Technical power pack heads with 1.94 intake valves installed

Well, I guess it would "work"..... Why would anyone do that?
Pics from Facespook marketplace ad in washington

 

Seats were junk so they installed larger valves.

 

Yep, heads might have needed seats so they figured hey, why not go bigger. The PP heads have smaller chambers than ‘461’s and ‘462’s and they may have wanted to keep the compression up on the engine being built.

 

Intake and Exhaust Ports are small on PP head..... is what I was referring too

 

No matter on a small inch street engine. I know we’re building hot rods here but they would be adequate for a bunch of engine combinations.

 

Someone with more experience than I do can answer this hopefully- at what point do we consider the intake valves shrouded?

 

I'd be more concerned with why 2 of the intake valves are out of the combustion chamber and into the deck surface, and the other 2 valves aren't. Maybe it's just the angle of the picture?

 

Good Eye.... looks like maybe crappy work. Two the valves sunk down in the seat farther. All so looks like one new valve , others maybe old reused. Light Beer also ....

 

I'll likely go 1.84 intakes on my power pack heads when I get around to the rebuild

 

No, they aren't actually, intake port size is only a few cc smaller because of the seat area for a smaller valve....only the valve seat area and throat were actually smaller. Rest of the port is just like a Fuelie/Hump head.
If the bigger valve seat was also correctly machined with the excess material below the seat also removed (aka "bowl hog") and the correct clearance machining around the edge of the chamber beside the intake valve (chamber "swept out") then that late version 520 casting can make a great head.....especially if some additional port work is also done.

We called them "Jr Fuelie's" since they have the same good closed chamber shape as the 292 and 186 Hump head castings, just smaller, they are 58cc chamber originally and about 60cc when fully finished up.

At any point where the valve rim to chamber wall or cylinder wall is less than the valve lift.
On an SBC head, you can never get fully unshrouded, best you can do is relieve it to the limits of either bore wall or head gasket fire ring.
It takes canted valve or hemi lay-out to fully remove shrouding.

In a quest for power, you unshroud to the limits your parts combination will allow.

 

This is a much better answer than I was anticipating… thank you.

So in situations such as this head, I have read that you can go too big to the point to where the valve shrouding negates any gains made by the larger valve. Is this something someone with an experienced eye can anticipate, or must it always be measured to know for sure?

For example, is it a safe bet to look at something like this and anticipate a loss or stagnation of performance in use?

 

Better breathing on a "stock" Power Pack engine. For sneaky reasons?

 

Bigger is not always better for sure! A group of us over on Inliners about 10 or 12 years ago debunked the age old myth that the closed chamber 194 Chevy 6 cylinder head was better for performance than the standard run of the mill open chamber 250/292 cylinder head. We did exhaustive dyno testing with both cylinder heads prepped identically with 1.84" intake valves and with 1.94" intake valves. Even though the 194 head added a full compression point to the engine, it always made at least 10 HP less than with the open chamber head. The 194 head, even with the smaller 1.84" valves is greatly shrouded compared to the open chamber head.
The late, great Kay Sissell even said in his catalog that the 194 cylinder head should never be considered as an option for enhancing performance. But the lure of the closed chamber head blinds many people hung up on the same swap done with the SBC back in that time period....

 

Shrouding is why I'm going 1.84 on my 283 instead of 1.94.

 

I wont say you are wrong....I dont know who told you that.... But you will have to prove that one....
I measured and compared the ports of '65, 283 powerpack heads off a pickup truck, with 3 different pairs of Camel hump heads probably 35 years ago, and powerpack heads had smaller runners. Google search info; Powerpack 1.38 cc intake runners, camel hump 160-172 cc intake runners

,

 

I actually have both a set of '57 power pack heads and a set of '64 461 double hump heads. I ought to take some comparative measurements. Both sets are untouched. I do remember thinking the power pack ports seemingly looking smaller

 

Intake and exhaust runners aren't all that big on old camel hump heads with slightly larger valves either!
The 1.94's will flow a little more mixture, but runners on PP or camel hump heads have always been the restriction. But these will flow better than the original 1.72" valves did. I wouldn't buy those heads, but if I already had them I'd run them on a mild build where you'll never rev the engine over 6k.

 

Untouched you are right.
But when you cut the 1.72 valve out to 1.94" valve and cut the bigger valve job into the head and do the bottom cuts below the seat correctly so that both heads are machined to the same size from the seat to the port opening you gain all those cc's in the port volume.Then it's just some work removing metal where they sometimes fill the roof of the bowl. I've noticed that to be hit or miss. The rest of the port from the top of the short side back to the inlet face is basically the same.
I'm talking specifically about the late version 520 castings (1966-67) and not any other head called "powepack", the chamber shape is a slightly shrunken copy of the slant edge closed chamber used on the 186 and 292 head..