Ad Radar
High Performance Pontiac
Click here to find out more!

'65 and later Cylinder Head design change

  
High Performance Pontiac
Item Posts    Sort Order

'65 and later Cylinder Head design change

 
thinman56 thinman56
User | Posts: 112 | Joined: 04/13
Posted: 03/24/14
08:11 AM

I had an hour to kill in the garage this weekend while I was making a batch of beer.  My wife hates the smell of it in the house, personally I love how it lingers for days.  Anyway, rather than clean up (which is what I should have done with the time), I decided to measure up the old '64 9773345 heads that came off my original 326, just to see if they were much different from the '67 140 heads I ended up using.  I know nobody cares much about these specific heads from a performance standpoint, but my question is this - was there a effort to make a design change to Pontiac heads from '64 to '65, other than the fact that the intake manifolds are different?  The reason I ask is that the intake ports on the 140's, even after mild porting, measured 150 cc's give or take a couple, while the 9773345's measured about 168 to 170 cc's.  I could feel the size difference with two fingers poking around in them.  This might not seem like much, but when I plug these two port sizes into the Virtual Dyno for my engine with no other changes, the difference is huge, like 40 hp and 40 ft-lbs of torque increase.  I've read some about smaller runners helping velocity and torque, but I could not find more details with a search.  I used the 140's for the 67 cc chambers, and they were partially rebuilt when I got 'em.  The 3345's are 72 cc's uncut.  Still, I kinda wish I'd used the original 3345 heads and shaved 'em to get the compression.  

It looks to me like the 9773345's were used for the 326, 389 and 421's in 1964, but the bigger engines used bigger valves (Wallace Racing stats).  Also, I'm always curious if anyone has actual dyno results to back up the Virtual Dyno numbers.

Thanks for any feedback.