Stock Gen V vs Gen VI Head Specs

[Supercharged111]

I have a 454 swapped Monte Carlo, but it's a Gen V motor. It has a Comp 256 cam and longtube headers, but is shackled with the Gen V heads and stock 4bbl intake. I've been thinking the cheap, easy route to make it breathe a little better would be stock Gen VI heads and a bit more cam with different intake, would simply retune the QJ as it seems more than big enough for mid 400hp of sea level BBC. I can't seem to find jack **** for flow, chamber volume, runner volume, valve sizes, etc. All I really know is that the GenV is a peanut port head and the GenVI is a small oval port but it's still a damn swirl port.

 

[Schurkey]

The Gen VI heads were written up in one of the hot-roddy magazines as being the big-block equivalent of the small-block "Vortec" heads--OEM castings that make a huge, huge, huge performance increase.

Load of crap.

They do offer something of a torque boost, very useful in pickups or other light trucks, but they're NOTHING like the giant-killer SBC Vortec iron heads. Nice combustion chamber, ****** ports.

Truthfully, they're more-closely related to the SBC swirl-port TBI heads. There's a giant ski-jump in the intake port just like the SBC swirl-ports. They're fine for low-rpm torque and fuel economy. They are DONE by 5,000 rpm.

If you insist on using them, be aware that you'll need valve rotator eliminator shims (16) which come in two varieties that I know of. There may be others, I haven't researched them for years. You MUST be CAREFUL on the intake valve guide bosses, some of them aren't machined to fit the rotator eliminator shims, and will require minor grinding at the base of the guide boss, where it meets the spring pocket. I had to grind two guide bosses on each head. The OEM springs are weak, and the valvetrain is not adjustable unless you convert using one of several methods. The easy way is to buy the special rocker studs having the small-diameter that screws into the head, and the standard 7/16 top thread. Then you can use any BBC rocker arm--roller or stock.

I have a pair of these heads in the barn right now, all set up and ready to go. I put them on my boat 454 years and years ago, and then took them off when I built a different engine for it.

Shining a flashlight into the intake port--note ski-jump on right side of valve guide:

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[Schurkey]

Another photo from the archive. Both intake and exhaust valve seats are hardened inserts. Kinda nice. Before I bolted these onto the boat engine, I tapered the blunt valve guide boss in the exhaust ports, They worked OK, certainly better than the worn-out, burnt-valve round-port heads that were on that engine before. The new engine got old-style Mk IV oval ports with big valves, and unfortunately bigger combustion chambers, Had to have domed pistons. These chambers are right around 100 cc.

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[Supercharged111]

How hard is it to use Mark4 heads? I know there's a difference in the coolant ports. I knew about the ski jumps already, but they're supposed to suck less than a peanut port and I think they'd bump compression too. I figure peanut ports are as ****** as it gets, so anything would be an improvement. I also am inclined to believing that the stock intake blows. Not looking for a fire breather as those cost money, more after some low hanging fruit here.

 

[Schurkey]

Victor-Reinz had a pair of head gaskets specifically designed to mount Mk IV heads onto a Gen 5 block. There were two part numbers, one for left and one for right. I don't remember the numbers, but that's ok, I think they're out-of-business.

Vortecpro (user name on several forums) has ported "peanut port" heads and gotten astonishing power from them.
http://vortecpro454.com/#xl_xr_page_engines

https://www.chevelles.com/forums/13...peanut-port-dyno-test-second-time-around.html

 

[Supercharged111]

That's more time and money than I care to invest, I'm more thinking cheap CL heads. Aluminum would be nice, but it looks like I'll be stuck with some form of stock for now. I would imagine those ported peanuts have been significantly chopped on. I can port match, trim guides, blend stuff, take out ski jumps, bit I'm not articulate enough to reshape an entire port. Are there any good resources that spec runner volume, dimensions, etc? I own both motors, but both are fully assembled good running motors.

 

[Schurkey]

First things to decide are
Camshaft specs
Compression
RPM range

and each one affects the others. When you have those sorted-out, you'll know what you need for cylinder heads, except that if your heads have exceptional flow, you may be able to go more-mild with the camshaft, which means you can be more conservative with compression.

Frankly, that's my favorite "trick". Great heads...mild cam and compression. Makes for a very durable and long-lived engine that can use regular fuel and still put a grin on my face.

 

[andy396]

Frankly, that's my favorite "trick". Great heads...mild cam and compression. Makes for a very durable and long-lived engine that can use regular fuel and still put a grin on my face.

When you say compression, how much are you talking about?

 

[Schurkey]

9.2 to about 10.2 depending on iron or aluminum heads, and how likely the engine is to be run hard with crappy gasoline. My 5.7L '88 K1500 has 9.57:1 compression, it runs on regular with no problems as the heads are aluminum, and the block has been zero-decked so there's good turbulence in the combustion chamber.

The boat had "about" the same with either the 454 Vortec heads and the crappy OEM pistons and block machining, and thin head gaskets; or the new engine with proper block machining and larger-combustion chamber heads, small-dome pistons and thicker gaskets. Either way, it'll run WOT as long as I want and not detonate. 'Course, the boat is helped out in that regard by a lakewater cooling system that has trouble staying warmer than 160 degrees.

Note that I mean TRUE compression, not bullshit "advertised" compression, where it "might" be that high except the pistons are so far down the hole due to improper block machining that it erases a heap of compression ratio.

 

[Supercharged111]

I know it's a Goodwrench reman, the big variable is who did it? Dad **** out a part number years ago that indicated it was in the 9:1 range. What I see now for a GenV reman is the garbage 7.5:1 motors. I need to yank the heads, ID the pistons, and measure how far down they are. Let's assume my target is 9:1 compression with less bad than stock peanut port heads. That's really where I'm at. I think that with a ~272 cam and a decent intake would yield 400+ MI crank hp and a boatload of torque. Add some spray and call it a day until you're ready to spend some money.