edelbrock sells two etec heads. One head is 64cc, the other 72. They have different valve confirgurations. What would be the suggestion for cc?
Thanks Roman