I'm working on a 67 Firebird with a 326 and an automatic. The 326 needs a rebuild but I also have a 421 shortblock I'm considering rebuilding instead. Will the 326 heads work with the 421, edelbrock performer manifold, performer cam and carb? I'm mostly concerned with having to big of a compression ratio. I'm looking for good torque numbers for the street.
It looks like there are 2 different 326's that year, one with 9.2 compression and the H.O. with 10.5. As for the 421 they usually had 10.5 to 10.75 compression ratio. (unles you're lucky enough to have a Super Duty, then you're looking at 12 and 13 to 1 !!)
So...if you've got the regular non H.O. 326 those heads would lower the CR of the 421 to something streetable on todays pump gas. Remember that pistons make a difference too. You could have dished pistons that would lower the CR, or domed that would raise it. If I were you, I'd drop the heads block and pistons off at a good automotive machine shop and get them to CC the heads and measure the deck height and pistons, and give you an actual CR number.
I'd build the 421. There's no replaement for displacement!!
Jay S
Thank's for the great info, Jay. The 326 is the 250 HP, engine code X1. Is that the lower CR head? The 421 is a '64 4 bolt mains version engine code (T) 35B. There's a T as the first digit but I couldn't find a closer code than 35B. It may have been rebuilt with low miles before it was stored outside under a cover so I'm going to have to go through it again. I haven't had a chance to tear it down yet. It has Flat top pistons with 4 deep valve reliefs.
Mark
Without knowing the cc's in the 326 heads combustion chamber there is no way to know what the CR will be. It is possible those 9.5 heads will increase the CR on the 421. Stan
The XI code 326 is one of the engines with 9.2 CR. The head code should be
140. Check out this site for tons of info on codes:According to the chart the 421 will have 11.65 cr with the 326 heads. A bit high for the street, I'd say.
Mark
Yup...that's too high alright! That's too bad. Maybe you should think about keeping an eye out for a set of heads that will work with the 421 and keep the 326 complete incase you want to return the car to original. Ebay might work if you can find something local so you don't get killed on shipping.
Jay S
There's a 78 pontiac in the local pick a part. I'll see if I can use the open chamber heads from that.
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