[350bird]

My 72'Firebird 350 has four bolt exhaust heads (7h1) which I am replacing with 77 6X-8 heads. The 6x have six bolts for headers on exhaust, but compression ratio was 7.6 on a 400. 6X heads have 98cc combustion chamber and my 7h1 had pontiact rated at 96 cc with 8.1. Pontiact usually overrates CR by .50 so they were about equal. The new 6X have been port-matched, but not polished. Also, with the new flat top valves I installed and the resurfacing of the heads the 6X are now 94.5 cc. Also, the 6X rocker arm supports are what I've been told are the "fixed or rigid " type. You crank the nut all the way down. I've been told this is not good. Couple questions:

1. I've been told that I should replace the rockers and support studs (posts) with "big block Chevy" parts. If so, do I use the same push rods? I have new lifters and a Chet Herbert P2 cam I am installing (mild idle - 5500 comparable to an Edelbrock Performer).

2. How do I get the compression ratio up on the heads.? the resurfacing probably took 8-10 thousands off. I believe you can cut as much as 50. How much should I take and when I do need to cut the intake to insure intake match? Also, should I leave the port-match alone or go on to the polish as well and if i do how much different will it make compared to the cutting of the heads? Or should I do both.

3. Any other suggestions. The 350 has over 100,00, but does not burn any oil and ran well before I took the old heads off to install headers and four barrell 600 cfm edelbrock.

[jimfulco]

Crane says their Kool Nuts (~$40) have a counterbored area at the inside bottom that allows adjustment of stock Pontiac rockers. I've heard that using stock BBC studs & nuts (self-locking) with stock Pontiac rockers & balls works but I'm not sure. On a Pontiac, you mill the intake face the same as the block face. Don't polish the intake ports, as they need to be a little rough. Doing the chambers & exhausts is OK.

www.cranecams.com/master/ranuts.htm

[adryan16]

Well, first off, you can use the BBC studs and nut, but you'll need to use your Pontiac rockers. Your stock one's will work fine, as I doubt you'll be buzzin this thing into the 6's and beyond. You can use the same pushrods, but you'll need to set the valves as you would on a typical SBC instead as Pontiac instructs. However, there's nothing wrong with the stock setup, and you don't crank them all the way down, there's an actual torque specification for them. Anyway,let me know how that cam works out, and what the specs are on it too.
Secondly, jim's right, don't polish the intake, just open them up. I don't like to be the bearer of bad news, but those heads aren't going to get you too far. They'll work just fine, but Pontiac started putting those on simply to cut down horsepower and decrease emissions. On a 350, they're not gonna do much for you compression wise. (the best I can come up with off the measurments I took from my 350 is 7.8:1, and that's being kinda optimistic). If you're set on using these heads, go ahead, but if you haven't gotten too far, I'd look into getting a set of late 60's high compression heads. Cast 12, 13, 16, 48, 64. All these work on a 350 and result in around nearly 10 with flattops. Let us know, what happens either way.

[BanditT/A]

hey 350bird,
6X heads are a pretty desireable head. pontiac made two versions of the 6X as i am sure you probably know. the 6X-4 and 6X-8. the 4's have around 90-92 ccs and 8's, well you know the 8's. anyway, since you are running a 350, i would not recommend the 6X-8's. the 8's came on 400's and 455's. on a 400 they are just 7.6:1 comp!! on a 350 they'd be like 7:1. not very desireable at all. poor performance, economy, etc. the 4's on a 350 leave you with around 7.6-7.8 comp. on a 400 they are like 8.2 and 455 is like 8.8-9.0 (with all being stock)

the 4's however came mostly on 350's and a few 400's got them but only in T/A's. i am gonna be using a set of 4's that i got from a 350 and putting them on a 455 for my T/A. compression will be around 9.6:1 with a decked block and unplaned heads and flat-tops.

a few years back i had a 77 firebird with 350 with 6X-4 heads (how i got the heads) and an a 350 automatic. the motor could barely move that car. my grandma coulda done circles around me with her walker.

i would recommend a few things. if you are dead set on a 350 than dump the heads and do what adryan said. go with earlier castings to bump compression. or you could find a 400 or 455 block and still use the 8's. (i'd go with the 455) or since 400 blocks are plentiful, you could buy a stroker kit for a 400 and make it a 455-461. Kauffman Racing makes kits as does pontiac dude. check out thier sites if interested.

but since your 350 has a 100,000 miles it is a good time to dump it. like i said pontiac put 400's in almost everything. find a station wagon motor and build it up. thats what i did, and ran 12.9's in a 68 firebird.

as far as the rockers, they get torqued to 20 ft/lbs when stock. and they are not adjustable with a STOCK valvetrain. you can use the big block studs (i think they are like 7/16, or something) check kauffmans site, they have a ton of info.

in conclusion, i think you would be much happier with a bigger motor. 400's and 455's have tons of torque and your 8's would work well on either one. hope this helps.
good luck and keep us posted!

[astroracer]

I have to agree with BanditT/A on ditching the 350. With 100K on it you will have an oil burner if you put a new set of heads on it. The heads will seal tighter and that will cause oil to blow by the rings. Been there, done that.
I put a set of '69 GTO heads (16's I believe?) along with the intake on my '73 350. It ran pretty good but immediately started using oil.
Mark