186 question for John Z or whoever else knows:)

[Gambitt]

I have a set of small valve 186 heads that I am going to have opened up and use on my 302.  What exactly do I need to know about this procedure to have them made exactly like a set of original large valve 186 heads?  Some shops have said there isn't any reason to enlarge the combustion chamber for the big valves, but I have read different.  I want to know what I need to tell the shops so that I can get this set of heads as close to original as possible.  Also, is there any particular type of equipment the machine shops should be utilizing to get the best possible head work done?  Thanks for the help.

 

[JohnZ]

The standard small-valve 186 heads DEFINITELY need the chamber wall adjacent to the intake valve cut to unshroud it when 2.02" valves are installed, just as the 461/462 heads require; if this isn't done, they'll flow less air with the 2.02's than they did with the 1.94's. I think the cutter used was on the order of 2.34" diameter, but I'm out of town this week and don't have access to my prints - any GOOD automotive machine shop will have the info, as most have done hundreds of heads this way. Photo below is of the 186 chamber with factory 2.02" valves - look closely at it and you can see the unshrouding cut adjacent to the intake valve.

[Gambitt]

Thanks John Z,

I knew I had seen you talk about his before...and I normally save all your posts for future reference, but I wanted to be sure about this before I have the shop start cutting.

If I ever get my 69 Z finished, I owe you and all the great people on here and on camaros.net a big thanks:)

  Gambitt

[Tinkerr]

For what its worth,
  I  would not let a shop work on my small block heads if I had to tell them what is necessary to install the 2.02 valves.the heads have only been around for 4 decades.If they aren't experienced enough to be able to educate you I'd look somewhere else.I had a set done several years ago,I took them to my machinist told him what I wanted to do. his questions were do you want them installed as they would have originally been done, do you want any extra work(porting)done.   
  T

[Gambitt]

Looking around...I found where someone posted this:

"Before you trust your 194 heads to someone to cut them for 202 valves, be sure they have a 78° cutter to relieve the area below the new valve seat. If they don’t use some type of cutter below the new seat, there will be a much smaller opening below the valve than on a factory 202 head. The clearance cut around the intake can easily be made with a large stone that will grind away part of the wall adjacent to the new intake valve."

Also, what have you heard about having heads "ceramic coated?"  I have been hearing this is a good thing to have done also.

[olympic69]

David Vizard did an exhaustive work on the 186 head _ How to Build and Modify Small Block V-8 CYLINDER HEADS_ , 1991 ISBN 0-87938-547-2

He shows, as JohnZ says, an unshrouding cut of 2.37" with a 0.25 radius into a 15 Deg floor on the intake. Also shows a cut on the exhaust side of 2.11" with 5/32" radius and 10 Deg floor.

Now then, my caveat is dont trust my numbers ( I would trust Mr H's). But you are leaving lots on the table if you dont make the cut(s). I highly recommend the book BTW.

[Gambitt]

Thanks, that is good information.  I will have to pick that book up.  I am still concerened about finding a good machine shop in my area...it seems they all wanna just cut the heads for bigger valves and not open them up, like they were from the factory.  I refuse to let just anyone work on these heads too...since I was several years finding them. 

   Gambitt