Gen VI 489 +20 build
 

The Offshore community seems to know the most about Gen VI big block Chevys, so here I am. If I could get some help, I'd appreciate it.
I have a 8.0L 489ci block bored .020. (4.30" x 4.25") ~494ci now. 10.2" deck. I'm putting a set of 502ci 12562934 heads on it that I had milled down to 108ccs. I'm going with a Lunati 20010723 Gen VI cam even though Lunati recommended a Mk IV with the same specs for some reason. (241/249 @.050" .625/.625)
What I'm trying to find out is mainly about the quench area and head gaskets. I have flat pistons with a piston to deck distance of .010". It was decked .010". I want to bump the compression as much as I can without causing problems. Initially I was going to use metal shim gaskets that are .018" squished, but I only found them for Mk IV and that also got me thinking about the quench area and the piston to head clearance. I think I'm going to be stuck with at least .027" thick gaskets for a total of .037" quench. This is a street motor with a little track time on Friday nights.

1st I haven't been able to measure the Piston to Valve clearance yet. Do you think I have anything to be concerned with? I'm hoping I don't have to grind valve reliefs.

2nd What do you think about .037" for the quench? Too close? This would give me 9.65:1 compression. .037" gaskets plus the .010" piston to deck would give me 9.48:1.

3rd and most important to me right now... I know the difference between Mk IV and Gen VI BBC head gaskets is that Mk IV has two coolant holes on each end and Gen VI only has one. I feel like I'm extremely limited on Gen VI head gaskets and everything I want is available in Mk IV. It's a heck of a lot cheaper too. Is the extra coolant passage that big of a deal on a street motor?


Thanks for any help!

https://c2.staticflickr.com/6/5669/3...a161ab53_k.jpg

Its a street engine. I would stop sweating the quench thing. Millions of bbc's running around with the pistons .020 in the hole with a .040 fel pro gasket.

Theres 100 other things in a build, that will make more of a power difference, than 2 tenths of a point of static.

I'm not sweating the quench for extra power as much as I'm sweating it for possible clearance problems. Piston to head clearance. The other thing is I'm really trying to keep the compression as high as I can with what parts I have. As far as how millions of other BBCs are running around with poorly built motors, I don't want to be one of them. If I can pay attention to a gasket thickness to get it right, I'd rather do that.

A mercury racing engine is poorly built?

Seriously? That's what you got out of what I wrote?

lets start from the top,their is no 8.0L block,is it a 7.4L or an 8.2L block?if it is a 7.4L with a .020 overbore that makes it 458.24 cu in.for us to give you good answers we need correct information.if you can get the block casting number i can tell you what block you have.

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.

Be careful with what you "know." I have an 8.0L block. 489ci. 4.28" x 4.25". Bored .020" so 4.30" x 4.25" making a 494ci.

http://www.jegs.com/p/Chevrolet-Perf...86gRoCHjDw_wcB


THere IS an 8.0 block, its a tall deck...

I have never, seen a MARK 4 "8.0" liter block.

Phroogly, that engine you posted , is not a Mark IV block .