Questions about swapping to Vortec heads...

[PBarrett]

I have a Mercruiser 5.7 engine, S/N 0D448389, that I would like to swap the heads to Vortec heads. I understand what is required to make the swap, but I am confused by what I read from Mercruiser. I have seen my engine listed as having 9.4 to 1 compression ratio and in another place, I see it listed as 8.5 to 1. Short of pulling the heads and CCing the piston configuration, is there some other foolproof method of finding out what I have? It makes no sense to pursue this head swap, if I already have 9.4 to 1 C/R, because the Vortec heads will have a smaller combustion chamber, thus increasing the C/R to unacceptable levels. It's a 1991 engine so I know it's not a Vortec roller engine. The engine has less than 300 hours on the clock and is in a 5500 lb. cruiser, so I only wish to swap heads for efficiency purposes and maybe a little better fuel economy. Any ideas?

Thanks,
PB

 

[scoflaw]

Re: Questions about swapping to Vortec heads...

You can find the volume of your old heads by the casting # on them. No need to pull. Compare that figure to the volume on the heads you are considering. You can also bleed off some compression, if needed, with a cam swap.

 

[John_S]

Re: Questions about swapping to Vortec heads...

Looks like that is a post '87 engine. You should have center bolt valve covers, self-aligning rockers, 64cc crate engine heads, with recessed pistons. Your compression ratio will be about the same unless you go with a different headgasket. You gain 30hp from the head design, not compression.

Verify with casting numbers.

 

[PBarrett]

Re: Questions about swapping to Vortec heads...

Thanks for the quick response.

Scoflaw - I don't know what I was thinking, of course I can use the head casting number to identify the heads. BTW, since the Motech site is no longer up, where can I get SBC casting number info?

John_S - Yes, post '87 with center bolt V/C. For some reason I just assumed that they were 76 CC heads, I didn't even think about a non-Vortec 64 CC head, that's why I was concerned about C/R. Like I said in my original post, I'm just trying to make what I have a little more efficient and maybe a little more economical to operate. The engine runs very good right now, but it takes a little bit to get the old girl up on plane.

I'll be on my boat next week, so I'll gather up the numbers I need and see what I have.

Thanks Guys,
PB

 

[Scott Danforth]

Re: Questions about swapping to Vortec heads...

dont forget the vortec manifold needed with the heads as well.

 

[Bondo]

Re: Questions about swapping to Vortec heads...

dont forget the vortec manifold needed with the heads as well.

Ayuh,... The Intake manifold,... exhaust is the same...

 

[dollarten]

Re: Questions about swapping to Vortec heads...

If everything lines up OK It will be a wise swap as the vortec heads are the most advanced heads that GM has ever built as far as the 5.7 engine goes . They offer much superior breathing over their older counterparts

 

[leedub]

Re: Questions about swapping to Vortec heads...

Been there, done that. Replaced non-Vortec heads (one was cracked) with new Vortecs as well as new 8 bolt intake. Didn't notice one bit of improvement either in acceleration or WOT. Seems like the exact same motor as before. I know they're supposed to put out another 30 hp or so, but I didn't see it! that said, there were certainly no ill effects of doing the upgrade aside from my deflating my wallet!

 

[leedub]

Re: Questions about swapping to Vortec heads...

Oh, and one more thing. If you do the swap, don't forget to plumb the coolant bypass next to the thermostat housing (on the intake manifold) to the circulating pump! Vortec heads aren't plumbed like the non-Vortecs to pass coolant between the block and the heads. I found out the hard way - the thing kept overheating shortly after leaving the dock!

 

[Bondo]

Re: Questions about swapping to Vortec heads...

Vortec heads aren't plumbed like the non-Vortecs to pass coolant between the block and the heads.

Huh,..??..??

 

[John_S]

Re: Questions about swapping to Vortec heads...

Between your two posts, I'd say something not right with your set-up. Vortec heads bolt on and work the same as standard gen I heads.

 

[leedub]

Re: Questions about swapping to Vortec heads...

Between your two posts, I'd say something not right with your set-up. Vortec heads bolt on and work the same as standard gen I heads.

No they don't. Vortecs bolt on with 8 bolts and non-vortecs with 12 (they require different intake manifolds). Also vortec L31 heads do not have internal coolant bypass ports like the gen 1 heads... which means that coolant can't circulate between the block and heads prior to the thermostat opening. This results in overheating.

There are many, many threads about this configuration on Chevy forums. Just google "Vortec coolant bypass", and you'll see what I mean. Also, my Edelbrock intake manifold manual specified this configuration.

