Tweet
I have a set of 1970 LT1 or z-28 186 heads. They have 2.02 intake valves and 1.60 exhaust valves. I know they also came with 1.94 and 1.50 valves. How do I tell if these were original 2.02 heads or if somebody added them? Thanks in advance for your help. GL
-
-
Re: 186 heads
Original 2.02/1.60" heads have radiused combustion chambers. It's about a 2.34" circular cut centered on the inlet valve to unshroud it. The 1.94/1/50" versions did not have this machining operation.
Of course, if the valve size was increased and the proper radiusing was done, it would be tough to tell.
Installing the larger valves without unshrouding the valve with this cut will actually reduce flow, but I think it was common to increase valve size and not unshroud the valve.
Duke -
Re: 186 heads
Thanks Duke I will get them out and see what they look like. I would suppose that 2.34 cut could be duplicated if necessary. Thanks again GLComment
-
Re: 186 heads
The factory unshrouding cut with 2.02 valves looked like this; most machine-shop conversions don't have it.
Comment
-
Re: 186 heads
Thanks John that helps!Comment
-
Re: 186 heads
A machine shop should be able to make the unshrouding cut if you increase valve size. Also the sides of the chamber should be hand blended out to the edge of the bore to eliminate any overhang.
I don't recommend increasing valve sizes if the 1.94/1.50" valves are installed. The major improvements in cylinder head flow are pocket porting, port matching, and a careful three angle valve seat with top 30 deg. cut on the inlet valve to eliminate excess overhang (leave ,010" overhang on each side with .040" inlet and .060" exhaust seat widths). Do this and the slight increase in valve size is not worth the loss of reliability IMO.
Enlarging the valves increases the propensity for a crack to develop between the seats. Of course, if your heads already have the larger valves go ahead and continue with this size. You can't go "back" once the seats are opening to the larger size.
DukeComment
-
Re: 186 heads
Hey Duke: They already have the 2.02 intake valves in them. Looking at the pic, the heads I have don't have the factory cut for the bigger valves. I have talked to the machine shop about cutting them as shown. The heads already have a nice pocket porting job done on them to smooth out all the rough casting edges. I will have the 3 angle valve job done on them as you suggested. I also have some Cosvega stuff to talk to you about but will do that off board. Thanks GLComment
-
Re: 186 heads
GL –
My best guess is a standard cut on the valve seats. Multiple angles or hardened valve seats would have been added. I believe you have a set of ‘59 aluminum heads #3772895. I cannot find a reference to that part number and think they were made at Chevrolet Grey Iron. Do they have GIF or a Chevy Bowtie logo cast near the date tag? Also, what is the O.D. of the valve seat inserts?
Mark #35760Comment
-
Re: 186 heads
Re the aluminum heads I have, GIF is cast into the heads with a casting number of 3772895. Casting date 6-24-59. They don't have any valve seat inserts. No Bowtie logo. There are several number/letter combos stamped into the ends of the heads purpose unknown to me. Also under some of the chambers there are small single numbers stamped into the head surface, purpose also unknown. Unlike the other known NOS set mine haven't been ported to death. If you want to know what I mean by that look up ebay item 4517841288 that is on right now.Comment
-
Re: 186 heads
Mark here is a pic of the combustion chamber of the aluminum head showing there are no valve seat inserts. Sorry for the quality but I need a better camera. GL
Comment
-
Re: 186 heads
GL –
Thank you, great information. I was disappointed about the valve seats since the previous GEN II and the new Gen III & IV (T6) aluminum heads have them. However, this supports a local Urban Legend that the ’59 aluminum heads were made from the cast iron head tooling. So the combustion chamber and runners were not tweaked to allow for valve seat inserts, backup metal for machining. I was thinking this head casting experiment was the beginning of revisions to combustion chamber shape, intake runner volume, and increased valve sizes. SB head flow improvements were becoming significant then, coinciding with the 327 development and horsepower push.
The Ebay examples are amazing considering all the machining had to be done by hand on individual setups. Production machining clamps would almost crush the aluminum castings and a special setup near impossible for the number produced. Notice the layout lines on the intake ports; this shows someone had access to the engineering drawing. Push rod clearance was probably tight too, because the metal shrink factors are different for iron and aluminum.
Mark #35760Comment
-
Re: 186 heads
Mark and GL-----
I was unaware that these small block aluminum heads did not have valve seat inserts. It's hard to imagine that the durability of these heads would have been very great. I don't think that there are any other PRODUCTION, SERVICE or aftermarket aluminum heads that don't have inserts on both the intake and exhaust, and most of these heads are modern alloys and heat treated, too. Not all aluminum heads have HARDENED or special material valve seat inserts, though. Many were just cast iron.In Appreciation of John HinckleyComment
-
Re: 186 heads
I rather think these aluminum heads were the nearly if not exactly the same as the iron 461X heads. They are fitted with 1.94 intake valves rather than the 1.72 intakes in the heads of the day and the same 1.50 exhaust. The heads on ebay have been ported from the stock configuration. Here is a pic of the stock intake ports. With the exception of the screw in studs I am not to sure the factory did a lot of machining that would be different than what was done to the iron heads. Wasn't there so don't know for sure but it doesn't look like it to me. GL
Comment
Comment