Gen VI 489 +20 build
01-04-2017, 05:42 PM
#11
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You are first saying you are thinking of running a .018 shim gasket, or a .027 gasket, or a .037 gasket. My suggestion, is/was, to run a standard .039 or whatever felpro gasket. Readily available, cheap, work well, and available for your particular situation "gen 6 heads on mark IV block". Will this increase the quench a bit, yes. Will it matter? No. Will the drop in static matter? No. Will running .037" for piston to head clearance be ok? Should be. Might be. I'd rather have a little more room. BBC's typically work well in the .040-.060 range. Being it isn't a competition deal, why risk it? You're running fairly poor performing cylinder heads, that don't do much for combustion quality, or airflow anyway.
The GEN 5/6 blocks, have coolant holes at the front of the block. Those holes MUST be blocked by the gasket, or , water will run right up and out the intake manifold, never cooling the rear of the engine. Felpro has this figured out. The 1037 Fel pro gasket, 4.370 bore .039 thick, fits Mark IV, GEN 5, and Gen 6 blocks. Bascially, the GEN 5 and 6, have holes in the deck at front of the block, that simply aren't used. Ever. The Mark IV blocks, do not have these holes at that location, even though some of the old gaskets had a hole cut into them. There was no hole in the block, so it didnt matter. Now, If you put on of those gaskets, on a GEN 5 or 6, yes, you would have an issue.
The GEN 5/6 blocks, have coolant holes at the front of the block. Those holes MUST be blocked by the gasket, or , water will run right up and out the intake manifold, never cooling the rear of the engine. Felpro has this figured out. The 1037 Fel pro gasket, 4.370 bore .039 thick, fits Mark IV, GEN 5, and Gen 6 blocks. Bascially, the GEN 5 and 6, have holes in the deck at front of the block, that simply aren't used. Ever. The Mark IV blocks, do not have these holes at that location, even though some of the old gaskets had a hole cut into them. There was no hole in the block, so it didnt matter. Now, If you put on of those gaskets, on a GEN 5 or 6, yes, you would have an issue.
What do you know about the heads? Seriously, not being an ass... I had them milled down to 108ccs for the compression. They had 118cc chambers. 2.19"/1.88".
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01-04-2017, 06:04 PM
#14
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Here's a couple. She's a work in progress. I just took it down off the rotisserie in June. I drove it all summer with a 408ci, then in September someone offered me a good deal on this 489ci. So, here I am... The body and interior are finished. I'm just waiting on doing the paint.
01-04-2017, 06:05 PM
#15
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01-04-2017, 06:14 PM
#16
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ok, for whatever reason, all this MARK IV talk, i assumed you stated you had a Mark IV block.
Anyhow, those heads you have, are standard GM rectangle port heads, that were designed in the 1960's. They havent changed much of anything to the design since then. Their combustion chamber design, and exhaust port, are lackluster by todays standards in bbc performance aftermarket heads. They were the standard heads on the 502 and 454/420HP crate engines, and everything from a 365HP 454 magnum mercruiser, to a 800sc supercharged 572 Mercruiser. I am pretty sure, they have 3/8 rocker stud bosses, unlike most earlier versions, that had the 7/16 holes.
How close to cutting into the intake valve seat did they get when milling to 110cc?
Anyhow, those heads you have, are standard GM rectangle port heads, that were designed in the 1960's. They havent changed much of anything to the design since then. Their combustion chamber design, and exhaust port, are lackluster by todays standards in bbc performance aftermarket heads. They were the standard heads on the 502 and 454/420HP crate engines, and everything from a 365HP 454 magnum mercruiser, to a 800sc supercharged 572 Mercruiser. I am pretty sure, they have 3/8 rocker stud bosses, unlike most earlier versions, that had the 7/16 holes.
How close to cutting into the intake valve seat did they get when milling to 110cc?
01-04-2017, 06:18 PM
#17
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Thats a cool engine GM came out with, for towing applications. 4.25 forged crank, vortec heads, etc. Pretty much a big brother to the old 454 L29 Vortec engines, like I have in my 1997 dually, and a bigger version of the old "tall deck" 427T engines.
http://www.gmserviceinsights.com/wp-...lock_crate.png
http://www.gmserviceinsights.com/wp-...lock_crate.png
01-04-2017, 06:25 PM
#18
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Thread Starter
ok, for whatever reason, all this MARK IV talk, i assumed you stated you had a Mark IV block.
Anyhow, those heads you have, are standard GM rectangle port heads, that were designed in the 1960's. They havent changed much of anything to the design since then. Their combustion chamber design, and exhaust port, are lackluster by todays standards in bbc performance aftermarket heads. They were the standard heads on the 502 and 454/420HP crate engines, and everything from a 365HP 454 magnum mercruiser, to a 800sc supercharged 572 Mercruiser. I am pretty sure, they have 3/8 rocker stud bosses, unlike most earlier versions, that had the 7/16 holes.
How close to cutting into the intake valve seat did they get when milling to 110cc?
Anyhow, those heads you have, are standard GM rectangle port heads, that were designed in the 1960's. They havent changed much of anything to the design since then. Their combustion chamber design, and exhaust port, are lackluster by todays standards in bbc performance aftermarket heads. They were the standard heads on the 502 and 454/420HP crate engines, and everything from a 365HP 454 magnum mercruiser, to a 800sc supercharged 572 Mercruiser. I am pretty sure, they have 3/8 rocker stud bosses, unlike most earlier versions, that had the 7/16 holes.
How close to cutting into the intake valve seat did they get when milling to 110cc?
I did see where the heads could be either 3/8" accessory holes or 7/16". So what makes them Gen VI heads? I know Gen VI blocks will accept Mk IV and Gen VI heads with the right gasket, which has been my big question.
I haven't picked up the heads yet, so I'm not sure how close they are. I had them mill ~.050" and they're supposed to be good for up to ~.125".
Yep. I figured I'd throw a nice cam at it with some compression. She should make some decent power. Mine is actually a 19256818. It's slightly different than the one in your link, but the same idea. I don't think mine was a Vortec. I'm not sure though.
Last edited by HawkX66; 01-04-2017 at 06:32 PM.
