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 .

I'm not doubting what you are saying about the .039" gasket. Sometimes safer is better. I'm just trying to get as much compression as I can as safely as I can. These are Gen VI 502 heads going on a Gen VI 8.0L block. I saw the 1037 gasket and figured that's what I'd end up with, but I want to exhaust all options before I decide. I'll take a closer look at the heads to see where the coolant hole ends up.
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".


Yes. Thanks.

https://c6.staticflickr.com/6/5599/3...3c1fbd99_z.jpg

Lets see some more pics of that Camaro.

Thats a Mark IV block in the picture?

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.

https://c3.staticflickr.com/6/5503/3...ede92e63_z.jpg

https://c6.staticflickr.com/6/5591/3...8f177c30_z.jpg

No. This one isn't a Mk IV. It's all Gen VI.

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?

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

The only thing Mk IV I was looking for was info about using a Mk IV gasket.
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.

Novody ever said anything about a mk4 block. THere was mention of going from a gen6 to a mk4 cam and difference betwee gen 6 and mk headgaskets and cooling.

I see that now.
Whats your thoughts on the quench clearance? Do you know if those heads have the 7/16 or 3/8 rocker stud bosses?

i never knew this engine existed,was it installed in any gm trucks or was it an over the counter replacement engine?

It's relatively new and available over the counter. I think was mentioned on a thread here in past month or so.

My understanding is that its an OTC deal. Mine is a 2015.

Looks like this company uses it

http://powertrainintegration.com/pi-thon-8-0l-v8-lpg/

what was the price tag on it,looks interesting.

$5977

Mine was kind of a long story... A builder owed a friend some money and gave him this motor for part of it. It was supposed to be a 540hp 502ci. I pulled the cam to put in one with a fuel pump lobe and discovered it was a truck cam. I pulled the head and it had small valves with Mk IV head gaskets. My buddy is going after the builder and charging him for my cam and heads. I paid $2,500 for it. He gave me a Lunati cam and lifter set along with the heads. The cam kit was $1,100 alone. I figured I still am doing well at $2,500 and some labor.

It interested me so I did some googling... seems to be built for cng/lpg and 4500 rpm max rpm (most likely because of cam im guessing) also from the piks of it online (the sale version not the op's) it looks like it has peanut port heads?? 19256827 though its hard to tell looking at a tiny screen

Though there might be a few different versions of the motor.

I really find it strange though as I thought gm had backed away from the bbc

I think there is a market, or demand, for alternative fuel engines. The bbc gas platform, works well on alternative fuels. Thats why valve seat materials have progressed alot as well.

The light truck market may have got away from the gas big blocks, but in the school busses, rvs, and things like that, it seems like they may be wanting to get away from diesel in some circumstances. The small LS engines they use in light duty pickups now, just wont make the low rpm power the big block engines can.

There are a few different versions. Mine had these heads. P/N: 19256821 2.06"/1.72" valves.

https://c5.staticflickr.com/1/298/30...f683cbbb_z.jpg


Here's the new heads:

https://c8.staticflickr.com/1/723/31...67bd4b2c_z.jpg

https://c7.staticflickr.com/1/589/31...00d2f198_z.jpg

Industrial/agricultual; pumps. generators, etc.....big market

There is a 632 (10.2L) out there with piston oilers and etc. Cool !

http://www.jegs.com/i/Chevrolet-Perf...28586/10002/-1

http://paceperformance.com/i-1999064...te-engine.html

Hard to tell on my phone, but man, that looks like some big ridges around the valves. I would think that would really kill airflow and create some hotspots

Could use some chamber work for sure. About 3-4 cc's worth but I'm sure it will run well.

Those pics were the heads before they had the work done. They'll definitely get some smoothing out.

So just to be sure, there's no way to block off the extra coolant passage on the Gen VI without the Gen VI gasket and it is necessary? I just want to make sure there wasn't any confusion with all the Mk IV vs Gen VI talk.

Great looking Camaro!!

I got my heads back this weekend and the coolant pouring up into the intake theory with Mk IV gaskets on a Gen 6 block doesn't work... The coolant passages in the head are connected. Can anyone else explain why you wouldn't want to run Mk IV gaskets on a Gen 6? I just don't see it. The only difference is the extra passage isn't machined on the block.

https://c3.staticflickr.com/1/384/31...6b833af6_k.jpg

https://c7.staticflickr.com/1/421/30...ba3d3c9c_k.jpg

Here's what my bowls look like now. It doesn't look like there is any real shrouding going on. I might still smooth them out a little and polish them. We'll see.

https://c3.staticflickr.com/1/595/31...a8cc6185_k.jpg


Again, thanks for any help.

Have you checked Cometic's website for the correct gaskets? They have a great selection for the gen 6 blocks. No need to chance it if the correct gasket is readily available

I'll check them out. I was looking at Jegs and Summit. Still, looking at it, it doesn't look like it's an issue. Thanks.

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