generalmopars

Ok my question is simple, Why does everybody have a hardon for #5 heads but nobody talks up the #6 heads, aren't they basically the same heads? just one set is from 68-69 & the others are from 70?. is there a difference? also id like to throw the #7s & 7as into the mix. Can somebody that Knows the Facts break these 4 sets of heads down for me. also I know the 7as have hardend exhaust seats. im just curious why EVERYBODY EVERYWHERE is like " ohhhhhh #5s,,,, ohhhh,,, ahhhh but the 6s don't get that same love. I have a factory 68 350 4bbl and 2 70 factory 4bbls and I don't notice a difference in design or performance so what gives? thanks guys. BTW all Cutlass Supreme engines, no rally 350s or ram rods, just typical 350s.

coppercutlass

#5's dont have the egr bumps. But anything pre 1973 had smaller chambers and is considered a better suited core for performance apps . I had a set of #4 heads that measured in at 62 cc's.

scottv442

I believe all #5, #6, #7, and #7a heads were 64cc, so all are good compression heads.

Out of the box, I personally like the #6 heads with valve rotators or even #7a with rotators and hardened seats already installed.

This quote from 442.com is the ghost that made the mythology everybodys fact:

Best Flowing SB Head

Dick Miller claims that #5 heads flow the best bone stock and untouched.

[ Thanks to Chris Urban, Bob Barry for this information ]

oldsmobiledave

The quote from 442.com is wrong. All 68-72 heads are approximately 68-69cc. Only the 1967 #4 heads are 64cc.

scottv442

that doesn't surprise me

joe_padavano

I'm shocked, SHOCKED I tell you...

NO Olds heads have "EGR bumps". Every single Olds head cast since the 1966 model year has A.I.R. bumps to provide enough material for the A.I.R. injection manifold ports to be drilled and tapped. That means every SBO head starting with #3 heads have the bumps.

There is a lot of bad or misleading Olds info out there that just won't die. Same thing goes for BBO heads. Does anyone really think that C heads flow appreciably better than any other Olds head (except J heads)? More to the point, most of the published data on head flow and chamber volume is based on measuring a SINGLE head or a pair of heads. These parts were mass produced and there was a lot of variability from one casting to the next.

Kennybill

#5's are the C's of the small block heads. I had a set of stock small valved #4s on a std. Bore 350 that drove in/13:80s. Till you hit #8s, there's not a lot of difference on stock from the factory heads.

joe_padavano

In fact, #5 and C heads were the only non-smog heads built for more than one model year, so there are more of them out there.

Kennybill

I should have rephrased it. When anyone wants to put better heads on a small block, they're usually told get #5s. When anyone wants to put better heads on a big block, they're usually told get C's. In reality in stock form same size valved, 4,5,6,7,7a are about the same flow. The same sized valved B,C,E,G are about the same but 5s and C's are more mentioned. Jmo.