bigcode99

i bought a set of cast heads date code k129 and j149. the casting #16 with small valves (1.96 int, 1.66 ext). looking at hp ratings, #16 large valves 2.11,1.77(330,335,350,366hp?) http://www.pontiacpower.org/cgi-bin/head.cgi are up there with the #12,#13, and#48(all around 350hp). the flow numbers were one of the best tested for stock heads. http://www.pontiacpower.org/ultimatehead.htm
my question is 1).do the small valve heads flow the same as large valve? 2).has any one taken small valve heads and machined them for large valves? 3). I was looking at the edlebrock heads and they have 2.11 intake and 1.66 ext., would it make sence to machine the cast heads to match the E-heads? i was told the runners would be miss matched?

 

lars

I've converted a lot of small valve heads to large valve. It's no problem. Here are a couple of things to do and consider:

First, on those heads, you want to run the Pontiac 2.11/1.77 valve combo. The Edelbrock heads run smaller exhaust valves due to much better flow in their exhaust ports. The Pontiac heads need the bigger exhaust valve. You can get some nice stainless swirl polished valves for Pontiac through SI or Ferrea (sp?).

After cutting for the big valves,and before doing final machining on the seat angles, blend the seat bowls back into the ports at least 1/2".

Keep in mind that a lot of the small valve heads are also low compression heads. The large-valve #16 heads have 72cc chambers, and this comp ratio is part of what gives you the 350 horse rating on the 400. Check the cc volume of your small vlave heads and verify what your comp ratio will be before you spend a ton of $$ on machine work and valves.

bigcode99

thanks lars. i'll check that