 

[zbnutcase]

Re: Questions about swapping to Vortec heads...

If everything lines up OK It will be a wise swap as the vortec heads are the most advanced heads that GM has ever built as far as the 5.7 engine goes . They offer much superior breathing over their older counterparts

Even better than the old "camel hump" 461 heads of the '60s

 

[PBarrett]

Re: Questions about swapping to Vortec heads...

Well I checked the numbers and I have 64 cc non-Vortec heads, so I ordered the necessary parts and will probably pull the boat in a couple of weeks.

Leedub, are you sure you don't mean that the Vortec heads and intake don't accommodate the hot exhaust passage under the intake manifold, so a choke stove is not recommended in a Vortec swap? I've never heard anything about coolant passages being different, just that you have to go to a electric choke. Since the Vortec head was designed for fuel injected engines, a choke was never part of the mix.

Anyway, thanks guys,
PB

 

[Scott Danforth]

Re: Questions about swapping to Vortec heads...

Oh, and one more thing. If you do the swap, don't forget to plumb the coolant bypass next to the thermostat housing (on the intake manifold) to the circulating pump! Vortec heads aren't plumbed like the non-Vortecs to pass coolant between the block and the heads. I found out the hard way - the thing kept overheating shortly after leaving the dock!

you sure you didnt use the LT1 reverse flow heads? Vortec's are the LT1 combustion chamber and ports in a standard Gen1 configuration.

 

[John_S]

Re: Questions about swapping to Vortec heads...

From a search, it does look like some people have an issue with this. Many were from one person posting same on multiple forums. Most seem to be fine with some bypass holes in thermostat. I found no posting issues using I/O thermostat housings. Raw water cooled Mercruiser's (vortecs) do not use a bypass hose. Closed cooling do run a hose from water pump to intake manifold.

I have '96 1/2 5.7L that was changed to vortec heads with edelbrock 2116. Raw water cooled and no bypass. I have never seen the wild temp fluctuations described with this issue, ie before the thermostat opens.

 

[leedub]

Re: Questions about swapping to Vortec heads...

From a search, it does look like some people have an issue with this. Many were from one person posting same on multiple forums. Most seem to be fine with some bypass holes in thermostat. I found no posting issues using I/O thermostat housings. Raw water cooled Mercruiser's (vortecs) do not use a bypass hose. Closed cooling do run a hose from water pump to intake manifold.

I have '96 1/2 5.7L that was changed to vortec heads with edelbrock 2116. Raw water cooled and no bypass. I have never seen the wild temp fluctuations described with this issue, ie before the thermostat opens.

I should have mentioned, I do have closed cooling on my Merc. It's a '94 5.7L, now with vortec heads and edelbrock 2116 (same as yours). After swapping the heads, the engine temp would creep up slowly to just around 200 (should be at 180). Once I added that bypass, temp stayed right at 180 all day long.

BTW, these are the exact heads I got (not the reverse flow): http://www.michiganmotorz.com/cylinder-head-chevy-vortec-19962011-p-963.html

 

[Bondo]

Re: Questions about swapping to Vortec heads...

Been there, done that. Replaced non-Vortec heads (one was cracked) with new Vortecs as well as new 8 bolt intake. Didn't notice one bit of improvement either in acceleration or WOT. Seems like the exact same motor as before. I know they're supposed to put out another 30 hp or so, but I didn't see it! that said, there were certainly no ill effects of doing the upgrade aside from my deflating my wallet!

Ayuh,... What were ya startin' with,..??

I can't believe ya didn't feel the kick in the pants difference,..??

What's the compression numbers for the motor,..?? is it tired,..??

Who tuned yer carb,..??

Which ignition,..??

 

[leedub]

Re: Questions about swapping to Vortec heads...

Ayuh,... What were ya startin' with,..??

I can't believe ya didn't feel the kick in the pants difference,..??

What's the compression numbers for the motor,..?? is it tired,..??

Who tuned yer carb,..??

Which ignition,..??

Yeah, I can't believe I didn't get that kick either! Compression is good, 150 on six of the cylinders, 140 on the other 2. I tuned the carb with a vacuum gauge, it was done correctly. The ignition is the standard Thunderbolt IV... have the right coil. Also has new cap, rotor, plugs and wires.

 

[bruceb58]

Re: Questions about swapping to Vortec heads...

Compression is good, 150 on six of the cylinders, 140 on the other 2.

Not sure I would call that good.