[goatheaven]

Hello

I'm building a 455 and have a set of 4x heads that were thrown in a package deal of parts. I'm having the block done now getting bored .30 over. Will these 4x heads give me enough power? Trying to achieve over 400 horse power. It is a 1970 YH Code block.I have TRW Forged pistons and Nodular Crankshaft. Was thinking of going with ram air IV Cam

Need help identifying the year and power and if these heads and if they are worth rebuilding. Attached a couple pics
Date Code H293

A few people have suggested 6x heads or even gong with aluminum heads. Are the 6x heads that much better than 4x??

Thanks in Advance for any advice on building a high performance 455 at reasonable price

[johnta1]

1st find the secondary code on the heads, this will determine the cr.

Look half way down on page:

Pontiac Heads

With the right chamber size it could make some decent HP.

[ponyakr]

"...Are the 6x heads that much better than 4x??"


I think the biggest advantage of the 6X heads is that they are less prone to cracking, between the valve seats. There have been LOTS of reports of cracked 4X heads. Some say it was because of the seat hardening process used on the 4X heads, which was improved on the 6X heads.

Don't know the real reason why, but I've read about the 4X cracking problem on several Pontiac forums.

http://forums.maxperformanceinc.com/...66#post5928466

https://www.hotrod.com/articles/0312...-racing-heads/

[goatheaven]

Thanks for input so far. Looked at wallace racing and the id code says 3 one head and 4 on the other. Is that good?? are they matching??

[goatheaven]

Also is the year of these 1973?

[ponyakr]

Originally Posted by goatheaven

Also is the year of these 1973?

Since the casting date was late '73, that would probably mean they were used on the engine in a '74 model car.

[goatheaven]

Thanks for info. Do you think I would get more horsepower with a set of 1976 6x8 heads? was thinking of buying the 6x because some people were telling me that 4x heads are smog heads

[ponyakr]

Originally Posted by goatheaven

Thanks for input so far. Looked at wallace racing and the id code says 3 one head and 4 on the other. Is that good?? are they matching??

I get different online info. If both have screw-in studs, 2.11 intake valves, & the same size chambers, they're close enuff to the same.

[ponyakr]

Originally Posted by goatheaven

Thanks for info. Do you think I would get more horsepower with a set of 1976 6x8 heads? was thinking of buying the 6x because some people were telling me that 4x heads are smog heads

Don't think the 6X heads will make any more power than 4X, if they have the same size chambers & are built the same. I suppose you could call both "smog" heads. Pontiac engines were equipped with an EGR valve, beginning in '73. So, maybe some call '73-up Pontiac engines "smog" engines.

There are quick drag racers using both heads.

The only bad thing I've read about the 4X heads is that they are more prone to cracking, between the seats.

[schultcd]

If the ID code is 4 on one head and 3 on the other then they are a mismatched pair. They probably have the same chamber volume but different intake valve sizes. The top row of this chart should actually be a column down the left side. Don’t know what happened there.